6. TROUBLE SHOOTING
IM 12B6C2-E-H
6-1. Introduction
As the EXA PH200 is a micro-processor
analyzing instrument, it performs continuous
self-checks to verify its correct working.
The error messages resulting from faults in
the working of the micro-processor system
are few. Incorrect programming by the user
can be fixed through programming with cor-
rected values. See the limits given in the
respective paragraphs.
In addition to that the EXA PH200 also
checks the electrodes to establish whether
these are still functioning within the limits
implemented through the service settings.
The EXA PH200 checks the glass electrode
impedance for a low value to know if it
hasn't broken or cracked.
The reference system is prone to more dis-
turbances than the glass electrode in gene-
ral. The impedance is measured and com-
pared to the programmed value in memory.
A high impedance signals a pollution of the
diaphragm.
Furthermore the sensors are checked at
calibration to see whether they still are reac-
ting fast enough to changes in pH.
After calibration the calculated asymmetry
potential and slope are checked to see if
these are still within the limits specified in the
software. The slow shift of the asymmetry
potential could signal a poisoning of the
reference system by the process.
The decrease of slope indicates a deteriora-
tion of the sensitivity of the glass electrode
or can show a coating building up at the
electrode.
The remedy for each fault is given very
shortly. Process conditions determine what
action can be taken to correct errors. As the
actual situation may vary, it is not possible
for us to give you a full solution for all cases.
If you have any problems or questions plea-
se consult your nearest Yokogawa sales or
service organisation for assistance.
There is a distinction made in the weight of
errors. All errors are signalled by the FAIL
area in the display. Only errors due to faults
in the measuring circuits also result in the
activation of the FAIL function switching the
22 mA signal §7-7. These are indicated by
an asterisk (*) in the error list.
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