IM 12A06S01-00EN-P
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8 CALIBRATION OF SC (Specific Conductivity)
Calibration should be made to obtain the correct conductivity reading. This reading depends
on the cell constant of the sensor and the correct temperature compensation of the
process. For both it is important to have a correct temperature reading of the sensor used.
8.1 Temperature calibration
For the accuracy of calibration of SC, it is important to have a precise temperature
measurement. Measure the temperature with a high-precision thermometer and adjust the
sensor reading (temp. offset) accordingly. For best accuracy, this should be done as near to
the normal operating temperature as possible.
8.2 Cell constant calibration
This cell constant is the so-called c.c. adjusted. Normally the cell constant of a conductivity
sensor does not change during operation, as long as it remains undamaged, and clean.
Therefore, it is vital that in any calibration check, the first step should be to clean the sensor,
or at least to check its cleanliness. After cleaning, ensure that the sensor is carefully rinsed in
distilled water to remove all traces of the cleaning medium.
Before starting calibration of the cell constant, it is important that the temperature reading of
the sensor is correct. If necessary the reading can be adjusted (temp offset) to the correct
value.
Calibration has to be done by the HOST system. For cell constant it can be done for
manual, automatic or by sample.
Note:
The standard instrument to be used in calibration with a process solution must always be
accurate. Yokogawa recommends the Model SC82 pocket conductivity meter.
Where temperature compensation is selected and configured for output1 and/or output2,
this compensation is effective during calibration. The calculated output is the value
converted to a conductivity value at the reference temperature set in Temperature settings
(see section 7.1.4).
8.2.1 Cell constant (manual)
The intention of this calibration routine is to fine-tune a sensor for which only the nominal cell
constant is known, or to recalibrate a sensor that has been changed (or damaged) during
operation.
Choose the 1st or 2nd temperature compensation to suit the calibration solution used.
The solution with an appropriate precision should be prepared or purchased. Allow the
sensor to reach stable readings for both temperature and conductivity before adjusting to
the value of the corresponding calibration solution.
8.2.2 Cell constant (automatic)
This routine is built around the test method described in International Recommendation
No. 56 of OIML (Organisation Internationale de Metrologie Legale). The new cell constant
is obtained by inserting the sensor in a known solution (see Appendix 5) and measuring
the SC value. Selection of the correct solution can be done by the HOST system, see
section 7.1.9.
Allow the sensor to reach stable readings for both temperature and conductivity.