Patent ID: 8056579

Claim:
A mass flow controller, comprising: a flow rate sensor section that measures a flow rate of a fluid flowing through a flow channel and outputs a flow rate measurement signal indicating a flow rate measurement value; a flow rate control valve disposed one of upstream and downstream of the flow rate sensor section; a calculation means for performing at least a proportional calculation on a deviation of the flow rate measurement value from a target flow rate setting value, to calculate a feedback control value to be supplied to an opening control signal output section; and the opening control signal output section configured to generate an opening control signal based on said feedback control value, and outputs the opening control signal to the flow rate control valve, the calculation means uses a gain value obtained by substituting said flow rate setting value into a function, and multiplies said gain value by the deviation in said proportional calculation, said function differs between a changing period that comprises a period from a point in time when said flow rate setting value changes by at least an amount, and a stable period that comprises a period other than the changing period; the function in said changing period returns a greater value as the flow rate setting value decreases, and the function in said stable period returns a smaller value as the flow rate setting value decreases or, regardless of the flow rate setting value, the function in said stable period returns constant.