Control Circuitry
Chapter Five: Theory of Operation
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Control Circuitry
The controller employs the above measurement technique and utilizes a control circuit that
provides drive current for the proportioning control valve. The flow controller accepts a
0 to 5 VDC set point signal, compares it to its own flow signal, and generates an error voltage.
This error signal is then conditioned by a PID (Proportional-Integral-Derivative) algorithm and
amplified so that it can reposition the controlling valve, thus reducing the controller error to
within the resolution specification of the instrument.
Since the control valve is normally closed, the 1179 unit pulls the plug away from the seat to
regulate the gas flow rate.
