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Calibration
February 2019
3.2.2
Recommended pH sensor standardization
For maximum accuracy, the sensor can be standardized in-line 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 does not change the sensor's slope, but simply adjusts
transmitter's reading to match that of a known process pH.
Procedure
1. While obtaining a process solution sample (we recommend that you take the
2. Measure and record the pH of the process solution sample with another
3. Adjust the transmitter to the standardized value.
3.3
Rosemount
Most industrial applications have a number of ORP reactions occuring in sequence or
simultaneously. 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/reduction 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.
WARNING
CORROSIVE SUBSTANCE
The solution used during the following check is an acid and should be handled with care.
Follow the directions of the acid manufacturer. Wear the proper protective equipment. Do
not let the solution come in contact with skin or clothing. If contact with skin is made,
immediately rinse with clean water.
Procedure
1. Make a temporary electrical connection between the sensor and the instrument.
2. Obtain a standard solution of saturated quinhydrone (PN R508-16OZ). To make this
3. Immerse the sensor in the standard solution. Allow one to two minutes for the ORP
4. Adjust the standardized control of the transmitter to the solution value shown in
28
time to approximately 47 -49 mV/pH. Once the slope reads below the 47-49 mV/pH
range, install a new sensor to maintain accurate readings.
sample close to the sensor), record the pH value that is shown on the transmitter
display.
temperature compensated, calibrated pH instrument. For best results, perform
standardization at the process temperature.
™
389/389VP ORP calibration
solution, add a few crystals of quinhydrone to either pH 4 or pH 7 buffer.
Quinhydrone is only slightly soluble, but only a few crystals are required.
sensor to stabilize.
Table
3-1.
Reference Manual
00809-0100-3389
Rosemount 389/389VP
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