Doppler Ultrasonic Flow Meters Operating Theory

Dynasonics Doppler ultrasonic flow meters are designed to operate on metal or plastic pipes containing liquids with suspended solids or entrained gases that act as reflectors. The Series DFX and UFX are applied on systems which contain liquids that contain these greater amounts of suspended "reflectors" (100 ppm and greater).

Doppler flow meters utilize two piezoelectric crystals contained within either one transducer head or two separate transducer heads to transmit ultrasonic sound energy into the fluid stream and receive reflected sound from reflectors (suspended solids or entrained gases) within the liquid. See Figure 1. In accordance with the theories of Christian Johann Doppler (circa 1842), if the liquid is moving (and therefore carrying the reflectors with it) and oscillating energy is imposed on the moving reflector, the reflected energy's frequency of oscillation will be altered with respect to the transmitted frequency. The magnitude of frequency change is directly proportional to the velocity of the reflector.

Dynasonics Doppler meters process the differences in transmitted and received frequencies and report the measurement as flow velocity.