Yokogawa EXAxt PH450 4-Wire Analyzer for pH and ORP - Manual (Page 53)

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8
TROUBLESHOOTING
8-1. General
The EXAxt is a microprocessor-based con-
verter that performs continuous self-diagnostics
to verify that it is working correctly. Error mes-
sages resulting from faults in the micro-proc-
essor systems itself are monitored. Incorrect
programming by the user will also result in an
error, explained in a message, so that the fault
can be corrected according to the limits set in
the operating structure. The EXAxt also checks
the sensor system to establish whether it is still
functioning properly.
In the main display screen is a “Status Informa-
tion” button that will show
For information
For warning - a potential problem is diag-
nosed, and the system should be checked.
For FAIL, when the diagnostics have confirmed
a problem, and the system must be checked.
This button gives access to a status report
page, where “The most applicable error” will
be displayed. ( “No errors” is displayed during
proper operation)
Explanation >> Description or error message
and possible remedies
Advanced troubleshooting >> Error code
screen that is used in conjunction with the
service manual. This data may also be needed
in the event that you request assistance from a
Yokogawa service department.
What follows is a brief outline of the EXAxt
troubleshooting procedures including possible
causes and remedies.
8-2. Calibration check
The EXAxt PH450G converter incorporates a
diagnostic check of the adjusted slope or zero
value during calibration. If the adjusted value
stays within the configured limits, it is accepted,
otherwise, the unit generates an error mes-
sage, and the calibration is rejected.
8-3. Predictive maintenance
EXAxt has a unique prediction feature. Calibra-
tion, and reference impedance data are stored
in software data logbooks. This data is then
used to calculate a prediction for maintenance
purposes.
See section 4-3-9 and 4-3-10.
8-4. Error displays and actions
All errors are shown in the “Main Display”
screen, however, the EXAxt makes a distinction
between diagnostic findings. The error mes-
sages may be set to OFF, WARN or FAIL. For
process conditions where a particular diagnos-
tic may not be appropriate, the setting OFF is
used. FAIL gives a display indication only of
that the system has a problem and inhibits the
relay control action, and can be set to trigger
the “Burn” function. “Burn-up or Burn-down”
drives the mA output signal to 21 mA or 3.6 mA
respectively.
8. TROUBLESHOOTING