Brooks Instrument 5851i - Manual (Page 31)

4-3
Installation and Operation Manual
X-TMF-5851i-MFC-eng
Part Number: 541B109AAG
September, 2009
Brooks ® Model 5851 i
Section 4 Maintenance
& Troubleshooting
Trouble Possible Cause Check/Corrective Action
Actual flow overshoots setpoint by Anticipate potentiometer out of adjustment. Adjust anticipate potentiometer. Refer to Section 3-5 .
more than 5% full scale.
Output stays at zero regardless Clogged Sensor. Refer to Section 4-4. Clean sensor. Refer to cleaning.
of setpoint and there is no flow
through the controller.
Clogged Control Valve. Check TP3 with the setpoint at 100%. If the voltage is greater than 11V, disassemble
and repair the control valve. Refer to Sections 4-4c and 2-10.
Valve override input is grounded. Check valve override input (Pin 12)
Defective PC Board. Replace PC Board. Refer to Section 4-4.
Output signal stays at +6.8V or 26 mA Valve stuck open or leaky. Clean and/or adjust control valve. Refer to cleaning procedure and/or Section 4-4C.
regardless of command and there
is flow through the controller.
+22.5V -28Vdc applied to the valve override input. Check the valve override terminal. (Pin 12)
Defective PC Board. Replace PC Board. Refer to Section 4-4.
Output signal follows setpoint Leaky control valve. Disassemble and repair valve. Refer to Section 4-4C.
at higher setpoints but will not go
below 2% (8% for all-metal seat).
Output signal follows setpoint Insufficient inlet pressure or pressure drop. Adjust pressure, inspect the filters and clean/replace as necessary.
at lower setpoints but does not reach
full scale.
Partially clogged sensor. Check calibration. Refer to Section 3-4.
Partially clogged valve. Disassemble and repair control valve. Refer to Section 4-4.
Valve out of adjustment. Adjust valve. Refer to Section 4-4.
Valve guide spring failure. Controller oscillates (see below).
Controller grossly out of calibration. Partially clogged sensor. Clean sensor, refer to the cleaning procedure.
Flow is higher than desired.
Controller grossly out of calibration. Partially clogged restrictor. Replace restrictor. Refer to Section 4-4.
Flow is lower than desired.
Controller oscillates. Pressure drop or inlet pressure excessive. Adjust pressures.
Oversized orifice. Check orifice size. Refer to Section 4-6.
Valve out of adjustment. Adjust valve. Refer to Section 4-4.
Anticipate potentiometer out of adjustment. Adjust anticipate potentiometer. Refer to Section 3-5.
Faulty pressure regulator. Check regulator output.
Defective PC Board. Replace PC Board. Refer to Section 4-4.
B. Bench Troubleshooting
1. Properly connect the mass flow controller to a +22.5-28 Vdc power
supply, setpoint source and connect an output signal readout device
(4-1/2 digit voltmeter recommended) to pins 2 and 10 of the D-
connector (refer to Figure 2-2). Apply power, set the setpoint to zero
and allow the controller to warm up for 45 minutes. Do not connect
to a gas source at this time. Observe the output signal and, if
necessary, perform the zero adjustment procedure (Section 3-3). If
the output signal will not zero properly, refer to the sensor
troubleshooting section and check the sensor. If the sensor is
electrically functional, the printed circuit board is defective and will
require replacement.
2. Connect the controller to a source of the gas on which it was
originally calibrated. Command 100% flow and adjust the inlet and
outlet pressures to the calibration conditions. Verify that the output
signal reaches and stabilizes at 5.00 volts or 20mA. Vary the
setpoint over the 2 to 100% range and verify that the output signal
follows the setpoint. Apply +22.5-28 volts to the valve override input
(pin 12) and verify that the output exceeds 100%. Connect the valve
override pin to ground and verify that the output signal falls below
2%. If possible, connect a flow measurement device in series with
the mass flow controller to observe the actual flow behavior and
verify the accuracy of the mass flow controller. If the mass flow
controller functions as described above, it is functioning properly and the
problem may lie
elsewhere.
Table 4-1 Bench Troubleshooting