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| Doppler ultrasonic flowmeter |
| 2011-8-13 9:23:12 |
Doppler ultrasonic flowmeter :
The probe emits sound waves into the fluid at a known angle, and measures the change in frequency between the emitted ultrasonic waves and the echoes reflected by particles or bubbles flowing with the fluid. The frequency of the echo changes due to the speed of the particles or bubbles. The reflected echo signal is captured by the probe and then demodulated by the electronic unit.
Ultrasonic waves will be scattered if they encounter tiny solid particles or bubbles in the propagation path. Therefore, the time difference method cannot be used to measure fluids containing such things. It can only be used to measure relatively clean fluids. The Doppler method uses the characteristic that ultrasonic waves are scattered. Therefore, the Doppler ultrasonic flowmeter is suitable for measuring fluids containing solid particles or bubbles. However, because scattering particles or bubbles exist randomly, the sound transmission performance of the fluid will also have different. If the fluid with poor sound transmission performance is measured, the scattering is strong in the low flow velocity region near the tube wall. On the contrary, the fluid with good sound transmission performance is dominant in the high velocity flow region, which makes the Doppler measurement accuracy Lower. Although the transmitting transducer is separated from the receiving transducer, so that only the scattering in the middle region of the flow velocity section can be received, the measurement accuracy is still lower compared with the time difference method.