Principle of Measurement

Ultrasonic beams are transmitted through a flowing liquid between sensors A and B in both upstream and downstream directions. The travel time or time of flight (TOF) is measured. With no flow the time in either direction is the same time. When flow starts a time difference will be seen that is directly proportionally to be velocity of the proceed according to the formula. This velocity is integrated with the inside area of the pipe and the flow is derived.