Ultrasonic flow or current meter

Claim 1

An ultrasonic flow or current meter comprising a pair of ultrasonic vibrators mounted on a pipe through which liquid to be measured flows; a first ultrasonic sing-around system connected to said pair of ultrasonic vibrators which propagates a train of ultrasonic pulses through said liquid in one direction with respect to flow direction of said liquid; a second ultrasonic sing-around system including a variable time delay circuit connected to said pair of ultrasonic vibrators which propogates a train of ultrasonic pulses through said liquid in the direction opposite to that of said first-mentioned ultrasonic pulses of said first ultrasonic sing-around system; phase detecting means for detecting the phase difference between said ultrasonic pulses in said first and second systems and producing a detected output signal in response to said phase difference; a control means connected to said second ultrasonic sing-around system to control the variable time delay circuit and said ultrasonic pulses in said second system so that the sing-around periods of said first and second sing-around systems are substantially the same at all times based on the detected output signal from said detecting means; a converting means receiving the output of said phase detecting means and supplying an output to said control means; and a flow velocity means connected to the output of said converting means and for producing an indication of the flow velocity of said liquid.