Pressure type flow rate control apparatus

A pressure type flow rate control apparatus for controlling flow rate of a fluid comprising:

• means for forming an orifice;
• means for maintaining a pressure P1 upstream of the orifice at more than twice a pressure p2 downstream of the orifice and for maintaining the pressure P2 downstream of the orifice at or less than atmospheric pressure;
• a control valve positioned upstream of the orifice for controlling flow to the orifice;
• a pressure detector for measuring pressure P1 between the control valve and the orifice;
• and,
• a calculation control means for receiving the measured pressure P1 and for calculating flow rate Qc through the orifice on the basis of the measured pressure P1 by a formula Qc=KP1, K being a constant, for receiving a flow rate command signal and for outputting a difference Qy between the flow rate command signal Qs and the calculated flow rate signal Qc to a drive unit for opening and closing the control valve;
• wherein the pressure P1 upstream of the orifice is adjusted by opening and closing of the control valve, thereby controlling the flow rate downstream of the orifice;
• wherein the calculation control means includes a temperature correction circuit for correcting the value of the calculated flow rate Qc depending on a gas temperature T1 at the upstream side of the orifice;
• and,
• wherein the control valve is coupled to an output of an inverting amplifier for receiving an output signal therefrom, said inverting amplifier receiving detected values of the upstream side pressure P1 and the downstream side pressure P2.