Table of Contents
Advertisement
7835
Hydrazine Monitor
9.4 Unscheduled Servicing
9.4.1 Monitor Malfunction
Diagnostic messages on the display are used to indicate
abnormal monitor operation – see Section 8, page 20.
Any unpredictable problems may be due to the standard- or
reagent-solutions; check flowrate of these solutions. If any
doubts exist regarding the integrity of these solutions, replace
with freshly-prepared solutions in the early stages of the
fault-finding investigations. The accuracy of the monitor is
governed by the condition of all the solutions involved that may
be made incorrectly, or contaminated.
Check mechanical components involved with the liquid handling
regularly for leaks or blockages, as they change the chemical
conditions around the electrode. The majority of problems are
associated with the chemistry and the liquid handling section.
9.4.2 Calibration Fail Alarm
Calibration problems, normally shown as a Last Cal. Failed
diagnostic message and alarm, indicate that the output of the
sensor is less than 25 % efficient and 80 µg kg
solution. The monitor calculates the corresponding minimum
outputs for other solution values. The problem is likely to be
resolved through one or more of the following checks:
1. Check that the red and blue sensor plugs are inserted fully
into the red and blue sockets, respectively.
2. Replace the standard solutions as a fresh solution may
solve the problem. Check that the solenoid valve is
energized (a loud click is produced when the calibration is
initiated) and that the standard solution is flowing through
the sensor.
3. Check that the standard solution value entered into the
monitor is correct for the solution used.
4. Check the sodium hydroxide solution dosing by
measuring the pH of the sample flowing through the
sensor; it must be at least 10.5.
5. Check that the two electrodes are clean. The silver
cathode can be cleaned only when the sensor is
refurbished. The platinum anode can be cleaned when
required – see Sections 9.4.3 and Section 9.4.4, page 25.
6. Check the condition of the gel in the sensor. In normal
operation the life is usually 3 to 6 months. The gel should
have even color, even consistency and no signs of
separation or drying out. If the gel shows signs of being
very liquid and leaks out of the sensor, refurbish the sensor
– see Section 9.4.5, page 25.
24
7. The shelf life of the gel before use can vary, but can be up
to 1 year providing that the syringe cap is fitted tightly and,
as in step 6, the gel must have even color, even
consistency and no signs of separation or drying out.
8. Remove any air trapped in the flow paths with a syringe
and then check the flow rates of both the standard
solution and the sample – see page 14.
9. Check the sample temperature reading on the display
against a thermometer reading of the sample.
If there are discrepancies between monitors and independent
laboratory results, investigate the points in steps 2, 3, 4 and 8.
Electronic problems are unlikely, but the operation of the
electronics can be checked using a current source to simulate
the output from the sensor. For details of this procedure, refer to
Section 9.4.6, page 26.
-1
. standard
9 Maintenance
IM/7835–EN Rev. P
Advertisement
Table of Contents
