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Servomex FluegasExact (2700D) Combustion Gas Analyser Service Manual
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COMBUSTION ANALYSERS
SERVOTOUGH FluegasExact
(2700D)
Combustion Gas Analyser
Service Manual
Part Number:
Revision:
Language:
02700002D
0
UK English
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SERVOTOUGH FluegasExact Service Manual
TABLE OF CONTENTS
1
INTRODUCTION ................................................................................................ 1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
Scope of this Manual .......................................................................................... 1
Safety Information ............................................................................................... 1
Service Philosophy ............................................................................................. 1
General Description ............................................................................................ 1
Location of External Components....................................................................... 4
Introduction to User Interface ............................................................................. 6
Displaying Faults or Alarms .............................................................................. 11
Displaying Diagnostics ...................................................................................... 12
Displaying Fault or Alarm Histories................................................................... 12
Software Revision History ................................................................................. 13
2
EQUIPMENT OVERVIEW ................................................................................ 14
2.1
2.1.1
Mechanical Overview ........................................................................................ 14
Sensor Head ..................................................................................................... 14
2.1.2
2.1.3
2.2
2.2.1
Flow Alarm Relay Box....................................................................................... 24
Control Unit ....................................................................................................... 26
Electrical Overview ........................................................................................... 28
Control Unit PCB............................................................................................... 28
2.2.2
Sensor Head Terminals PCB ............................................................................ 32
2.3
2.3.1
2.3.2
2.3.3
2.4
2.5
Operating Principles.......................................................................................... 34
Zr703 Oxygen Sensor Module .......................................................................... 34
Tfx1750 Combustibles Transducer Module ...................................................... 35
1760 Flow Alarm Sensor Module ...................................................................... 38
Electrical Connections ...................................................................................... 39
Sample Connections ......................................................................................... 48
3
SPARES LIST ................................................................................................... 49
3.1
3.2
3.3
3.4
3.5
Control Unit Spares........................................................................................... 49
Sensor Head Spares......................................................................................... 50
Flow Alarm Relay Box Spares .......................................................................... 51
Sample Probes ................................................................................................. 52
Manuals ............................................................................................................ 53
4
FAULT FINDING ............................................................................................... 54
4.1
4.2
Introduction ....................................................................................................... 54
Fault and Alarm Messages ............................................................................... 55
2.1.1.1
2.1.1.2
2.2.1.1
2.2.1.2
2.2.1.3
2.2.1.4
2.2.1.5
2.2.1.6
2.2.1.7
2.2.2.1
2.2.2.2
2.2.2.3
2.2.2.4
2.2.2.5
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Sensor Compartment ........................................................................................... 15
Terminal Compartment ......................................................................................... 22
Power Supplies and Relay Outputs ...................................................................... 28
Microcontroller ...................................................................................................... 28
Analogue Current Outputs .................................................................................... 29
ADC Subsystem ................................................................................................... 29
Zirconia Sensor Electronics .................................................................................. 30
Flow Alarm Sensor Electronics............................................................................. 30
Combustibles Sensor Electronics ......................................................................... 31
Power Supply ....................................................................................................... 32
Thermocouple Amplifier ....................................................................................... 32
Sensor Head Temperature Control ...................................................................... 32
Sensor Head Temperature Monitor ...................................................................... 33
Solenoid Valve Interlocks ..................................................................................... 33
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4.3
4.4
4.5
4.5.1
4.5.2
4.5.3
4.5.4
4.5.5
4.6
4.6.1
4.6.2
4.6.3
4.6.4
4.6.5
4.6.6
4.6.7
4.7
4.7.1
4.7.2
4.7.3
4.7.4
4.7.5
Diagnostic Values ............................................................................................. 57
Fault Symptoms Shortcut Guide ....................................................................... 59
Initial Inspection / Start-up Problems ................................................................ 60
Initial Checks ..................................................................................................... 60
Control Unit AC Power Supply Checks............................................................. 61
Control Unit Display and DC Power Supply Checks ........................................ 63
Keypad Checks ................................................................................................. 65
Heater Checks .................................................................................................. 65
Measurement Problems .................................................................................... 74
Definitions ......................................................................................................... 74
Discussion ......................................................................................................... 75
Oxygen Measurement Checks ......................................................................... 77
Combustibles Measurement Checks ................................................................ 79
Flow Alarm Measurement Checks .................................................................... 81
Pneumatics System Checks ............................................................................. 85
Aspirator Interlock Failure ................................................................................. 87
Analyser Problems ............................................................................................ 88
Analogue (mA) Output Failure .......................................................................... 89
Relay Output Failure ......................................................................................... 91
Auto Calibration Failure .................................................................................... 91
Blow Back Failure ............................................................................................. 93
Analyser Does Not Keep Correct Time or Date ................................................ 93
5
PARTS REPLACEMENT PROCEDURES ....................................................... 94
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
5.11
5.12
5.13
5.14
5.15
5.16
5.17
5.18
5.19
Control Unit Access .......................................................................................... 94
Control PCB Removal and Replacement ......................................................... 95
Control Unit Transformer Removal and Replacement...................................... 99
Firmware Installation ....................................................................................... 100
Display Removal and Replacement................................................................ 101
Keypad Removal and Replacement ............................................................... 103
Sensor Head and Terminal Box Cover Removal and Replacement .............. 103
Terminals PCB Removal and Replacement ................................................... 107
Solenoid Valve Removal and Replacement ................................................... 111
Solid State Relay Removal and Replacement ................................................ 111
Zirconia Cell Removal and Replacement ....................................................... 112
Combustibles Cell Removal and Replacement .............................................. 114
Flow Alarm Removal and Replacement ......................................................... 116
Cell Connector Removal and Replacement ................................................... 120
Aspirator Removal and Replacement ............................................................. 122
Internal Filter / Sintered Flame Arrestor Removal and Replacement ............. 123
Thermostat Removal and Replacement ......................................................... 124
Thermistor Removal and Replacement .......................................................... 125
Band Heater Removal and Replacement ....................................................... 125
APPENDIX A DETAILED ANALYSER PERFORMANCE TESTING .................................... 127
A.1
A.2
A.3
A.4
A.5
A.6
A.7
A.8
A.9
A.10
A.11
A.12
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Notes and Conditions...................................................................................... 127
Gas Samples Required ................................................................................... 127
Visual Inspection ............................................................................................. 128
Sensor Head Leak Test .................................................................................. 129
Interconnection Tests...................................................................................... 129
Initial Power-Up............................................................................................... 129
Analogue Output Span Setup ......................................................................... 129
Relay Operation Test ...................................................................................... 130
Sensor Head Temperature Control................................................................. 130
Sensor Head Sample Flow and Vacuum Test ................................................ 130
Combustibles Sensor Zero Adjustment .......................................................... 131
Sensor Calibration .......................................................................................... 131
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APPENDIX B ANALYSER SOFTWARE ‘SUPER-CALIBRATION’ MODE ........................... 132
B.1
B.2
B.3
B.4
B.5
B.6
B.7
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Introduction ..................................................................................................... 132
Menu Structure ............................................................................................... 132
Accessing Super-Calibration .......................................................................... 132
Configuring the Combustibles Sensor ............................................................ 133
Setting the Display Precision of the Combustibles Measurement .................. 134
Returning to Factory Default Settings ............................................................. 135
Exiting Super-Calibration ................................................................................ 135
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LIST OF FIGURES
Figure 1.1 FluegasExact Product Components ......................................................................... 2
Figure 1.2 Sensor Head Overview ............................................................................................. 4
Figure 1.3 Control Unit Overview ............................................................................................... 5
Figure 1.4 FluegasExact Keypad Display .................................................................................. 6
Figure 1.5 Menu Structure A ...................................................................................................... 8
Figure 1.6 Menu Structure B ...................................................................................................... 9
Figure 1.7 Menu Structure C .................................................................................................... 10
Figure 2.1 Sensor Head Overview ........................................................................................... 14
Figure 2.2 Dual Sensor Assembly ............................................................................................ 16
Figure 2.3 Dual Sensor Head Flow Schematic ........................................................................ 17
Figure 2.4 Dual Sensor Head with Flow Alarm Flow Schematic .............................................. 18
Figure 2.5 O2 Sensor Head Flow Schematic............................................................................ 19
Figure 2.6 O2 Sensor Head with Flow Alarm Flow Schematic ................................................. 20
Figure 2.7 COe Sensor Head Flow Schematic ......................................................................... 21
Figure 2.8 Sensor Head Terminal Enclosure Detail (Dual Configuration) ............................... 22
Figure 2.9 Sensor Head with Flow Alarm Terminal Enclosure Detail (Dual Configuration) ..... 23
Figure 2.10 Flow Alarm Relay Box ........................................................................................... 24
Figure 2.11 Flow Alarm PCB Assembly .................................................................................. 25
Figure 2.12 Control Unit Overview ........................................................................................... 27
Figure 2.13 Zirconia Sensor Construction ................................................................................ 34
Figure 2.14 Tfx1750 Sensor Construction ............................................................................... 36
Figure 2.15 Tfx1750 Sensor Element Detail ............................................................................ 37
Figure 2.16 1750 Flow Alarm Sensor Construction ................................................................. 38
Figure 2.17 Oxygen Sensor Only Interconnection Wiring Schematic ...................................... 40
Figure 2.18 Combustibles Sensor Only Interconnection Wiring Schematic ............................ 42
Figure 2.19 Dual Sensor Interconnection Wiring Schematic ................................................... 44
Figure 2.20 Flow Alarm Relay Box Interconnection Wiring Schematic .................................... 46
Figure 2.21 Sensor Head Sample Connections ....................................................................... 48
Figure 4.1 Initial Checks ........................................................................................................... 60
Figure 4.2 Control Unit AC Power Supply Checks ................................................................... 61
Figure 4.3 Display and DC Power Supply Checks ................................................................... 63
Figure 4.4 Initial Heater Checks ............................................................................................... 66
Figure 4.5 Sensor Head Heater Checks .................................................................................. 67
Figure 4.6 Thermistor Temperature Curve ............................................................................... 69
Figure 4.7 Zirconia Sensor Heater Checks .............................................................................. 70
Figure 4.8 COe Sensor Heater Checks.................................................................................... 72
Figure 4.9 Oxygen Measurement Checks ................................................................................ 77
Figure 4.10 Combustibles Measurement Checks .................................................................... 79
Figure 4.11 Flow Alarm Amplifier Board................................................................................... 82
Figure 4.12 Flow Alarm Relay Board ....................................................................................... 83
Figure 4.13 Pneumatics System Checks ................................................................................. 85
Figure 4.14 Final Analyser Checks .......................................................................................... 88
Figure 4.15 Analogue Output Checks ...................................................................................... 89
Figure 4.16 Relay Output Checks ............................................................................................ 91
Figure 5.1 Control Unit Access................................................................................................. 94
Figure 5.2 Control Unit Internals .............................................................................................. 96
Figure 5.3 Measurement Transducer DIP Switch Configurations ............................................ 98
Figure 5.4 Control Unit Transformer Detail .............................................................................. 99
Figure 5.5 Display and Keypad Mounting Details .................................................................. 102
Figure 5.6 Sensor Head Overview ......................................................................................... 104
Figure 5.7 Sensor Head Terminal Enclosure Detail (without Flow Alarm) ............................. 108
Figure 5.8 Zirconia Sensor Installation Details ....................................................................... 113
Figure 5.9 Combustibles Sensor Installation Details.............................................................. 115
Figure 5.10 Flow Alarm Installation Details ............................................................................ 117
Figure 5.11 Flow Alarm Signal Amplifier Board Installation Details ....................................... 118
Figure 5.12 Dual Sensor Configuration Layout ...................................................................... 120
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LIST OF TABLES
Table 2.1 Interconnecting Cable Requirements ....................................................................... 39
Table 2.2 Oxygen Sensor Only Interconnecting Wiring ........................................................... 41
Table 2.3 Combustibles Sensor Only Interconnecting Wiring .................................................. 43
Table 2.4 Dual Sensor Interconnecting Wiring......................................................................... 45
Table 2.5 Flow Alarm Relay Box Interconnecting Wiring ......................................................... 47
Table 4.1 Analyser AC Power Connections ............................................................................. 62
Table 4.2 Transformer Connection and Winding Details ......................................................... 62
Table 4.3 Keypad Connections ................................................................................................ 65
Table 4.4 Sensor Head Voltage Selection at TB9.................................................................... 68
Table 5.1 Control Unit Electrical Power Voltage Selection ...................................................... 98
Table 5.2 Terminal PCB Voltage Selection Links .................................................................. 109
Table 5.3 Sensor Head Internal Wiring Schedule .................................................................. 110
Table 5.4 Flow Alarm Internal Wiring – Flow Amplifier Board ................................................ 119
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1 INTRODUCTION
1.1
Scope of this Manual
This manual contains essential information for the servicing of the Servomex 2700D
(FluegasExact) Combustion Gas Analysers.
This service manual is intended for use by Servomex trained service personnel. The
manual contains technical descriptions, fault diagnosis information, parts removal, refitting
and test instructions.
1.2
Safety Information
Important safety information is highlighted in this manual as WARNINGs and CAUTIONs,
which are used as follows:
WARNING
Warnings highlight specific hazards which, if not taken into account, may
result in personal injury or death.
CAUTION
Cautions highlight hazards which, if not taken into account, can result in damage to the
analyser or to other equipment or property.
This manual also incorporates “Be aware of” information, which is used as follows:
This highlights information which is useful for you to be aware of (for example, specific
operating conditions, and so on).
1.3
Service Philosophy
WARNING
All servicing should be referred to qualified personnel.
Repairs to printed circuit boards are affected by module replacement. Component
replacement is not recommended. The only exceptions to this are the mains fuses on the
Control Unit and terminal box PCB’s, and the heater fuses on the Control Unit PCB.
1.4
General Description
All Servomex adaptor flanges, interface flanges, probe support tubes, stand-offs and
thermal spacers, including the integral flange on the Sensor Head, are suitable for
fitting onto the standard flanges that their descriptive names imply, either raised face
(<1.6mm) or flat faced.
Servomex flanges do not comply with any national or international standards and the
analyser’s maximum process pressure is limited to 5psig.
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The Servomex 2700D Combustion Gas Analyser measures combustion and similar gases
to provide an analysis of the oxygen concentration and / or the level of unburned
combustibles. The analyser comprises two separate core units:
A Sensor Head mounted directly onto the flue wall.
A Control Unit mounted remotely from the Sensor Head.
These may be mounted up to 300m (975ft) apart, or 100m (325ft) when the combustible
measurement option is fitted.
In addition, optional utilities units and an integrated Flow Alarm are available. Utilities units
supply the Sensor Head with calibration gases and instrument air. The integrated Flow
Alarm offers indication of sample flow status and is supplied with an external Relay Box for
customer connections.
The Sensor Head is flange mounted on to the flue wall and houses the measurement
sensors in a heated epoxy painted aluminium enclosure. A probe assembly projects
through the duct wall into the process gas to extract a gas sample for analysis. A
comprehensive range of sample probes and filters are available to enable the analyser to
be used in a wide range of applications and process conditions. Electrical connections are
made to a terminal enclosure located on the side of the Sensor Head.
Key
1.
2.
3.
4.
Description
Key
Terminals enclosure
Sensor Head
4” mounting flange
Sample probe
5.
6.
7.
8.
Description
Sample probe filter (optional)
Control unit
Wall mounting brackets
Keypad and display
Figure 1.1 FluegasExact Product Components
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The Control Unit houses the sensor electronics, microprocessor, keypad, display and user
wiring connections in an epoxy painted aluminium enclosure. The Control Unit may be
either wall or panel mounted (using an optional panel mount kit). Cable entries are located
on the bottom of the Control Unit enclosure.
2700D units are available in five configurations based on the Servomex Zr703 zirconia
oxygen sensor and the Servomex Tfx 1750 thick film calorimeter combustibles sensor.
Oxygen only.
Combustibles only.
Both oxygen and combustibles measurement (dual).
Oxygen only with Flow Alarm.
Both oxygen and combustibles measurement (dual) with Flow Alarm.
Isolated current outputs (0-20mA or 4-20mA) are provided to allow the analyser to be
connected to a chart recorder, data logger, PLC, PC, DCS or ESD system as required. The
analyser is provided with a single analogue output for each measurement provided. Each
output has a minimum and maximum output range. For the oxygen sensor 0-1% is the
minimum range and 0-25% is the maximum. For the 1750702 combustibles sensor 0500ppm is the minimum range and 0-6000ppm is the maximum (over range of 30000ppm).
The analogue outputs may be independently set to have live zero (4-20mA) or true zero (020mA), to freeze or follow during calibration and blow back, and to jam either high or low
during analyser fault conditions. Oxygen only and dual analysers can be configured with an
optional Flow Alarm that provides a low flow warning which can be used to detect
plugging/blockage during operation.
The analyser has four software configurable relay outputs. The user may assign any of
these relay outputs to be either concentration alarms, analyser fault alarms, auto calibration
relay drives, blow back relay drives, calibration in progress signals or blow back in progress
signals.
The analyser has two digital inputs, suitable for voltage free relay contact actuation, to
trigger an auto calibration or a blow back sequence remotely.
The 2700D is designed for use in modern industrial environments with emphasis on
durable, rugged construction, low cost of ownership, reliable performance, simple operation
and ease of service.
A number of optional features are available for the 2700D. These include the following:
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Sample probes.
Differently threaded entries for electrical connections.
Corrosive purge ports.
Hazardous area purge.
Sensor Head flange mounting options.
Control unit mounting options.
Integrated Flow Alarm.
Utilities panels.
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1.5
Location of External Components
Figures 1.2 and 1.3 identify the key features of the Sensor Head and Control Unit
respectively. Refer to Section 5 for replacement procedures.
Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Description
Analyser mounting flange, 4” ANSI 150lb.
Sample vent port, 1/8” NPT (INT).
Sample probe connection, 1/2” NPT (INT).
Calibration gas inlet, 1/4” OD compression fitting.
Purge gas exit, 1/4” NPT (INT) or breather fitting.
Spare inlet (Blanked).
Purge gas entry, 1/4” NPT (INT) or blanking plug.
Signal cable entry, 3/4” NPT (INT) or specified adaptor.
Mains cable entry, 3/4” NPT (INT) or specified adaptor.
Aspirator air supply inlet, 1/8” NPT (INT).
Figure 1.2 Sensor Head Overview
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Key
1.
2.
3.
4.
5.
6.
Description
LCD display and keypad.
Door hinges.
3/4” NPT (INT) threaded cable conduit entries or optional adaptors as required.
Wall mounting brackets.
Enclosure breather fitting (optional) or blanking port.
1/4” NPT (INT) threaded enclosure purge fittings (optional) or blanking screws.
Figure 1.3 Control Unit Overview
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1.6
Introduction to User Interface
Refer to Figure 1.4.
20.95 %
Oxygen
50 ppm
COe
MENU
ENTER
MEASURE
QUIT
CALIBRATE / VIEW
SERVICE / SETUP
Key
1.
2.
3.
4.
5.
6.
7.
Description
LCD showing measurement display.
ENTER key.
ARROW keys.
MENU key.
MEASURE key.
QUIT key.
Main menu display.
Figure 1.4 FluegasExact Keypad Display
The 2700D Control Unit user interface consists of a tactile 8 button keypad and a back lit
LCD (2 lines x 16 characters). During normal use the LCD will display either the
measurement or menu display. A user can toggle between the measurement or menu
display via the tactile keypad.
The functions of the keys on the keypad are:
6
MEASURE
Returns the analyser to the measurement display.
MENU
Activates the main menu display of the screen editor.
QUIT
Aborts the current activity and returns to the previous menu level.
In the menu, the arrow keys select the desired option. When entering
numeric information, the left and right arrow keys are used to move between
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digits and the up and down arrow keys are used to change the value of each
digit. The active digit is highlighted by blinking. The user presses the
‘ENTER’ key to indicate that the numeric input is complete and the data is to
be saved. If the ‘QUIT’ key is pressed then the data is not saved and the
input is aborted.
In the measurement display the scrolls through any alarm and/or fault
messages active.
ENTER
Indicates that the menu selection is to be processed or that numerical input is
complete.
To initiate any menu operation the MENU key should be pressed. The LCD will then
present the top level menu, which in turn leads on to other menus.
At each menu, the user highlights the desired option using the arrow keys and then presses
ENTER. Blinking is used to highlight the selected menu option. During any menu
operation the fundamental measurements are still being made by the analyser and all
relevant outputs, alarms and diagnostics remain active.
Some menu operations require the use of a password. There are two passwords, a
supervisor password (2700) which gives access to SETUP, SERVICE, VIEW and
CALIBRATION and an operator password (2000) which gives access to CALIBRATION
and VIEW only. Both passwords are factory set and may be changed if required.
The measurement display is shown in figure 1.4. The top line of the display shows the
current measured value (with its units) for each of the sensors fitted. In normal operation
the bottom line of the display labels the gases measured.
The MEASURE key may be used to return the analyser to the measurement display at any
time. Further details on the operation of the user interface are available from the Quickstart
manual.
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1
2
VIEW
Go to 2
CONFIGURE
Go to 3
VIEW
Software version
Oxygen sensor output voltage in mV
Oxygen sensor temperature in °C
Oxygen sensor high calibration point in mV
Oxygen sensor low calibration point in mV
Combustibles sensor output voltage in mV
Combustibles sensor temperature in °C
Combustibles sensor high calibration point in mV
Combustibles sensor low calibration point in mV
Sensor head temperature in °C (if connected)
DIAGNOSTICS
HISTORY
3
4
ALARM
Alarm history events
FAULT HISTORY
Fault history events
CONFIGURE
ENTER
Operator Password – Go to 4
0000
Supervisor Password – Go to 5
CALIBRATE / VIEW
CALIBRATE
MANUAL CALIBRATE
OXYGEN
LOW CAL
COe
HIGH CAL
AUTO CALIBRATE
Calibration Procedure
OXYGEN
SETUP AUTO CAL
Calibration Procedure
COe
OXYGEN & COe
SETUP AUTO CAL
5
VIEW
Go to 2
CALIBRATE / VIEW
Go to 4
SERVICE / SETUP
Go to 6
Initiate Automatic Calibration
Figure 1.5 Menu Structure A
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6
SERVICE
SET OUTPUTS
mA OUTPUTS
SET TO 0mA / 4mA / 20mA
RELAYS
SET TO DISABLED
SET TO ENABLED
HISTORY
DELETE HISTORY
SET UP
ASSIGN
NONE
AL1
ALARMS
OXYGEN
AL2
RELAYS
COe
A
HIGH
FOLLOW
LOW
Setup Alarm
level &
Hysteresis
Setup Procedure
1/2/3/4
mA OUTPUTS
FREEZE
OXYGEN
SET RANGE
COe
FREEZE
A
FOLLOW
0-20mA
4-20mA
SET LOW POINT
FILTER
JAM HIGH / LOW / NONE
OXYGEN
Setup Filtration
COe
BLOWBACK
SET UP BLOWBACK
Blowback Setup Procedure
START BLOWBACK
Initiate Blowback
CLOCK
Clock Setting Procedure
UTILITY
PASSWORD
AUX AIR
SUPERVISOR
Password Setting Procedure
OPERATOR
YES
Always set to “YES”
NO
ENGLISH
LANG
FRANCAIS
DEUTSCH
Figure 1.6 Menu Structure B
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It is advised that the parameters for the Calibration Tolerances, Combustibles Output
Ranges and Filters are set as follows.
CONFIGURE
ENTER
0000
CALIBRATE
MANUAL CALIBRATE
OXYGEN
LOW CAL
COe
HIGH CAL
CAL LEVEL
CAL TOL
Calibration Tolerance
(Factory Default Settings)
AUTO CALIBRATE
Oxygen Low
Oxygen High
COe Low
COe High
SETUP AUTO CAL
OXYGEN
0.2%
1.0%
150ppm
150ppm
COe
OXYGEN & COe
LOW CAL
LOW & HIGH CAL
CAL LEVEL
SET UP
CAL TOL
Minimum COe Output Range
ASSIGN
mA OUTPUTS
500ppm
OXYGEN
Maximum COe Output Range
COe
30,000ppm*
Minimum Oxygen Output Range
1.0%
Maximum Oxygen Output Range
COe
25.0%
*Note: max working range of
sensor is 10,000ppm
FILTER
OXYGEN
COe
Filter Settings
(Factory Default Settings)
Oxygen
COe
4
5
Figure 1.7 Menu Structure C
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1.7
Displaying Faults or Alarms
In normal operation the bottom line of the measurement display shows each measurement
gas name. Should a fault or alarm occur then the lower line of the display will detail the
nature of the fault or alarm. Should more than one fault and/or alarm be active then arrows
are shown in the last character of the bottom line. If both a fault and an alarm are present
then the fault display will take precedence. It will not be possible to view any alarms
present until the fault is cleared. The up and down arrow keys on the keypad may be used
to scroll through these messages.
The fault messages that may appear are as follows:
OXYGEN LOW
Oxygen too low for COe measurement.
OXYGEN C LOW
Oxygen sensor temperature low.
OXYGEN C HIGH
Oxygen sensor temperature high.
COe mV LOW
Combustibles sensor output voltage low.
COe mV HIGH
Combustibles sensor output voltage high.
COe C LOW
Combustibles sensor temperature low.
COe C HIGH
Combustibles sensor temperature high.
COe mV OUTPUT LOW
Combustibles sensor sensitivity low (updates after
calibration only).
COe CONC HI
Combustibles sensor has been exposed to very high COe
levels.
SENSOR C LOW
Sensor Head temperature low.
SENSOR C HIGH
Sensor Head temperature high.
AUTO CAL FAIL
Auto calibration out of tolerance error.
COe WARMING
Combustibles sensor is warming up.
O2 WARMING
Oxygen sensor warming up.
DISP OVER RANGE
Combustibles reading exceeds sensor f.s.d.
mV OUT OF TOLERANCE
Combustibles sensor coarse zero is incorrectly set.
See section 4 of this manual for further details and remedial actions.
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1.8
Displaying Diagnostics
The VIEW function allows the user to interrogate the analyser diagnostics. No password is
required to access the view function. The VIEW functions are updated dynamically and
values may change while they are being viewed.
To access this display, press the MENU key, select VIEW then select DIAGNOSTICS from
the view menu. The VIEW option is also available from the CONFIGURE menu.
The diagnostics appear as a scrollable list of values and associated descriptions. There
are up to nine diagnostics depending on which sensors are fitted. The keys are used
to switch between the following diagnostic measurements:
OXYGEN SENSOR mV
Oxygen sensor output voltage in mV.
OXYGEN SENSOR C
Oxygen sensor temperature in C.
COe SENSOR mV
Combustibles sensor output voltage in mV.
COe SENSOR C
Combustibles sensor temperature in C.
PROBE HEAD C
Optional Sensor Head temperature in C.
COe SENSOR HIGH
Combustibles sensor output voltage in mV, at current high
point calibration.
COe SENSOR LOW
Combustibles sensor output voltage in mV, at current low
point calibration.
OXYGEN SENSOR HIGH
Oxygen sensor output voltage in mV, at current high point
calibration.
OXYGEN SENSOR LOW
Oxygen sensor output voltage in mV, at current low point
calibration.
The difference between SENSOR HIGH and SENSOR LOW mV values is the
sensitivity (cell output). These values are only updated after a successful High or Low
calibration is performed.
Pressing the MEASURE key will return the analyser to the default measurement display.
1.9
Displaying Fault or Alarm Histories
The VIEW function allows the user to interrogate the analyser alarm or fault histories in
addition to the analyser diagnostics.
No password is required to access the VIEW function. The VIEW functions are updated
dynamically and values are live.
To access this display, press the MENU key and then select VIEW. From the VIEW menu
select HISTORY then choose between ALARM HISTORY and FAULT HISTORY.
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1.10 Software Revision History
The table below summarises the last revision of the software used in the 2700D.
02710/652/1
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December 2006
Release
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2 EQUIPMENT OVERVIEW
2.1
Mechanical Overview
2.1.1
Sensor Head
Refer to Figure 2.1.
Key
1.
2.
3.
4.
Description
Mounting flange
Sensor Head base casting
Insulation spacer
Terminal box casting
Key
5.
6.
7.
8.
Description
Terminal box cover
Terminal cover screws
Sensor Head cover
Sensor cover screws
Figure 2.1 Sensor Head Overview
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The Sensor Head assembly mounts directly onto the flue wall via a 4" flange (1). The
Sensor Head assembly consists of two main components, the sensor compartment and the
terminal box. The Sensor Head base casting (2) and cover casting (7) form a heated oven
housing the sensors and sample pipe work.
All gas sampling and measurement takes place within this heated sensor compartment.
The terminal box casting (4) and terminal box cover casting (5) form an enclosure housing
the Sensor Head PCB and all interconnecting and user connections. The terminal box
casting (4) is screwed to the Sensor Head base casting (2) by two bolts. An insulating
spacer (3) and two sealing gaskets provide thermal isolation between the sensor
compartment and the terminal box. O-ring seals on the covers and appropriate cable
glands (not supplied) make the two compartments weatherproof (IP66 and NEMA 4X). An
electrical earth connection is provided (refer to Figure 2.8) on the outside of the terminals
enclosure.
2.1.1.1
Sensor Compartment
Refer to Figure 2.2.
The sensor compartment cover is secured by four captive M6 screws and is sealed by an
O-ring. With the cover removed, access is given to the gas sensors and sampling pipe
work. Figure 2.2 describes a dual sensor analyser (oxygen and combustibles sensors).
For other Sensor Head versions the sensor compartment construction is similar but with the
unused sensor(s) removed.
The Sensor Head base and cover form an insulated oven (insulation not shown for clarity).
The oven is heated by a 500W band heater (1) located around the chest assembly (12).
The temperature of the chest assembly is controlled at approximately 245C via the
thermistor (13). An over temperature thermostat (4) is fitted to prevent overheating should
the temperature control fail.
The gas sample is extracted from the flue using an aspirator (2) screwed into the chest
assembly. For analysers incorporating a Zr703 zirconia sensor, a reference air sample is
derived from the aspirator supply, via a capillary tube (8). For analysers incorporating a
Tfx1750 sensor, an auxiliary air supply is also derived from the aspirator supply, via a flame
trap (5) and auxiliary air flow restrictor (7).
Refer to Figure 2.3.
A solenoid valve (8), interlocked to the Sensor Head and Zr703 zirconia sensor (where
fitted) temperature, is provided as standard to prevent sample gases condensing in the
Sensor Head pipe work when the Sensor Head temperature is too low.
Flame traps (3) and a filter/flame arrestor (11) are provided to prevent accidental ignition of
the flue by the hot sensors should the flue gas become flammable. The reference air
capillary tube (7) also behaves as a flame arrestor.
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Key
1.
2.
3.
4.
5.
6.
Description
Band heater
Aspirator assembly
Flame trap
Over temp thermostat
Flame trap
Tfx1750 combustibles sensor
Key
7.
8.
9.
10.
11.
12.
13.
Description
Auxiliary air restrictor
Aspirator / reference air pipe
Zr703 oxygen sensor
Base casting
Sintered filter/flame arrestor
Chest assembly
Thermistor
Figure 2.2 Dual Sensor Assembly
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Key
1.
2.
3.
4.
5.
6.
7.
8.
Description
Key
Chest assembly
Sample aspirator
Flame trap
Tfx1750 sensor
Auxiliary air restrictor
Flame trap
Aspirator/reference air inlet
Solenoid valve
9.
10.
11.
12.
13.
14.
15.
16.
Description
Zr703 sensor
Breather
Flame arrestor
Calibration/blow back inlet
Heated enclosure
Internal filter
Sample gas inlet
Sample gas outlet
Figure 2.3 Dual Sensor Head Flow Schematic
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Key
1.
2.
3.
4.
5.
6.
7.
8.
Description
Chest assembly
Sample aspirator
Flame trap
Tfx1750 sensor
Auxiliary air restrictor
Flame trap
Aspirator/reference air inlet
Solenoid valve
Key
9.
10.
11.
12.
13.
14.
15.
16.
17.
Description
Zr703 sensor
Breather
Flame arrestor
Calibration/blow back inlet
Heated enclosure
Internal filter
Sample gas inlet
Sample gas outlet
Flow alarm
Figure 2.4 Dual Sensor Head with Flow Alarm Flow Schematic
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Key
1.
2.
3.
4.
5.
6.
Description
Chest assembly
Sample aspirator
Flame trap
Aspirator/reference air inlet
Solenoid valve
Zr703 sensor
Key
7.
8.
9.
10.
11.
12.
13.
Description
Breather
Flame arrestor
Calibration/blow back inlet
Heated enclosure
Internal filter
Sample gas inlet
Sample gas outlet
Figure 2.5 O2 Sensor Head Flow Schematic
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Key
1.
2.
3.
4.
5.
6.
7.
Description
Chest assembly
Sample aspirator
Flame trap
Aspirator/reference air inlet
Solenoid valve
Zr703 sensor
Breather
Key
8.
9.
10.
11.
12.
13.
14.
Description
Flame arrestor
Calibration/blow back inlet
Heated enclosure
Internal filter
Sample gas inlet
Sample gas outlet
Flow Alarm
Figure 2.6 O2 Sensor Head with Flow Alarm Flow Schematic
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Key
1.
2.
3.
4.
5.
6.
7.
Description
Chest assembly
Sample aspirator
Flame trap
Tfx1750 sensor
Auxiliary air restrictor
Flame trap
Aspirator/reference air inlet
Key
8.
9.
10.
11.
12.
13.
14.
15.
Description
Solenoid valve
Breather
Flame arrestor
Calibration/blow back inlet
Heated enclosure
Internal filter
Sample gas inlet
Sample gas outlet
Figure 2.7 COe Sensor Head Flow Schematic
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2.1.1.2
Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Terminal Compartment
Description
Solid state relay
Terminal block TB2
Terminal block TB7
Solenoid valve
Solenoid valve retaining nut
Terminal PCB earth connection
Terminal block TB9
Mains protection cover
Terminal block TB8
Terminal block TB1
Key
Description
11.
12.
13.
14.
15.
16.
17.
18.
M4 cover fixing screw
Mains fuse F1
Terminal block TB3
Terminal block TB4
Terminal block TB6
Terminal block TB5
M4 Terminal PCB fixing screws
Wiring support P-clip + EMC
ferrite
19. Transformer
20. Earth stud
Figure 2.8 Sensor Head Terminal Enclosure Detail (Dual Configuration)
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Key
1.
2.
3.
4.
Description
Fuse
M4 PCB fixing screws
Terminal block TB1
Terminal block TB3
Key
5.
6.
7.
Description
Flow sensor tuning potentiometer
Signal amplifier PCB
Terminal block TB2
Figure 2.9 Sensor Head with Flow Alarm Terminal Enclosure Detail (Dual
Configuration)
Removal of the 4 screws and lid gives access to the Sensor Head PCB and user electrical
connections. Electrical cables fitted with suitable glands are fed through the appropriate
entry holes and wired to the terminals shown in Figure 2.8 (Refer to Installation manual for
user connections). Any unused cable entries should be fitted with appropriate blanking
plugs.
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2.1.2
Flow Alarm Relay Box
Refer to Figure 2.10.
The Flow Alarm Relay Box consists of a die cast aluminium enclosure (6) in which the
threshold detector board (3) is mounted. The enclosure has two ¾” NPT gland entries (9),
(which can be removed if M20 entries are required), and an EMC earth stud (8). A clear
cover (10) protects the user from the mains rated relays (4). Interconnection to the Sensor
Head is made via terminal block TB2 (2) and relay connections are made via terminal block
TB1 (7).
Key
1.
2.
3.
4.
5.
Description
Nylon spacer
Terminal block TB2
Threshold detector board
Relays
Flow alarm set point adjustment
Key
6.
7.
8.
9.
Description
Aluminium enclosure
Terminal Block TB1
EMC earth stud
Mains protection cover
Figure 2.10 Flow Alarm Relay Box
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Key
Description
1. M6 Screw
2. M6 Washer
3. Mains protection cover
Key
4.
5.
6.
Description
Spacer
Flow alarm relay board
M6 Washer
Figure 2.11 Flow Alarm PCB Assembly
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2.1.3
Control Unit
Refer to Figure 2.12 Control Unit Overview
The housing consists of a die cast aluminium enclosure (16) with a hinged die cast
aluminium door (3) secured by four captive M6 screws (2) and sealed by an O-ring (5). This
enclosure houses most of the control electronics for the 2700D analyser. Three holes into
the enclosure are provided for optional purge connections (13), a breather fitting (15) or
sealed plugs. An electrical earth connection is provided (not shown in figure 2.5) on the
outside of the enclosure.
Menu navigation is via a tactile keypad and backlit LCD (1) secured onto the hinged door
using twelve M4 hex head screws and sealed using an O-ring (4). The control electronics
and user wiring connections (7) are contained on a single PCB (10) screwed directly onto
the enclosure casting. A toroidal transformer (11), attached to the enclosure casting, is
mounted underneath the control PCB. A protection cover (6) protects the PCB from
accidental damage. A transparent cover (8) is provided to protect the user from hazardous
voltages.
User and interconnecting wiring to the Control Unit is via the 3/4" NPT (internal) threaded
entries (14) on the bottom side of the enclosure casting.
The Control Unit may be mounted on to a wall via mounting straps (12) or alternatively into
a rack or panel (panel mounting kit not shown).
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Key
1.
2.
3.
4.
5.
6.
7.
8.
Description
Display and keypad
Captive screws for door
Cast aluminium hinged lid
Display O-ring seal
Door O-ring seal
PCB protection cover
User wiring connections
Mains protection cover
Key
9.
10.
11.
12.
13.
14.
15.
16.
Description
PCB fixing screws
Control PCB
Transformer
Wall mounting straps
Optional purge ports
Wiring entry ports
Optional breather fitting
Cast aluminium enclosure
Figure 2.12 Control Unit Overview
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2.2
Electrical Overview
2.2.1
Control Unit PCB
2.2.1.1
Power Supplies and Relay Outputs
Mains power connects to the PCB via terminal block TB3. The ‘live’ side is fused by F1.
Fused mains power is fed to connectors PL6 and PL7 where the mains transformer primary
is connected.
The transformer secondary windings connect to PL5, supplying a 18-0-18V heater supply,
and a 10.5-0-10.5V supply for the ±5V regulated DC supplies.
There is a dedicated regulated +5V DC supply for the relay coils, 4-20mA output DC-DC
converters and the LCD backlight. The rest of the Control Unit electronics is powered from
a separate +5V and -5V DC supply.
Fuses F2, F3, F4 and F5 protect both sides of the 18-0-18V AC supplies to the Zirconia and
Tfx cell heaters.
There are four relay outputs controlled by the microcontroller. Each relay provides a singlepole changeover function on terminal block TB4 and is driven by an individual control line
from the microcontroller.
2.2.1.2
Microcontroller
The microcontroller has external flash EEPROM which contains the system software, the
analyser configuration and calibration data.
The microcontroller directly drives the LCD, an analogue input multiplexer and an
analogue-to-digital converter. There are two PWM outputs from the microcontroller which
are used to drive the isolated current outputs.
A serial data chain monitors the keypad, ‘autocal’ and ‘blow back’ inputs, configuration links
and drives the Zirconia and Tfx cell heater inhibit signals, ‘system OK’ LED and relay
outputs.
A real-time clock/calendar IC with its own 32.768kHz crystal is connected to the
microcontroller via an SPI synchronous serial data link. A 0.1F “Supercap” capacitor
provides power for the real-time clock when there is no mains power.
A supply voltage supervisor/reset IC is used to drive the microcontroller reset line. The IC
provides a clean power-up reset, brown out protection and a manual reset input (SW1).
There is a red LED on the RESET line which turns on when the microcontroller is reset.
The LED can be seen through a hole in the metal cover over the PCB.
The green “System OK” LED is toggled on and off by the software to indicate correct
operation. The LED can be seen through a hole in the metal cover over the PCB.
Switch SW4 A and B is used by the software to determine the analyser configuration (O2,
COe, or dual measurement). These are factory set to match the Sensor Head configuration
and need only be altered when replacing the main PCB with a spare. Note that early
Control Units were fitted with a main PCB whose configuration was determined by links
(LK3 & LK4). The configuration links (LK3, LK4) are surface-mount links which tell the
software whether the PCB is for an oxygen-only, combustibles-only or dual gas analysis.
These links were fitted during manufacture and are not field-alterable.
The Zirconia cell heater inhibit (ZINH) only enables the heater when the cell temperature is
above 50C. This is to ensure that the Sensor Head is connected and working and the cell
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temperature measurement signals are working. The Zirconia cell will be heated to 50C by
the Sensor Head heater. This interlock ensures that the cell heater controllers do not
operate if their temperature feedback signals are broken, as this could damage the cell by
overheating it. Note that if the system software is not running, both cell heating methods will
be inhibited.
Potentiometer RV2 adjusts the LCD contrast/viewing angle. The display may disappear
altogether if this potentiometer is not correctly adjusted.
If the PCB is removed from the enclosure, the “Autocal” and “Blow Back” inputs will
only work if the PCB centre mounting hole is electrically connected to the PCB earth
tag.
Operation of the Sensor Head with the PCB removed from the enclosure is not
recommended as the enclosure provides the heat sink.
2.2.1.3
Analogue Current Outputs
There are two identical, galvanically isolated, current output circuits; one assigned to each
gas measurement. Single-gas analysers only have one current output.
The “Oxygen” current output will be described (also referred to as Channel A):
An isolated ±15Vdc supply is generated by two DC-DC converters, with their outputs
connected in series. The PWM output from the microcontroller is fed via an opto-isolator to
control an analogue multiplexer. A voltage 3V above the -15V rail is generated and used as
the “signal 0V”. This ensures that signals are always within the common-mode range of the
multiplexer and op-amp. A 2.5V reference voltage (with respect to “signal 0V”), trimmed by
RV4, is fed to one input of the multiplexer. The other multiplexer input is connected to
“signal 0V”. The multiplexer output is fed to a passive low-pass filter which produces a DC
voltage proportional to the duty cycle of the PWM waveform. The op-amp and MOSFET
transistor convert this voltage to a current sink at TB2 pin 16. Current is sourced at TB2 pin
15 from the isolated +15V rail.
The current output is calibrated by RV4 to give 20mA at 95% duty cycle, thus limiting the
maximum current (even under fault conditions) to 21mA. The current output will work with
load resistances up to 1kΩ (21V maximum output).
2.2.1.4
ADC Subsystem
Five analogue signals are monitored by the microcontroller via the ADC subsystem.
Zirconia sensor output mV.
Zirconia sensor temperature.
Combustibles sensor output mV.
Combustibles sensor temperature.
Sensor Head temperature (optional).
The five inputs and a reference 0V are fed to an analogue multiplexer. A 2.5V reference is
provided for the ADC, a -0.25V level is derived from the 2.5V and the multiplexer output is
amplified and offset by 2xVin+0.25V. This allows the ADC to handle slightly negative
voltages from the multiplexer.
The ADC is clocked at 245 kHz; this clock is derived from the microcontroller system clock
output. The multiplexer and ADC are controlled by the microcontroller; the ADC output data
is transmitted to the microcontroller via a serial data link.
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2.2.1.5
Zirconia Sensor Electronics
Sensor output signal processing:
The zirconia cell output is amplified by an instrumentation amplifier with a gain of 6, and
then filtered by a 4-pole active low pass filter with a cut off frequency of about 1Hz. The
filter output is fed to the ADC subsystem.
Heater control and temperature signal processing:
The zirconia cell heater is powered by the 18-0-18V AC supply from the mains transformer,
controlled by a triac on each side. The cell temperature is sensed by a thermocouple. The
thermocouple amplifier is situated in the Sensor Head terminal box and provides a
10mV/°C temperature signal to the control PCB via TB2 pins 9 and 10. This signal is
buffered and fed into the heater control loop, and attenuated to a level suitable for the ADC.
The temperature set-point is defined by a -2.5V reference (derived from the ADC 2.5V
reference) applied via a 3.57kΩ precision resistor. The temperature feedback is the
thermocouple amplifier output voltage (1V/100°C) applied via a 10kΩ precision resistor.
The error amplifier subtracts one from the other and gives an output of 1V/°C which is
applied to a 267kΩ resistor to generate a heater demand current. A differentiator subtracts
from the heater demand current if the rate of rise of cell temperature exceeds
250°C/minute. This is in order to prevent damage to the cell caused by extreme thermal
shocks. The heater demand current is then inverted and integrated and the integrator
output voltage is compared with 0V.
To keep the cell electrically symmetrical the controller output is synchronised to the mains
zero-crossings, so only complete cycles of AC are applied to the heater. If the integrator
output is negative then power is applied to the heater; if the output is positive then no power
is applied. When power is applied to the heater current is drawn from the integrator via a
267kΩ resistor which causes the integrator output to ramp positive.
There is a hardware over temperature shutdown which disables the heater if the measured
temperature goes above about 830°C. The heater may also be disabled by the
microcontroller via a comparator and FET switch.
A separate rectifier and voltage regulator provides a +10V supply for the cell temperature
buffer amplifier.
The Sensor Head temperature signal is buffered and attenuated and fed to the ADC via the
analogue multiplexer.
2.2.1.6
Flow Alarm Sensor Electronics
The Flow Alarm sensor electronics is split between the Sensor Head enclosure and an
external Flow Alarm Relay Box.
The flow sensor is in the form of a resistive bridge arranged so that, predominantly, one
pair of resistors is exposed to the gas flow. This bridge is powered by a current source, set
by RV1 to produce the required level of self-heating. The cooling effect produced by a gas
flow unbalances the bridge and results in a differential output that is then amplified to give
an indication of flow.
Basic temperature compensation is applied to this signal in the form of an offset.
Temperature sensing is performed by the bridge itself by measuring the voltage drop due to
the current source. Compensation is set by RV2 for a typical operational flow rate.
The compensated output is then corrected for zero offset by RV3 to produce the required
flow signal. It should be noted that all adjustments described above are factory set to match
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the flow sensor and must not be subsequently altered. This means that the flow sensor and
Signal Amplifier Board must only be replaced as a matched pair.
The flow indication signal is connected from the Sensor Head to the external Flow Alarm
Relay Box via customer field wiring. Here, the signal is fed into a threshold comparator
where it is compared to a low Flow Alarm level set by switch S1. This switch is settable by
the user between 10% and 90% of span flow.
The thresholds representing zero flow and span flow are established by the flow calibration
process and set using RV1 and RV2 respectively. During calibration, the correct setting of
each potentiometer in turn is indicated by means of red and green LEDs. These voltage
levels are also used by a window comparator that checks the flow signal is within the
calibrated range. An in-range condition is indicated on a green LED and an out of range
condition (flow fault) is indicated on a red LED.
The low flow status and fault status signals are then used to drive relays RL2 and RL1
respectively via switches S2A and S2B. These switches allow the relay drives to be
disabled, allowing calibration to be carried out without generating alarm or fault conditions.
Switches S3A and S3B allow the operation of the relays to be inverted.
2.2.1.7
Combustibles Sensor Electronics
Sensor output signal processing:
The Combustibles sensor is in the form of a resistive bridge which is driven by a chopped
constant-current supply. The supply is chopped at 218 Hz. The timing is controlled by a
small microcontroller to ensure accurate timing of the glitch-blanking function (see below).
The current source is mirrored to keep the bridge common-mode voltage low.
The bridge output is buffered by a difference amplifier and then fed to two gain stages. The
gain blocks have a DC gain of 1 so as not to amplify offset voltage errors. A synchronous
detector is used to null out offset errors and amplifier noise. When the bridge is driven with
current the synchronous detector has a gain of +1; when the bridge is not driven the
synchronous detector is switched to a gain of -1. The output of the synchronous detector is
integrated over several cycles by a second-order low-pass filter with a cut off frequency of
0.1 Hz.
Thus the output is:
((signal + noise + offsets) - (noise + offsets)) = signal.
An analogue switch is placed between the synchronous detector and the low-pass filter to
provide blanking of the large transients which are generated when the bridge drive is
switched on and off. The transients occur due to the finite response time of the current
mirror. The switch is driven by the microcontroller to ensure that the blanking control is
“locked” to the chopping of the bridge drive current, and to ensure that a constant
percentage of the signal is blanked out since any variation in this would appear as a
variation in system gain.
A zero-offset adjustment circuit is provided which sinks a current from one side of the
bridge to compensate for the coarse offset error inherent in the bridge. Rotary switch SW2
provides approximately 15000ppm of adjustment in 1000ppm steps, the exact step size
depends on cell sensitivity and calibration. Switch SW3 selects which side of the bridge the
current is taken from, and hence the polarity of the adjustment. The software zero
calibration removes the remaining zero offset.
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Heater control and temperature signal processing:
The cell temperature is controlled by a PID controller. The output of the controller is
modified by the power applied to the heater to ensure that the controller is stable over the
full range of heater supply voltage.
A platinum resistance temperature (PRT) sensor monitors the cell temperature as part of a
resistive bridge. The bridge output is an error voltage which is fed to the PID controller.
The PRT voltage is buffered and fed to the ADC. The heater control set point is fixed at
305C. The set point is defined by the parallel combination of R19 and R20.
The High Sulphur (refer to section 4.6.2) variant operates at an elevated
temperature of 400ºC. This is achieved by the addition of a shunt resistor (1.5kΩ)
across Sensor Head terminals TB6 3 & 4. The combustibles temperature
diagnostic will continue to show an operating temperature of 305ºC.
The output of the PID controller (modified by the heater power) is integrated and fed to the
heater drive circuit. The drive circuit is almost identical to that used in the Zirconia heater
circuit (see section 2.2.1.5).
2.2.2
Sensor Head Terminals PCB
2.2.2.1
Power Supply
Mains power connects to the board assembly via terminal block TB1. The “live” side is
fused by F1. The fused mains power is routed to the primary winding of the mains
transformer via the voltage selector terminals TB9. Fused mains power also connects to
TB8 where the Sensor Head heater, solid state relay and over-temperature thermostat are
connected in series. Capacitors C14, C15 and C18 provide RF suppression.
The transformer secondary windings provide a nominal 15-0-15 Vac to the rectifier diodes
D1 to D4. IC1 is a conventional linear regulator providing a nominal 12V dc at TP1 with
respect to TP2. Note that 0V (TP2) is not connected to the ‘chassis’ at the Sensor Head.
Vc is an unregulated supply of nominally 20Vdc connected only to IC5.
+V is a rectified AC supply of nominally 14Vdc connected only to the solenoid valve via R13
and TB7.
2.2.2.2
Thermocouple Amplifier
The thermocouple from the zirconia oxygen sensor connects to IC2 via TB2. IC2 is a
thermocouple amplifier which incorporates the cold junction reference and provides an
output of 10mV/C at TB3, terminals 7 and 8. Under normal operating conditions, the output
is nominally 7.00Vdc and this signal is transmitted to the temperature control circuit located
in the Control Unit. Should either or both of the zirconia sensor thermocouple wires become
disconnected, the amplifier output will increase to some value within the range 8 to 12 V dc.
This will cause the temperature control circuit to shut off to protect the cell from damage.
2.2.2.3
Sensor Head Temperature Control
The chest assembly is temperature controlled at nominally 240C using a band heater
(connected at TB8 terminals 1 and 2), and a thermistor sensor located in the block
(connected at TB7 terminals 7 and 8). This sensor has a nominal value of 750 ohms at 240
C and is connected in a full bridge configuration with R1, RN1 and RN2. IC3a (1, 2 and 3)
and IC3b (5, 6 and 7) form a voltage to pulse generator. While operating within the
proportional control band, there will be a pulsed output from IC3 pin 7 which is inverted by
one of the drivers of IC5. This output at IC5 pin 10 switches the solid state relay at TB7
terminals 3 and 4. Visual indication of the heater operation is provided by D10, which
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should be continuously illuminated during the initial warming phase, then pulsing on-off
about one or two times per second when the temperature controller is controlling normally.
2.2.2.4
Sensor Head Temperature Monitor
A voltage representing the Sensor Head temperature is available at TB3 terminals 1 and 2
and may be transmitted to the Control Unit for diagnostic purposes. This has a non-linear
relationship with temperature and is approximately 1.6V dc at room temperature (and
below), increasing to approximately 6.6V dc at the operating temperature of 240 C.
2.2.2.5
Solenoid Valve Interlocks
The solenoid valve connected to TB7 terminals 1 and 2 is a 12Vdc coil which isolates the
air supply to the aspirator when the Sensor Head and measurement sensor temperatures
are below their operating temperatures. The solenoid valve is powered via the ‘driver’ circuit
IC5 and diode logic D5, D6, D7 and D8.
IC4 amplifiers are used as level comparators in which all 4 outputs must switch ‘high’ for
the solenoid valve to be energised. IC4 pin 14 will switch ‘high’ when the chest assembly
thermistor reaches approximately 215C (1.3kΩ). IC4 pin 1 will switch ‘high’ when the
zirconia sensor exceeds 600C. For oxygen only assemblies, TB7 terminals 5 and 6 are
linked. In each case, hysteresis is provided to ensure a clean transition at the switching
threshold.
Visual indication of solenoid operation is by D13.
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2.3
Operating Principles
2.3.1
Zr703 Oxygen Sensor Module
Key
1.
2.
3.
4.
Description
Zirconia heater
Thermocouple
Diaphragm suspension
Reference gas inlet
Key
5.
6.
7.
8.
Description
Zirconia crucible
Zirconia disc
Platinum electrode
Sample gas inlet
Figure 2.13 Zirconia Sensor Construction
The Zr703 cell is a zirconia type oxygen transducer. The sensing element of the transducer
is a disc manufactured from yttria stabilised zirconia. When this material is heated to a
temperature above 600 C it becomes permeable to oxygen ions. The passage of oxygen
ions through the zirconia produces an electric current that is sensed by electrodes
measuring the voltage across the zirconia disc.
Refer to Figure 2.13.
The sensor consists of a yttria stabilised zirconia disc (6) mounted in a tube of the same
material (5). The faces of the disc are coated with platinum electrodes (7) and the assembly
is mounted in a small temperature controlled tubular oven (1). The temperature of the oven
is measured with a thermocouple (2).
When the two sides of the disc are exposed to gases containing differing concentrations of
oxygen, oxygen ions pass through the zirconia disc giving rise to a potential difference
across the two platinum electrodes (7). The magnitude of the potential difference is
proportional to the logarithm of the ratio of the oxygen concentrations on the two sides of
the disc.
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In the 2700D analyser ambient air is used as a reference on one side of the disc (4) while
the sample gas extracted from the flue is presented to the other side (8). The oxygen
content of air is very constant at 20.95%. The output difference from the cell is governed by
the Nernst equation:
20.95
V = KT ln
C
V
T
C
K
=
=
=
=
Voltage across the zirconia disc in mV.
Absolute temperature of the zirconia in K.
Concentration of oxygen in the sample gas in %.
Constant (0.0215 mV/K).
The cell operating temperature in the 2700D is 700 C (973K). The output voltage from the
cell is hence given by:
20.95
V = 20.9 ln
mV
C
When the sample gas contains combustible components then, due to the high
temperature of the sensor, these will burn at the sensor disc consuming oxygen.
The measured oxygen level will then be reduced accordingly. However, this
measurement error is typically <500ppm O2 during normal operation.
2.3.2
Tfx1750 Combustibles Transducer Module
Refer to Figure 2.14.
The transducer operates by oxidation of the COe (carbon monoxide and its equivalents) in
the gas stream to form CO2 at the surface of a heated catalyst coated sensor element (1).
The process is exothermic and the heat generated raises the temperature of the sensor.
The temperature increase is measured electrically to produce a signal that varies linearly
with the COe concentration in the sample gas.
Earlier pellistor sensors have been successfully used to measure the lower explosive limit
(LEL) of gases. This involves the measurement of percentage levels of combustibles. The
use of pellistor sensors for low level CO detection has been limited by cross sensitivity to
other combustible gases in the gas sample and poor base line stability resulting in drift.
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In the Tfx 1750 thick film calorimeter transducer these problems have been reduced by the
following means.
a)
Improved catalyst selection and lower operating temperature resulting in much
higher selectivity to CO.
b)
Improved oven design with indirect heating of the sensor surface. This ensures that
the sample gas is heated to the same temperature as the sensor element before
reaching the catalyst surface.
c)
Better sample flow conditions so that the sensor surface is relatively free from
convection cooling effects.
The sensor element (1) is suspended from a ceramic disk (2). The sensor and mounting
disc are mounted onto a metallic housing (4).
The sensor housing assembly is located within an oven (9). The oven is heated by a band
heater (7) and its temperature is measured by a platinum resistance thermometer (6).
Key
1.
2.
3.
4.
5.
Description
Sensor element
Ceramic disc
Sample gas inlet
Metallic housing
Electrical connections
Key
6.
7.
8.
9.
Description
Resistance thermometer
Band heater
Sample gas outlet
Oven
Figure 2.14 Tfx1750 Sensor Construction
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Sample gas flows in through the sample inlet (3). The sample gas passes through a heat
exchanger formed by a narrow annular channel between the metallic housing (4) and the
oven body (9). This ensures that the sample gas is heated to the same temperature as the
catalyst before reaching the sensor element. The majority of the sample gas flows straight
through the sample gas outlet (8). A small amount of the sample gas diffuses back to the
sensor element (1) where the reaction occurs. The flow of sample gas through the sample
gas outlet (8) forms an aspirator that removes combustion products away from the sensor
surface.
The temperature change of the element is measured via the four electrical connections (5).
Refer to Figure 2.15.
The sensor element consists of a ceramic disc (5) onto which is printed a platinum
resistance electrode (6). The sensor is partitioned into 4 quadrants (1, 2, 3, 4). Two of the
quadrants (1 and 3) are coated with the catalyst. The other two quadrants (2 and 4) are not
coated with the catalyst. The combustion reaction occurs only at the catalyst coated
quadrants of the sensor, changing the resistance of those quadrants, and thus changing
the resistive balance of the circuit. The four quadrants of the sensor are electrically
connected in a bridge configuration so that the temperature difference between the catalyst
coated and non-catalyst coated quadrants can be measured.
Key
Description
1. Coated bridge quadrant
2. Uncoated bridge quadrant
3. Coated bridge quadrant
Key
Description
4. Uncoated bridge quadrant
5. Ceramic disc
6. Platinum electrode
Figure 2.15 Tfx1750 Sensor Element Detail
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2.3.3
1760 Flow Alarm Sensor Module
Refer to Figure 2.16.
The Flow Alarm Sensor consists of a housing in which a reference and a measure disc are
mounted. Platinum tracks are printed on each of the discs to form a resistive bridge circuit.
Initially, both discs are heated to a temperature set point above the sensor’s ambient
temperature. The full flow of sample gas enters the sensor via the inlet pipe, flows past the
measure disc, and cools it, thus unbalancing the bridge circuit. This bridge imbalance is
measured and used to produce an output signal proportional to the sample gas flow. The
output signal is then used to trigger a threshold alarm set point (set using the Relay Box)
which, in turn, switches a relay in the connected Relay Box (refer to section 2.1.2).
Figure 2.16 1750 Flow Alarm Sensor Construction
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2.4
Electrical Connections
The interconnecting wiring specification is given in Table 2.1. Wiring schedules for oxygen
only, combustibles only, dual sensor, and Flow Alarm Relay Box are given in Table 2.2,
Table 2.3, Table 2.4, and Table 2.5 respectively.
The maximum loop resistance limit of 4Ω is required only for the sensor heater lines (2 lines
per sensor). The sensor outputs, temperature signals and bridge supply wires need not be
limited by this restriction on resistance. Depending on the installation environment it may
prove more cost effective to use interconnecting cables with more twisted pairs but with a
smaller cross section per core and, where necessary, to run heater wires in parallel to
produce the required maximum loop resistance.
Table 2.1 Interconnecting Cable Requirements
Sensor
Configuration
Interconnection Type
Conductor Size
& Max
Separation
1.0mm2
1.5mm2
2.5mm2
100m
150m
300m
Oxygen Only
3 twisted pairs with overall screen. Maximum
loop resistance 4 Ohms for heater connections
Combustibles
Only
6 twisted pairs individually screened, minimum
1.0mm2 cross section. Maximum loop
resistance 4 Ohms for heater connections
100m
Oxygen and
Combustibles
Minimum 9 twisted pairs individually screened,
minimum 1.0mm2 cross section. Maximum loop
resistance 4 Ohms for heater connections
100m
Flow Alarm
Relay Box
Minimum 3 cores with overall screen
1.0mm2
100m
For optional Sensor Head temperature display at Control Unit add 1 extra twisted pair
to cable specification.
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Figure 2.17 Oxygen Sensor Only Interconnection Wiring Schematic
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Table 2.2 Oxygen Sensor Only Interconnecting Wiring
Sensor Head
Terminal
TB3-1
TB3-2
TB3-3
TB3-4
TB3-5
TB3-6
TB3-7
TB3-8
TB3-9
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Control Unit
Terminal
Function
Optional Sensor Head temperature measurement
Zirconia sensor output
+ve
TB1-9
-ve
TB1-10
-ve
TB1-7
+ve
TB1-8
TB2-7
Zirconia sensor heater supply (polarity not
important)
Zirconia sensor temperature output
Overall cable screen connection
TB2-8
+ve
TB2-9
-ve
TB2-10
Connected to
case (earth)
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Figure 2.18 Combustibles Sensor Only Interconnection Wiring Schematic
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Table 2.3 Combustibles Sensor Only Interconnecting Wiring
Sensor Head
Terminal
TB5-1
TB5-2
Combustibles sensor temperature output
TB5-5
TB5-6
TB5-7
TB5-8
TB5-9
TB5-10
TB5-11
TB5-12
Stud
Terminal “S”
TB5-13
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TB2-1
Combustibles sensor heater supply (polarity not
important)
TB5-3
TB5-4
Control Unit
Terminal
Function
Combustibles sensor bridge supply
Combustibles sensor bridge output
Combustibles Sensor Bridge offset correction
TB2-2
Ground
TB2-5
-ve
TB2-4
+ve
TB2-3
+ve
TB1-1
-ve
TB1-6
+ve
TB1-3
-ve
TB1-2
+ve
TB1-4
-ve
TB1-5
Combustibles sensor temperature ground
TB2-6
Individual screens and unused cores
Connected to
case (earth)
Overall cable screen connection
Connected to
case (earth)
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Figure 2.19 Dual Sensor Interconnection Wiring Schematic
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Table 2.4 Dual Sensor Interconnecting Wiring
Sensor Head
Terminal
TB5-1
TB5-2
Combustibles sensor temperature output
TB5-5
TB5-6
TB5-7
TB5-8
TB5-9
TB5-10
TB5-11
TB2-1
Combustibles sensor heater supply (polarity not
important)
TB5-3
TB5-4
Control Unit
Terminal
Function
Combustibles sensor bridge supply
Combustibles sensor bridge output
Combustibles Sensor Bridge offset correction
TB2-2
Ground
TB2-5
-ve
TB2-4
+ve
TB2-3
+ve
TB1-1
-ve
TB1-6
+ve
TB1-3
-ve
TB1-2
+ve
TB1-4
-ve
TB1-5
TB5-12
Combustibles sensor temperature ground
TB2-6
TB5-13
Overall cable screen connection
Connected to
case (earth)
TB3-1
Optional Sensor Head temperature
measurement
TB3-2
TB3-3
TB3-4
TB3-5
TB3-6
TB3-7
TB3-8
Stud
Terminal “S”
TB3-9
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Zirconia cell output
+ve
TB1-9
-ve
TB1-10
-ve
TB1-7
+ve
TB1-8
TB2-7
Zirconia sensor heater supply (polarity not
important)
Zirconia sensor temperature output
TB2-8
+ve
TB2-9
-ve
TB2-10
Individual screens and unused cores
Connected to
case (earth)
Overall cable screen connection
Connected to
case (earth)
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Figure 2.20 Flow Alarm Relay Box Interconnection Wiring Schematic
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Table 2.5 Flow Alarm Relay Box Interconnecting Wiring
Flow Alarm
Relay Box
Function
Flow Sensor PCB
TB1-1
Relay Box +12Vdc supply
TB3-1
TB1-2
Flow alarm signal output
TB3-2
TB1-3
Relay Box 0V
TB3-3
Not used
Stud terminal ‘S’ of
main Sensor Head
PCB
TB1-5
Not used
-
TB1-6
Not used
-
Screen
Stud terminal ‘S’ of
main Sensor Head
PCB
TB1-4
EMC earth
stud
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2.5
Sample Connections
Refer to Figure 2.21 for the position and type of gas connections to the Sensor Head.
Key
1.
2.
3.
4.
5.
6.
7.
Description
Sample vent port, 1/8” NPT (INT).
Sample probe connection, 1/2” NPT (INT).
Calibration gas / blow back inlet, 1/4” OD compression fitting.
Purge gas exit, 1/4” NPT (INT) or breather fitting.
Spare entry.
Purge gas entry, 1/4” NPT (INT) or blanking plug.
Aspirator air supply inlet, 1/8” NPT (INT).
Figure 2.21 Sensor Head Sample Connections
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3 SPARES LIST
WARNING
2700D spares must be supplied by Servomex to comply with personal
safety requirements and to maintain performance specification.
The spares listed in this section are for 2700D analysers only. For models prior to this,
please refer to original documentation supplied with the analyser, or contact Servomex
for assistance.
The spares lists below refer to all current spares for the 2700D, some of which are only
available to Servomex Service Centres. Please contact Servomex for spares advice
and availability.
3.1
Control Unit Spares
Recommended Qty
Description
Spare Part
Number
No. of Analysers
1-3
4-9
10+
Complete Control Unit
Consult
Servomex
0
0
1
Control Unit PCB Kit (common board)
S2710906A **
0
1
2
Control Unit PCB – O2 Only
S2710903A
0
1
2
Control Unit PCB – COe Only
S2710913A
0
1
2
Control Unit PCB - Dual
S2710923A
0
1
2
Transformer Kit
S2710910
0
1
1
Keypad / Display Assembly
S2710354
0
1
1
Complete Mains Protection Cover Kit
S2700996 *
0
0
1
Corrosive Purge Kit
S2710995
0
0
0
Enclosure Breather Kit
S2700991 *
0
0
0
Wall Mounting Kit
S2710997
0
0
0
Rack Mounting Kit
S2710996
0
0
0
Complete Enclosure Gasket Kit
S2700999 *
0
1
1
Complete Fuse Kit
S2700998 *
1
1
2
* Spare part contains items used in the Control Unit, Sensor Head and Flow Alarm Relay
Box.
** The ‘common board’ must only be fitted into 2700D Control Units with a serial number of
20,000 or higher.
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3.2
Sensor Head Spares
Description
Complete Sensor Head
Spare Part
Number
Consult
Servomex
S2720993
S2720992
S2720902A
S2720912A
S2720922A
S2720906A
S2720926A
S2720995
Recommended Qty
No. of Analysers
1-3
4-9
10+
0
0
1
Solenoid Valve Kit
0
1
1
Solid State Relay Kit
0
1
1
0
1
2
Terminals PCB – O2 Only (No Flow Option)
Terminals PCB – COe Only (No Flow Option)
0
1
2
Terminals PCB – Dual (No Flow Option)
0
1
2
Terminals PCB – O2 Only (Flow Option)
0
1
2
Terminals PCB – Dual (Flow Option)
0
1
2
Zr703 Zirconia Oxygen Sensor
1
1
2
Tfx1750 Combustibles Sensor – High
S1750702 **
1
1
2
Sensitivity (<1000vpm SOx)
Tfx1750 Combustibles Sensor – High
S2720831 **
1
1
2
Sulphur (<2500vpm SOx)
Flow Alarm Module
S2720762A
1
1
2
Cell Connector – O2 Only (No Flow Option)
S2720991
0
0
0
Cell Connector – COe Only (No Flow Option) S2720950
0
0
0
Cell Connector – Dual (No Flow Option)
S2720949
0
0
0
S2720932
0
0
0
Cell Connector – O2 Only (Flow Option)
Cell Connector – Dual (Flow Option)
S2720930
0
0
0
Aspirator Inlet – O2 Only
S2720988
0
0
0
Aspirator Inlet/Aux Air Feed Restrictor &
S2720943 **
0
0
0
Flame Trap Kit – COe Only
Aspirator Inlet/Aux Air Feed Restrictor &
S2720929 **
0
0
0
Flame Trap Kit – Dual
Calibration / Blow Back Inlet Pipe
S2720456
0
0
0
Aspirator Kit
S2720987 **
1
2
2
Complete Flame Trap / Filter Kit
S2720928 **
1
2
3
Thermostat & Thermistor Kit
S2720994
1
2
3
Band Heater – 120Vac
S2720924
0
1
1
Band Heater – 240Vac
S2720925
0
1
1
Thermal Spacer Spare
S2720361
0
0
0
Mini pz Purge Controller – ATEX/IECEx
S2760702
0
0
1
4" ANSI Flange Gasket Kit
S2720985
1
2
3
4" Weld-On Flange Mounting Kit
S2720984
0
0
0
Complete Enclosure Gasket Kit
S2700999 *
0
1
1
Complete Fuse Kit
S2700998 *
1
1
2
Complete Mains Protection Cover Kit
S2700996 *
0
0
1
Aspirator & Filter/Flame Arrestor Seals Kit
S2720927
1
1
1
Anti Scuff Grease (ROCOL ASP)
S2700990
1
1
1
* Spare part contains items used in the Control Unit, Sensor Head and Flow Alarm Relay
Box.
** Anti scuff grease (ROCOL ASP) application recommended to select parts in spares kit.
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3.3
Flow Alarm Relay Box Spares
Recommended Qty
Description
Spare Part
Number
No. of Analysers
1-3
4-9
10+
Complete Relay Box – Safe Area
S2720933A
0
1
2
Complete Relay Box – ATEX/IECEx
S2720935A
0
1
2
Relay Box PCB
S2720905A
0
1
2
Complete Mains Protection Cover Kit
S2700996 *
0
1
1
* Spare part contains items used in the Control Unit, Sensor Head and Flow Alarm Relay
Box.
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3.4
Sample Probes
2700D Sample Probes – Description
Spare Part Number
Silicon Carbide Filter Kit
S2740998
Probe Tube Coupling
2344-2294
Probe Shroud
S2740996A
Probe Support Disc*
S2740995
Thermal Spacer Flange Kit
02750997
High Temperature Standoff
02750995
Probe Retention Flange Kit
02750998
<700°C, Probe, Open Ended, 0.5m
S2740701A
<700°C, Probe, Open Ended, 1.0m
S2740701B
<700°C, Probe, Open Ended, 1.5m
S2740701C
<700°C, Probe, Filtered, 0.5m
S2740702A
<700°C, Probe, Filtered, 1.0m
S2740702B
<700°C, Probe, Filtered, 1.5m *
S2740702C
<700°C, Probe, Filtered, 2.0m * & **
S2740702D
<700°C, Probe, Filtered, 2.5m * & **
S2740702E
<700°C, Probe, Filtered, 3.0m * & **
S2740702F
<1000°C, Probe, Open Ended, 0.5m
S2740704A
<1000°C, Probe, Open Ended, 1.0m
S2740704B
<800°C, Probe, Open Ended, 1.5m
S2740704C
<700°C, Probe, Open Ended, 2.0m
S2740704D
<1000°C, Probe, Filtered, 0.5m
S2740705A
<1000°C, Probe, Filtered, 1.0m
S2740705B
<700°C, Probe Support, 1.5m
S2740997C
<700°C, Probe Support, 2.0m
S2740997D
<700°C, Probe Support, 2.5m
S2740997E
<700°C, Probe Support, 3.0m
S2740997F
<1750°C, Ceramic Probe, 0.5m
02740707A
<1750°C, Ceramic Probe, 1.0m
02740707B
<1750°C, Ceramic Probe, 1.5m
02740707C
* Item 4, Probe Support Disc is required for Items 13 to 16 when replacing the <700°C
filtered probe in a Supported Probe Installation.
**
52
Items 14, 15 and 16. Filter probes exceeding 1.5m in length are only available as part
of a supported probe installation and should not be used alone.
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3.5
Manuals
For the latest manuals, please consult your local Servomex Business Centre.
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4 FAULT FINDING
4.1
Introduction
This section is included as a guide to possible fault symptoms and their diagnosis. It is
based, as far as possible, on field experience but it is acknowledged that guides such as
these are never comprehensive. Constructive criticism and suggestions for additions and
improvement are always welcome and should be sent to the Product Manager.
Sections 4.2 and 4.3 provide guidance on the fault and diagnostic messages which may be
displayed on the analyser Control Unit. These sections advise the meaning of the
messages and the limits within which diagnostic signals should remain during normal
operation.
Fault finding advice is found from Section 4.5 onward and has been sequenced on the
basis of an engineer attending site to fix a non-functioning analyser.
Section 4.5 deals with powering up the analyser and getting the Sensor Head and sensors
up to operating temperature.
Section 4.6 deals with measurement performance problems.
Section 4.7 deals with analyser faults (mainly in the Control Unit).
The introductory flow charts in each section may also be useful as a set of checks to be
carried out during initial commissioning.
WARNING
The electrical power used in this equipment is at a voltage high enough
to endanger life. It is essential that only suitably trained and competent
personnel are allowed access to hazardous live parts.
It may be necessary to fault find with the electrical power connected.
Where this is necessary extreme caution should be exercised.
Removal of the plastic insulating covers in the Control Unit and Sensor
Head may expose the user to potentially lethal voltages resulting from
external electrical connections to the relay contacts even when electrical
power is disconnected from the Control Unit itself.
The 2700D Sensor Head weighs approximately 17kg (38lbs), care must
be taken when handling.
The analyser may contain toxic, corrosive, flammable or asphyxiant
gases. Vent the analyser to a safe area and flush with air before
commencing work.
The Sensor Head is heated and may be attached to a hot flue. The
external surfaces will be uncomfortably hot even after power down for
several hours. Exercise care when handling the Sensor Head even
when un-powered on a hot flue.
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4.2
Fault and Alarm Messages
The 2700D software provides on-line monitoring for a number of fault conditions and also
provides warning messages when certain parameters are outside normal limits which may
result in poor instrument performance. The procedure to display any active fault messages
is given in section 1.6 of this manual.
The procedure to display fault and alarm histories is given in section 1.8 of this manual.
Fault/Warning
Message
Notes
DISP OVER
RANGE
This message occurs when the COe reading exceeds the preset
limit of 30000vpm.
OXYGEN LOW
This warning message only applies when the auxiliary air software
setting is configured to NO (factory set to YES). This warning is
raised when the oxygen level in the measured sample gas is <1%.
OXYGEN C
LOW
This indicates that the temperature of the zirconia oxygen sensor is
too low. The fault will be displayed if the temperature of the zirconia
sensor is less than 650C.
OXYGEN C
HIGH
This indicates that the temperature of the zirconia oxygen sensor is
too high. The fault will be displayed if the temperature of the zirconia
sensor is greater than 750C.
COe mV LOW
This indicates that the combustibles sensor output voltage is low
enough to result in saturation of the analogue to digital convertor.
The fault will be displayed if the combustibles sensor output voltage
is less than or equal to -109mV.
COe mV HIGH
This indicates that the combustibles sensor output voltage is high
enough to result in saturation of the analogue to digital convertor.
The fault will be displayed if the combustibles sensor output voltage
is greater than or equal to +1113mV.
COe C LOW
This indicates that the temperature of the combustibles sensor is too
low. The fault will be displayed if the temperature of the
combustibles sensor is less than 275C.
COe C HIGH
This indicates that the temperature of the combustibles sensor is too
high. The fault will be displayed if the temperature of the
combustibles sensor is greater than 350C.
COe mV
OUTPUT LOW
This indicates that combustibles sensor sensitivity (span) is too low
(message clears after a successful High or Low calibration is
performed) and needs replacement. This occurs when the sensor
sensitivity falls below 5mV per 1000vpm of calibration gas.
mV OUT OF
TOLERANCE
This indicates that the combustibles sensor mV signal was outside
the range -60 to +60mV during the last low point (Zero) calibration,
and that the combustibles sensor coarse zero setting needs
adjustment. (Message clears after a successful low calibration is
performed).
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Fault/Warning
Message
Notes
COe CONC HI
This indicates that the combustibles sensor has been exposed to a
COe concentration exceeding 15000vpm. This message is logged in
the fault history. If combustibles sensors are exposed to high levels
of COe their performance and life will be impaired.
SENSOR C
HIGH
This indicates that the Sensor Head temperature is too high. This
fault should only be seen on analysers where the optional Sensor
Head temperature interconnection is made between the Sensor
Head and the Control Unit. The fault will be displayed if the
temperature of the Sensor Head chest assembly is greater than
265C.
SENSOR C
LOW
This indicates that the Sensor Head temperature is too low. This
fault should only be seen on analysers where the optional Sensor
Head temperature interconnection is made between the Sensor
Head and the Control Unit. The fault will be displayed if the
temperature of the Sensor Head chest assembly is lower than
225C and/or the correct conditions have not been met to energise
the Sensor Head solenoid.
AUTO CAL FAIL
This indicates that an automatic calibration procedure has failed
because the resultant change in the calibration parameters was
outside of the defined tolerance value. The tolerance value is
defined as part of the auto calibration set up procedure. (Message
clears after a successful calibration is performed).
It is normal for the analyser to display an “OXYGEN C LOW” fault during power up of
the Sensor Head. The fault will be displayed until the zirconia sensor achieves its
normal operating temperature range.
It is normal for the analyser to display a “COe C LOW” fault during power up of the
Sensor Head. The fault will be displayed until the combustibles sensor achieves its
normal operating temperature range.
It is normal for the analyser to display a “SENSOR C LOW” fault during power up of
the Sensor Head. The fault will be displayed until the Sensor Head and zirconia sensor
achieve their normal operating temperature range.
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4.3
Diagnostic Values
The 2700D software allows the user to interrogate a number of critical diagnostic values.
The procedure to display the diagnostic values is given in section 1.7 of this manual.
Diagnostic
Notes
OXYGEN
SENSOR mV
This is a live measurement of the output voltage, in mV, across the
zirconia disc in the oxygen sensor. The principles of operation of the
oxygen sensor are given in section 2.3.1. The voltage is related
logarithmically to the ratio of the oxygen concentrations at the
reference air side, and the sample sides of the zirconia disc. The
output will be very close to zero at ambient air levels and increases
by 48mV per decade as the oxygen concentration falls (for more
information refer to section 2.3.1).
OXYGEN
SENSOR C
This is a live display of the temperature of the zirconia oxygen sensor
as measured by its thermocouple. The normal operating value of the
sensor is 70010C. The temperature displayed is inaccurate below
80C with a minimum value that can be displayed of approximately
38C, (due to saturation of the thermocouple amplifier IC on the
Sensor Head terminal PCB). A fault condition will be generated
should the temperature be outside of the range 650 to 750C.
OXYGEN
SENSOR HIGH
mV
This is the measurement of the output voltage, in mV, across the
zirconia disc in the oxygen sensor at the time of the last successful
high point (Span) calibration.
OXYGEN
SENSOR LOW
mV
This is the measurement of the output voltage, in mV, across the
zirconia disc in the oxygen sensor at the time of the last successful
low point (Zero) calibration.
COe mV
This is a live, amplified measurement of the output voltage (AC)
across the combustibles sensor bridge circuit. The principles of
operation of the combustibles sensor are given in section 2.3.2. The
displayed value is in the range -125 to + 1125mV. The displayed
voltage for a sample with no carbon monoxide should be in the range
-60 to +60 mV. The sensitivity of individual combustibles sensors will
vary widely depending on the sensor type, age and other factors. The
change in the sensor output voltage display should be, typically, in
the range 25 to 80mV for a 1000ppm change in the carbon monoxide
concentration.
COe C
This displays the temperature of the combustibles sensor as
measured by its platinum resistance thermometer. The normal
operating temperature is 305C for the high sensitivity variant, and
400C for the high sulphur variant, (regardless of which variant is
fitted, the COe C display will always reference the standard
operating temperature of 305C). A fault condition will be generated
should the temperature be outside of the range 275 to 350C.
COe SENSOR
HIGH mV
This is the amplified COe sensor signal level at the time of the last
successful high point (Span) calibration.
COe SENSOR
LOW mV
This is the amplified COe sensor signal level at the time of the last
successful low point (Zero) calibration.
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58
Diagnostic
Notes
PROBE HEAD
C
This shows the temperature of the Sensor Head chest assembly as
measured by its controlling thermistor. This is only available if the
optional interconnecting wiring is fitted between the Sensor Head and
the Control Unit. The normal operating temperature is 24510C. A
fault will be generated if the chest assembly temperature exceeds
265C. Due to the logarithmic temperature response of the thermistor
device (see Figure 4.6) the displayed temperature value is unreliable
below 150C and has a minimum display limit of approximately
100C.
SOFTWARE
VERSION
This shows the software part number and revision level fitted in the
Control Unit. Refer to Section 1.8 for software revision history.
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4.4
Fault Symptoms Shortcut Guide
This section categorises the fault symptoms observed, however, it should be noted that
certain faults listed under one sub-section may also occur at another phase of testing.
Category/Symptom
Reference
Initial Inspection/Start Up
See Section 4.5
Instrument does not power up
See Section 4.5.1
Instrument blows fuses
See Section 4.5.2
Display not illuminated and no text displayed
See Sections 4.5.2 & 4.5.3
Text displayed but backlight not illuminated
See Section 4.5.3
Display illuminated but no text
Incorrect or no response to key presses
See Section 4.5.4
Sensor Head temperature incorrect or will not warm up.
Zirconia Sensor temperature incorrect or will not warm
up.
See Section 4.5.5
Combustibles Sensor temperature incorrect or will not
warm up.
Measurement Faults
See Section 4.6
Oxygen reading incorrect or outside specification
See Sections 4.6.2 and 4.6.3
Combustibles reading incorrect or outside specification
See Sections 4.6.2 and 4.6.4
Analyser Faults
See Section 4.7
Analogue output readings not working or inaccurate
See Section 4.7.1
Relay outputs not operating
See Section 4.7.2
Analyser does not start an Auto calibration
Auto calibration fault indicated
See Section 4.7.3
Analyser does not start Blow back
Auto calibration or blow back timings slip
See Sections 4.7.4 & 4.7.5
Analyser does not keep correct time and date
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4.5
Initial Inspection / Start-up Problems
4.5.1
Initial Checks
Start
Step 1
Is power available at the analyser?
No
Yes
Check wiring, circuit
breakers and intermediate
junction boxes
Step 2
Check for the following:
No text on display
Backlight not illuminated
mA outputs at 0mA
Green watchdog LED on control
unit PCB not illuminated
Step 3
Are ALL the above true?
Yes
Go to Section 4.5.2
No
Step 4
Does the display function normally?
(text displayed + backlight
illuminated)
No
Go to Section 4.5.3
Yes
Step 5
Does the display respond to the
keypad?
No
Go to Section 4.5.4
Yes
Step 6
Are sensor and probe head
operating temperatures correct?
No
Go to Section 4.5.5
Yes
Step 7
End
See Sections 4.6 and 4.7 for other symptoms
Figure 4.1 Initial Checks
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4.5.2
Control Unit AC Power Supply Checks
Start
With the power to the
analyser turned off, check
mains fuse F1 and its rating
Put plug in correct position.
Replace F1
Blown
Ok
Check AC power wiring is
correctly terminated and
ferruled. See Table 4.1
Ok
Incorrect
Incorrect
Check that the transformer
primary connector is
plugged into the correct
socket – PL6 for 220V, PL7
for 110V
Ok
Re-terminate wiring
Replace transformer
Replace Control Unit PCB
Windings opencircuit or
short-circuit
Incorrect
Check transformer primary
winding. See Table 4.2
Ok
Check continuity of Control
Unit PCB. See Table 4.1
Ok
Disconnect PL5. Replace
F1 (if blown). Apply power
and check transformer
output. See Table 4.2
F1 blows
or voltage
incorrect
Replace transformer
Volts Ok
Disconnect power.
Reconnect PL5 then
reconnect power.
F1 blows
Replace Control Unit PCB
Ok
Go to Figure 4.1
Step 4
Go to Figure 4.1
Step 2
Figure 4.2 Control Unit AC Power Supply Checks
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Table 4.1 Analyser AC Power Connections
AC Power Terminals
Function
110V Operation
220V Operation
TB3 Pin 1
Live
PL7 Pins 2 & 4
PL6 Pin 4
TB3 Pin 2
Neutral
PL7 Pins 1 & 3
PL6 Pin 1
TB3 Pin 3
Earth
Chassis/Case
Chassis/Case
PL6 Pins 2 & 3 are
linked
Table 4.2 Transformer Connection and Winding Details
Winding
Pin No
Wire Colour
Resistance
Open-circuit
Voltage
@115 or 230V
Connector 1
Secondary 1
7
Orange + Sleeve
6
Orange
5
Orange
4
NO CONNECTION
3
Green + Sleeve
2
Green
1
Green
Centre-tap
0.5 10%
Secondary 2
21V
Centre-tap
0.8 10%
36V
Connector 2
4
Blue
3
Red
2
Purple
1
Brown
9.3 10%
Primary 1
N/A
9.3 10%
Primary 2
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4.5.3
Control Unit Display and DC Power Supply Checks
Start
Is text visible on the
display?
Check display connector is correctly
located on Control Unit PCB and ribbon
cable is properly crimped. See Note 1
No
Yes
Yes
Is text visible now?
>1Hz
Check main 5V power rail.
See Note 2
Incorrect
Ok
No
Check watchdog
LED flash rate
<1Hz
Replace Control
Unit PCB
Replace display
module
No
Is processor RESET
LED illuminated
Is the display
backlight illuminated?
Yes
Yes
No
Yes
Replace Control
Unit PCB firmware
Check ribbon cable is secure and
not damaged. See Note 1
Is backlight illuminated now?
No
Check aux 5V power rail.
See Note 3
Ok
Incorrect
Are ALL diagnostics
correct?
No
Yes
Check -5V power rail.
See Note 4
Replace display
module
Replace Control
Unit PCB
Incorrect
Ok
Go to Figure 4.1
Step 5
Figure 4.3 Display and DC Power Supply Checks
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DC power is distributed through the Control Unit by 3 major supply rails. Their function is as
follows:
Main +5V
Provides power to the microcontroller, LCD and signal processing
circuitry. If this rail fails, no text will be displayed on the LCD, the
microcontroller watchdog LED will not flash and mA outputs will read
0mA.
Auxiliary +5V
Provides power to the LCD backlight, relay coils and mA output circuits. If
this rail fails, display text will not be backlit, no relays will energise and
mA outputs will read 0mA.
-5V
Provides power to the signal processing circuitry. If this rail fails the LCD
and watchdog LED can work normally, but all measurements and
diagnostic values will be incorrect.
Unless the display module is working correctly, the remainder of the analyser will not
function properly. This is because of the way in which display functions are handled in the
microcontroller operating system. If the display module is disconnected or unable to
respond to display write commands, the microcontroller cannot function normally. In this
event, the mA outputs will fall to 0mA and the flash rate of the Watchdog LED decreases
from 5 times per second to approximately once every 2 to 3 seconds.
64
Note 1:
Check the setting of contrast control RV2 (adjacent to the LCD connector). If
this is adjusted incorrectly, the display can appear to be blank. Check insulating
washers are fitted between the display PCB and retaining screws and spacers
(refer to Section 5.5).
Note 2:
With the power to the analyser turned on, measure the voltage between pin 3 of
the LCD connector (positive) and TB2 terminal 5 (0V). Pin 1 of the LCD
connector is identified by the red stripe on the cable. The voltage should be 5V
5%.
Note 3:
With the power to the analyser turned on, measure the voltage between pin 1 of
the LCD connector (positive) and TB2 terminal 5 (0V). Pin 1 of the LCD
connector is identified by the red stripe on the cable. The voltage should be 4.2V
10%.
Note 4:
With the power to the analyser turned off, disconnect all field wiring and remove
the metal cover over the Control Unit PCB. Reconnect the mains supply, keypad
and LCD, power up the unit, then measure the voltage between pin 3 of U2
(negative) and test point TP3 (0V). U2 is mounted on the heat sink in the top-left
corner of the PCB. Pin 3 is the rightmost pin of U2. The voltage should be -5V
5%.
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4.5.4
Keypad Checks
1. Check that the keypad connector is correctly plugged into PL2 on the Control Unit PCB.
The flexible tail of the keypad should not be twisted or damaged. Ensure that the
connector is correctly aligned with PL2. It is possible to misalign the connector if care is
not taken.
2. Check that the analyser software is operating. A green LED should be visible through
one of the small holes in the bottom-left corner of the Control Unit PCB cover. This LED
flashes at about 5Hz when the software is operating correctly. A red LED is visible
through another small hole in the bottom-left corner. This LED should not be illuminated
if the software is operating correctly. If the red LED is flashing or on all the time then
there is a fault on the PCB or in the software and the PCB should be replaced.
3. Check the operation of the keypad. Disconnect the keypad connector from the Control
Unit PCB. Connect one lead of a continuity tester to pin 3 of the keypad connector. (Pin
1 is identified by a small triangle moulded into the connector body).
Check that each key operates correctly. Each key should connect one pin to the
common pin 3 according to the following table:
Table 4.3 Keypad Connections
Quit
1
Right
6
Down
2
Up
7
Left
4
Menu
8
Enter
5
Measure
9
If the keypad is faulty it must be replaced. Otherwise replace the Control Unit PCB.
4.5.5
Heater Checks
Having ensured that basic Control Unit functions are working, the next priority is to ensure
that the Sensor Head and sensor(s) are at satisfactory and stable operating temperatures.
This is an essential pre-condition for satisfactory measurement performance.
Heater Control Algorithms and Interlocks
1. From a cold start, heater power is applied immediately to the Sensor Head band
heater and combustibles sensor. The Control Unit does not apply power to the zirconia
sensor until the zirconia has naturally heated to approximately 65ºC.
2. The aspirator air solenoid valve is interlocked with the Sensor Head and zirconia
sensor temperatures. The solenoid is not energised until the Sensor Head temperature
reaches 235C and the zirconia sensor (if fitted) reaches 650C.
3. The same rules also apply for a warm start, but the following should be noted to
prevent false diagnosis. When the Control Unit first applies power to a sensor, it
monitors the rate at which it heats. If the rate is too slow, the processor inhibits heating,
waits for a period and then tries again. This means that during a warm start, the sensor
temperatures can fall for a few minutes before warming normally. This period is usually
less than 15 minutes, but depends upon ambient conditions and starting temperatures.
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Start
Step 1
Check the following:
Sensor Head temperature diagnostic (if connected)
Zirconia sensor temperature diagnostic (if fitted)
Combustibles sensor temperature diagnostic (if fitted)
Step 2
Is Sensor Head temperature OK?
No
Go to Figure 4.5
Yes
Step 3
Is the Zirconia Sensor temperature
OK?
No
Go to Figure 4.7
Yes
Step 4
Is the combustibles sensor
temperature OK?
No
Go to Figure 4.8
Yes
End
See Sections 4.6 and 4.7 for other symptoms
Figure 4.4 Initial Heater Checks
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Start
Check wiring, terminations,
circuit breakers and
intermediate junction boxes
Remove Sensor Head terminals
box lid. Are either LEDs D10 or
D13 illuminated. See Note 1.
No
No
Is AC power available at the
Sensor Head? See Note 2.
Yes
Yes
Measure voltage between TP1
and TP2 on Terminals PCB.
Voltage = 12 ± 0.7V?
Yes
Ok
No
Blown
Replace Terminals PCB
Check that the transformer
primary is wired correctly at
TB9. See Table 4.4
Check state of LED D10
Off
On
Is Sensor Head
over / under
temperature?
Over
With the power to the Sensor
Head turned off, check fuse F1
Put link wire in
correct position.
Replace F1.
Are diagnostics Ok?
Yes
No
No
Check voltage between
TB3 pins 1 and 2.
Voltage = 6.6 ± 0.7V?
Under
Incorrect
Ok
Flashing
Check heater wiring is isolated
from earth. See Note 3
Yes
Check wiring between
Sensor Head and
Control Unit. See
Section 2.4
Go to Figure 4.4
Step 3
Is Sensor Head under
temperature?
No
Yes
See Note 5
See Note 6
See Note 4
Temporarily short out
TB7 pins 7 and 8. Does
LED D10 turn off?
No
Replace
Terminals
PCB
Yes
Check temperature control
thermistor and wiring are not open
circuit. Replace if needed.
Figure 4.5 Sensor Head Heater Checks
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NOTE 1
The heater status indicator LED on the terminal PCB should be flashing if the
heater is controlling the temperature correctly.
The LED will be ON if the Sensor Head is under temperature and OFF if the
Sensor Head is above the control temperature.
NOTE 2
The power wiring of the 2700D differs from earlier Servomex combustion
analysers (the 700B and 700EX). Power for the 2700D Control Unit and
Sensor Head should generally be wired from a common isolating switch.
WARNING
Powering down the Control Unit does not automatically remove power
from the Sensor Head (unless both have been wired from a common
isolating switch).
If the Sensor Head is powered down separately from the Control Unit,
then the Control Unit will continue to supply heater power to the zirconia
and combustibles sensors.
Table 4.4 Sensor Head Voltage Selection at TB9
Pin Number
Function
1
220/240V Tap
2
AC Supply Input
A link wire is fitted to TB9 to select the
operating voltage.
3
110/120V Tap
For 110/120V operation link Pins 2 and 3.
4
100V Tap
For 220/240V operation link Pins 1 and 2.
NOTE 3
Disconnect AC power wiring from TB1. Check insulation resistance between
both Live and Earth, and Neutral and Earth via TB1. If earth is not fully
isolated, check the isolation of the band heater, thermostat and solid state
relay. The wiring to each may be isolated via TB8. Replace damaged
components and/or wiring as needed. If these 3 components are fully isolated
but the fault persists at TB1, replace the Terminals PCB. Reconnect AC power
wiring to TB1 only when all associated faults are cleared.
NOTE 4
If the heater status LED is ON but the Sensor Head fails to heat correctly,
verify the following:
The voltage at TB-7 terminal 4 with respect to terminal 3 is in the range +5
V dc to +9Vdc. If necessary change the solid state relay.
The over temperature thermostat connected at TB-8 terminals 5 and 6 is
closed. If necessary replace the thermostat.
The heater connected at TB-8 terminals 1 and 2 is not open circuit or
intermittent. The ‘240Vac’ heater has a resistance of approximately 110Ω
at room temperature and the ‘120Vac’ heater has a resistance of
approximately 28Ω at room temperature. If necessary replace the heater.
If the heater status LED is ON, the solid state relay should also be ON.
Check the voltage drop across the solid state relay, connected at TB-8
terminals 3 and 4, is not greater than 2 Vac. If necessary replace the solid
state relay.
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NOTE 5
If the heater status LED is OFF and the Sensor Head fails to get hot, verify the
following:
Check the resistance of the chest assembly thermistor (TB7 terminals 7
and 8) against the curve shown in Figure 4.6. (At least one lead of the
thermistor will need to be disconnected for this check.). A low impedance
or short-circuit thermistor will cause the control circuit to switch off and the
Sensor Head will fail to heat. Replace the thermistor if necessary.
Check the control circuit operation. A short circuit between TB7 terminals 7
and 8 will cause the control LED to switch off, and an open circuit (or high
impedance) will cause the control LED to switch ON. Replace the PCB if
necessary.
If the heater status LED is OFF but the Sensor Head is over temperature,
proceed as follows. Fit a temporary short circuit connection between TB-7
terminals 7 and 8, verify the following:
If the voltage at TB-7 terminal 4 with respect to terminal 3 exceeds 3.0 V
dc replace the terminal PCB.
If the voltage at TB-7 terminal 4 with respect to terminal 3 is less than 3.0
V dc replace the SSR.
Remove the temporary short circuit link and ensure correct operation.
1000000
100000
10000
1000
100
0
50
100
150
Temperature in C
200
250
300
Figure 4.6 Thermistor Temperature Curve
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Start
Check Oxygen Sensor ºC Diagnostic.
Is temperature 700 ± 10ºC
and stable to ± 1ºC
Yes
Go to Figure 4.4
Step 4
No
Yes
Is temperature
>150ºC
No
Blown
Disconnect zirconia heater
wires from TB2 pins 7 and
8 at Control Unit
Ok
Check zirconia cell
heater resistance.
See Note 6.
Sensor
replaced
Check fuses F2 and
F4 in Control Unit
Ok
Check zirconia
temperature signal.
See Note 7.
Check each wire is
isolated from earth
(1MΩ)
Ok
<1MΩ
Check wiring, junction
boxes, Sensor Head
Terminals PCB and
zirconia sensor for faults.
Repair or replace parts as
needed.
Replace Control
Unit PCB
Fix carried out
Figure 4.7 Zirconia Sensor Heater Checks
NOTE 6
With the power to the analyser turned off, measure the resistance between
terminals 7 and 8 of terminal block TB2 on the Control Unit. The heater
resistance should be 8 10%. Note that the measured resistance will
include the heater cable which could be up to 4. If the heater cable is long
and the resistance reading is low, check the heater resistance at the Sensor
Head, terminals 3 & 4 of terminal block TB4, to ensure that the heater is not
short-circuit. If the heater is faulty, replace the Zirconia cell.
If the temperature diagnostic is unstable, check that the zirconia heater and
temperature signal wiring (as described in Note 7) are isolated from earth.
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CAUTION
If a zirconia cell is found to have an open circuit heater coil, ensure correct operation of the
zirconia heater control circuit in the Control Unit and thermocouple amplifier in the Sensor
Head.
This may be checked as follows:
With the zirconia cell disconnected, fit a temporary short circuit between pins 1
and 2 of TB2 in the Sensor Head, then power up the analyser. The output voltage
of the thermocouple amplifier between Sensor Head TB3 pins 7 and 8 should be
0.4 to 0.7V DC and the heater voltage at TB3 pins 5 and 6 should be
approximately 36V AC.
Now remove the temporary short circuit. The output of the thermocouple amplifier
should rise to between 8 and 12V DC and the heater voltage should fall to zero.
If the thermocouple amplifier does not switch as described, replace the Sensor
Head Terminals PCB.
If the heater drive does not react as described, replace the Control Unit PCB.
NOTE 7
Check the zirconia temperature measurement at the Sensor Head.
Ensure the thermocouple connected at TB2 terminals 1 and 2 is securely
connected with the correct polarity (refer to Table 5.3). Ensure the
thermocouple is not damaged or open circuit. Correct as necessary and
verify performance.
Temporarily disconnect the thermocouple wires from TB2 terminals 1 and
2 and temporarily fit a short circuit link. The correct voltage at TB3 terminal
7 with respect to 8 is 0.4 to 0.7Vdc. If necessary replace the Terminal
PCB.
Temporarily open-circuit TB2 terminals 1 and 2. The correct voltage at TB3
terminal 7 with respect to 8 is between 8.0 and 12.0Vdc. If necessary
replace the Terminal PCB.
Check the zirconia cell temperature measurement at the Control Unit TB2
terminals 9 and 10. This voltage must be the same as measured at the Sensor
Head.
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Start
Check COe Sensor ºC Diagnostic. Is
temperature 305 ± 5ºC
and stable to ± 1ºC
Yes
End
See Sections 4.6 and 4.7 for
other symptoms
No
Yes
Is temperature
>150ºC
Check fuses F3 and
F5 in Control Unit
No
Disconnect COe heater
wires from TB2 pins 1 and
2 at Control Unit
Ok
Check COe band
heater resistance.
See Note 8.
Sensor
replaced
Blown
Check each wire is
isolated from earth
(1MΩ)
Ok
Ok
Check Coe PRT.
See Note 9.
<1MΩ
Check wiring, junction
boxes, Sensor Head
Terminals PCB and COe
sensor for faults. Repair or
replace parts as needed.
Replace Control
Unit PCB
Fix carried out
Figure 4.8 COe Sensor Heater Checks
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Note 8:
With the power to the analyser turned off, measure the resistance between
terminals 1 and 2 of terminal block TB2 on the Control Unit. The heater
resistance should be 11.4 10%. Note that the measured resistance will
include the heater cable which could be up to 4. If the heater cable is long
and the resistance reading is low, check the heater resistance at the Sensor
Head, terminals 1 & 2 of terminal block TB6, to ensure that the heater is not
short-circuit. If the heater is faulty, replace the sensor
If the temperature diagnostic is unstable, check that the sensor heater and
platinum resistance thermometer wiring (as described in Note 9) are isolated
from earth. Also visually inspect the sensor and verify that the gap in its band
heater is not located over the platinum resistance thermometer. If so, rotate
the band heater until the gap is approximately 90º from the platinum
resistance thermometer.
Note 9:
02700002D/0
With the power to the analyser turned off, measure the resistance between
terminals 3 and 4 of terminal block TB2 on the Control Unit. The resistance
should be between 100 and 200 depending on the temperature of the
transducer. If the measured resistance is about 3.3k then the PRT is opencircuit. Measure the resistance between TB2 terminals 4 and 5. The
resistance should be less than 10. More than 10 indicates an open circuit
in the Sensor Head or interconnecting cable. If the PRT is faulty, replace the
Tfx sensor.
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4.6
Measurement Problems
This section assumes that:
Both the Control Unit and Sensor Head are powered.
The Control Unit display and keypad are operational.
The Sensor Head and sensor(s) are stable at their respective operating temperatures.
Work through Section 4.5 if any of the above assumptions are untrue.
4.6.1
Definitions
When investigating reported measurement problems it is critical that the customer’s
terminology matches the examples shown below.
Drift is a general long term movement (trend) of the output signal level at constant
concentration which appears unrelated to ambient temperature but is systematic (i.e.
constant, in one direction).
In order to differentiate drift from other potential effects (shown below), a minimum 36 hour
period on chart is required before drift may be diagnosed.
Other fault symptoms as indicated below should be diagnosed and eliminated before
attempting to deal with drift only problems.
Other Phenomena:
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4.6.2
Discussion
Since the 2700D uses faster measurement technology than in-situ zirconia, pellistor-based
CO or cross-stack infra-red analysers, there is considerable scope for confusion because
the 2700D will reveal trends in the combustion process which were previously invisible. In
some instances the performance of the 2700D is so much at variance to customer
expectations that it can be perceived as operating incorrectly.
Drift - The most problematic definition is drift - customers often describe any deviation from
expected behaviour as ‘drift’. Language also causes problems - for example the literal
translation of the German term used to describe the effect of temperature on the reading is
‘temperature drift’.
Variable Span Sensitivity - To date this phenomenon has only been reported on the
Combustibles measurement. Some reports have been erroneous because customers have
not understood that the Tfx sensor is a partial pressure measurement device and that
therefore the span sensitivity is directly proportional to variations in flue and ambient
pressure. The majority of remaining instances have been due to poor installation of the
utilities panel (check for leaks and pressure drop; particularly if the utilities panel is not colocated with the Sensor Head) and/or inconsistencies in the calibration method.
If this problem is reported, ensure that the aspirator pressure at the Sensor Head is correct.
If the utilities panel is not co-located with the Sensor Head, you must take account of the
pressure drop in the aspirator air supply line.
Check that the calibration gas flow rate and settling time are consistent each time the
analyser is calibrated. Failure to observe these precautions can lead to inconsistent
calibration results.
Decreasing Span Sensitivity - Again, this complaint is predominantly made about the
combustibles measurement. The Tfx catalyst now has improved stability and resistance to
poisoning and carbonisation.
Tfx sensors may lose 10% of span sensitivity is the first few days on process as the catalyst
conditions itself. This is entirely normal and is not grounds for replacing the sensor.
Although catalyst sensitivity can be adversely affected by poisons such as SO2, the
simplest way to kill a Tfx sensor is to leave it on a process with consistently high levels of
CO. This combination of factors is guaranteed to reduce Tfx sensitivity to zero in a short
period of time.
Two versions of the Tfx sensor are available to suit differing process conditions. For well
controlled processes where the COe concentration does not routinely exceed 1500ppm for
long periods, and SOx concentrations do not exceed 1000vpm, the high sensitivity sensor
should be used. For less well controlled applications (typically coal or heavy oil burning
plant) where SOx concentrations exceed 1000vpm, the high sulphur sensor should be
used. Refer to technical datasheet for detailed information on combustibles sensor variant
applications.
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Temperature Following - In the majority of cases, this will not be visible while the analyser
is on process except if the analyser is subject to large daily temperature swings (30ºC or
more) and the process is known to be well controlled. The temperature co-efficient of the
analyser has been improved from earlier models.
If the Sensor Head build is correct and the problem persists, check that the COe coarse
zero is set correctly (i.e. 0V 60mV, refer to Appendix A). If the coarse zero is outside
these limits, the temperature co-efficient of the analyser will be degraded.
Noise - Complaints regarding noise generally have two causes:
1. The fast analyser response exceeds customer expectations or the ability of the
combustion control system to respond. If the control system is not fast enough, the
analyser response time can be slowed by the use of the software filter.
2. Poor electrical installation, particularly between the Control Unit and Sensor Head. If
non-recommended cables are used or the screens are incorrectly terminated then the
combustibles measurement can be susceptible to EMI.
Spiking - The issues discussed in Noise also apply to reports of spiking. Spiking on the
combustibles measurement can only be detected when the unit is running on calibration
gas or when the combustion process is off. If spiking is only said to occur when the
combustibles measurement is on process, then it is most likely that the analyser is working
correctly and revealing variations in the process which have not been visible to the
customer before.
Instability, Steps and Ramps - There have been relatively few reports of these
phenomena. Like drift, the term ‘instability’ can be used imprecisely. Likely causes of
instability in the oxygen measurement have already been covered under the headings of
Temperature Following, Noise and Spiking. However, there is one additional issue which
affects only the combustibles measurement. If the aspirator air supply pressure is changed
during operation, this could lead to a step change in COe reading.
Slow Speed of Response / No Response to Process Changes - If either of these are
reported, the pneumatics system must be checked before presuming that either or both
sensors need to be replaced (see Section 4.6.6 for details). The 2700D Sensor Head
design has significantly reduced instances of blocked internal pipework compared to earlier
Servomex combustion analysers. The only known instances have occurred when the
Sensor Head has been left unheated on the process for a long period. Blockages will affect
the Tfx sensor most since its output is more flow dependent than the zirconia sensor. By
contrast, because changes in the oxygen level on most processes is relatively slow, sample
diffusion within the Sensor Head will allow the zirconia sensor to track process trends quite
closely.
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4.6.3
Oxygen Measurement Checks
Start
Does the oxygen reading
appear to be valid?
No
Check zirconia cell wiring.
See Section 2.4
Ok
Yes
Check operation of
zirconia electronics.
See Note 1
Check zirconia cell output.
See Note 2
Faulty
Replace Control
Unit PCB
Faulty
Replace
zirconia cell
Ok
Fix carried out
Is response time
satisfactory on calibration
gas?
No
Check pneumatics
system.
See Section 4.6.6
Yes
Does the analyser
respond to process
changes?
No
Yes
Does the oxygen
measurement perform to
specification?
No
See Section
4.6.2
Yes
End
See Sections 4.6 and / or 4.7 for other symptoms
Figure 4.9 Oxygen Measurement Checks
The instructions opposite assume that manual calibration gas valves are fitted. If the
system uses solenoid valves, use the analyser to drive the valves and monitor the
oxygen mV readings via TB1 terminals 7 and 8 in the Control Unit.
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Note 1:
With the analyser operating and the Zirconia sensor at operating temperature,
monitor the oxygen sensor output voltage diagnostic. Apply the high
calibration gas (air), wait 5 minutes, then check that the diagnostic reading is
zero 5mV. Next apply the O2 low calibration gas (0.3% O2), wait 5 minutes,
then check the diagnostic reading. The reading should be as predicted by the
Nernst equation (see section 2.3.1) 5mV. If all is in order, perform a manual
high and low calibration of the oxygen sensor, overriding any “out of tolerance”
warnings.
If the diagnostic readings are not correct, turn off the power to the Control Unit
and disconnect the wiring from terminal block TB1 terminals 7 and 8. Fit a wire
link between terminals 7 and 8. Turn on the power to the Control Unit and
monitor the oxygen sensor output voltage diagnostic. The reading should be
close to 0V and stable to 0.1mV (drift less than 0.1mV per minute). Remove
the wire link and reconnect the field wiring to TB1. If the Control Unit
electronics are faulty, replace the Control Unit PCB.
Note 2:
With the analyser operating and the Zirconia sensor at operating temperature,
measure the zirconia sensor output voltage at the Control Unit TB1 terminals
8 (positive) and 7 (negative), or at the Sensor Head TB3 terminals 4 (positive)
and 3 (negative). Apply the high calibration gas (air), wait 5 minutes, then
check that the cell output is zero 5mV. Next apply the oxygen low calibration
gas (0.3% O2 typical), wait 5 minutes, then check that the change in the cell
output is as predicted by the Nernst equation (see section 2.3.1) 5mV. If the
cell output is outside specification it must be replaced.
A lower than expected oxygen reading is a normal instrument response to the presence
of combustibles components in the sample gas stream and may not be an instrument
fault. The reduction in the oxygen reading reported is dependent on the combustibles
level present and cell type. If there is sufficient combustibles in the sample gas to
consume all of the oxygen present, resulting in oxygen reducing conditions at the cell
electrode, then a zero oxygen reading may occur.
The 2700D analyser is designed to withstand conducted and radiated RF interference
in accordance with the European EMC directive. However, higher field strengths may
affect the oxygen reading, usually offsetting the reading from its true value. Good EMC
wiring practice and separation / screening of 2700D cables from RF sources should
prevent EMC problems from arising
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4.6.4
Combustibles Measurement Checks
Start
Are COe mV LOW or COe
mV HIGH alarms active?
Yes
Check Tfx sensor wiring and
cell resistance. See Note 1
No
Fault
Corrected
Ok
Ok
Check operation of Tfx
electronics. See Note 2
Faulty
Replace Control
Unit PCB
Check pneumatics
system.
See section 4.6.6
No
adjustment
Insert air @ 600ml/min at
calibration port.
Is Coe mV = 0V ± 60mV?
No
Adjust Tfx cell coarse
zero.
See Note 3
Yes
Ok
Check response to span
calibration gas?
See Note 4
Low
sensitivity
Replace Tfx sensor
Ok
Does the combustibles
measurement perform to
specification?
No
See section 4.6.2
Yes
End
See Section 4.7 for other symptoms
Figure 4.10 Combustibles Measurement Checks
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The point at which the pneumatics are checked is different from the Oxygen
measurement because the response of the Tfx sensor is highly dependent on sample
flow rate. Whereas diffusion from the calibration port will allow the zirconia sensor to be
checked (albeit slowly), the pneumatics system must be fully functional to obtain
representative results from the Tfx sensor.
Note 1:
With the power to the analyser turned off, check the wiring between the
Sensor Head and Control Unit conforms to Section 2.4. If no faults are found,
check the Tfx sensor resistance to verify that it is not faulty. Measure the
resistance between Sensor Head terminal TB6 terminals 5 and 6, and 7 and
8. Each pair of terminals should measure the same resistance within a few
Ohms, from 35 at 25C to 70 at 300C (all 20%). Measure the resistance
between TB6 terminals 6 and 8, and 6 and 9. Each pair of terminals should
measure the same resistance within a few Ohms, from 26 at 25C to 52 at
300C (all 20%). Measure the resistance between Control Unit TB1 terminals
2 and 5, 3 and 4. Each pair of terminals should measure less than 10. Any
incorrect measurement indicates a wiring problem in the Sensor Head or
faulty sensor.
Note 2:
With the power to the analyser turned on, check the drive to the Tfx sensor to
verify that it is not faulty. Measure the voltage across TB1 terminals 1 and 6.
Use a voltmeter on its DC mV range. The voltmeter will measure the average
voltage across the Tfx sensor, which should be between 170mV and 560mV
depending on the resistance of the sensor as measured in Note 1 above.
Higher resistance gives a higher voltage. If the cell resistances are OK but
there is no voltage, replace the Control Unit PCB.
If the cell drive voltage is OK, then with the analyser operating and the Tfx
sensor at operating temperature, monitor the combustibles sensor output
voltage diagnostic. Turn the Tfx coarse zero adjust switch SW2 and check that
the voltage display changes. The minimum displayed voltage is -125mV and
the maximum displayed voltage is +1125mV. Between these two points the
voltage should change by approximately 60mV per switch step. Return SW2
to its original setting. If the diagnostic voltage does not change, replace the
Control Unit PCB.
Note 3:
Refer also to section A11 in Appendix A.
With the analyser operating and the Tfx sensor at operating temperature,
monitor the combustibles sensor output voltage diagnostic. Apply the zero
calibration gas (air), wait 5 minutes, then check that the diagnostic reading is
0mV 60mV. Adjust SW2 and SW3 to improve the zero reading if necessary.
There may be a delay of up to 30 seconds between a switch change and an
update to the displayed diagnostic value. If the displayed voltage is below 125mV or greater than +1125mV the analogue to digital convertor input is
saturated, so the switch settings may need to be moved several positions
before a valid reading can be displayed. If the coarse zero cannot be set
within the required limits, change the Control Unit PCB.
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Note 4:
Refer also to section A12 in Appendix A.
Next apply the CO span calibration gas, wait 5 minutes, then check the
diagnostic reading. The difference between the zero and span readings
should be 15mV. If the difference is less than this value, change the Tfx cell.
If all is in order, perform a manual high and low calibration of the combustibles
sensor, overriding any “out of tolerance” warnings.
The output signal from the combustibles sensor is proportional to the sample and
ambient pressures. Should the process or ambient pressures change the combustibles
sensor output will change proportionally.
The Sensor Head will frequently be operating at a pressure just below ambient
atmospheric pressure. Therefore any gas leakage through calibration fittings, pipe
work, valves, gas regulators and flow metres may affect the measured reading.
The Tfx1750 sensor will have a small cross sensitivity to other gas species that may be
present in the sample stream. Some variation in both zero and span is to be expected if
the composition of the sample stream changes.
The 2700D analyser is designed to withstand conducted and radiated RF interference
in accordance with the European EMC directive. However, higher field strengths may
affect the combustibles reading, usually offsetting the reading from its true value. Good
EMC wiring practice and separation/screening of 2700D cables from RF sources
should prevent EMC problems from arising.
4.6.5
Flow Alarm Measurement Checks
Refer to Figure 4.11.
Symptoms
Flow alarm Relay Box has no illuminated LED’s.
Flow alarm cannot be calibrated.
Flow alarm relay in ‘Fault’ condition.
Relays not activating correctly.
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Key
1.
2.
3.
4.
Description
Terminal Block 1 (12Vdc power)
Terminal Block 2 (flow alarm sensor connections)
Terminal Block 3 (connections to Relay Box)
Fuse FS11 (250mA)
Figure 4.11 Flow Alarm Amplifier Board
Measurement and Diagnosis
Check 12Vdc present at TB1 terminals1 and 2 with respect to 0Vdc on TB3 terminal4.
Check Flow Alarm Relay Box supply fuse FS11.
Check 12Vdc is present on at TB3 terminal1 with respect to TB3 terminal4.
Check the voltage at TB3 terminal 2 with respect to TB3 terminal 3. This should be
between approximately 3Vdc (no flow) and 9Vdc (normal flow) in operation.
Check flow alarm sensor wires are correctly terminated on TB2 terminals 1 to 4. Refer
to Table 5.4.
Check resistance of flow alarm sensor bridge circuit. Flow alarm sensor wires should
be removed from TB2 for the purposes of this test.
Check resistance between blue / red & green / yellow wires is between 50-60Ω at
20°C, or 78-94Ω when Sensor Head is at operating temperature.
The Flow Alarm Signal Amplifier Board and 1760 flow alarm sensor are factory
paired/matched. They should only be replaced as a matched pair.
The Flow Alarm Signal Amplifier board has three potentiometers fitted (RV1, 2 & 3).
RV1 & RV2 are factory set and sealed with red sealing varnish. These should not be
adjusted. RV3 is also factory set so that a signal voltage of 3.0Vdc is present with no
flow of sample gas. There should be no need to adjust this, but if adjustment is required
it should only be performed under the instruction of a Servomex Engineer.
The Flow Alarm Relay Box electronics board is powered from the Flow Alarm Signal
Amplifier Board. The +12Vdc supply to the Flow Alarm Relay Box is protected by Fuse
FS11.
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Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Description
Zero calibration potentiometer, DS1 & DS2 LED’s
Span calibration potentiometer, DS3 & DS4 LED’s
Low Flow Alarm status potentiometers DS5 & DS6 LED’s
Low Flow Alarm set point adjustment S1
Terminal Block TB1 (connections to Sensor Head Flow Alarm Signal Amplifier
Board)
Low Flow status relay
Flow Fault status relay
Terminal Block TB2 (relay terminals)
Relay enable switch S2
Relay phase switch S3
Figure 4.12 Flow Alarm Relay Board
Check interconnecting wiring between the Flow Alarm Signal Amplifier board and the
Flow Alarm Relay Box board. Refer to Table 2.5.
Check 12Vdc is present at TB1 terminal1 with respect to TB1 terminal 3.
Check the voltage at TB1 terminal 2 with respect to TB3 terminal 3. This should be
between approximately 3Vdc (no flow) and 9Vdc (normal flow) in operation.
Check that one LED of each Green / Red LED pair is ON.
Check Relay operation enable switch (S2) is set to ON to allow relays ‘Flow Fault’ and
‘Flow Alarm’ to operate.
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Force the ‘Alarm’ relay to operate (indicating low flow) by adjusting the alarm setpoint
rotary switch (S1) anticlockwise until DS5 (red) is ON and DS6 (green) is OFF. Check
relay contact status changes on TB2 terminals 4, 5 and 6. Changeover operation of this
relay will depend on the setting of the phase selection switch S3.
Check ‘Phase’ selection switch (S3) is set to the required operational state as required
by the customer control system.
Check Zero and Span potentiometers RV1 and RV2 operate correctly following
instructions defined in installation manual for Flow Alarm calibration and set-up.
LED
COLOUR
LED ON STATUS
DUTY
DS1
DS2
DS3
DS4
DS5
DS6
RED
GREEN
RED
GREEN
RED
GREEN
Calibration set-point low
Calibration set-point OK
Calibration set-point high
Calibration set-point OK
Low Flow Alarm ‘ACTIVE’
Low Flow Alarm ‘OFF’
Zero calibration threshold set-point
Span calibration threshold set-point
Flow alarm status indication
Should either DS1 or DS3 (red LED’s) be illuminated then a ‘FAULT’ condition will exist
and the relay will operate (flow measurement outside of calibrated set-points). Its mode
of operation depends on the setting of the phase switch S1. DS1 or DS3 red LED’s
indicate that current sample flow is outside of calibrated settings. The Flow Alarm
should be recalibrated following the instructions in the Installation manual.
DS5 red LED ON indicates the sample flow has fallen below the flow % threshold set
by the Flow Alarm set point switch S1. DS6 green LED ON indicates the flow is above
the threshold set by the switch S1.
The terminals on the Flow Alarm amplifier board are labelled TB1, 2 and 3. These
should not be confused with TB1, 2 and 3 on the lower Terminals PCB.
The 12Vdc supply to TB1 terminal 1 is from the lower terminals board TB7 terminal 4.
The 12Vdc supply to TB1 terminal 2 connects to Solid State Relay Terminal 3.
The 0Vdc supply to TB3 terminal 4 is from the lower terminals board TB7 terminals 5
and 6.
The Terminals TB3 terminal1, 2 and 3 are for customer connection wires to the
associated Flow Alarm Relay Box.
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4.6.6
Pneumatics System Checks
Start
Check flue pressure is not
less than -200mmWG
See Note 1
Flue pressure
too low
Application problem.
Consult Servomex
Ok
Check aspirator pressure
and flow rate.
See Note 2
Outside limits
Check aspirator.
See Note 3
Ok
Low
flow
Check sample flow.
See Note 4
Inspect internal
filter for evidence
of blockage
Dust
present
Check probe for
damage. Add or
replace filter as
necessary
Flow
Ok
End
Go back to Sections
4.6.3 or 4.6.4 or see
Section 4.7 for other
symptoms
Check pipework
in Sensor Head
for evidence of
blockage
Blocked
No
Clear
Check
probe tube
Condensate
Did previous
test reveal
Sensor Head
temperature
Consult
Servomex
Yes
Replace
pipework
Dust
Add or replace filter as necessary
Application problem.
Consult Servomex
Figure 4.13 Pneumatics System Checks
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Note 1:
Connect a manometer to the calibration gas port on the Sensor Head and
measure the flue pressure relative to atmosphere. For a completely accurate
reading the aspirator air supply should be turned off, however in normal
circumstances the influence of the aspirator is minimal.
The internal aspirator is not designed to overcome flue pressures below 200mmWG. If the flue pressure is below this limit then an alternative method
of extracting a sample is required.
Note 2:
Connect a flow meter in series with the aspirator air supply together with a
pressure gauge. Check that the aspirator pressure at the Sensor Head is
equal to the pressure marked in the Sensor Head terminals compartment;
adjust the pressure regulator on the utilities panel if necessary.
Once the aspirator pressure is set correctly, check the flow rate is between 1.0
and 1.5 litres/min.
Note 3:
If the aspirator flow rate is >1.5 litres/min, there is probably a leak at the
seating of the aspirator assembly.
If the flow rate is <1.0 litres, the aspirator jet is blocked. Clean or replace the
aspirator jet as necessary. Also check that the filters in the air line and the line
itself are clear of oil before reconnecting the air supply. If contamination is
found, verify that the air supply is instrument grade air. If there is no flow at all,
check that the Sensor Head solenoid valve is open. Refer to Section 4.6.6 and
clear any faults as necessary.
Note 4:
This test estimates the sample flow by introducing a check gas whose
composition is markedly different to the sample being drawn by the analyser.
The test is best performed with the oxygen measurement (if fitted) since the
response of the zirconia sensor is far less flow dependent than the Tfx sensor.
With process sample flowing through the analyser, make a note of the current
value of oxygen and/or combustibles on the display.
Select a calibration gas which is significantly different from the value given by
the process sample (instrument air is normally suitable). Pass 600cc/min of
this calibration gas through a flow meter and needle valve into the calibration
port, the analyser display should now display the calibration gas value.
Gradually reduce the flow of the calibration gas in steps, allowing time for the
change in measurement on the display. Now increase the calibration gas flow
gradually until the reading approaches the original calibration gas value. At
this point, the calibration gas flow is approximately equal to the normal sample
gas flow.
The process sample flow through the 2700D should be approximately
300cc/minute for an oxygen only analyser. The combustibles only and dual
sensor analysers should have a sample flow of approximately 240cc/minute.
Flows significantly below this indicate a partially blocked sample path (sample
probe, internal filter, etc) or an incorrectly set aspirator air supply.
If the analyser reading goes directly to the check gas value then the analyser
is not drawing a sample and the cause must be investigated.
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4.6.7
Aspirator Interlock Failure
The solenoid valve on the terminal enclosure must be energised for the aspirator air supply
to be applied to the aspirator. In order for the solenoid valve to be energised, the gas
sensor(s) and the Sensor Head must all have reached a satisfactory temperature.
Use the VIEW menu to determine the temperature of the Sensor Head (if the optional probe
head temperature connections are installed) and also the temperature of the gas sensor(s).
Verify the following:
The oxygen sensor (if fitted) is at or above 650C.
The Sensor Head temperature is at or above 235C.
If any of these conditions are unsatisfactory, refer to Section 4.5.5 and correct the fault.
If all the temperatures are satisfactory, check the operation of the solenoid valve as
follows:
Remove the Sensor Head terminal enclosure cover. (Do not remove any protective
covers within the terminal enclosure).
Temporarily disconnect the solenoid valve wire at TB7 terminal 2 and ensure the
solenoid valve is closed.
Temporarily reconnect the above solenoid valve wire to TP2 (0V) on the terminal PCB.
The solenoid valve should be heard to energise and be open. The resistance of the
solenoid valve coil is approximately 80Ω at room temperature.
Re-connect the solenoid valve wire to TB7 terminal 2 or replace the valve if necessary.
If the temperatures are satisfactory and the solenoid valve still operates incorrectly, replace
the terminal PCB.
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4.7
Analyser Problems
Fault finding guidance within this section assumes that:
Both the Control Unit and Sensor Head are powered.
The Control Unit display and keypad are operational.
The Sensor Head and sensor(s) are stable at normal operating temperatures.
Oxygen and/or combustibles measurements are stable when viewed at the Control Unit
display.
Work through Sections 4.5 and 4.6 if any of the above assumptions are untrue.
Start
Step 1
Do analogue (mA) outputs work
correctly?
No
Go to Section 4.7.1
Yes
Step 2
Do relays operate correctly?
No
Go to Section 4.7.2
Yes
Step 3
Does manually initiated auto
calibration operate correctly?
No
Go to Section 4.7.3
Yes
Step 4
Does manually initiated blow back
operate correctly?
No
Go to Section 4.7.4
Yes
Step 5
Does timed auto calibration and/or
blow back operate correctly?
No
Go to Section 4.7.5
Yes
End
Figure 4.14 Final Analyser Checks
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4.7.1
Analogue (mA) Output Failure
Before carrying out any fault finding, check the following at the Control Unit:
Check that the analogue output assignments are correctly configured and enabled
within the analyser software.
In the “Setup” menu, check the range, “0-20/4-20", “freeze/follow” and “jam
high/low/none” settings for each analogue output.
If an output is set to jam high or low, check that there is no condition prevailing that is
causing the output to jam.
If an output is set to freeze, it will freeze during calibration (both manual and automatic)
and blow back.
Start
Is analogue output load resistance
less than 1000Ω and interconnecting
cable correctly installed within the
screw terminal block on the control
PCB?
No
Check wiring and
intermediate
junction boxes
Incorrec
t
Replace Control
Unit PCB
No
Set up analogue
outputs as per
Appendix A.7
Yes
Verify basic operation of analogue
output(s). See Note 1
Ok
Is accuracy ± 0.1mA
Yes
Go to Figure
4.13 Step 2
Figure 4.15 Analogue Output Checks
The analyser is provided with a jam on fault facility for the analogue outputs. The jam
facility operates by forcing the analogue output to a user configurable high (21mA) or
low (0mA) level should any of the possible fault conditions occur. The two possible
analogue outputs can be separately configured to either jam high, jam low or not to jam
in the analyser software.
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Note 1:
90
Verify operation of the analogue outputs using the “SET OUTPUTS” option in
the “SERVICE” menu in the analyser software as follows:
Disconnect the field wiring from the analogue output terminals and
connect a mA meter across each pair of terminals. If a mA meter is not
available, fit a resistor of 1k or less across each pair of terminals and
measure the voltage across the resistor. Divide the measured voltage by
the resistance to obtain the current.
Using the “Service” menu, set the analogue outputs to 0mA and check
that each output measures 0.1mA or less.
Set the analogue outputs to 20mA and check that the readings are 20mA
0.1mA. If resistors and a voltmeter are used, the calculated current must
be based on the measured resistance of the resistor and not its nominal
value. The analogue output span can be adjusted with RV3 and RV4, but
this should be done with the analogue outputs connected to the
equipment that they are to be used with (also see Appendix A7).
Set the analogue outputs to 4mA and check the readings are 4mA
0.1mA.
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4.7.2
Relay Output Failure
Before carrying out any other fault finding, check that the relay assignments are correctly
configured and enabled within the analyser software.
Start
Is all interconnecting wiring correctly
installed within the screw terminal
block on the control PCB?
No
Check wiring and
intermediate
junction boxes
Yes
Verify basic operation of relay
outputs. See Appendix A.8
Incorrec
t
Replace Control
Unit PCB
Go to Figure
4.13 Step 3
Figure 4.16 Relay Output Checks
4.7.3
Auto Calibration Failure
Symptoms
Auto calibration fault indicated.
Analyser does not start an auto calibration.
Poor accuracy following calibration.
Auto calibration is not activated by closure of external contacts.
Measurements and Diagnosis
02700002D/0
Check that the auto calibration configuration is correctly configured and enabled
within the analyser software. Check that the contents of the calibration gas samples
have been correctly entered into the analyser software.
Check that the time and date have been correctly set in the analyser software.
Check that the auto calibration start time and date have been correctly configured.
Check that a blow back procedure has not been configured to start at the same
time, or immediately before, the auto calibration. If an auto calibration attempts to
start while a blow back is in progress then the auto calibration will be aborted.
For remote auto calibration actuation via remote contact closure, check that
connecting wiring is correctly installed and that the external initiation contacts are
closed for at least 15 seconds.
Check that the calibration gases have been correctly connected to the calibration
gas port. Check that the calibration gases are not empty and have been turned on.
Check that the calibration gas flow rate is 600 20ml/min.
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Check that there are no leaks in the interconnecting calibration gas piping and that
any flow meters and needle valves fitted operate correctly.
Check for correct operation of the calibration gas solenoid valves. Perform a leak
test to verify cross seat leakages. Check the wiring between the solenoid valves
and the relay outputs. Check that the relay outputs are correctly allocated in the
analyser software.
Check for inappropriate calibration tolerance values (too tight) stored in the
software parameters. Increase the calibration tolerances if necessary.
Otherwise refer to the particular transducer measurement error faults in Section 4.6.
If an “AUTO CAL FAIL” fault has occurred then the only way to disable the fault is to
perform a successful automatic calibration. Perform a single cycle immediate auto
calibration to clear the fault.
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4.7.4
Blow Back Failure
Symptoms
Analyser does not start a blow back process.
Blow back is not activated by closure of external contacts.
Measurements and Diagnosis
4.7.5
Check that the blow back configuration is correctly configured and enabled within
the analyser software.
Check that the time and date have been correctly set in the analyser software.
Check that the blow back start time and date have been correctly configured.
Check that an auto calibration has not been configured to start at the same time, or
immediately before, the blow back. If a blow back attempts to start while an auto
calibration is in progress then the blow back will be aborted.
For remote blow back actuation via remote contact closure check that connecting
wiring is correctly installed and that the external initiation contacts are closed for at
least 15 seconds.
Check that there are no leaks in the interconnecting calibration gas piping and that
any flow meters and needle valves fitted operate correctly.
Check for correct operation of the blow back solenoid valve. Perform a leak test to
verify cross seat leakage. Check the wiring between the solenoid valves and the
relay outputs. Check that the relay outputs are correctly allocated in the analyser
software.
Analyser Does Not Keep Correct Time or Date
Symptoms
Time and/or date requires frequent correction or does not work.
Measurements and diagnosis
02700002D/0
Check that the internal clock has been correctly set and the instrument has not
been powered down for a period exceeding one month.
Replace the control PCB and re-validate analyser performance.
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5 PARTS REPLACEMENT PROCEDURES
5.1
Control Unit Access
Key
Description
1. Door
2. Captive M6 screws (4 off)
3. M4 retaining screws (4 off)
Key
Description
4. Plastic insulating cover
5. Hinge pins (2 off)
Figure 5.1 Control Unit Access
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The Control Unit is fitted with a hinged die cast aluminium door sealed by a silicon rubber
O-ring and secured by four captive M6 screws. Inside of the Control Unit a transparent
plastic insulating cover protects the user from access to electrical terminals that may be
exposed to hazardous high voltages.
Removal
Refer to Figure 5.1.
1. Undo the 4 captive M6 screws (2) and open the hinged door (1).
WARNING
Removal of the plastic insulating cover exposes the user to potentially
lethal voltages. It is essential that only suitably trained and competent
personnel are allowed access to hazardous live parts.
2. To gain access to the electrical power and relay contact terminals, remove the 4 M4
retaining screws (3) and lift out the clear plastic cover (4) which insulates the terminals.
Refitting
1. Check that all the electrical connections are secure and refit the clear plastic cover (4)
and secure it with the 4 retaining screws (3). Do not use any thread lock on these
screws.
2. Check that the O-ring seal in the door is correctly located and undamaged. Wipe the Oring and mating surfaces to remove any dust or grease.
3. Close the hinged door (1) and secure it with the 4 captive screws (2).
5.2
Control PCB Removal and Replacement
There are four versions of the control PCB that may be fitted to the analyser defined by the
sensor configuration and build date of the product. 2700D Control Units with a serial
number of 20,000 or later are fitted with a common control board that can be configured for
the three sensor configurations, set by DIP switches. 2700D Control Units with a serial
number below 20,000 still require one of three control boards which are listed in Section 3.
The common control board must not be fitted into an older Control Unit for compliance
reasons.
Refer to Figure 5.2.
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Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Description
Keypad ribbon cable connection
LCD ribbon cable connection
Metal protection cover
M4 mains protection cover retaining screws (4 off)
M4 PCB retaining screws (8 off)
Transformer secondary connection
Transformer primary connection
M4 PCB earth wire connection
FLASH memory chip
M4 Transformer earth connection
Sensor configuration DIP switches
Figure 5.2 Control Unit Internals
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Removal
1. If a new control PCB is to be fitted after removal, then note the analyser software
settings and sensor configuration before proceeding.
2. Switch off all electrical power to both the Control Unit and Sensor Head. Isolate any
power sources connected to the relay terminals.
WARNING
Removal of the plastic insulating cover may expose the user to
potentially lethal voltages resulting from external electrical connections
to the relay contacts even when electrical power is disconnected from
the Control Unit itself. It is essential that only suitably trained and
competent personnel are allowed access to hazardous live parts.
3. Refer to Section 5.1. Open the Control Unit door and remove the transparent plastic
insulation cover.
4. Disconnect all the wires from the terminals and withdraw the cables to allow clearance
for removal of the metal protection cover and the PCB.
5. Unplug the keypad ribbon cable (1) and the LCD ribbon cable (2) from the control PCB.
6. Remove the 5 off M4 cover retaining screws (4) retaining the metal cover (3) to the
control box casting. Remove the metal cover (3) from the control box.
7. Remove the M4 screw (8) for the PCB earth wire connection.
8. Unplug the transformer primary (7) and secondary (6) connectors from the control PCB.
9. Remove the 7 off M4 PCB retaining screws (5) and the hexagonal pillar and lift out the
control PCB.
Refitting
1. Replace using the reverse procedure.
Locate and secure the PCB earth connection onto the cast boss on the Control
Unit enclosure before locating the PCB in the Control Unit.
When refitting the PCB ensure that the heat sink plate locates securely on the
bosses on the Control Unit casting before tightening fixings.
Ensure that the transformer wires, transformer earth and PCB earth wires are not
trapped under the PCB before tightening fixings.
2. Ensure that the transformer primary connection (PL6 or PL7 in Figure 5.2) and the
main power fuse rating are appropriate for the electrical supply voltage (see Table 5.1).
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Table 5.1 Control Unit Electrical Power Voltage Selection
Nominal Voltage
Transformer primary
connection
Main power fuse (F1) rating
100 / 110 / 120 Vac
PL7
T 3.15A HRC
220 / 240 Vac
PL6
T 1.6A HRC
3. If a new control PCB has been fitted, then this will have a default software
configuration. Refer to the 2700D Quickstart manual for detailed instructions on setting
software parameters.
4. Refer to Figure 5.3. Ensure the measurement transducer configuration DIP switches
are set to the correct positions for the sensors located in the sensor enclosure of the
Sensor Head. Sensor ON is when the switch is positioned away from the text “O2”
and/or “CO” (the down position).
5. Refer to Appendix A for detailed analyser performance checking.
ON
ON
CO
COe ONLY
O2
CO
OXYGEN & COe
O2
CO
O2
OXYGEN ONLY
ON
Figure 5.3 Measurement Transducer DIP Switch Configurations
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5.3
Control Unit Transformer Removal and Replacement
The Control Unit is provided with a toroidally wound twin primary, dual secondary,
transformer mounted underneath the control PCB in the Control Unit.
Key
Description
1. Transformer
2. M6 retaining screw
Key
Description
3. Earth connection
Figure 5.4 Control Unit Transformer Detail
Removal and refitting
1. Refer to Section 5.2. Remove the control PCB from the Control Unit.
2. Disconnect the M4 transformer earth connection (3) from the boss inside of the control
box enclosure.
3. Remove the M6 retaining screw (2) and lift out the transformer.
4. Replace using the reverse procedure. When refitting the transformer, rotate the
transformer so that the wires route towards the top right hand corner of the Control Unit
enclosure.
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5.4
Firmware Installation
The 2700D analyser is supplied with firmware, with a user selectable interface in English,
French or German. The firmware is supplied preloaded into a FLASH memory chip.
Refer to Figure 5.2.
Removal and refitting
1. Switch off all electrical power to both the Control Unit and Sensor Head. Isolate any
power sources connected to the relay terminals.
WARNING
Removal of the plastic insulating cover may expose the user to
potentially lethal voltages resulting from external electrical connections
to the relay contacts even when electrical power is disconnected from
the Control Unit itself. It is essential that only suitably trained and
competent personnel are allowed access to hazardous live parts.
2. Refer to Section 5.1. Open the Control Unit door and remove the transparent plastic
insulation cover.
3. Disconnect all the wires from the terminals and withdraw the cables to allow clearance
for removal of the metal protection cover.
4. Unplug the keypad ribbon cable (1) and the LCD ribbon cable (2) connectors from the
control PCB.
5. Remove the 5 off M4 cover retaining screws (4) retaining the metal cover (3) to the
Control Unit casting. Remove the metal cover (3) from the control box.
6. Using an appropriate extraction tool remove the microcontroller chip from the control
PCB.
When fitting a new memory chip in the control PCB ensure that the chamfered
corner on the chip is correctly located within the socket on the PCB.
7. Replace using the reverse procedure.
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5.5
Display Removal and Replacement
Refer to Figure 5.5.
Removal and refitting
1. Switch off all electrical power to the Control Unit.
WARNING
Removal of the plastic insulating cover may expose the user to
potentially lethal voltages resulting from external electrical connections
to the relay contacts even when electrical power is disconnected from
the Control Unit itself. It is essential that only suitably trained and
competent personnel are allowed access to hazardous live parts.
2. Refer to Section 5.1. Open the Control Unit door. Do not remove the transparent mains
protection cover.
3. Remove the 2 off M3 cover retaining screws and washers (2) and remove the display
protection cover (1) from the display( 4).
4. Unplug the display ribbon cable (8) from the control PCB. Release the display ribbon
cable (8) from the ribbon cable clamp (9).
5. Remove the 2 off M3 cover spacers and washers (3). Remove the 2 off M3 display
retaining screws and washers (5). Lift off the liquid crystal display (4) from the keypad
(7).
6. Replace using the reverse procedure; ensure that the display module is fitted with the
cable at the bottom of the module.
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Key
Description
1. Display protection cover
2. M3 cover retaining screws (2)
3. M3 cover spacers + insulation
washers (2)
4. Liquid crystal display
5. M3 display retaining screws +
insulation washers(2)
6. M4 keypad retaining screws (2)
Key
7.
8.
9.
10.
11.
12.
Description
Keypad
Display ribbon cable
Display ribbon cable clamp
Keypad ribbon cable
Keypad retaining frame
O-ring seal
Figure 5.5 Display and Keypad Mounting Details
When refitting the LCD/display with the 2 off M3 retaining screws (5) and M3 cover
spacers (3) ensure that the washers are fitted in order to prevent the screws bottoming
out in the threaded spacers. Also ensure the insulating washers are fitted between the
LCD and stainless steel washers.
When fitting the protection cover (1) with the 2 off M3 retaining screws (2) then ensure
that the washers are fitted in order to prevent the screws bottoming out in the threaded
spacers. Do not use thread lock on these screws.
Examine the ribbon cable clamp (9) and replace if damaged. If the keypad has been
replaced then fit a new ribbon cable clamp in all cases.
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5.6
Keypad Removal and Replacement
Refer to Figure 5.5.
Removal and refitting
WARNING
Removal of the plastic insulating cover may expose the user to
potentially lethal voltages resulting from external electrical connections
to the relay contacts even when electrical power is disconnected from
the Control Unit itself. It is essential that only suitably trained and
competent personnel are allowed access to hazardous live parts.
1. Switch off all electrical power to the Control Unit.
2. Refer to Section 5.5. Remove the display.
3. Unplug the keypad ribbon cable (10) from the control PCB.
4. Remove the 12 off M4 keypad retaining screws (6). Remove the keypad retaining
frame (11) and lift out the keypad (7) from the recess in the hinged door
5. To replace, check that the O-ring seal (12) in the door is correctly located and
undamaged. Wipe the O-ring and mating surfaces with a damp cloth to remove any
dust or grease. Replace the keypad using the reverse procedure.
5.7
Sensor Head and Terminal Box Cover Removal and Replacement
Refer to Figure 5.6.
The Sensor Head is designed to be flange mounted directly on to the flue wall and is
heated. Service access to the Sensor Head and its terminal enclosure may be restricted.
Depending on installation location it may be advisable to remove the Sensor Head from the
flue wall to provide convenient service access. The installation details for the Sensor Head
vary depending on the sample probe type in use and the specific flange mounting
arrangement. Refer to the 2700D Installation manual for specific details on the mounting
arrangement in use.
The terminals compartment is sealed for dust and moisture ingress by an O-ring secured
into the terminal compartment lid. The sensor compartment is similarly sealed by an O-ring
located in the Sensor Head base.
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Key
1.
2.
3.
4.
Description
Mounting flange
Sensor head base casting
Insulation spacer
Terminal box casting
Key
5.
6.
7.
8.
Description
Terminal box cover
Terminal cover screws
Sensor head cover
Sensor cover screws
Figure 5.6 Sensor Head Overview
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Removal
WARNING
The 2700D Sensor Head, excluding the probe assembly, weighs
approximately 17Kg (38 lbs), care must be taken when handling.
The analyser may contain toxic, corrosive, flammable or asphyxiant
gases. Vent the analyser to a safe area and flush with air before
commencing work.
The Sensor Head is heated and may be attached to a hot flue. The
external surfaces will be uncomfortably hot even after power down for
several hours. Exercise care when handling the Sensor Head even
when un-powered on a hot flue.
1. Connect an air supply or other inert gas to the calibration gas port at a flow rate of 600
ml/min. Allow the Sensor Head to flush for 10 minutes to remove potentially toxic and
flammable gases from the Sensor Head pipe work.
2. Turn off the aspirator air supply and then isolate the electrical supply to the Sensor
Head and Control Unit. The Sensor Head can then be left to cool while the flow of air or
other inert gas is maintained.
3. If service access to the Sensor Head is limited when attached to the flue then remove
the Sensor Head from the flue.
4. To gain access to the Sensor Head terminal PCB and the electrical terminations
proceed as follows: Undo the 4 off captive M6 screws (6) and remove the terminal box
cover (5). To gain access to the electrical power terminals remove the M4 retaining
screw and lift out the clear plastic cover which insulates the terminals.
WARNING
Removal of the plastic insulating cover when the Sensor Head is
powered exposes the user to potentially lethal voltages. It is essential
that only suitably trained and competent personnel are allowed access
to hazardous live parts.
5. To gain access to the Sensor Head oven compartment proceed as follows: Undo the 4
off captive M6 screws (8) and remove the sensor compartment cover (7).
WARNING
The sensor compartment is heated to a temperature of 250C and may
be attached to a hot flue. Removal of the sensor compartment cover
exposes the user to potentially hazardous hot components. If the sensor
compartment cover is to be removed then it is recommended that the
Sensor Head be left for 2 hours to cool down first after electrical
isolation.
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Replacement
1. Check that the electrical connections to the Terminals PCB are secure and refit the
clear plastic insulating cover. Do not use thread lock on these screws.
2. Check the O-ring seals in the terminal compartment lid and in the Sensor Head base
are correctly located and undamaged. Wipe the O-rings and mating surfaces with a
damp cloth to remove any dust or grease.
3. Refit the terminal compartment lid and sensor compartment lid and secure with the M6
captive screws.
4. If necessary remount the Sensor Head to the flue and power up the Sensor Head using
the procedure detailed in the installation manual.
CAUTION
If the sensor is mounted with the terminal box vertically above the Sensor Head body then
the accuracy and service life may be reduced.
Ensure that mounting bolts are tightened evenly to ensure the Sensor Head and any
mounting flanges seal properly. Particular care must be taken if the Sensor Head is
mounting onto a raised face flange.
When refitting a Sensor Head always check the integrity of the flange sealing gasket.
Servomex always recommend this gasket is replaced when refitting a Sensor Head.
The Sensor Head must not be left unpowered when mounted on an active (hot) flue. If
the sample probe is not to be fitted immediately then a suitable blanking flange should
be used. Do not plug the hole with the Sensor Head.
A sachet of anti-seize compound (part number 1761-3211) is supplied as standard as
part of the analyser’s ‘loose items’ kit and is available for use on the Sensor Head
mounting bolts and studs. Failure to use the anti-seize compound may make the fixings
difficult to remove in the future.
When refitting the Sensor Head onto an active (hot) flue, ensure a continuous flow of
air or other inert gas is supplied to the calibration port. This flow should be maintained
until the Sensor Head is powered and has reached operating temperature.
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5.8
Terminals PCB Removal and Replacement
Refer to Figure 5.7.
There are five versions of the Terminals PCB that may be fitted to the analysers defined by
the sensor configuration fitted. Section 3 lists the part numbers of the five spare PCB’s.
It is critical that the correct Terminals PCB is fitted to maintain correct operation of the
Sensor Head. Please note the optional Flow Alarm module also dictates which
Terminals PCB type should be fitted.
Removal
1. Refer to Section 5.7 (and Figure 5.11 if a Flow Alarm module is fitted). Remove
terminal compartment cover and disconnect the electrical power from both the Control
Unit and Sensor Head. Remove the M4 protection cover retaining screw (11) and
remove the protection cover (8) that insulates the mains rated electrical power
connection beneath it.
WARNING
Removal of the plastic insulating cover may expose the user to
potentially lethal voltages if the electrical supply is not disconnected first.
It is essential that only suitably trained and competent personnel are
allowed access to hazardous live parts.
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Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Description
Solid state relay
Terminal block TB2
Terminal block TB7
Solenoid valve
Solenoid valve retaining nut
Terminal PCB earth connection
Terminal block TB9
Transparent protection cover
Terminal block TB8
Terminal block TB1
Key
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Description
M4 cover fixing screw
Mains fuse F1
Terminal block TB3
Terminal block TB4
Terminal block TB6
Terminal block TB5
M4 Terminal PCB fixing screws
Wiring support P clip + EMC ferrite
Transformer
Earth stud
Figure 5.7 Sensor Head Terminal Enclosure Detail (without Flow Alarm)
If the Sensor Head is fitted with a Flow Alarm module, the Flow Alarm signal amplifier
PCB sits above items (3) and (19). See Section 5.13 for Flow Alarm PCB removal.
108
1.
Disconnect all mains power and electrical interconnecting wiring from terminal blocks
TB1, TB3 and TB5 and withdraw the cables to allow clearance for removal of the PCB.
Disconnect any interconnecting wiring shield connections from the ground post at the
bottom edge of the PCB. Make a note of the schedule of the interconnecting wiring to
facilitate later reconnection.
2.
Remove the clip (18) and EMC ferrite supporting the internal sensor wiring. Disconnect
all internal wiring to the sensor compartment from terminal blocks TB2, TB4, TB6, TB7,
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TB8 and the sensor wiring screen from PCB fixing screws (if fitted). Withdraw the
internal wiring to allow clearance for removal of the PCB.
3.
Disconnect the terminal PCB earth wire from the terminal box casting (6).
4.
Remove the remaining 5 off M4 PCB fixing screws (17) and lift out the terminal PCB.
Replacement
1. The mains operating voltage is set by connecting together the appropriate terminals in
terminal block TB9 (see Table 5.2). If a new Terminals PCB is being fitted then set the
correct mains operating voltage.
Table 5.2 Terminal PCB Voltage Selection Links
Nominal Voltage
Configuration Set Up
100V ac
Link TB9-2 to TB9-4
110 / 120V ac
Link TB9-2 to TB9-3
220 / 240 V ac
Link TB9-2 to TB9-1
2. Locate the Terminals PCB over the mounting holes and secure with 5 of the 6 M4 fixing
screws (17). Do not fit the remaining screw that locates the wiring support P clip (18)
until the internal sensor wiring is completed.
3. Internal combustibles cell wiring must pass through the EMC ferrite.
4. Reconnect the internal sensor wiring in accordance with the wiring schedule in Table
5.3.
5. Reconnect the mains power and interconnecting wiring. Connection details should have
been noted on disconnection. Interconnecting wiring schedules and diagrams are given
in Section 2.4.
6. Check that all electrical connections are secure then refit the clear plastic cover (8) and
secure it with the retaining screw (11). Do not use any thread lock on this screw.
7. Replace the terminal compartment cover as detailed in Section 5.7.
8. Follow the start-up procedure listed in the installation manual and the basic operational
checks detailed in Appendix A.
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Table 5.3 Sensor Head Internal Wiring Schedule
Terminal
TB2-1
TB2-2
TB4-1
TB4-2
TB4-3
TB4-4
TB6-1
TB6-2
TB6-3
TB6-4
TB6-5
TB6-6
TB6-7
TB6-8
Function
Zirconia thermocouple
Zirconia cell outputs
Colour
-ve
WHITE
+ve
GREEN
-ve
BLUE
+ve
YELLOW
RED
Zirconia heater output
Polarity not important
RED
BEIGE/BLACK
Combustibles cell heater
Polarity not important
BEIGE/BLACK
RED
Combustibles cell temperature
Polarity not important.
Combustibles cell supply voltage
Combustibles cell output
RED
+ve
BROWN
-ve
GREEN
+ve
BLUE
-ve
YELLOW
PCB MOUNTING
Combustibles cell braided screen (chassis earth)
CRIMP LUG
TB7-1
Solenoid valve
Polarity not important
BLACK
TB7-2
TB7-3
TB7-4
TB7-5
TB7-6
TB7-7
TB7-8
TB8-1
TB8-2
TB8-3
TB8-4
TB8-5
TB8-6
Solid state relay drive connections
BLACK
-ve
BLUE
+ve
RED
Not used
Link fitted
BLUE
Block temperature thermistor
Used on all versions
Polarity not important
WHITE
Block band heater
Polarity not important
BEIGE
Solid state relay power output connection
Polarity not important
Over-temperature thermostat
Polarity not important
BLUE
WHITE
BEIGE
GREY
GREY
BEIGE
BEIGE
Earlier 2700D builds were fitted with over-temperature thermostats with mauve wiring.
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5.9
Solenoid Valve Removal and Replacement
Refer to Figure 5.7.
The 2700D solenoid valve is fitted with a 12Vdc actuating coil.
Removal and refitting
1. Refer to Section 5.7. Remove the terminal compartment cover and switch off the
electrical power to the Sensor Head and Control Unit.
WARNING
Removal of the plastic insulating cover may expose the user to
potentially lethal voltages if the electrical supply is not disconnected first.
It is essential that only suitably trained and competent personnel are
allowed access to hazardous live parts.
2. Disconnect the compressed air supply to the solenoid valve. Remove the
interconnecting pipe to the Sensor Head aspirator air inlet and associated 1/4" OD
compression fitting.
3. Depending on the type of tool at hand it may be necessary to remove the Terminals
PCB (and Flow Alarm PCB if fitted) in order to access the solenoid valve retaining nut
(5). Check with the tool being used that the retaining nut can be removed without the
tool fouling the Terminals PCB. If necessary remove the Terminals PCB as described
in Section 5.8.
4. Disconnect the electrical supply to the solenoid valve from terminal block TB7 terminals
1 and 2.
5. Remove the solenoid valve retaining nut (5). Lift out the solenoid valve body through
the hole machined in the casting. Lift out the solenoid valve actuating coil from the
inside of the terminal box.
6. Replace using the reverse procedure. Ensure that a new fibre sealing washer (supplied
with kit) is refitted between the valve body and the enclosure.
5.10 Solid State Relay Removal and Replacement
Refer to Figure 5.7.
Removal and refitting
1. Refer to Section 5.7. Remove the terminal compartment cover and disconnect the
electrical power from the Sensor Head.
WARNING
Removal of the plastic insulating cover may expose the user to
potentially lethal voltages if the electrical supply is not disconnected first.
It is essential that only suitably trained and competent personnel are
allowed access to hazardous live parts.
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2. Remove the transparent insulation cover from the top of the solid state relay.
Disconnect the four electrical connections from the solid state relay. Remove the 2 off
M4 retaining screws and lift out the solid state relay.
3. Replace using the reverse procedure. Ensure that the solid state relay and its
transparent insulation cover are fitted in the correct orientation, and that the red wire is
connected to terminal 3 and the blue wire to terminal 4.
5.11 Zirconia Cell Removal and Replacement
Refer to Figure 5.8.
WARNING
When undoing or retightening the pipe work associated with the oxygen
sensor, always use two spanners and take care not to twist the cell
otherwise it may be damaged. The zirconia cell is provided with
machined flats to assist in removing fittings without stressing the cell.
Removal and refitting
1. Refer to Section 5.7. Switch off the electrical power to both the Sensor Head and
Control Unit and remove the terminal compartment cover and sensor compartment
cover.
WARNING
Removal of the sensor compartment cover may expose heated parts.
Ensure that the internal temperature has dropped to a safe level before
working on them.
2. Refer to Figure 5.7. Disconnect the zirconia sensor wiring from terminal blocks TB2 (2)
(thermocouple wires) and TB4 (14) (heater and signal wires) on the Terminals PCB.
Withdraw the signal wires into the sensors compartment. Take note of the wire
positions and ensure that the new sensor wires are routed in the same manner.
3. Refer to Figure 5.8. Disconnect the reference air pipe (8) compression fittings at the
bulk head, auxiliary air restrictor (9) and the flame trap (10) and remove the reference
air pipe.
4. Disconnect zirconia cell (4) from the cell connector (1) by undoing the 3/8" compression
fitting nut (2). Release this cell nut by using an appropriate spanner on the nut (2) and
on the adjacent flats (3) on the oxygen cell so as not to twist the cell. If the cell
connection is stuck, keep undoing the compression nut (2) and use the jacking shoulder
to pull the stuck ferrules from the cell.
5. A course mesh filter (7) is attached to the reference side of the zirconia cell using a
second 3/8" compression fitting nut (6). Remove the nut (6), and filter (7) using two
spanners and the machined flats on the cell (5) in the same manner as above. Retain
the filter for reuse on the new cell.
6. Replace using the reverse procedure. The new sensor will be provided with a fibreglass
sleeve insulating the cell wires. Refer to Table 5.3 for cell wiring connection details.
7. Follow the start-up procedure listed in the installation manual and the basic operational
checks detailed in Appendix A.
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Key
1.
2.
3.
4.
5.
Description
Cell connector
3/8” nut, sample side
Flats on cell
Zirconia cell
Flats on cell
Key
6.
7.
8.
9.
10.
Description
3/8” nut, reference side
Mesh filter
Reference air pipe
Auxiliary air restrictor
Flame trap
Figure 5.8 Zirconia Sensor Installation Details
Figure 5.8 shows a dual sensor configuration without a Flow Alarm module fitted.
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5.12 Combustibles Cell Removal and Replacement
Refer to Figure 5.9.
Removal and refitting
1. Refer to Section 5.7. Switch off the electrical power to both the Sensor Head and
Control Unit and remove the terminal compartment cover and sensor compartment
cover.
WARNING
Removal of the sensor compartment cover may expose heated parts.
Ensure that the internal temperature has dropped to a safe level before
working on them.
2. Refer to Figure 5.7. Disconnect the combustibles sensor wiring from terminal block TB6
(15) on the Terminals PCB. Withdraw the signal wires through the EMC ferrite and
back into the sensors compartment. Take note of the wire positions within the Sensor
Head and ensure that the new sensor wires are routed in the same manner.
3. Refer to Figure 5.9. Disconnect the 1/8" compression fitting (4) at the junction between
the combustibles sensor (3) and the cell connector (6). Use two spanners on the 1/8"
nut (4) and the hexagonal section on the cell connector (5). Avoid twisting the cell
connector fitting.
4. Disconnect the 1/8" compression fitting (2) at the junction between the combustibles
sensor (3) and the flame trap (1). Use two spanners as above to avoid twisting the
flame trap.
5. Replace using the reverse procedure. The new sensor comes complete with PTFE
sleeving and braided screen over the cell wires. Refer to Table 5.3 for cell wiring
connection details. Ensure that the wires are routed away from the filter block and the
band heater, and are passed through the EMC ferrite.
CAUTION
When fitting a new combustibles sensor ensure that the gap in the combustibles sensor
band heater is not located directly over the platinum resistance thermometer. Failure to do
this may result in drifting performance.
6. Follow the start-up procedure listed in the installation manual and the basic operational
checks detailed in Appendix A.
When fitting the high sulphur variant of the combustibles cell, ensure the high
temperature shunt assembly is replaced in TB6 terminals 3 and 4 (refer to Figure 5.7).
To aid removal of the combustibles cell, it may be necessary to remove the zirconia cell
and aspirator air pipe.
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Key
Description
1. Flame trap
2. 1/8” compression fitting, outlet
3. Combustibles sensor
Key
Description
4. 1/8” compression fitting, inlet
5. Hexagonal section
6. Cell connector
Figure 5.9 Combustibles Sensor Installation Details
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5.13 Flow Alarm Removal and Replacement
Refer to Figure 5.8.
WARNING
When undoing or retightening the pipe work associated with the Flow
Alarm Sensor, always use two spanners and take care not to twist the
cell otherwise it may be damaged.
Removal and refitting
The Flow Alarm Sensor and associated signal amplifier board must be replaced
together as they make up a paired/matched module.
1. Refer to Section 5.7. Switch off the electrical power to both the Sensor Head and Control
Unit and remove the terminal compartment cover and sensor compartment cover.
WARNING
Removal of the sensor compartment cover may expose heated parts.
Ensure that the internal temperature has dropped to a safe level before
working on them.
2. Refer to Figure 2.9 (in Section 2.1.1.2). Disconnect the flow alarm sensor wiring from
terminal block TB2 (7) on the Flow Alarm signal amplifier board. Disconnect the Relay Box
interconnecting wiring from terminal block TB3 (4). Also disconnect supply wiring from
terminal block TB1 (3). Withdraw the Flow Alarm signal wires through into the sensors
compartment. Take note of the wire positions and ensure that the new sensor wires are
routed in the same manner.
3. Refer to Figure 5.10. Using two spanners, disconnect the 1/8” compression fittings at the
junction between the flow sensor (1) and the Flow Alarm mounting arms (3). Avoid twisting
the Flow Alarm mounting arms.
4. Lift flow sensor away from the cell connector (2).
5. Replace with the new flow sensor using the reverse procedure. Refer to Table 5.4 for flow
alarm sensor wiring. Ensure the flow alarm sensor wiring is routed away from the chest
assembly and band heater.
6. Refer to Figure 5.11. Remove 2 off M4x12 screws (3), 1 off M4x8 screw (1), and washers
(4). If EMC ferrite is fitted, move to one side to allow the removal of the Flow Alarm signal
amplifier board.
7. Remove Flow Alarm signal amplifier board by carefully lifting away from the terminals
enclosure.
8. Refit new PCB using the reverse procedure. Refer to Table 5.4 for flow alarm sensor wiring.
9. Follow the start-up procedure listed in the installation manual and the basic operational
checks detailed in Appendix A.
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Key
Description
1. Flow alarm
2. Cell connector
Key
Description
3. Flow alarm 1/8” welding fitting (2)
Figure 5.10 Flow Alarm Installation Details
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Key
Description
1. M4x8 Screw (2)
2. Wiring support P-clip
3. M4x12 Screw
Key
Description
4. M4 Washer (3)
5. Flow Alarm signal amplifier board
Figure 5.11 Flow Alarm Signal Amplifier Board Installation Details
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Table 5.4 Flow Alarm Internal Wiring – Flow Amplifier Board
Terminal
TB1-1
TB1-2
Function
+12Vdc Supply
Colour
+ve
RED/WHITE
+ve
RED
TB2-1
TB2-2
TB2-3
BLUE
YELLOW
Flow alarm signals from 1760 sensor
GREEN
TB2-4
TB3-4
RED
0Vdc Supply
-ve
BLUE
The terminals on the Flow Alarm amplifier board are labelled TB1, 2 and 3. These
should not be confused with TB1, 2 and 3 on the lower Terminals PCB.
The 12Vdc supply to TB1 terminal 1 is from the lower terminals board TB7 terminal 4.
The 12Vdc supply to TB1 terminal 2 connects to Solid State Relay Terminal 3.
The 0Vdc supply to TB3 terminal 4 is from the lower terminals board TB7 terminals 5
and 6.
The Terminals TB3 terminal1, 2 and 3 are for customer connection wires to the
associated Flow Alarm Relay Box.
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5.14 Cell Connector Removal and Replacement
Key
1.
2.
3.
4.
5.
6.
7.
8.
Description
Band heater
Aspirator assembly
Flame trap
Chest assembly
Over temperature thermostat
Combustibles sensor
Reference air pipe
Zirconia oxygen sensor
Key
9.
10.
11.
12.
13.
14.
15.
16.
17.
Description
O-ring seal
Internal filter / sintered flame trap
Base casting
Thermistor retaining screw
Calibration / blow back pipe
Cell connector mounting nut
Auxiliary air restrictor
Flame trap
Link pipe
Figure 5.12 Dual Sensor Configuration Layout
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Removal and refitting
1. Refer to Section 5.7. Switch off the electrical power to both the Sensor Head and
Control Unit and remove the sensor compartment cover.
WARNING
Removal of the sensor compartment cover may expose heated parts.
Ensure that the internal temperature has dropped to a safe level before
working on them.
2. Refer to Figure 5.12. Disconnect the reference air pipe (7) compression fittings at the
bulkhead, restrictor (15) and aspirator (2). Remove the reference air pipe (7).
3. For the oxygen only and dual sensor configurations refer to Figure 5.8. Disconnect
zirconia cell (4) from the cell connector (1) by undoing the 3/8" compression fitting nut
(2). Release this cell nut by using an appropriate spanner on the nut (2) and on the
adjacent flats (3) on the oxygen cell, so as not to twist the cell. If the cell connection is
stuck, keep undoing the compression nut (2) and use the jacking shoulder to pull the
stuck ferrules from the cell. Temporarily support the zirconia cell to prevent rotation so
as not to unduly stress the cell wiring.
4. For the combustibles only and dual sensor configurations refer to Figure 5.9.
Disconnect the 1/8" compression fitting (4) at the junction between the combustibles
sensor (3) and the cell connector (6). Use two spanners on the 1/8" nut (4) and the
hexagonal section on the cell connector (5). Avoid twisting the cell connector fitting.
Refer to Section 5.13 if a Flow Alarm module is fitted.
5. Refer to Figure 5.12. Undo the lower 3/8" compression fitting (14) at the junction
between the cell connector and the sintered flame arrestor internal filter (10). Use two
spanners to prevent the sintered flame arrestor (10) from twisting during initial breaking
of the joint. If the ferrule is stuck, keep undoing the compression nut and use the
jacking shoulder to pull the stuck ferrule from the flame arrestor. Temporarily support
the cell connector to prevent rotation during this operation.
6. Replace using the reverse procedure. Ensure that the sintered flame arrestor (10) is
fully tightened before refitting the cell connector.
If the sintered flame arrestor (10) is loosened during cell connector replacement, the
copper seal between the sintered flame arrestor and chest assembly should be
replaced.
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5.15 Aspirator Removal and Replacement
Refer to Figure 5.12.
Removal and refitting
1. Refer to Section 5.7. Disconnect the electrical power from both the Sensor Head and
Control Unit and remove the sensor compartment cover.
WARNING
Removal of the sensor compartment cover may expose heated parts.
Ensure that the internal temperature has dropped to a safe level before
working on them.
2. Undo the compression fittings connecting the aspirator / reference air pipe (7) to its
bulk head fitting, restrictor (15) (if fitted) and to the aspirator (2). Lift out the aspirator /
reference air pipe.
3. Unscrew and remove the aspirator (2) from the chest assembly (4). Remove and
discard the old annealed copper sealing washer.
4. Check that the vent hole, (underneath the aspirator), through the chest assembly is not
blocked. Clean the assembly if necessary.
5. Replace using the reverse procedure. Ensure a new annealed copper sealing washer
is fitted.
If a new aspirator is fitted, lightly smear some release compound (spare part number
S2700990) on the threads entering the chest assembly. Failure to do this may make
the aspirator difficult to remove in the future.
An annealed copper washer is used as a seal between the aspirator and the chest
assembly. These may only be used once and must be replaced when the aspirator is
refitted.
CAUTION
Use only the recommended release compound, ROCOL ASP dry film anti scuffing paste
(spare part number S2700990), on any heated components. The use of ‘Silver Goop’ or
other similar release agents may result in permanent damage to the combustibles sensor
(if fitted).
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5.16 Internal Filter / Sintered Flame Arrestor Removal and Replacement
Refer to Figure 5.12.
Removal and Refitting
1. Refer to Section 5.7. Disconnect the electrical power from both Sensor Head and
Control Unit and remove the sensor compartment cover.
WARNING
Removal of the sensor compartment cover may expose heated parts.
Ensure that the internal temperature has dropped to a safe level before
working on them.
2. Disconnect the 1/8" compression fitting at the flame trap (3).
3. Disconnect the reference air pipe (7) compression fittings at the bulkhead, restrictor
(15) (if fitted) and the aspirator assembly (2) and remove the reference air pipe.
4. Disconnect the lower 3/8" compression fitting (14) at the junction between the cell
connector and the sintered flame arrestor internal filter (10). If the ferrule is stuck, keep
undoing the compression nut and use the jacking shoulder to pull the stuck ferrule from
the flame arrestor. Temporarily support the cell connector to prevent rotation during this
operation.
5. Pull back the sensor assembly and temporarily support in order not to over stress the
sensor wiring.
The internal filter / sintered flame arrestor may be difficult to remove due to long
durations of operation at 245C. It must be removed using a suitable long reach
socket.
6. Unscrew the sintered flame arrestor internal filter (10) from the chest assembly (4).
Discard the used annealed copper sealing washer.
7. Replace using the reverse procedure, using a new annealed copper washer.
If a new sintered flame arrestor internal filter is fitted, lightly smear some release
compound (spare part number S2700990) on the threads entering the filter block.
Failure to do this may make the flame arrestor / internal filter difficult to remove in
the future.
An annealed copper washer is used as a seal between the flame arrestor and the
filter block. These may only be used once and must be replaced when the flame
arrestor is refitted.
CAUTION
Use only the recommended release compound, ROCOL ASP dry film anti scuffing paste
(spare part number S2700990), on any heated components. The use of ‘Silver Goop’ or
other similar release agents may result in permanent damage to the combustibles sensor
(if fitted).
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5.17 Thermostat Removal and Replacement
Removal and Refitting
1. Refer to Section 5.7. Disconnect the electrical power from both Sensor Head and
Control Unit and remove both the sensor compartment cover and terminal
compartment cover. Remove the transparent insulating cover from the terminal
enclosure.
WARNING
Removal of the plastic insulating cover may expose the user to
potentially lethal voltages if the electrical supply is not disconnected first.
It is essential that only suitably trained and competent personnel are
allowed access to hazardous live parts.
Removal of the sensor compartment cover may expose heated parts.
Ensure that the internal temperature has dropped to a safe level before
working on them.
2. Refer to Figure 5.7. Disconnect the thermostat wires from terminal block TB8 (9) on the
Terminals PCB. Withdraw the wires back into the sensors compartment. Take note of
the wire routing within the Sensor Head and ensure that the new thermostat wires are
routed in the same manner.
3. Refer to Figure 5.12. Remove the two M3 screws that retain the over temperature
thermostat (5) to the chest assembly (4). Lift out the over temperature thermostat.
4. Replace using the reverse procedure. The new thermostat will be provided with a fibre
glass sleeve insulating the cell wires. This is a safety feature and should not be
omitted. Refer to Table 5.3 for cell wiring connection details. Ensure that the wires are
routed away from the chest assembly, band heater, and combustibles sensor body (if
fitted).
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5.18 Thermistor Removal and Replacement
The thermistor is located within a hole in the chest assembly and is used to monitor the
temperature control of the band heater.
Removal and Refitting
1. Refer to Section 5.7. Disconnect the electrical power from both Sensor Head and
Control Unit and remove both the sensor compartment cover and the terminals
compartment cover.
WARNING
Removal of the sensor compartment cover may expose heated parts.
Ensure that the internal temperature has dropped to a safe level before
working on them.
2. Refer to Figure 5.7. Disconnect the white wires from terminal block TB7 (3) on the
Terminals PCB. Withdraw the wires back into the sensors compartment. Take note of
the wire route within the Sensor Head and ensure that the new thermistor wires are
routed in the same manner.
3. Refer to Figure 5.12. Remove the M4 screw (12) and washer then lift out the
thermistor. The washer is designed to overlap a small area of the hole to trap the
thermistor in place.
4. Replace using the reverse procedure. Ensure that the wires are routed away from the
chest assembly, band heater, and combustibles sensor body (if fitted). Ensure that the
leads to the block thermistor are not pinched by the washer retaining the thermistor
within the chest assembly.
One of the thermistor wires is identified with a black band. However, when refitting the
thermistor, polarity is not important.
5.19 Band Heater Removal and Replacement
Removal and refitting
1. Refer to Section 5.7. Disconnect the electrical power from both Sensor Head and
Control Unit and remove both the sensor compartment cover and terminal
compartment cover. Remove the transparent insulating cover from the terminal
enclosure.
WARNING
Removal of the plastic insulating cover may expose the user to
potentially lethal voltages if the electrical supply is not disconnected first.
It is essential that only suitably trained and competent personnel are
allowed access to hazardous live parts.
Removal of the sensor compartment cover may expose heated parts.
Ensure that the internal temperature has dropped to a safe level before
working on them.
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2. Refer to Figure 5.7. Disconnect the band heater wires from terminal block TB8 on the
Terminals PCB. Withdraw the heater wires into the sensor compartment. Take note of
the wire route within the Sensor Head and ensure that the new heater wires are routed
in the same manner.
3. Refer to Figure 5.12. Undo the 2 off 1/8" compression fittings and remove the
calibration / blow back pipe (13).
4. Refer to Section 5.11 and remove the zirconia cell (if fitted).
5. Refer to Section 5.12 and remove the combustibles cell (if fitted).
6. Refer to Section 5.14 and remove the cell connector.
7. Refer to Section 5.17 and remove the over temperature thermostat.
8. Refer to section 5.18 and remove the thermistor.
To remove the band heater it may be necessary to remove the Sensor Head enclosure
breather fitting (refer to Figure 1.2 (5)). This will allow easier access to the band heater
tensioning screw.
9. Note the orientation of the band heater tensioning screw. Loosen the band heater
tensioning screw and slide the band heater off the filter block.
10. Replace using the reverse procedure.
When refitting the band heater over the filter block, orientate the tensioning screw at
the 45 position as shown in Figure 5.12. For optimum band heater reliability torque the
tensioning screw to 3-5Nm.
The top of the band heater should be between 0 and 5mm below the top face of the
chest assembly.
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APPENDIX A
DETAILED ANALYSER PERFORMANCE TESTING
A.1 Notes and Conditions
The performance tests detailed in this section are based on the factory test specification for
the 2700D analyser.
WARNING
The electrical power used in this equipment is at a voltage high enough
to endanger life. It is essential that only suitably trained and competent
personnel are allowed access to hazardous live parts.
It may be necessary to fault find with the electrical power connected.
Where this is necessary extreme caution should be exercised.
Removal of the plastic insulating covers in the Control Unit may expose
the user to potentially lethal voltages resulting from external electrical
connections to the relay contacts even when the electrical power is
disconnected from the Control Unit itself.
Carbon monoxide is a toxic gas. When sampling gases containing
carbon monoxide ensure that adequate precautions are taken to ensure
that any vented gases are safely extracted.
The Sensor Head is heated and may be attached to a hot flue. The
external surfaces will be uncomfortably hot even after power down for
several hours. Exercise care when handling the Sensor Head even
when un-powered on a hot flue.
A.2 Gas Samples Required
The gas samples required to adjust and test the analyser depend on the configuration of
the analyser under test. Refer to table A.1. The gas samples are introduced via the
calibration gas inlet port. The inlet pressure and flow should be controlled externally to give
a gas flow rate of 600 50 ml/min.
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Table A.1 Utility Gas Sample Requirements
Service
Aspirator supply
Gas
Regulated clean dry
instrument air *
Press.
(psig)
0-10
Flow
(L/min)
0-2
O2
COe
Dual
* Oxygen only Sensor Heads can be configured for nitrogen aspiration as standard builds.
Dual build Sensor Heads can be configured for nitrogen aspiration as special builds,
(consult Servomex for details). Pressure and flow rates remain as per instrument air.
Calibration gas
O2 ‘HIGH CAL’
COe ‘LOW CAL’
Regulated clean dry air
0-10
0.6
0.020
Calibration gas
O2 ‘LOW CAL’
0.3% O2 balance N2 **
0-10
0.6
0.020
X
**Calibration gas composition can be between 0.25% and 2.5% O2 in N2
Calibration gas
COe ‘HIGH
CAL’
1,000 ppm(v) CO balance
air ***
0-10
0.6
0.020
X
*** Calibration gas composition can be between 500ppm(v) and 1,000ppm(v) in air
depending on the measuring range selected.
A.3 Visual Inspection
Check that all wiring is neatly dressed and securely terminated. Check both Sensor Head
and Control Unit for loose or damaged O-ring enclosure seals.
In the Sensor Head terminal box:
Check voltage selection link is set to the appropriate supply voltage and the correct
voltage label is fitted.
Check fuse F1 fitted is 6.3A (voltage independent).
In the Control Unit:
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Check that the transformer primary flying lead is connected to the correct socket.
PL7 for 110V (nominal) or PL6 for 240V (nominal).
Check that the fuse F1 fitted is 3.15 A for 110V (nominal) or 1.6 A for 240V
(nominal).
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A.4 Sensor Head Leak Test
Seal the calibration gas inlet, the aspirator air inlet, sample vent port and the internal
reference air pipe (not applicable for COe only or N2 aspirated versions). Connect a
manometer to the sample inlet port and pressurise the internal pipework to between 500
and 600mmWG. Seal the manometer and ensure that the level does not fall by more than
5mm in 2 minutes.
CAUTION
Extreme care should be exercised when using leak detection fluids such as ‘SNOOP’ with
the Sensor Head assembly. Avoid wetting any electrical components. Special care should
be exercised to avoid wetting the band heaters, thermistors, thermostats, Tfx ceramics and
glass fibre insulated wires.
A.5 Interconnection Tests
Connect the Control Unit to the Sensor Head using test cable looms. Ensure that all
interconnections are correctly wired and terminated in accordance with interconnection
drawings in section 2 of this manual.
A.6 Initial Power-Up
Connect the Sensor Head to nominal required power supply. If necessary adjust RV2 on
the control PCB (viewing angle adjustment for the LCD display) to give the best display
contrast when viewed perpendicularly from the front.
From a cold start, verify that the aspirator solenoid valve operates after a time interval of
not less than 15 minutes and not more than 60 minutes after power on. The precise time
interval will depend on the Sensor Head configuration.
A.7 Analogue Output Span Setup
Perform the following tests.
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If a zirconia sensor is fitted then select the ‘set analogue outputs’ option in the
service menu and select 20mA for the oxygen analogue output. If necessary adjust
RV4 on the control PCB until the analogue output reads 20.00 0.01mA.
If a combustibles sensor is fitted then select the ‘set analogue outputs’ option in the
service menu and select 20mA for the combustibles output. If necessary adjust
RV3 on the control PCB until the analogue output reads 20.00 0.01mA.
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A.8 Relay Operation Test
Perform the following tests.
Select the ‘set relay outputs’ option in the service menu and select ‘disable’. Verify
that terminals 2 and 3, 5 and 6, 8 and 9, 11 and 12 on terminal block TB4 are short
circuit. Verify that terminals 1 and 3, 4 and 6, 7 and 9, 10 and 12 are open circuit.
Select the ‘set relay outputs’ option in the service menu and select ‘enable’. Verify
that terminals 2 and 3, 5 and 6, 8 and 9, 11 and 12 on terminal block TB4 are open
circuit. Verify that terminals 1 and 3, 4 and 6, 7 and 9, 10 and 12 are short circuit.
A.9 Sensor Head Temperature Control
Wait until both the Sensor Head and Control Unit have been switched on for a minimum of
90 minutes. Perform the following tests:
Verify that the green LED (D10) on the terminal PCB is flashing at equal intervals,
indicating that the chest assembly temperature is under control.
Check the final stabilised Sensor Head temperature by measuring the voltage
between TB3 terminals 1 and 2 (ground) in the Sensor Head terminal box. This
voltage should be 6.6 0.4V.
Select the VIEW option from the main menu. Check that the zirconia sensor
temperature is 700 10C.
Check that the combustibles sensor temperature is 300 20C.
A.10 Sensor Head Sample Flow and Vacuum Test
With the Sensor Head power on and at stable temperature perform the following tests:
130
Blank off the calibration gas inlet. Attach a manometer to the sample inlet. Increase
the compressed air pressure at the sample inlet to 4psig. The vacuum at the
sample inlet should be greater than 210mmWG (O2 only) or 140mmWG (COe only
and dual).
Attach a 500ml/min flow meter to the sample inlet. With the aspirator supply
pressure set to 4psig the sample flow rate should be in the range 200 to 450ml/min.
Adjust the aspirator air supply pressure until the flow meter indicates a flow of
300ml/min (O2 only) or 240ml/min (COe only or dual sensor). Check that the
aspirator air supply pressure is in the range 3 to 7psig.
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A.11 Combustibles Sensor Zero Adjustment
If a combustibles sensor is fitted then perform the following adjustments:
Ensure that the unit has been sampling ambient air (COe zero calibration gas) for
at least 5 minutes before making the following adjustments.
Check that switch SW2 on the control PCB is set to the zero position.
Select the VIEW option in the main menu and observe the combustibles sensor
output voltage. If the voltage measured is negative then set switch SW3 on the
control PCB to the upper position. If the voltage is positive then set switch SW3 to
the lower position.
Adjust switch SW2 clockwise one step at a time until the voltage is within the range
-60 to +60mV. Note that there may be a delay of up to 30 seconds between a
switch change and a voltage change seen on the display.
A.12 Sensor Calibration
WARNING
Connect analyser probe inlet and vent to an extraction system for the
remainder of this test.
With the Sensor Head power on and at stable temperature perform the following
adjustments.
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Ensure the aspirator is running with a pressure between 3 and 5psig.
With an air sample applied to the calibration gas inlet at 600 50ml/min flow rate
perform a HIGH point calibration of the zirconia sensor (if fitted) and a LOW point
calibration of the combustibles sensor (if fitted).
With a nominal 0.3% O2 in N2 sample applied to the calibration gas inlet at 600
50ml/min flow rate perform a LOW point calibration of the zirconia sensor (if
fitted). Verify that the analyser display reads within 0.02% O2 of the given gas
concentration.
If a combustibles sensor is fitted perform the following tests. With a nominal
500ppm CO in air sample applied to the calibration gas inlet at 600 20ml/min flow
rate perform a HIGH point calibration of the combustibles sensor (if fitted). Verify
that the analyser display reads within 10ppm CO of the certified gas concentration.
The analyser can be removed from its extraction system for the final test.
Disconnect the calibration gases. With the analyser sampling instrument air
through the sample inlet port verify that the analyser display reads 20.95 0.2% O2
and/or 0 10ppm combustibles.
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APPENDIX B
ANALYSER SOFTWARE ‘SUPER-CALIBRATION’ MODE
B.1 Introduction
This section details the super calibration (supercal) functions of the Servomex 2700D
analyser. This includes configuration of the analyser, i.e. installing transducers, as well as
the functions available for service and calibration use.
B.2 Menu Structure
To enter supercal mode, use the procedure described in Section B.3.
CONFIGURE COe
COe RANGE
RESTORE DEFAULTS
PRECISION
B.3 Accessing Super-Calibration
Access to the supercal function is via a special key sequence. Starting from the Measure
screen, the sequence is as follows:
Press