E-Zine July 2009
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Pulse repetition ultrasonic flowmeters (sometimes called sing-around ultrasonic flowmeters) also alternately transmit ultrasonic energy into the pipe in the direction and against the direction of flow.
In this design, receipt of an ultrasonic pulse triggers the sending of a new ultrasonic pulse.
The frequency of the pulses is measured, and the following equation expresses their relationship to flow rate.
Phase shift ultrasonic flowmeters measure the phase shift between two continuous cyclic ultrasonic signals, one traveling upstream, and the other traveling downstream.
The following equation describes the relationship between phase angle and flow rate when the frequency of the cyclic ultrasonic signal is constant.
The following equation describes the relationship between the phase angle and flow rate when the frequency of the cyclic ultrasonic signal is varied to control the phase angle difference.
Excerpted from The Consumer Guide to Ultrasonic and Correlation Flowmeters