New Ultrasonic Flow Meter. Modification of the Sing-around Method for Use in Heat Meters.

摘要

A new ultrasonic flow meter using a modified sing-around method has been developed especially for use in small heat meters. In such applications the fluid temperature often varies rapidly which strongly changes the speed of sound. As a result of this serious errors are introduced into the flow measurements made with the conventional sing-around techniques. In the present method the fluid velocity is evaluated by a new algorithm. With this algorithm correct flow velocities are obtained even in the case of rapidly changing fluid temperature. Further the dynamic range of the flow meter is increased appreciably by the use of ultrasound transducers with suitable geometry. At the beginning of the paper the requirements governing the design of the flow meter are discussed in detail as well as the error sources. After the development of improved algorithm the design of the flow meter body as well as electronic circuitry is described, where a special zero crossing detector is used to improve the accuracy and the dynamic range of the meter. Finally, preliminary results of the test measurements with the flow meter are reported which show the strongly improved meter accuracy for flow with rapid temperature changes. For the new flow meter a velocity range of 3.5 cm/s plus or minus 5% (10 l/h in a diam 10 mm pipe) to 140 cm/s plus or minus 0.5% (400 l/h in a diam 10 mm pipe) has been proven. (With 26 refs.).