The working priciple of ultrasonic flow meter is that when the ultrasonic beam propagates in the liquid, the flow of the fluid will cause a small change in the propagation time, and the change of the spreading time is proportional to the liquid velocity, so the liquid velocity can be calculated out . This series ultrasonic flow meter contains : handheld ultrasonic flow meter which is the most widely used; wall-mounted ultrasonic flow meter, open channel flow meter etc