Flow rate adjusting device and control method of flow rate adjusting device

A control method of a flow rate adjusting device, wherein the flow rate adjusting device comprises

• an ultrasonic flow metering portion configured to perform a flow rate measuring operation to measure a flow rate of a liquid flowing through a measurement flow channel based on a propagation time difference between ultrasonic waves oscillated by a pair of oscillators arranged upstream and downstream in the measurement flow channel, the liquid flowing through the measurement flow channel,
• a flow rate adjusting portion configured to move a valve body along an axis in a direction closer to or away from a valve hole to adjust a flow rate of a liquid flowing out of the measurement flow channel, and
• a flow rate setting unit configured to set a set flow rate value of a liquid to be adjusted by the flow rate adjusting portion,
• the control method comprising:
• a flow rate adjusting step of controlling the flow rate adjusting portion to perform a flow rate adjusting operation to move the valve body to a target position so that a measured flow rate value of a liquid measured by the ultrasonic flow metering portion is the set flow rate value, the target position varying in accordance with a flow rate difference between the measured flow rate value and the set flow rate value;
• an anomaly detecting step of detecting whether or not there is an abnormal state where the ultrasonic flow metering portion is unable to perform the flow rate measuring operation due to a bubble present in the measurement flow channel;
• and
• a bubble releasing step of, in response to the anomaly detecting step detecting presence of the abnormal state, controlling the flow rate adjusting portion to move the valve body by a predetermined distance in a direction away from the valve hole and then stop the valve body.