| abstract |
A gas flow control system defines a flow path between a gas inlet and outlet, the system comprising a mass flow controller 200, a pressure sensor 206 and an electronic controller 210. The mass flow controller 200 includes a mass flow sensor 202 for sensing the mass flow along the flow path and a control valve 218 for controlling the mass flow through the outlet. The pressure sensor 206 measures fluctuations in gas pressure along the flow path. The electronic controller 210 generates a control signal as a function of the sensed mass flow and measured pressure fluctuations so as to provide a constant flow of gas at the outlet, irrespective of the fluctuations in pressure of gas at the inlet. The pressure sensor 206 is ideally situated upstream of the control valve 218, measuring pressure in the dead space 216a between the mass flow sensor 202 and the control valve 218. |