KROHNE IFC 210 E-EEx EN - Manual (Page 70)

Sect. 7.5 Part C Special applications, functional checks, service, and order numbers
IFC 210 E 05/2002
70
7.5 Checking the primary head
This method describes the testing of the primary head and its interconnecting cables at the
installation location of the signal converter.
CAUTION!
The following applies to primary heads in hazardous areas:
Installation, electrical connection, commissioning and maintenance work may only
be carried out by persons who have been trained for work in hazardous areas and
are authorized to do so.
Always switch off power source before starting work on the subrack connections.
Required measuring instruments and tools
•
Ohmmeter with at least 6 V measuring voltage range
•
or AC voltage/resistance bridge
•
Note: accurate measurements in the electrode area can only be obtained with
an AC voltage/resistance bridge. The measured resistance also heavily
depends on the electrical conductivity of the process liquid.
Preparations
•
Switch off the power supply.
•
Pull plug-in unit out of the subrack.
•
Fill the measuring tube of the flowmeter completely with process liquid.
•
Please note: the following measurements must only be carried out
for connections which are occupied (used).
The Nos. in brackets ( _ _ _ ) identify the power terminals at the primary head.
Action
Resistance measurements at the plug connector
XA, electrical connection to primary head:
signalling cable (max. 5-pin) and field current
cable Typical result Incorrect result for 1 – 3 =
defective primary head,
return to factory for repair,
refer to last-but-one page !
If lower, interwinding fault. 1 Measure resistance of cables between
Pins d30 and d32 (7 and 8) 30 – 170
Ω
If higher, wire break.
2 Measure resistance of cables between
Pins d8/z8 and d30
(1 and 7) or Pins d8/z8 and d32
(1 and 8) > 20 M
Ω If lower, interwinding fault
to PE or FE.
3 If lower, drain measuring tube and repeat
measurement; if still too low, short-circuit in
electrode wires.
If higher, break in electrode wires or
electrodes contaminated.
Measure resistance of cables between
Pins d8/z8 and z6 (1 and 2), and also
between Pins d8/z8 and z10 (1 and 3).
Always use the same measuring lead
on Pin d8/z8 (1)! 1 k
Ω
– 1 M
Ω
(see Note above).
Both values should
be approx. equal.
If values differ considerably, break in
electrode wires or electrodes contaminated.
4 When signal cable B (type BTS/
bootstrap) is used:
measure resistance between
the following lines:
Pins d8/z8 and d6 (1 and 20),
Pins d8/z8 and d10 (1 and 30),
Pins d6 and d10 (20 and 30),
Pins z6 and d6 (2 and 20),
Pins z10 and d10 (3 and 30). > 20 M Ω If lower,, line fault.
Check connection cables, replace signal
cable if necessary.