Table of Contents
Advertisement
8.4.2 Monitor Diagnostic Information
Out of Service Alarm
This alarm relay output is a normally energised relay which de-
energises in the following circumstances:
a) Loss of mains supply.
b) Calibration Failed – the calculated electrode slope value is
outside the acceptable limits or the response of the electrode
is too slow. The 'CAL FAIL' l.e.d. on the front panel is
illuminated with the appropriate text on the 20-character
display.
c) Flowcell temperature out of limits – the measured
temperature is not within 5°C of the Control Temperature.
'TEMP. CONTROL ERROR' is indicated on the 20-character
display.
d) 'OUT OF SAMPLE' alarm – a float switch in the constant head
unit detects the loss of sample. 'OUT OF SAMPLE' is
indicated on the 20-character display.
e) 'OUT OF SERVICE' alarm – displayed when the pump is
switched off.
✶
Note. The heater is switched off by the software when
an 'OUT OF SAMPLE' condition is detected.
Calibration Fail Alarm
A calibration failed condition occurs after a two point calibration if
the calculated slope value is less than 80% or if the electrode
output is unstable. The failure could be caused by a number of
factors which should be investigated.
In the 'CAL. FAILED (SLOPE)' case some indication of the
problem may be obtained from the slope value.
Slope value just below 80%
a) Check the reagent solution flows.
b) Check condition of the reagent solutions.
c) Check condition of the standard solutions.
d) See Malfunction of the Electrode Section 8.4.3.
Slope value grossly abnormal
a) Check operation of the solenoid valves and flow of the
standard solutions.
b) Check condition of the standard solutions.
c) Check the reagent solution flows.
d) Check condition of the reagent solutions.
e) Check liquid level in reference electrode – see Malfunction
of the Electrode Section 8.4.3.
f) Check electrode connections in the co-axial plugs and
sockets, and inside the microprocessor unit.
g) See Malfunction of the Electrode Section 8.4.3.
h) Check operation of the Microprocessor Unit by following the
procedure in Section 6.2.10, Electrical Calibration.
Calibration Failed (Slow)
In the 'CAL. FAILED (SLOW)' case the failure is usually due to
slow electrode response, but may be due to an unstable (noisy or
drifting) electrode output:
a) Check for air bubbles trapped on chloride electrode surface.
Remove if necessary and ensure that the temperature sensor
is not positioned too low down in the flowcell.
b) Check electrode connections in the co-axial plugs and
sockets, and inside the microprocessor unit.
c) See Malfunction of the Electrode Section 8.4.3.
8.4.3 Malfunction of the Electrode
Caution. Suspected faulty electrodes cannot be
disassembled to investigate any problems.
a) Check for surface deposits on the chloride electrode sensing
surface. See Section 8.5.
b) Check performance of chloride electrode by substitution.
c) Check level of filling solution in reference electrode; top up if
necessary.
d) Check that the rubber stopper has been moved away from the
filling solution hole in the reference electrode.
e) Reference electrode liquid junction partially or completely
blocked, replace electrode if required.
8.5 Reconditioning the Chloride Electrode
In time the response time of the chloride electrode may become
extended and the general performance deteriorates to an
unacceptable level. The electrode loses its normal grey-brown
appearance but can be re-chloridised as follows:
1) Requirements
✶
Note. Do not use acid preserved with mercuric ions
Caution. Strong ammonia solutions and strong nitric
acid are both very poisonous and corrosive. Care should be
taken not to inhale the fumes of either or to get any on skin or
clothing. Any slight spillage on skin, clothing or working
surfaces should be washed away with plenty of water.
Chemicals
a) Plating solution
Hydrochloric acid, 0.1M (500ml)
b) Cleaning solutions
Ammonia solution 50% (250ml)
8 MAINTENANCE...
33
Advertisement
Table of Contents
