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Manual: 152-082010 301-305-306_303-307 Series Page 26 of 35
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.
Action: Shut off all flow. For the standard 0 – 5 VDC output, adjust the zero potentiometer (see
Section 4.3) located on the upper right inlet side of the flow meter until the meter
indicates zero. For the optional 4 - 20 mA output, adjust the zero potentiometer so that
the meter indicates slightly more than 4 mA, i.e. 4.03 to 4.05 mA. This slight positive
adjustment ensures that the 4 - 20 mA transmitter is not in its cut-off region. The error
induced by this adjustment is approximately 0.3% of full scale.
Symptom: Flow meter is out of calibration and non-linear.
Cause: Leaks in the gas inlet or outlet fittings.
Action: Check all fittings for leaks by placing soap solution on all fittings between gas supply and
final destination of gas. Check flow meter for leaks. Replace if required or recalibrate as
necessary.
Symptom: Little or no flow, even when the valve is in override OPEN.
Cause: Blocked orifice or incorrect pressure across the flow controller
Action: Verify that there is 10 to 15 psig pressure across the instrument. If the differential
pressure across the instrument is correct, the orifice may be obstructed. Remove all gas
pressure and shut off power supply. Remove the valve.
4.3. Adjustments
1. Connect power to “D” connector as specified in Section 2.5. Allow the instrument to warm up for at
least 30 minutes (60 minutes for best accuracy). Note the flow signal decays toward zero. Run ~20% of
flow range (~1 VDC) through instrument for 5 minutes.
2. Completely shut off the flow and wait for 2 minutes. For the standard 0 – 5 VDC output, adjust the
zero potentiometer located on the lower inlet side of the flow meter (see Figure 4-2) until the meter
indicates zero. For the optional 4 - 20 mA output, adjust the zero potentiometer so that the meter
indicates slightly more than 4 mA, i.e. 4.03 to 4.05 mA. This slight positive adjustment ensures that the
4 - 20 mA transmitter is not in its cut-off region. The error induced by this adjustment is approximately
0.3% of full scale.
3. Turn on gas supply to inlet of instrument and adjust the flow rate to the desired full scale flow as
indicated by a reference flow meter/controller. If the instrument to be calibrated is a controller, adjust
the flow rate by setting the command to 100% of full scale.
4. Perform this step only if a calibrated reference flow meter is available. Adjust Span pot (see Figure
4-2) until the indicated flow reads full scale (5.00 VDC or 20 mA) and the reference meter/controller
reads the desired full scale flow rate.
5. Record flow meter/controller and flow reference outputs for flow rates of 20%, 40%, 60%, 80% and
100% and make sure data are within ± 1% of full scale.