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...8 MAINTENANCE
8.5.2 Low/High Calibration Factor Value
a) Check and, if necessary, replace the standard solutions.
b) Check and, if necessary, replace the reagent solution.
c) Switch 'Energise AUTO ZERO valve' to YES on
Programming Page 2.2.
d) Lift the zero calibration solution tube out of the container
and ensure that air is being drawn into the tube.
Caution. Clean up any spillages from the second
mixer chamber.
e) Switch 'Energise AUTO ZERO valve' to NO and set
'Energise SECONDARY CAL valve' to YES.
f) Lift the secondary calibration solution tube out of the
container for a few seconds and ensure that air is being
drawn into the tube.
Important Note. It cannot be stressed strongly
enough that the five-weekly chemical rinse with the
ammonia/detergent solution is vitally important. It is also very
effective at reducing calibration problems, drift and signal
noise. Any evidence of white or blue precipitate in the mixer
or reaction coil must be removed with the rinse solution.
g) Carry out a monitor response test – see Section 8.5.3.
8.5.3 Monitor Stability/Response Test
a) Check that the temperature on both heaters is under
control and stable.
b) Switch 'Default calibration parameters' to YES on
Programming Page 2.1.
c) Switch 'Energise AUTO ZERO valve' to YES on
Programming Page 2.2.
d) Run the monitor for 30 minutes.
e) Use the
/
buttons to generate a sensible reading of
the sample on the display on Programming Page 0. Note
the reading over a 30 minute period to ensure a stable
reading.
f) Switch 'Energise AUTO ZERO valve' to NO and 'Energise
SECONDARY CAL valve' to YES.
g) Run the monitor for 30 minutes. Note that the reading on
Programming Page 0 has changed by approximately the
value of the secondary solution and is stable over a
30 minute period.
h) If successful, set the monitor to normal operation, i.e. de-
energise the SECONDARY CAL valve and carry out a
baseline calibration – see Programming Page 2.3.
32
8.5.4 Simple Electronic Response Test
a) Remove the optical system cover.
b) Switch 'Default calibration parameters' to YES on
Programming Page 2.1.
c) Switch 'Lamp on continuous' to YES on Programming
Page 2.2. This stops the drain/fill sequence.
d) Place a thin card between the lamp housing and the
measuring cuvette (see Fig. 8.3A) to stop the light
reaching the measuring photocell.
e) Wait six seconds and note that the reading on the display
on Programming Page 0 goes off the scale.
f) Remove the card and place it between the lamp housing
and the reference photocell housing to stop the light
reaching the measuring photocell (see Fig. 8.3B).
g) Wait six seconds and note that the reading goes to zero.
Note also that the intensity of the light, seen through the
plastic prism on top of the lamp housing, increases.
h) Remove the card and set the monitor to normal mode via
Programming Pages 2.1 and 2.2.
8.6 Setting Up the Optical System
This lamp is pre-set at the factory and normally needs no
further adjustment. Also, the lamp is run well below its rated
voltage and should have a long life. However, in the unlikely
event of exciter lamp or cuvette board failure, the optical
system will require resetting. Section 8.6.2 explains how to
adjust the lamp alignment to ensure that the maximum amount
of light is hitting the photoelectric cell. Section 8.6.3 explains
how to set a new cuvette board, i.e. balance the two outputs
from the photocells. If only the cuvette board is being replaced,
then the lamp alignment requires no adjustment. However,
both steps need to be carried out if the lamp position has been
disturbed.
8.6.1 Replacing the Exciter Lamp – Fig. 8.4
a) Remove (pull off) the optical system cover (see Fig. 4.6).
b) Switch off the instrument, unscrew the three spring-loaded
positioning screws (Fig. 8.4) and lift off the lamp mounting plate.
Caution. Do not touch the glass envelope of the
new lamp; use a tissue to hold it.
c) Pull out the old lamp and fit a new one.
d) Temporarily switch on the instrument and check that the
lamp illuminates during each drain/fill cycle.
e) If the lamp is working, switch off the instrument and secure
the lamp mounting plate. Ensure that the springs are in
place. Switch on the instrument.
Now align the lamp – see Section 8.6.2.
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