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Doppler ultrasonic flowmeter measurement based on Doppler in physics
2012-3-27 14:33:51

的测量原别是以物理学中的多普勒效应为基础的。 The measurement of Doppler ultrasonic flowmeter is based on the Doppler effect in physics. According to the acoustic Doppler effect, when there is relative motion between the sound source and the observer, the frequency of the sound perceived by the observer will be different from the frequency emitted by the sound source. This frequency change due to relative motion is directly proportional to the relative speed of the two objects.

测量方法中,超声波发射器为一固定声源,随流体一起运动的固体颗粒起了与声源有相对运动的“观察者”的作用,当然它仅仅是把入射到固体颗粒上的超声波反射回接收据. In the measurement method of the Doppler ultrasonic flowmeter , the ultrasonic transmitter is a fixed sound source. The solid particles moving with the fluid play the role of an "observer" that moves relative to the sound source. The ultrasonic waves on the solid particles are reflected back to the receiving data. The frequency difference between the transmitted sound wave and the received sound wave is the Doppler frequency shift of the sound wave due to the movement of solid particles in the fluid. Since this frequency difference is proportional to the fluid velocity, the velocity can be obtained by measuring the frequency difference. Then the flow rate of the fluid can be obtained. Therefore, a necessary condition for ultrasonic Doppler flow measurement is that the fluid medium to be measured should be a two-phase medium containing a certain number of solid particles or bubbles that can reflect sound waves. This working condition is actually one of its great advantages, that is, this flow measurement method is suitable for the measurement of two-phase flow, which is a difficult problem for other flow meters. Therefore, as a promising two-phase flow measurement method and flow meter, ultrasonic Doppler flow measurement method is being increasingly applied.


采用声学多普勒原理丈量液体流量,即可丈量多相流(污浊的液体,如市政污水、产业废水、原油、油水混合物、泥浆、矿浆、纸浆、果汁等),又可丈量单相流(较纯净的液体,如自来水、江河原水、海水、化工液体等),应用范围较为广泛。 The Doppler ultrasonic flowmeter uses the acoustic Doppler principle to measure liquid flow, which can measure multiphase flow (fouling liquids such as municipal sewage, industrial wastewater, crude oil, oil-water mixtures, mud, pulp, pulp, juice, etc.), Measurable single-phase flow (pure liquid, such as tap water, river water, seawater, chemical liquid, etc.), which has a wide range of applications. When measuring multiphase flow, because the liquid contains reflective particles such as bubbles, solid particles, suspended matter, etc., the Doppler signal is a relatively narrow frequency band flow rate. When it is a certain uniform value (sufficient straight pipe section can ensure its flow rate Distribution is more stable), you can get higher measurement accuracy. When measuring single-phase flow, the liquid contains fewer reflective particles. At this time, compared with the Doppler signal when measuring multi-phase flow, there is a big difference. Generally, when a clean liquid flows through an elbow, tee, or half-open valve, the flow velocity distribution is turbulent and turbulent, which is called a turbulent state; when passing through a straight pipe section, the flow rate tends to stabilize. In this way, from the turbulent to the stable activity, the interface is born. This interface is called the pressure interface or the shear wave interface. The speed of this interface is unstable around elbows, tees, and half-open valves (1 to 2 times the length of the pipe's inner diameter). When leaving the elbow, tee, half-open valve, etc. (4 to 5 times the length of the inner diameter of the pipe), the interface flow rate is basically the same as the uniform flow rate of the fluid. When leaving more than 10 times the length of the inner diameter of the pipe, this interface disappears and becomes a stable flow velocity distribution. When measuring single-phase flow, the measurement point can be selected at a length of 4 to 5 times the inner diameter of the pipe. At this time, the Doppler signal can be obtained at the pressure interface. However, this signal is weak and the frequency band is wide. It is necessary to make a special spectrum analysis circuit and amplifying operation circuit to ensure the measurement accuracy of the Doppler ultrasonic flowmeter when measuring single-phase flow.