Yokogawa EXA ISC202 2-wire Conductivity Transmitter/Analyzer - Manual (Page 63)

IM 12D06A03-01E
Calibration 6-1
6. CALIBRATION
6-1 When is calibration necessary?
Calibration of conductivity instruments is normally not required, since Yokogawa delivers a wide range
of sensors, which are factory calibrated traceable to NIST standards. The cell constant values are nor-
mally indicated on the top of the sensor or on the integral cable. These values directly can be entered in
service code 03 (section 5-3-1). If the cell has been subjected to abrasion (erosion or coating) calibration
may be necessary. In the next section two examples are given. Alternatively calibration may be carried
out with a simulator to check the electronics only.
NOTE:
During calibration the temperature compensation is still active. This means that the readings are
refered to the reference temperature as chosen in service code 20 (section 5-3-4, default 25 °C).
alibration is normally carried out by measuring a solution with a known conductivity value at
a known temperature. The measured value is adjusted in the calibration mode. On the next
pages the handling sequence for this action is visualised. Calibration solutions can be made up
in a laboratory. An amount of salt is dissolved in water to give a precise concentration with the
temperature stabilised to the adjusted reference temperature of the instrument (default 25 °C). The
conductivity of the solution is taken from literature tables or the table on this page.
Alternatively the instrument may be calibrated in an unspecified solution against a standard instrument.
Care should be taken to make a measurement at the reference temperature since differences in the type
of temperature compensation of the instrument may cause an error.
NOTE:
The standard instrument used as a reference must be accurate and based on an identical
temperature compensation algorithm. Therefore the Model SC72 Personal Conductivity Meter of
Yokogawa is recommended.
Typical calibration solutions.
The table shows some typical conductivity values for sodium-chloride (NaCl) and Potassium cholide
(KCl) solutions which can be made up in a laboratory.
Table 6-1. NaCl values at 25 °C (IEC 60746-3) Table 6-2. KCl values at 25 °C
Weigth % molal
(m) mg of KCl /
kg of solution Conductivity
0.3 0.001 74.66 0.1469 mS/cm
0.5 0.002 149.32 0.2916 mS/cm
1 0.005 373.29 0.7182 mS/cm
3 0.01 745.263 1.4083 mS/cm
5 0.1 7419.13 12.852 mS/cm
10 1.0 71135.2 111.31 mS/cm
The table is derived from the Standards laid down in ‘International
Recommendation No. 56 of the Organisation Internationale de
Métrologie Legale’.
Weigth % mg/kg Conductivity
0.001 10 21.4 μS/cm
0.003 30 64.0 μS/cm
0.005 50 106 μS/cm
0.01 100 210 μS/cm
0.03 300 617 μS/cm
0.05 500 1.03 mS/cm
0.1 1000 1.99 mS/cm
0.3 3000 5.69 mS/cm
0.5 5000 9.48 mS/cm
1 10000 17.6 mS/cm
3 30000 48.6 mS/cm
5 50000 81.0 mS/cm
10 100000 140 mS/cm