Patent ID: 8082946

Claim:
A fluid flow control apparatus, comprising: a proportional flow valve having a fluid inlet and a fluid outlet; a pneumatic proportional control valve in communication with said proportional flow valve for modulating said proportional flow valve; a frictional flow element having a frictional flow element fluid inlet in fluid communication with said fluid outlet of said proportional flow valve and having a frictional flow element fluid outlet spaced from said frictional flow element fluid inlet, said frictional flow element creating a pressure drop between said frictional flow element fluid inlet and frictional flow element fluid outlet; an upstream pressure sensor; a downstream pressure sensor; a controller in communication with said upstream pressure sensor, said downstream pressure sensor and said pneumatic proportional control valve, said controller further comprising: one or more processors; a computer readable memory; and a set of computer readable instructions stored on said computer readable memory and executable by the one or more processors, the set of computer readable instructions comprising instructions executable to: receive an upstream pressure signal receive a downstream pressure signal; calculate an error signal; calculate a valve control signal based on the upstream pressure signal, downstream pressure signal and error signal; wherein the computer executable instructions further comprise instructions executable to: calculate the error signal based on proportional, integral and derivative values for the upstream pressure signal and the downstream pressure signal, and add an error gain to the error signal.