High-frequency transducers and correlation method to enhance ultrasonic gas flow metering

Research activities carried out in past years have shown that in gas networ ks some constraints exist on the frequency at which ultrasonic transducers can be operated. The study of the transmission and attenuation of the signa l and noise mechanisms gives us a defined suitable frequency range K.R. Wil d, A European collaboration to evaluate the application of multi-path ultra sonic gas flow meters, paper presented at 4th International Symposium on Fl uid Flow Measurement, Denver, CO, 1999). A working frequency of 500 kHz pro ves to be the most suitable to avoid noise effects. This frequency is above the noise level detected in gas pipelines. Moreover, the signal loss due t o attenuation of ultrasound in gas is still negligible. In parallel, the use of this frequency allows the application of efficient numerical techniques such as the cross-correlation method for signal proces sing. An initial process based on this method has been developed for gas fl owmeters. It provides low uncertainty for the parameters involved in the fl ow measurement process. A single-path flowmeter equipped with this system has been tested on the Ga z de France test facilities. Its accuracy is better than 1.5% from 250 to 1 000 m(3)/h without initial adjustment. An auto-calibration process also for ms part of the system, using a systematic comparison between ultrasonic mea surement of sound velocity and a theoretical approach. The signal-to-noise ratio remains large enough to perform the measurements correctly, even with a control valve installed close to the flowmeter. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.