PRESSURIZED ENCLOSURE,
SWITCHING ON THE CHROMATO-
GRAPH
The electronics area of the chromatograph is press-
urized. It is constantly purged with a non-inflamm-
able gas to prevent explosive gas from entering this
area.
The power supply to the chromatograph must only
be switched on when the electronics area has been
sufficiently purged. An automatic feature ensures
this is the case in a division 1 area. In a division 2
area, you must switch on the chromatograph your-
self once you have assessed that the electronics area
has been sufficiently purged.
Starting the automatic purging time
Switch on the external power switch. The excess
pressure is produced in the chromatograph.
The purging time commences once the purging
pressure has been produced and the flow is suffi-
cient. The Purge lamp lights up while purging time.
Once the purging time has expired and the ON/OFF
pushbutton is at
ON
at the same time, the purging
time controller switches the power supply to the
chromatograph, to the control room panel and to the
isolating relay via a contactor. The purging valve is
switched over such that only losses resulting from
leaks are compensated. The Purge lamp goes out.
The Ready lamp lights up if the ON/OFF pushbut-
ton is at
OFF
.
The purging time controller switches off the power
supply if the pressure in the housing becomes too
low or too high. A new purging procedure com-
mences.
Key switch,
bypassing of purging time controller
For certain maintenance operations it is necessary to
open the electronics door without switching off the
chromatograph. You must first possess an appropriate
permit. Then set the key switch to Bypass before open-
ing the electronics door.
NOTE:
The power supply to the chromatograph is switched on imme-
diately if you set the key switch to
Bypass
and then switch on
the purging time controller!
WARNING:
Never activate the key switch before an expert
has guaranteed that the atmosphere at the
chromatograph location does not present an
explosion hazard and will remain so for the
duration of the maintenance work (permit!).
We recommend that you install a gas warning
device in the vicinity of the chromatograph
during the maintenance work.
Purging time monitoring unit
The monitoring unit is fitted in the electronics area of
the explosion-proof chromatograph. It has been espe-
cially adapted for this purpose. All parts are explosion-
proof and must be wired according to Siemens circuit
diagrams, otherwise the explosion protection is can-
celled.
The set purging time is also part of the explosion pro-
tection. The explosion protection is cancelled if the set-
tings are changed.
Pressure/flow monitor
Control panel
ON
OFF
PURGE
READY
Bypass
Purging gas valve
Explosion protection
1EXPLO.CHP, Stand Dezember 22, 1999
9
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