Recommended Ph Sensor Standardization; Rosemount 389/389Vp Orp Calibration; Calibration - Emerson Rosemount 389 Instruction Manual

Calibration and maintenance
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.
1.
2.
3.
3.3

Rosemount 389/389VP ORP Calibration

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.
3.3.1

Calibration

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.
2.
24
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. Once the slope reads below the 47-49 mV/pH
range, install a new sensor to maintain accurate readings.
While obtaining a process solution sample (we recommend that you take the
sample close to the sensor), record the pH value that is shown on the transmitter
display.
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.
Adjust the transmitter to the standardized value.
Make a temporary electrical connection between the sensor and the instrument.
Obtain a standard solution of saturated quinhydrone (PN R508-16OZ). To make this
solution, add a few crystals of quinhydrone to either pH 4 or pH 7 buffer.
389/389VP