What are the Two Types of Ultrasonic Flow Meters?
Classification by use principle
(1) Doppler ultrasonic flow meter
The Doppler ultrasonic flow meter uses the principle of the Doppler effect to measure fluid flow.
(2) Time difference ultrasonic flow meter
Time difference ultrasonic flow meter uses the principle that the time difference between the propagation of sound waves in the fluid downstream and upstream is proportional to the fluid velocity to measure fluid flow.
Read More about: Types of Ultrasonic Flow Meters
What is the Difference Between Time Difference Time and Doppler Flow Meter?
1. Different measurement principles.
The main principle of the time difference method is that when the ultrasonic beam propagates in the liquid. The flow of the liquid will cause a slight change in the propagation time. The change in its propagation time is proportional to the flow rate of the liquid. At zero flow, the time required for the two sensors to transmit and receive sound waves is the same (the only technology that can actually measure zero flow).
When the liquid flows, the sound wave transmission time in the upstream direction is greater than the sound wave transmission time in the downstream direction. The Doppler method works by utilizing the characteristic that ultrasonic waves will be scattered if they encounter tiny solid particles or bubbles on the propagation path.
2. Different applicable media.
The time difference ultrasonic flowmeter can only measure relatively clean liquids, and it cannot work well when it encounters more solid particles or bubbles.
The Doppler method uses the scattered characteristics of ultrasonic waves for measurement, so the Doppler method is suitable for measuring fluids containing solid particles or bubbles, but clean liquids cannot be measured.
3. Different measurement accuracy.
The time difference method has higher measurement accuracy, while the Doppler method has lower measurement accuracy. Since the scattered particles or bubbles exist randomly, the sound transmission performance of the fluid is also different. If the fluid with poor sound transmission performance is measured, the scattering is stronger in the low velocity area near the pipe wall.
However, the scattering of the fluid with good sound transmission performance is dominant in the high velocity area, which makes the measurement accuracy of the Doppler method lower. Although the structure of separating the transmitting transducer and the receiving transducer is adopted, so that only the scattering in the middle area of the velocity section can be received. However, compared with the time difference method, the measurement accuracy of Doppler is still lower.
4. Different working conditions.
The time difference method is suitable for full pipe measurement. The Doppler method is suitable for measuring the flow of full pipes, non-full pipes, open channels, etc.
