Brooks Instrument SLA5800 Series - Manual (Page 48)

4-2
Brooks ® Digital MFC's & MFM's
Section 4 Maintenance &
Troubleshooting Installation and Operation Manual
X-TMF-SLA5800-MFC-eng
Part Number: 541B027AAG
April, 2013
5. Flow signal matched setpoint but, actual flow is not correct.
Clogged restrictor. If the MFC's restrictor becomes clogged, a much
larger flow stream will pass through the sensor rather than going
straight through the restricotr. The symptom of this condition is a
substantially reduced actual flow with a flow signal which matches the
setpoint.
6. Flow rate in excess of 100% at zero setpoint.
Valve Override pin set to open. If Vallve Override (VOR) pin is active,
the valve will be forced open or closed. Set this pin to it's normal level
before setting a setpoint.
7. Flow/Flow signal 'Unstable'
Model SL5800 Series MFC performance is tuned during calibration at
the conditions specified on the order. If the conditions in use (inlet and
outlet pressure, temperature, attitude, gas or mixture type) are different
or become different over time, the MFC may not perform as it didwhen
it left the factory.
DeviceNet Version Only
8. Failure of the flow rate or flow signal to achieve setpoint.
Specifically for a DeviceNet MFC, there may be problems associated
with the network communication link. One common problem is due to
data mismatches of the Input/Output (I/O) Assemblies. For proper
communication ove rthe DeviceNet network, the MFC must be set up
with the same I/O assemby as the network master. Confirm these I/O
settings are correct.
4-1-1 Troubleshooting Analog or DeviceNet version
This section contains suggestions to help diagnose MFC related problems
in the gas distribution system and answers commonly asked questions.
Failure of the flow rate or flow signal to achieve setpoint.
1. Insufficient pressure drop across the MFCs (low or no pressure). If there
is not enough pressure differential across the MFC, it is impossible for
the MFC's orifice to pass the full scale flow rate. To check for this
condition, compare the actual inlet/outlet pressure drop with that
specified on the order. Increase the pressure if necessary.
2. If pressure settings are correct and flow signal does not match setpoint,
a secondary issue could be the gas type. If checking the MFC with a
surrogate gas, ensure that there is enough pressure to the MFC in
order to flow the correct amount of the surrogate gas.
3. Setpoint is below minimum. MFCs may have a settable low flow cutoff
for the setpoint command. If setpoint is below this value, then the MFC
will not attempt to control.
4. Clogged sensor tube. If the MFC sensor tube is clogged, the flow signal
will be very low or zero while the actual flow will be at the valve's
maximum rate.