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...8 MAINTENANCE
8.3 Shutdown Procedure
8.3.1 Short Term
The monitor can be left with the power switched off for up to 24
hours without any detrimental effects. When returned to
normal monitoring mode, the monitor should be run on sample
for 30 minutes, followed by a calibration – see Section 7.
If the probe is left in the monitor with no liquids flowing, the
internal filling solution becomes more concentrated by
evaporation of water through the membrane. The probe output
drifts when normal operation is resumed and many hours may
be required to re–establish stability. In such cases normal
performance can sometimes be restored by unscrewing the
glass electrode 2 to 3 turns and then returning it to its original
position, thus allowing fresh filling solution to flow between it
and the membrane. If this procedure is not successful replace
the membrane and filling solution.
If the probe is likely to be out of use for more than one day,
remove from the monitor and store with the lower part of the
body immersed in a small quantity of liquid in a beaker or other
suitable vessel. 0.1M ammonium chloride is the best storage
solution (but it is essential that all traces of the storage solution
are rinsed away with clean water before use); otherwise, a
small amount of the EDTA reagent (Reagent 1) is suitable.
8.3.2 Long Term
When the monitor is required to be shut down for more than 24
hours, proceed as follows:
a) Switch of the monitor.
b) Close the sample valve upstream of the monitor.
c) Dismantle the probe and return to its box. First the glass
electrode is unscrewed, then the rest of the probe emptied,
rinsed and drained. Store the glass electrode with its end in
a teat containing a neutral buffer solution, taking care not to
cover the reference element.
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Table 8.1 Unscheduled Servicing Messages
d) Clean sample pipework both inside and outside the
monitor, constant head unit, and filtration system (if used).
e) Remove pressure plate from peristaltic pump.
8.4 Unscheduled Servicing
The monitor indicates abnormal operation by means of signals
on the 20 character dot matrix display and l.e.d's. The
indications are listed in Table 8.1.
8.4.1 Malfunction of the Monitor
It should always be remembered that any unpredictable
problems may be due to the standard or reagent solutions, or
their flow through the flowcell. If any doubts exist regarding the
integrity of the solutions, they should be replaced with freshly
prepared solutions in the early stages of the fault finding
investigations.
Note. The accuracy of the monitor is governed by the
condition of these solutions which may be incorrectly
made or contaminated.
In general, any problems are likely to be due to the electrodes,
which may require refurbishment (see Section 8.4.3), but may
be due to other parts of the liquid handling section of the
monitor.
Mechanical components which are involved with the liquid
handling, for example, pumps, valves, tubing and tubing
connections etc., should be systematically checked for correct
operation, and for leaks or blockages which change the
chemical conditions around the sensor. The majority of all
problems are found to be associated with the chemistry and
the liquid handling section.
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