Emerson Model 372 pH Sensor HF Resistant pH Sensor Instruction Sheet
Industry Manual Repository
Join the AnalyzeDetectNetwork and Read This Manual and Hundreds of Others Like It! It's Free!
Model 372 pH Sensor
HF Resistant pH Sensor
For additional information, please visit our website at
Materials of Construction: Ultem, Viton1, glass, Kynar
Process Connections: 3/4" forward (insertion) and 1"
reverse (submersion) MNPT
Insertion Depth: 2.2 in. to 8.3 in.
Measured Range: 0 to 12 pH (0-14 pH if no sodium ions
Pressure Range: -13 to 135 psig
(6.9 to 1035 kPa abs)
Temperature Range: -5 to 50°C [23 to 122°F] (100°C
[212°F] if no fluoride ions are present)
Temperature Compensation: Pt 100
Weight/Shipping Weight: 0.4 kg/0.9 kg (1 lb/ 2 lb)
pH Glass Type: Hemispherical
Glass Diameter: 7.8mm
Glass Impedance: Less than 400 MΩ @ 25°C.
Acidic Error: Less than .01 pH in 1.0M HCl @0.0pH
Reference Type: Double junction with saturated KCL in
Specifications subject to change without notice.
Viton is a registered trademark of E.I. du Pont de Nemours and Co.
Before removing the sensor, be absolutely certain
that the process pressure is reduced to 0 psig and
the process temperature is lowered to a safe level!
SENSOR/PROCESS APPLICATION COMPATIBILITY
The wetted sensor materials may not be compatible
with process composition and operating conditions.
Application compatibility is entirely the responsibility of the user.
FIGURE 1. Sensor Dimensions
Special Conditions for safe use
1. All pH/ORP sensors have a plastic enclosure which must only be cleaned with a damp cloth to avoid the danger due
to a build up of an electrostatic charge.
2. All pH/ORP sensor Models are intended to be in contact with the process fluid and may not meet the 500V r.m.s.
a.c. test to earth. This must be taken into consideration at installation.
1. It is recommended that electrodes be stored in their original
shipping containers until needed.
2. Do not store at temperatures below -5°C (23°F).
3. Electrodes should be stored with a protective cap containing
KCl solution (PN 9210342).
4. For overnight storage, immerse the sensor in tap water or a
4 pH buffer solution.
5. A pH glass electrode has a limited shelf life of one year.
1. Remove electrode from shipping container.
2. Remove the protective boot covering the electrode bulb.
3. Rinse away salt film with clean water, then shake the electrode so that the internal solution fills the bulb, thus removing
any air trapped there.
Do not allow lubricant to coat electrode bulb or reference
junction. If it does, wipe it clean before installation.
For sensor orientation, see Figure 2.
For wiring, see Figures 3 and 4.
TWO POINT BUFFER CALIBRATION
Select two stable buffer solutions, preferably pH 4.0 and 10.0
(pH buffers other than pH 4.0 and pH 10.0 can be used as
long as the pH values are at least two pH units apart).
A pH 7 buffer solution reads a mV value of approx.
zero, and pH buffers read approximately ± 59.1 mV
for each pH unit above or below pH 7. Check the pH
buffer manufacturer specifications for millivolt values
at various temperatures since it may affect the actual
value of the buffer solution mV/pH value.
1. Immerse sensor in the first buffer solution. Allow sensor to
equilibrate to the buffer temperature (to avoid errors due
to temperature differences between the buffer solution
and sensor temperature) and wait for reading to stabilize.
Value of buffer can now be acknowledged by
2. Once the first buffer has been acknowledged by the analyzer/transmitter, rinse the buffer solution off of the sensor
with distilled or deionized water.
3. Repeat steps 1 and 2 using the second buffer solution.
4. The theoretical slope value, according to the Nernst equation for calculating pH, is approximately 59.17 mV/pH. Over
time the sensor will age, both in the process and in storage,
and will result in reduced slope values. To ensure accurate
readings, it is recommended that the electrode be replaced
when the slope value falls below 47 to 49 mV/pH.
FIGURE 3. Wiring Model 372-01 (with preamp)
RECOMMENDED pH SENSOR
For maximum accuracy, the sensor can be standardized online or with a process grab sample after a buffer calibration
has been performed and the sensor has been conditioned to
the process. Standardization accounts for the sensor junction
potential and other interferences. Standardization will not
change the sensor’s slope but will simply adjust the analyzer’s reading to match that of the known process pH.
Electrodes should respond rapidly. Sluggishness, offsets,
and erratic readings are indicators that the electrodes may
need cleaning or replacement.
1. To remove oil deposit, clean the electrode with a mild
2. To remove scale deposits, soak electrodes for 30 to 60
minutes in a 5% hydrochloric acid solution.
3. Temperature effect on life expectancy: If glass electrode
life expectancy is 100% @ 25°C (77°F), then it will be
approximately 25% @ 80°C (176°F), and approximately
5% @ 120°C (248°F).
FIGURE 2. Sensor Orientation
FIGURE 4. Model 372-02 (without preamp)
Cable (Required Selection)
25 ft cable with integral preamp for Models 54e, 1055, 3081, 4081, and 5081
15 ft cable for remote preamp (Models 54e, 1055, 3081, 4081, and 5081)
Emerson Process Management
2400 Barranca Parkway
Irvine, CA 92606 USA
Tel: (949) 757-8500
Fax: (949) 474-7250
© Rosemount Analytical Inc. 2011