Chapter Five: Maintenance and Troubleshooting Troubleshootin
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Set Point Buffer and Flow Switching Circuit
The buffer amplifier prevents the Flow Controller from loading the set point signal. The voltage
at the output of the second set point buffer should track the voltage on the arm of the Set Point
Control by ±2 mV when the flow is on. If this signal is incorrect at the Channel Input
Connector, trace the signal back to the Set Point Control to determine where the fault lies.
A negative voltage (approximately - 0.1 V) at the Channel Input Connector indicates that the
field effect transistor (FET) is ON. If the Flow Lamp is on, then the FET is defective or the drive
to the gate is incorrect. The drive under these conditions should be -15 V ±1 V.
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