To measure a flow velocity and a volume of discharge simply and with high accuracy by solving the problem in conventional techniques that ultrasonic waves are transmitted and received at a predetermined angle with a direction of a stream current, that the propagation distance of the ultrasonic waves up to an opposite bank becomes longer than the width of a river so as to lower the intensity of an ultrasonic signal, that identical devices are required on the upstream side and the downstream side because the ultrasonic waves are transmitted and received twice from the upstream side toward the downstream side and from the downstream side toward the upstream side and that the devices become large-sized and high-cost.
The flow-velocity measuring device and the discharge-volume measuring device are provided with: a transmitter which sends out sound waves into an object fluid; a receiving part composed of a plurality of receivers used to receive a signal from the transmitter; a phase-difference detection means which detects a phase difference between received signals from the receivers or a time-difference detection means which detects a time difference; a computing means by which the flow velocity and the discharge volume of the object fluid are found on the basis of the detected phase difference or the detected time difference; and a display.
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