Ultrasonic Flowmeter

An ultrasonic flowmeter comprising an elongate duct through which fluid flows when the flowmeter is in use. Ultrasonic transducers are arranged respectively to transmit and receive ultrasonic pulses propagated through such fluid when the flowmeter is in use. Electronic circuitry is connected to the transducers to provide a measure of the time delay between emission of an electronic pulse from one of the transducers and reception of the pulse by the other of the transducers. The circuitry is constructed to enable an output to be provided which is dependent upon that delay and which is indicative of the rate of flow of fluid through the duct. The transducers are located respectively at opposite ends of the duct and are arranged to transmit and receive ultrasonic pulses propagated through the fluid substantially parallel to the duct from one end thereof to the other. The transducers are provided with respective vibratory surfaces which transmit and/or receive ultrasound, which vibratory surfaces have a diameter which exceeds the cross-sectional diameter of the duct.