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4.4 Manual Grab Sample Facility
A facility is provided to pass a grab sample through the monitor
manually which has been taken from another sample point. If
required, the same procedure can be used to introduce
standard solutions to check the monitor calibration. Proceed
as follows:
a) Put 100 ml of sample into a clean, well rinsed container.
This will run the monitor for 25 minutes approximately.
b) Remove the secondary calibration container tube. Rinse in
high purity water and transfer it to the grab sample container.
c) Energize the secondary calibration valve (see Section 6,
Programming Page 2.2). This will bring up the 'Out of
Service' alarm and prevent an automatic calibration from
taking place. Return to the main display page. On multi-
stream versions of the monitor it will be necessary to switch
to single stream operation (see Section 4.3).
d) The display should stabilize on the grab sample value after
16 minutes approximately which can them be noted.
e) Remove the tube from the container, rinse and return it to
the secondary calibration container. Run the monitor for a
further five minutes.
f) Return the monitor to normal operation by de-energizing
the secondary calibration valve.
Measurement taken
4s
Lamp illuminated
5s
Cuvette
overflows
Fig. 4.6 Drain/Fill Sequence
Drain valve operates –
cuvette drains
3s
Cuvette fills
65s variable
4 LIQUID HANDLING SECTION
4.5 Optical System – Figs. 4.6 and 4.7
The optical system comprises a tungsten halogen exciter lamp
mounted between two photocells. The light falling on the
measuring photocell first passes through the measuring
cuvette containing the reacted sample and then through a
colored filter. This filter selects the specific wavelength
required
for
the
correct
(approximately 470 nm). The light can be seen via the prism
on top of the lamp housing. Its intensity is controlled by the
output from the reference photocell.
Although the reaction of the sample is continuous, the actual
optical measurement of the reacted sample is based on a
nominal 80-second cycle controlled by the microprocessor –
see Fig. 4.6.
The temperature of the optical system is controlled using a mat
heater and a PT100 temperature sensor. This temperature is
kept to the same value as that of the reaction block to avoid
convection currents in the measuring cuvette.
Information. The exciter lamp operates well below
the specified operating voltage. This design gives a lamp
life of many years.
Reference Photocell
Plastic
Housing
Prism
Lamp
Mounting
Plate
Important Note. The Optical System Cover must
be in place when the monitor is running. This cover
excludes the effects of ambient temperature and light.
Fig. 4.7 The Optical System
operation
of
the
monitor
Lamp
Measuring
Housing
Cuvette
Measuring Photocell
Housing
Optical System
Heater Mat
Below Optical
System
Base Plate
Drain Pinch
Valve
Optical System
Cover
13
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