25
6.3 Electrical Checks
Carry out the electrical checks detailed in Sections 6.3.1 and
6.3.2.
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
350mA into a 14 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
Zener diode safety barrier devices are fitted to the katharometer
system as detailed in Table 6.1 and are checked at the time of
manufacture. To ensure absolute safety, check that the barriers
are correctly earthed by carrying out an appropriate test before
using the katharometer system.
Warning .
• The zener diode safety barrier devices are certified
intrinsically safe and form part of the certified
intrinsically safe system. Appropriate safety
precautions MUST be taken to prevent any
incendive electrical discharges in the hazardous
area when testing the barriers.
• If the tests identify a faulty barrier, it MUST be
replaced by a new unit OF THE SAME TYPE – see
Table 6.1. The barriers are sealed units and repairs
ARE NOT permitted.
6 SETTING UP
Table 6.1 Zener Diode Safety Barriers
6.3.3 Checking Intrinsically Safe Earth
Check that the resistance between the earth terminal
connecting zener barriers in the 6553 Display Unit and the
application plant system high integrity earth does not exceed
0.1 . Also check the low flow alarm zener barrier (if fitted in the
cubicle) and the application plant system high integrity earth
does not exceed 0.1 .
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