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7.4 Unscheduled Maintenance
If the instrument fails to produce results as expected, the
following checks should be made for the messages displayed.
The majority of problems are overcome by thorough cleaning of
the optical windows in the flowcell and or a sensor calibration.
7.4.1 Transmitter Diagnostic messages
Cal Fail (7997 200 and 300 Series only)
Indicates that the expected step change between a zero and
span calibration was not produced by the sensor, i.e. zero
response from the sensor.
a) Repeat calibration.
b) If using a dry calibration standard, ensure that the optical
windows on the dry standard are clean and dry.
c) If using solutions, check that the flowcell has been
thoroughly cleaned, and rinse well between solutions.
d) If using solutions, check both zero and formazine solutions.
e) Check electrical connections to sensor.
f)
Check the sensor 12V supplies, using a suitable voltmeter,
both at the transmitter terminals and sensor junction box –
see Table 3,1 for connection details.
g) Check transmitter response to an electrical input by injecting
0 and 3V into the following terminals and noting the voltage
on the Sensor Voltage display in the software:
Wall mounting
–ve to terminal 7
Panel mounting
–ve to terminal 6
Small errors in displayed voltage can be removed by
electrical calibration. Large errors would indicate an
electronic fault.
Cleaner Fail (7997 200 and 300 Series only)
Indicates that the transmitter was unable to detect the correct
operation of the cleaner; either the cleaner did not rotate or failed
to park in the correct position.
a) Check the electrical connections to the sensor.
b) Check the sensor 12V supplies, using a suitable voltmeter,
both at the transmitter terminals and sensor junction box –
see Table 3.1 for connection details.
c) Check operation of the cleaner unit by disconnecting the
white lead from the transmitter terminal block (Cleaner
Initiate signal). Touch and release the white lead to the 0V
terminal – see Table 3.1 for connection details. This initiates
a cleaning cycle, which can be observed when the cleaner is
removed from the flowcell.
NV Memory Error
Indicates that the contents of the nonvolatile memory has not
been read correctly during power up. To rectify the problem,
switch off the power, wait 10 seconds, and switch on again. If
the problem persists contact the Company.
7.4.2 Unstable or Erratic Readings
This is usually caused by air bubbles in the sample and is usually
more pronounced on the low level 7997 200 Series sensors due
to their greater sensitivity. These bubbles are usually as a result
of degassing of the sample, caused by a drop in sample
pressure, or a rise in temperature. Frequent cleaning of the
+ve to terminal 4
optical windows will help to prevent bubbles building up on the
+ve to terminal 9
windows. It is recommended that the De-bubbler unit is installed
– see Section 2.3.6. If the problem persists refer to Section 7.4.3
Where the noise level gradually gets worse over a period of time,
this usually indicates that solids are building up in the flowcell.
Increasing the flowrate through the flowcell, may reduce this
build up. Ultimately the flowcell needs to be cleaned manually.
7 MAINTENANCE...
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