3
98.8
H2–C
O2
U
I
I
N O
N
S E
Hydr
ogen Purity
& Purge Gas Monitor
Range
Range Selector
Switches
Digital
Display
Units
1
2
3
1
2
3
Zer
o
Zer
o
Range
F1
F2
Zero
Adjustment
AK102
All the various system options comprise one or more of the
following units with the further option of fitting the display and
power supply units in a cubicle.
2.1
Model 6553 Display Unit
The display unit must be mounted in a
safe
area and is suitable
for panel mounting or installation into a control cubicle. The unit
houses one or two Model 4689 digital display units, each
equipped with a range selector switch and protected access for
zero adjustment – see Fig. 2.1.
The AK102 version is a dual 3-range instrument, designed to
provide 100% redundancy.
The AK103 version is a single 3-range instrument.
2.1.1
Range Display
A selector switch for each display provides independent
parameter selection as follows:
Position (1)
Percentage of Hydrogen in Air by volume
.
This is the hydrogen purity measurement of the
coolant gas during normal operation of the
system. The display covers a range of 85 to 100%
or 80 to 100% hydrogen in air depending on the
range selected. An alarm output and a
retransmission signal (4 to 20mA) are provided for
this switch position only.
Position (2)
Percentage of Hydrogen in CO
2
/Argon by volume
.
This range is for use in hydrogen filling or purging
operation. Alarm and retransmission signals are
inhibited in this switch position.
Position (3)
Percentage of Air in CO
2
/Argon by volume
.
This range is for use in carbon dioxide (or argon)
filling or purging operations. Alarm and
retransmission signals are inhibited in this switch
position.
A further option of providing remote indication of range selector
switch may be available, depending on the number of alarms
specified.
The 4689 Display Units provide software specific to the
katharometer systems with relay action of the alarms fixed as
'fail safe'. All user-programmable data can be protected from
unauthorized alteration by a programmable 5-digit security
number.
The zero adjustments on the front panel enable remote zeroing
of the katharometers mounted in the
hazardous
area. The
adjustment access for a particular display is adjacent to the
display and at the same level.
The 4689 has a protective case that can be removed for access
to the interior without removing the whole unit from the control
panel.
The 4689 contains encapsulated zener diode safety barrier
devices to limit the electrical energy that can be supplied from
the instrument circuits into the
hazardous
area. These devices
are located below the display units, on a rail that
MUST
be
earthed (grounded). A metal screening arrangement segregates
the connections made to equipment in the
hazardous
area. The
unit is protected on the mains input side by two fuses, one for
each circuit, accessible from the front of the panel.
Fig. 2.1 Model 6553 Display/Control Units
2
DESCRIPTION
U
I
I
N O
N
S E
Hydr
ogen Purity
& Purge Gas Monitor
Range Selector
Switche
Digital
Display
Unit
1
2
3
Zer
o
Range
F1
Zero
Adjustment
AK103
