Rosemount Analytical 372 Operating Manual

SPECIFICATIONS

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

are present)

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

cross-linked polymer

Specifications subject to change without notice.

1

Viton is a registered trademark of E.I. du Pont de Nemours and Co.

Model 372 pH Sensor

HF Resistant pH Sensor

Instruction Sheet

PN 51A-372/rev.B
January 2011

FIGURE 1. Sensor Dimensions

MILLIMETER

INCH

STORAGE

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.

ELECTRODE PREPARATION

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.

NOTE

Do not allow lubricant to coat electrode bulb or reference
junction. If it does, wipe it clean before installation.

For additional information, please visit our website at

www.emersonprocess.com/raihome/liquid/.

WARNING

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!

WARNING

The wetted sensor materials may not be compatible
with process com position and operating conditions.
Application compat ibility is entirely the

responsi-

bility of the user.

CAUTION

SENSOR/PROCESS APPLICATION COMPATIBILITY

ATEX DIRECTIVE

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.

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).

NOTE

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
analyzer/transmitter.

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.

RECOMMENDED pH SENSOR
STANDARDIZATION

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.

MAINTENANCE

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
non-abrasive detergent.

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 4. Model 372-02 (without preamp)FIGURE 3. Wiring Model 372-01 (with preamp)

Emerson Process Management

2400 Barranca Parkway
Irvine, CA 92606 USA
Tel: [phone]
Fax: [phone]

http://www.raihome.com

© Rosemount Analytical Inc. 2011

ORDERING INFORMATION

Code Cable (Required Selection)

01 25 ft cable with integral preamp for Models 54e, 1055, 3081, 4081, and 5081
02 15 ft cable for remote preamp (Models 54e, 1055, 3081, 4081, and 5081)

372 -01 EXAMPLE

MODEL

372 pH SENSOR

FIGURE 2. Sensor Orientation