Calibrate And Maintain - Emerson Rosemount 140 Quick Start Manual

May 2020
6

Calibrate and maintain

6.1 Calibrate the sensor
Emerson does not calibrate the Rosemount 140/141/142 sensors at the
factory. The cell constant on the label is a nominal value only. The true cell
constant can differ from the nominal value by as much as ±five percent.
For improved accuracy, calibrate the sensor using either a solution of known
conductivity or a referee meter and sensor. If using a standard solution,
choose one having conductivity in the recommended operating range for
the sensor cell constant.
Do not use standard solutions having conductivity less than about 100
µS/cm for calibration. They are susceptible to contamination by atmospheric
carbon dioxide, which can alter the conductivity by a variable amount as
great as 1.2 µS/cm (at 77 °F [25 °C]). Because 0.01/cm sensors must be
calibrated in low conductivity solutions, it is best to calibrate them against a
referee meter and sensor.
6.1.1 Calibrate using a standard solution
If using a standard solution, choose one having conductivity in the
recommended operating range for the sensor cell constant.
Procedure
1. Immerse the rinsed sensor in the standard solution and adjust the
transmitter reading to match the conductivity of the standard.
2. Calibrate the sensor.
For an accurate calibration:
Quick Start Guide
a. Choose a calibration standard near the midpoint of the
recommended conductivity range for the sensor.
b. Do not use calibration standards having conductivity less than
100 µS/cm.
c. Turn off automatic temperature compensation in the
transmitter.
d. Use a standard for which the conductivity as a function of
temperature is known.
e. Use a good quality calibrated thermometer with an error rate
less than ±0.1 °C to measure the temperature of the standard.
f. Follow good laboratory practice. Rinse the beaker and sensor
at least twice with standard. Be sure the rinse solution
reaches between the inner and outer electrodes by tapping
and swirling the sensor while it is immersed in the standard.
Quick Start Guide
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