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6.3 Electrical Checks
Carry out the following electrical checks:
6.3.1 Power Supply Unit Output
Warning. This unit is part of the certified
intrinsically safe system. Appropriate safety precautions
must be taken to prevent any incendive electrical
discharges in the hazardous area when carrying out this
task.
Testing the output may only be carried out with the
hazardous area cable disconnected.
1) Electrically isolate the PSU.
2) Remove the cover from the PSU.
3) Disconnect the output wires to the hazardous area at
terminals TB2+ and TB2–.
Warning. Ensure that proper electrical safety
precautions are taken at all times when undertaking this
procedure.
4) Switch on the PSU and check that the output measures
350 mA into a 14 ohm load.
5) On completion of tests isolate the unit and reconnect the
output wires to the hazardous area.
6) Replace the cover on the unit.
6.3.2 Zener Diode Safety Barrier Devices
The zener diode safety barrier devices (MTL 7055ac) in the 6553
Monitor Unit are checked at the time of manufacture. To ensure
absolute safety when fitting a new instrument, check that the
barriers in the monitor are properly earthed by carrying out a
routine test before using the analyser system.
Warning.
•
This unit is part of the certified intrinsically safe system.
Appropriate safety precautions must be taken to
prevent any incendive electrical discharges in the
hazardous area when carrying out this task.
•
If these tests reveal a faulty zener barrier, the barrier
MUST be replaced by a new unit. The barrier is a sealed
unit and no repair is permitted. The correct zener
barriers are certified intrinsically safe and conform to the
ATEX
Directive
9/94/EC,
BAS 99 ATEX 7285.
6.3.3 Checking System Earth
Check that the resistance between earth terminals on the
analyser system and the application plant system safety earth
does not exceed one ohm.
6 SETTING UP
certificate
number
21
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