US Patent 7117104 Ultrasonic liquid flow controller

An ultrasonic flow meter includes a conduit, a first ultrasonic transducer, a second ultrasonic transducer, and a controller. The first ultrasonic transducer is disposed at a first position about a first portion of the conduit to transmit a first ultrasonic signal and to receive a second ultrasonic signal. The second ultrasonic transducer is disposed at a second position about a second portion of the conduit that is spaced apart from the first position along a length of the conduit to transmit the second ultrasonic signal and to receive the first ultrasonic signal. The controller is configured to cross-correlate the first and second received ultrasonic signals and generate a resulting time-domain signal, analyze the resulting time-domain signal to determine a difference in transit time between the first and second received ultrasonic signals, and calculate a rate of flow of a fluid in the conduit based upon the determined difference.