The propagation time method and the Doppler effect method are commonly used in ultrasonic flowmeters to measure the average velocity of a fluid. Like other speed meters, it is a meter that measures volumetric flow. It is an unobstructed flow meter and does not need to be inserted if the ultrasonic transmitter is installed outside the pipe. It is suitable for almost all liquids, including slurries, with high precision. However, the contamination of the pipe will affect the accuracy.