User Manual

<8. CALIBRATION OF SC (Conductivity)>
8-2
IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
NOTE
Whenasensorisexchangedorreplaced,sensorwellnessdatashouldbereset.
When a sensor is replaced, the replacement can be recorded manually into a logbook. (Refer to
thegure6.9.)
8.1 Cell constant (manual)
Theintentionofthiscalibrationroutineistone-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.
Calibration here is performed by measuring a solution with known conductivity at the set
reference temperature. The calibration solution of an accurate concentration should be prepared
by dissolving a certain amount of solute in water. Allow the conductivity to become stable at the
set reference temperature (initial setting of 25°C) of the instrument and obtain the conductivity
fromliteraturedata,etc.Appendix2showstheconductivityvaluesofsodiumchloride(NaCl)asa
typicalexample.
8.2 Cell constant (automatic)
ThisroutineisbuiltaroundthetestmethoddescribedinInternationalRecommendationNo.
56 of OIML (Organisation Internationale de Metrologie Legale). It allows the direct use of the
solutions prescribed in the test method, automatically selecting the appropriate temperature
compensation.Thelook-uptableisusedtondanappropriateconductivityreadingforthe
measuredtemperature.SeeAppendix2forOIMLsolutions.
8.3 Air calibration
It is not necessary to conduct general air calibration unless the cable length is long and a low
conductivity needs to be measured.
With the clean dry cell in open air, the reading should be zero. The air cal compensates for
excesscablecapacitance,andgivesabetteraccuracyatlowreadings.Thisshouldbedone
when a sensor is installed or replaced. After some time in service, a dirty sensor may well show
a high zero offset because of fouling. Clean the sensor and try again. Moreover, air calibration
should be made in an environment free of electromagnetic interference.
NOTE
The temperature compensation is not performed around zero. In this case, a warning may be
issued.See“●Foralltemperaturecompensation”onApp.2-8.