ME2900 Ultrasonic Flow Meter is a type of flow meter that uses ultrasonic waves to measure the flow rate of a fluid. The principle behind ultrasonic flow meters is based on the Doppler effect. When an ultrasonic wave is transmitted through a fluid, the frequency of the wave is shifted by an amount proportional to the velocity of the fluid. By measuring the frequency shift of the wave as it travels through the fluid, the velocity of the fluid can be determined.