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IM 12D06D05-01E
APPENDIX 3
Calibration solutions for conductivity
Note!
This section should be read in conjunction with the calibration section (Chapter 6) and the mainte-
nance section (Chapter 7). The calibration (cell constant) of a sensor does not change unless the
sensor is damaged.
Itcanalsoappeartochangebecauseofcoatingoftheelectrodes,orpartialblockage.Because
these changes should be handled as described in the maintenance section, it does not make
sensetoregularlyrecalibratetheISC450G.
A calibration check, however, is another matter. When the objective is clearly defined as a diagnos-
tic exercise a regular check can bring an extra level of security and confidence to the measure-
ment.
Sensordamage,and/orcoatingscanbedifficulttoseeandthecalibrationcheckcanconfirmtheir
presence, by a deviation from the known solution conductivity. The remedial action should be to
clean the sensor, and carefully check for blockage or damage (not simply to recalibrate).
Higher conductivity solutions should be used where possible. The lower the conductivity of the test
solution, the easier it is to contaminate. Carbon dioxide from the air can be quickly absorbed to
causeanerror.Allcontainersmustbesuitablyclean,andallmaterialssuitablypure.Outsideofa
well-equipped laboratory these conditions are hard to meet.
EXAxtISC450GisprogrammedwiththefollowingtableofconductivityofPotassiumChloride
(KCl)solutionsat25°C.ThisisusedintheAutomaticCellConstantsettingcalibrationfeature.
(Seechapter6oncalibration)ThetableisderivedfromtheStandardslaiddownin“International
RecommendationNo.56oftheOrganisationInternationaledeMétrologieLegale”.
Table 11-2. KCl values at 25 °C
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