IM 12D08N04-01E
7-2
7. Maintenance
7-2. Periodic maintenance of the sensor
NOTE
Maintenance advice listed here is intentionally general in nature. Sensor maintenance is
highly application specific.
In general conductivity/resistivity measurements do not need much periodic mainte-
nance. If the EXA indicates an error in the measurement or in the calibration, some
action may be needed (ref. chapter 8 trouble shooting). In case the sensor has become
fouled an insulating layer may be formed on the surface of the electrodes and conse-
quently, an apparent increase in cell constant may occur, giving a measuring error. This
error is:
2 x (Rv / Rcel) x 100 %
where:
Rv = the resistance of the fouling layer
Rcel = the cell resistance
NOTE
Resistance due to fouling or to polarisation does not effect the accuracy and operation of
a 4-electrode conductivity measuring system.
If an apparent increase in cell constant occurs cleaning the cell will restore accurate
measurement.
Cleaning methods
1. For normal applications hot water with domestic washing-up liquid added will be
effective.
2. For lime, hydroxides, etc., a 5 ...10% solution of hydrochloric acid is recommended.
3. Organic foulings (oils, fats, etc.) can be easily removed with acetone.
4. For algae bacteria or moulds, use a chlorous solution (bleaching liquid*).
WARNING
Never use hydrochloric acid and bleaching liquid simultaneously. The very poisonous
chlorine gas will result.