Self-diagnosis method for flow rate control device

A self-diagnosis method of a flow rate control device including a pressure control valve provided in a flow path;

• a flow rate control valve provided downstream side of the pressure control valve;
• a restriction part provided downstream side of the pressure control valve;
• and a pressure sensor provided downstream side of the pressure control valve and upstream side of the restriction part, wherein the flow rate control valve includes a valve element seated on/off a valve seat, and a piezoelectric element for moving the valve element to seat on/off the valve seat,
• the self-diagnosis method of the flow rate control device comprising:
• a step (a) for measuring a pressure drop characteristic of a fluid pressure by using the pressure sensor, after the pressure control valve has been changed to a closed state from a state where the pressure control valve is in an open state, and the opening degree of the flow rate control valve is larger than the opening degree of the restriction part, while the fluid is flowing from the upstream side of the pressure control valve to the downstream side through the flow rate control valve and the restriction part;
• a step (b) for measuring the pressure drop characteristic of the fluid pressure by using the pressure sensor, after the pressure control valve changed to the closed state from a state where the pressure control valve is in an open state, and the opening degree of the flow rate control valve is smaller than the opening degree of the restriction part, while the fluid flows from the upstream side of the pressure control valve to the downstream side through the flow control valve and the restriction part;
• a step (c) for determining whether there is an abnormality by comparing the pressure drop characteristic measured in the step (a) with a corresponding reference pressure drop characteristic stored in advance;
• a step (d) for determining whether there is an abnormality by comparing the pressure drop characteristic measured in the step (b) with a corresponding reference pressure drop characteristic stored in advance;
• and
• a step (e) for determining that there is an abnormality in the distance between the valve seat and the valve element of the flow control valve, when an abnormality is found only in the step (d), among the determinations made in the step (c) and the step (d).