Emerson Rosemount 389 Instruction Manual page 31

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Instruction Manual
Quinhydrone is only slightly soluble, but only a few crystals are required (refer to
Section for an alternate ORP standard solution).
Immerse the sensor in the standard solution. Allow 1-2 minutes for the ORP sensor
to stabilize.
Adjust the standardized control of the transmitter to the solution value shown in
Table 3-1.
The resulting potentials, measured with a clean platinum electrode and saturated
KCl/AgCL reference electrode, should be within ±20 millivolts of the value shown in
Table 3-1. Note solution temperature to ensure accurate interpretation of results.
The ORP value of saturated quinhydrone solution is not stable over long periods of
time. Therefore, make these standards fresh each time they are used.
Table 3-1: ORP of Saturated Quinhydrone Solution (millivolts)
pH 4 Solution
Temp ºC 20
mV Poten- 268
tial
Remove the sensor from the buffer, rinse, and install in the process.
25 30
264 260
Calibration and maintenance
pH 7 Solution
20 25
94 87
30
80
25