KROHNE IFC 110 Converter - Manual (Page 76)

Sect. 7.6 Part C Special applications, functional checks, service, and order numbers
76 IFC 110 F 05/2003
7.6 Checking the flow sensor
Always switch off the power supply before opening the housing.
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.
• Remove the cover from the terminal compartment (remove 2 screws).
• Pull out the two plug-in terminals SC (5-pin, signal line) and FP (4-pin, field current supply
line), see illustration in Section 8.1.
• Fill the measuring tube of the flowmeter completely with process liquid.
• Please note: the following measurements must only be carried out for plug-in terminals
which are occupied (used).
Action Typical Incorrect result for
Resistance measurements at result 1–3 = defective flow sensor,
plug-in terminals SC (5-pin, signal line) return to factory for repair,
and FP (4-pin, field current supply line) refer to last-but-one page !
1 Measure resistance between wires 30 – 170 Ω If lower,
7 and 8 interwinding fault.
If higher,
wire break.
2 Measure resistance between wires > 20 M Ω If lower, interwinding fault
1 and 7 or between wires 1 and 8 to PE or FE.
3 Measure resistance between wires 1 k Ω – 1 MΩ If lower, drain measuring tube
1 and 2 and between 1 and 3 (see ”Note” above) and repeat measurement;
(same measuring conductor always on Both values should if still too low, short-circuit in
wire 1 ! ) be approx. equal electrode wires.
If higher, break in electrode wires
or electrodes contaminated.
If values differ considerably,
break in electrode wires or
electrodes contaminated.
4 When signal line B (type BTS/ > 20 M Ω If lower,
bootstrap) is used: line fault.
measure resistance between
the following lines: Check connection cables,
1 and 20 / 1 and 30 / 20 and 30 replace signal line if necessary.
2 and 20 / 3 and 30