【Transit Time Type】
Ultrasonic waves are transmitted into a liquid alternately from the 2 sensors attached to the outside of the pipe, and difference between the propagation time of the ultrasonic wave in the upstream direction and the propagation time in the downstream direction is detected to obtain the flow velocity. Then, the flow rate is calculated by multiplying the cross section area of the pipe diameter.
【Doppler Type】
The sensor transmits ultrasonic into the liquid through the pipe wall. Ultrasonic reflects the granules or air bubbles in the liquid. When the liquid flows, echos come back to the sensor with a different frequency besed on the flow velocity. We can calculate the flow velocity based on the frequency change.