IM 12B6C2-E-H
4-4-4. On-line impedance checks
The EXA PH200 transmitter is delivered from
the factory with an impedance check disab-
led. To activate this impedance checking
refer to §7-5. The impedance check works
on both measuring and reference electrode,
but not in the same way. The measuring
electrode is checked for presence of a high
impedance on the input side. An open cir-
cuit is signalled by an error E5. A short cir-
cuit is signalled by an error E4. The impe-
dance of the reference electrode is meas-
ured (RZ). The actual value (in kilo Ohm) can
be called up from the display routine in the
maintenance menu. When pH is measured
in high purity water it is necessary to adjust
the reference impedance for the low con-
ductivity of the solution. In general a high
impedance value can be related to a dia-
phragm clogging, fouling or non-immersion
of the sensors. If the value exceeds the limit
set an error E6 is generated. Activation and
limit setting (*IM.LMT) is done from the servi-
ce level §7-5.
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