Emerson Rosemount 396P Quick Start Manual page 38

Quick Start Guide
3. Repeat
Once the transmitter has acknowledged both buffer solutions, a sensor
slope (mV/pH) is established (the slope value can be found within the
transmitter). The slope value should read about 59.1 mV/pH for a new
sensor and will decrease over time to approximately 47-49 mV/pH.
Postrequisites
Once the slope reads below the 47-49 mV/pH range, install a new sensor to
maintain accurate readings.
Standardize pH sensor
For maximum accuracy, you can standardize the sensor in-line or with a
process grab sample after performing a buffer calibration and conditioning
the sensor to the process. Standardization accounts for the sensor junction
potential and other interferences. Standardization does not change the
sensor's slope, but simply adjusts the transmitter's reading to match that of
a known process pH.
Procedure
1. While obtaining a process solution sample, record the pH value that
is shown on the transmitter display.
Emerson recommends taking the sample close to the sensor.
2. Measure and record the pH of the process solution sample with
another temperature compensated, calibrated pH instrument.
For best results, perform standardization at the process temperature.
3. Adjust the transmitter to the standardized value.
3.2 Calibrate Rosemount 396P and 396PVP oxidation
reduction potential (ORP) sensors
Most industrial applications have a number of ORP reactions occuring in
sequence or simultaneously. Reagents can oxidize or reduce several
components. Theoretically, the ORP potential is absolute, because it is the
result of the oxidation/reduction equilibrium. However, the actual measured
potential is dependent on many factors, including the condition of the
surface of the ORP platinum electrode. Therefore, allow the sensor one to
two hours to become conditioned to the stream when it is first set up or
after cleaning it.
Procedure
1. Make a temporary electrical connection between the sensor and the
instrument.
2. Obtain an ORP standard solution (PN R508-8OZ) or make one by
adding a few crystals of quinhydrone to either pH 4 or pH 7 buffer.
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Step 1 and Step 2 using the second buffer solution.
November 2020
Emerson.com/Rosemount