Rosemount 396P And 396Pvp Orp Sensors - Emerson Rosemount 396PVP Instruction Manual

Section 4: Start-Up & Calibration
March 2017
2. Measure and record the pH of the process solution sample with another temperature
compensated, calibrated pH instrument. For best results, standardization should be
performed at the process temperature.
3. Adjust the analyzer/transmitter value to the standardized value.
4.2

Rosemount 396P and 396PVP ORP Sensors

4.2.1 Sensor preparation
Most industrial applications have a number of ORP reactions occurring in sequence or simulta-
neously. There can be several components that are oxidized or reduced by the reagents that are
used. Theoretically, the ORP potential is absolute because it is the result of the oxidation-reduc-
tion equilibrium. However, the actual measured potential is dependent on many factors,
including the condition of the surface of the ORP platinum electrode. Therefore, the sensor
should be allowed 1-2 hours to become "conditioned" to the stream when first set-up or after
being cleaned.
4.2.2 ORP Calibration
1. Make a temporary electrical connection between the sensor and the instrument.
2. Obtain an ORP standard solution, or a standard solution can also be made quite simply by
adding a few crystals of quinhydrone to either pH 4 or pH 7 buffer. Quinhydrone is only
slightly soluble therefore a few crystals will be required. (Refer to Section 4.3. for an alter-
nate ORP standard solution).
3. Immerse the sensor in the standard solution. Allow 1-2 minutes for the ORP sensor to stabi-
lize.
4. Adjust the standardize control of the instrument to the solution value shown in Table 5-1
(below) or on the label of the standard solution. The resulting potentials, measured with a
clean platinum electrode and saturated KCl/AgCl reference electrode, should be within ±20
millivolts of the value. Solution temperature must be noted to ensure accurate interpretation
of results. The ORP value of saturated quinhydrone solution is not stable over long periods of
time. Therefore, these standards should be made up fresh each time they are used.
5. Remove the sensor from the buffer, rinse and install in the process.
TABLE 4-1. ORP of Saturated Quinhydrone Solution (In Millivolts)
Temp °C
Millivolt Potential
36
pH 4 Solution pH 7 Solution
20 25 30 20 25
268 264 260 94 87
Instruction Manual
LIQ-MAN-396P-396PVP
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Start-Up and Calibration