4-2
Brooks
®
Digital MFC's & MFM's
Section 4 Maintenance &
Troubleshooting
Installation and Operation Manual
X-TMF-SLA5800-Series-RevB-MFC-eng
Part Number: 541B187AAG
June, 2016
4-1-1
Troubleshooting Analog or Digital
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. You may have to
calculate the equivalent flow using the thermal correction factors. Ex.: a
device built and sized for hydrogen will have a small orifice and will be
unable to achieve higher flows of a heavier gas such as N2.
3. 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, also, the valve is likely to drive to max opening (100%).
4. 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 restrictor. The symptom of this condition is a
substantially reduced actual flow with a flow signal which matches the
setpoint.
5. Flow rate in excess of 100% at zero setpoint.
Valve Override pin set to open or sensor tube is clogged (see above). If
Valve Override (VOR) pin is active, the valve will be forced open or
closed. Set this pin to its normal level before setting a setpoint.
6. Flow/Flow signal 'Unstable'
Model SLA5800 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 did when
it left the factory.
Bus System Devices Version Only
7. Failure of the flow rate or flow signal to achieve setpoint.
Specifically for a bus system device 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 over a bus system device network, the MFC
must be set up with the same I/O assembly as the network master.
Confirm these I/O settings are correct.
NOTE: This information and all other detailed DeviceNet information is available in
the Brooks DeviceNet Supplement Instruction Manual.
