FLOW RATE CONTROL METHOD

PURPOSE:To provide the flow rate control method which speedily performs the flow rate control without any overshoot by switching a flow rate control system halfway. CONSTITUTION:This flow rate controlling method controls the flow rate of fluid by controlling a flow control valve 10 interposed in a fluid flow passage 4 from a flow rate control part 22, and stationary manipulated variables of the flow control valve corresponding to plural flow rate set values are previously measured and stored as a table. If a flow rate set value abruptly varies, a stationary manipulated variable corresponding to the new flow rate set value is found on the basis of the table and then an initial manipulated variable which is smaller that said value is outputted to abruptly supply fluid by an amount up to a certain extent less than the flow rate set value; and then speed type PID control is started immediately and slow valve operation is performed on the basis of the initial manipulated variable. Consequently, the flow rate is speedily varied to the flow rate set value without causing any overshoot.