Transit Time Principle – A Guide

em-tec BioProTT™ Clamp-On Transducers uses the transit-time ultrasound principle to operate. These transducers comprise of four piezoceramics accommodated in a fixed location inside the transducer body. The piezoceramics are set in a particular angle α in connection with the flowing medium. Tubing inserted into the transducer’s cavity is enclosed by the piezoceramics in an “X” pattern.

Transit-Time Ultrasound Principle

The X pattern arrangement of the em-tec BioProTT™ Clamp-On Transducers acoustically illuminates the entire cross section of the flow channel by four sound paths. As a result, all velocities that contribute to the flow profile are taken into consideration and the overall flow rate can be accurately determined.

A high frequency voltage impulse is applied in order to excite the piezoceramics and pass ultrasound waves from one ceramic to the opposite one, with each one serving alternately as transmitter and receiver. The electronics of the flow transmitter measures the duration of time it takes the signal to move from one crystal to another (transit time).

When the ultrasound beam moves from one crystal to the other, it should pass through the tubing and medium inside the cavity of the transducer. The fluid moving through the tubing will affect the ultrasound beam. Signals that travel with the fluid flow will have quicker transit time and those that travel against the flow will have slower transit times. The difference between the downstream transit times (with the flow) and upstream transit times (against the flow) is proportional to the volumetric flow rate.

This information has been sourced, reviewed and adapted from materials provided by em-tec GmbH.

For more information on this source, please visit em-tec GmbH.


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