Unscheduled Servicing; Wet-Section Malfunction; Calibration Fail Alarm; Hydrazine Sensor Check - ABB Navigator 550 Operating Instructions Manual

Navigator 500
Hydrazine analyzer

A.5 Unscheduled servicing

A.5.1 Wet-section malfunction
Diagnostic messages on the display are used to indicate
abnormal wet-section operation – refer to Appendix A.1, page
63.
Some problems may be due to the standard solution or reagent
solutions – check flow rates 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 wet-section is governed by
the condition of all the solutions involved some may have been
made incorrectly or have become contaminated.
Check mechanical components involved with the liquid handling
regularly for leaks or blockages, as they change the chemical
conditions around the electrode.
Ensure the liquid flow paths are free of air bubbles. This can be
done by attaching a syringe to the outlet of the hydrazine sensor
and pulling sample or standard through the liquid flow path.
A.5.2 Calibration fail alarm
Calibration problems, normally shown as a Cal. Failed
diagnostic message and alarm, indicate that the output of the
sensor is less than 40 % efficient. 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 (an audible click is produced when the
calibration is initiated) and that the standard solution is
flowing through the sensor – air bubbles should be visible
at the bottom of the standard solution Boyle Mariotte tube
– see Fig. A.1.
Boyle Mariotte tube in
Standard Solution 2
(High) tank
Fig. A.1 Boyle Mariotte tube in standard solution 2
(high) tank
66
3. Check that the standard solution value entered into the
4. Check the sodium hydroxide solution dosing by
5. Check that the two electrodes are clean. The silver
6. Check the condition of the gel in the sensor. In normal
7. Remove any air trapped in the flow paths with a syringe
8. Check the sample temperature reading on the display
If there
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 A.4, page 65.
A.5.3 Hydrazine sensor check
Before checking the sensor, ensure the fault condition is not due
to incorrect sample and calibration flow rates caused by an air
bubble in the sensor or flow line. To remove air, lift the platinum
electrode slightly and allow some liquid to escape, carrying any
Navigator 500 bubbles with it. Alternatively, connect a syringe to the sensor
outlet and apply slight suction – refer to Fig. 8.6, page 59.
wet-section is correct for the solution used.
measuring the pH of the sample flowing through the
sensor; it must be at least 10.5.
cathode can be cleaned only when the sensor is
refurbished. The platinum anode can be cleaned when
required – see Section 8.4.2, page 58.
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 8.4, page 58.
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 then check the flow rates of both the standard
solution and the sample – see page 20.
against a thermometer reading of the sample.
are discrepancies between wet-sections and
OI/AHM550–EN Rev. A