An ultrasonic meter falls into the classification of inferential meters. Unlike positive displacement meters that capture volume to totalize volume, inferential meters measure flowing gas velocity to totalize volume. Ultrasonic meters use sound waves to measure flowing gas velocity to infer volume. Ultrasonic meters have been around for many years, primarily in liquid measurement. However, we are seeing more and more applications in the natural gas industry.
An ultrasonic flow meter normally operates based upon the time-of-flight or the Doppler principle. A meter utilizing the Doppler principle requires “particles” in the flow stream to reflect waves. When people think of the Doppler principle, they think of weather and police radar. The rain and your car are the “particles” used to reflect the waves. This sort of meter is common in liquid measurement because bubbles can be introduced into the liquid to reflect the waves.