Calibration; When Is Calibration Necessary - YOKOGAWA SC202G User Manual

6. CALIBRATION

6-1 When is calibration necessary?

Calibration of conductivity/resistivity 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 normally indicated on the top of the sensor or on the integral cable. These values can be
entered directly 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 calibra-
tion 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
referred to the reference temperature as chosen in service code 20 (section 5-4, default 25 °C).
Calibration 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 visualized. 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 stabilized 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) solutions which can be
made up in a laboratory.
Table 6-1. NaCl values at 25°C (IEC 60746-3)
Weight % mg/kg
0.001 10
0.003 30
0.005 50
0.01 100
0.03 300
0.05 500
0.1 1000
0.3 3000
0.5 5000
1 10000
3 30000
5 50000
10 100000
Conductivity
21.4 μS/cm
64.0 μS/cm
106 μS/cm
210 μS/cm
617 μS/cm
1.03 mS/cm
1.99 mS/cm
5.69 mS/cm
9.48 mS/cm
17.6 mS/cm
48.6 mS/cm
81.0 mS/cm
140 mS/cm
NOTE:
For resistivity measurement the standard resistivity
units of the calibration solution can be calculated
as follows:
R = 1000/G kΩ·cm (if G = μS/cm)
Example:
0.001 weight %
R = 1000/21.4 = 46.7 kΩ·cm
Calibration 6-1
IM 12D08B02-01E