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2 DESCRIPTION
All the various system options consist of one or more of the
following units with the further option of fitting the monitor and
power supply units in a cubicle. Specific information relating to a
cubicle option will be supplied separately.
2.1 Model 6553 Gas Monitor
The Gas Monitor is a unit suitable for panel mounting or in a
control cubicle in the safe area. The various monitor options use
one or two digital displays with protected access for zero
adjustments and may also have a range selector switch – see
Fig. 2.1.
N O
I I
N
U
Upper Digital
Display Unit
Lower Digital
Display Unit
(when fitted)
Range Selector
Switch
Fig. 2.1 Model 6553 Gas Monitor
2.1.1 Dual Range Display
When a dual range display is fitted, the range selector switch
may be used to select parameters as follows:
Position (1)
Percentage of hydrogen in air, by volume, shown
on the upper display.
Position (2)
Percentage of hydrogen in carbon dioxide, by
volume, shown on the lower display.
Position (3)
Percentage of air in carbon dioxide, by volume,
shown on the lower display.
The upper display is single range, and is preprogrammed to
indicate the hydrogen purity measurement of the coolant gas
under normal operation of the system.
Ranges (hydrogen purity in air):
100 to 85% or 100 to 80% (4689501 display)
85 to 100 % or 80 to 100% (4689503 display)
with two alarm set points. Two alarm outputs and a value
retransmission signal are also available.
With a second (lower) display fitted (4689500), this may be
dual range marked 0 to 100% hydrogen in carbon dioxide and 0
to 100% air in carbon dioxide for use in the hydrogen purging
operation. A range selector switch is fitted with the dual range
display, and a value retransmission signal and two alarms are
available. With the dual range display there is a further option of
providing remote indication of the range selector switch
position. There is a further option of fitting a second single range
bottom display similar to the top display. An alarm output and a
value retransmission signal are available from this display option.
Each display defaults to indicate NOT IN USE when not
selected.
The Model 4689 displays are dedicated variants of the
Company's Model 4600 Series Indicator/Controllers. With this
special variant (4689), the displays and alarm indicators on the
front panel remain the same but software control is specific to
the Katharometer systems. All user programmable data can be
protected from unauthorized alteration by a programmable
5-digit security number.
The zero adjustments on the front panel of the monitor allow
remote zeroing of the katharometers in the hazardous area. The
adjustment access for a particular display is adjacent to the
display and at the same level.
The monitor unit has a protective case which can be removed for
access to the interior without removing the whole monitor unit
from the panel.
The monitor also contains encapsulated zener barrier units to
limit the electrical energy level that can be applied from the
instrument circuits into the hazardous area. These zener barrier
units are located below the display units, on a bus-bar which
MUST be earthed (grounded). A metal screening arrangement
segregates the connections made to equipment in the
hazardous area. A main fuse is fitted inside the monitor case for
the electricity supply line.
2.2 Model 006540203 or 006548000 Katharometer
Analyser Panel – Fig. 2.2
Each panel comprises a metering valve, a drying chamber, a
thermally lagged katharometer and a flowmeter. These items are
mounted on a flat panel suitable for fixing to a vertical surface
close to the sample point. The katharometers are calibrated for
the hydrogen purity measurement as well as hydrogen in carbon
dioxide and air in carbon dioxide.
Each sealed katharometer assembly incorporates a Wheatstone
Bridge made up of fine glass coated platinum filaments. One pair
of parallel arms is sealed in the reference gas and the other pair
exposed to the sample gas.
3
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