Only applicable to products with at least minimum suspension elements or bubbles because the measurement of the speed is done by circulating elements and not by flow mass. For this reason, they are not applicable to clean flows.
The Doppler system uses the ultrasonic beam reflection in sonically reflective materials, ie solid elements or air bubbles carried over a fluid flowing or fluid turbulence itself, if the fluid is clean.
SENSOTEC INSTRUMENTS has numerous devices of fixed installation for measurement of flow by transit time available, being the most common ones the MICRONICS UF D5000 y el PF D550