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300-302 Series Page 22 of 31
This section contains service and calibration information. Some portions of the instrument are
delicate. Use extreme care when servicing the instrument. Authorized Maintenance
With proper care in installation and use, the instrument will require little or no maintenance. If
maintenance does become necessary, most of the instrument can be cleaned or repaired in the field.
Most procedures may require recalibration. Do not attempt these procedures unless calibration
references are available. Entry into the sensor or tampering with the printed circuit board will void
warranty. Do not perform repairs on these assemblies while the unit is still under warranty.
4.1. Troubleshooting
Symptom: Output reads strong indication of flow with no flow present. Zero pot has no effect.
Cause: Power shorted out.
Action: Turn power supply off for a few seconds, and then turn it on again. If this is ineffective,
disconnect the power supply from the unit. Check that the power supply voltages
are correct. Incorrect voltages most likely signify a faulty regulator chip inside the
supply. If the power supply display returns to zero after the instrument has been
disconnected there may be a short from the unit to ground.
Symptom: Hastings 300 output continues to indicate flow with no flow present, or indicates
±14 volts. Power supply inputs are correct (see the above troubleshooting tip) and
zero pot has no effect.
Cause: Faulty IC chip(s) on the main PC board.
Action: Replace main PC board. (See sections 4.5 and 6.1)
Symptom: Output of flow meter is proportional to flow, but extremely small and not correctable
by span pot.
Cause: Sensor is not being heated.
Action: Shut off gas supply and disconnect the power to the flow meter. Remove cover and
PC board from unit. Check the resistance from pins 1 to 2, and 3 to 4 (refer to
figures in section 6) of the sensor module. These pins should read 1650 Ω nominal
resistance. Also check that the resistance from pins 5 to 6, and 7 to 8 are 400 Ω
nominal value. Incorrect resistance values indicate that the sensor unit needs to be
replaced.
Symptom: Sensor has proper resistance readings, but little or no output with flow.
Cause: Plugged sensor.
Action: Shut off gas supply and disconnect the power to the flow meter. Remove cover and
PC board from unit. Remove and inspect sensor. If sensor has evidence of clogging,
clean or replace as applicable.
Symptom: flow meter reads other than 0.00 VDC with no flow or there is a small flow when the
flow meter reads 0.00 VDC.
Cause: Zero pot is out of adjustment.
4. Maintenance