Ultrasonic flowmeter including means to measure pipe geometry

Claim 1

An ultrasonic flowmeter for measuring the flow rate of a fluid conducted through a pipe whose internal diameter is not exactly known, the flowmeter comprising: A. a pair of transducers mounted on the exterior of said pipe at upstream and downstream positions; B. means to alternately excite the upstream and downstream transducers whereby an acoustic pulse emitted by the excited transducer is propagated through the fluid along a path within the pipe whose length depends on the distance between the transducers at an angle to the longitudinal flow axis of the pipe and is received by the other transducer; C. a flow rate measuring system coupled to the transducers to determine the time delay differences between the upstream and downstream transit times along said path to derive therefrom the flow velocity of the fluid; D. means to generate an auxiliary acoustic pulse that is propagated in a direction normal to the flow axis to produce a first echo at the interface of the inner surface of the pipe and the fluid on one side of the pipe and a second echo at the interface of the inner surface of the pipe and the fluid at the diametrically-opposed side; and E. means to detect said first and second echoes and to measure the difference between the travel times of said echoes to determine the inner diameter of the pipe and to apply the value thereof to said flow rate measuring system whereby said inner diameter can be factored into the flow rate measurement to determine the actual length of the path within the pipe.