Hoffer Flow Controls CAT3-AC-MIL User Manual page 28

20 Troubleshooting
5.
6.
7-2-2 Symptom: Flow indication with no flow present
This symptom indicates the presence of electrical noise
pickup.
1.
2.
3.
4.
HP-325
ohms between pin A and pin B. A short or an open
indicates a defective pickup coil and the pickup coil
must be replaced.
With an established flowrate, configure the digital
multimeter to measure AC volts, using the two volt
scale. Connect the positive lead to pin A of pickup
coil. And the negative lead to pin B of pickup coil.
Depending on the flowrate an approximate voltage
reading of 10 millivolts to 1 volt should be
measured.
If zero volts are measured, a stalled rotor condition
is indicated. Remove the flow sensor from the
piping. Refer to flow sensor manual.
Disconnect the signal cable from the electronics unit
and from the flow sensor. Check the continuity of
each lead of the cable. If defective replace or repair.
With the signal cable disconnected from the flow
sensor measure the DC resistance of the pickup coil.
The resistance should read between 1500 and 2200
ohms between pin A and pin B. A short or an open
indicates a defective pickup coil and the pickup coil
must be replaced.
Verify cable shield connection.
Verify electronics unit enclosure
connection to ships ground.