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Chapter 3 Operation Series 830/840/860 Instruction Manual
3-4 IM-83/84/86-H
Mass Flow Controller Features
Over-Range and Cold Sensor Lockout Circuit
Side-Trak Models incorporate an over-range circuit which disables
the output signal when the sensor is heating to its normal operating
range, or if an over flow condition exists. The operation of this cir-
cuit can be verified by observing the 5 VDC (20 mA) output signal
during power up.
The cold sensor lockout safety circuit automatically closes the
valve if a fault condition is detected that could result in uncon-
trolled flow (valve wide open). The circuit operates by monitoring
the temperature of the sensor elements. If the temperature falls be-
low a preset limit the circuit forces the output signal to a fixed high
level which disables the output signal. The cold sensor lockout cir-
cuit is enabled during initial start-up. This feature is not available if
liquid is present in the flow path.
There are several conditions which could trigger the cold sensor
lockout circuit:
1. Operation at a temperature below the instrument’s rating.
2. Power failure while running at or near full scale. Upon resump-
tion of power, the valve will remain closed until the minimum
operating temperature is again reached.
3. Sensor failure.
If needed, the cold sensor lockout circuit and/or over-range indicator
can be disabled by removing CR1 from the main 830 circuit board.
Controller Auto Shut-Off Feature
All flow controllers are normally provided with an Auto Shut-Off
feature that closes the valve at a command signal level of approxi-
mately 2% of full scale, or less. (All electromagnetic valves fail
normally-closed). On 840 controllers, this value can be reduced.
Contact the factory for details on this option.