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Ultrasonic flowmeter measurement is based on the Doppler effect in physics
2012-4-16 14:17:50

是近十几年来随着集成电路技术的发展才出现的一种非接触式仪表,适于测量不易接触、观察的流体以及大管径流量。 Ultrasonic flowmeter is a non-contact meter that has appeared with the development of integrated circuit technology in the past decade. It is suitable for measuring fluids that are not easy to contact and observe, as well as large pipe flow. The ultrasonic flowmeter does not need to install measuring elements in the fluid, so it does not change the flow state of the fluid and does not generate additional resistance. The installation and maintenance of the instrument can be performed without affecting the operation of the production pipeline, so it is an ideal Energy-saving flowmeter.
As a new type of flow meter, the ultrasonic flow meter is gradually increasing its usage. Because of the wide use, many technicians have been exposed to the installation and commissioning of ultrasonic flowmeters. There will often be several kinds of failure manifestations, which have troubled many technicians. Now we will analyze some of the failure phenomena as follows: First, the failure phenomenon: unstable readings and drastic changes Cause analysis: the pipeline where the ultrasonic flow sensor is installed is subject to large vibrations or changes in flow Solution (such as a flow meter installed downstream of a regulating valve, a pump, or a downflow orifice). Solution: Modify the flow sensor away from the source of vibration or move it upstream of the device that changes the flow state. 2. Symptom: The reading is not accurate. Analysis of the reasons for the large errors: 1. Ultrasonic flowmeter sensors are installed on the top and bottom of the horizontal pipeline to interfere with the ultrasonic signal. Solution: Install the sensors on both sides of the pipe. 2. The ultrasonic flowmeter sensor is installed on the pipe where the water flows downward, and the pipe is not full of fluid. Solution: Mount the sensor on a fluid-filled pipe section. 3. There are devices that make strong flow fluctuations, such as: venturi, orifice plate, vortex, turbine, or partially closed valve, which are within the range of the sensor transmitting and receiving, making the reading inaccurate. Solution: Install the sensor away from the above device, the sensor upstream from the device 30D, downstream from the device 10D or move upstream of the device. 4. The input pipe diameter of the ultrasonic flowmeter does not match the inner diameter of the pipe. Solution: Modify the pipe diameter to match. 3. Failure phenomenon: The sensor is good, but the flow rate is low or there is no flow rate analysis: 1. The paint and rust outside the pipeline have not been removed. Solution: Clear the pipeline again and install the sensor. 2. The piping surface is uneven or the ultrasonic flowmeter is installed at the welding seam. Solution: Grind the pipe flat or away from the weld. 3. The roundness of the pipeline is not good, the inner surface is not smooth, and there is pipe-lining fouling. This may happen if the pipe is cast iron. Solution: Choose a place with smooth inner pipe material or lining, such as steel pipes. 4, the measured medium is pure or solid suspended matter is too low. Solution: Choose other types of instruments that are suitable. 5. The sensor is installed on the fiber glass pipe. Solution: Remove the glass fiber. 6, the sensor is installed on the casing, it will weaken the ultrasonic signal. Solution: Move the sensor to the unsleeved pipe section. 7, the sensor is not well coupled with the pipeline, the coupling surface has gaps or bubbles. Workaround: Reinstall the couplant. 4. Failure phenomenon: When the control valve is partially closed or the flow is reduced, the reading will increase. Analysis: The sensor is installed too close to the downstream of the control valve. When the valve is partially closed, the flow meter actually measures the reduced flow rate of the control valve to increase the flow rate. As the caliber is reduced, the flow rate increases. Solution: Move the sensor away from the control valve, and move the sensor 30D upstream of the control valve or move the sensor to the control valve 5D upstream of the control valve. V. Failure phenomenon: The ultrasonic flowmeter works normally. Suddenly the ultrasonic flowmeter no longer measures the flow. Reason analysis: 1. The measured medium changes. Solution: Change the measurement method. 2. The measured medium is gasified due to high temperature. Solution: cool down 3. The temperature of the measured medium exceeds the limit temperature of the sensor. Solution: Cool down 4. The coupling agent under the sensor is aged or consumed. Solution: Recoat the coupling agent 5. Due to high frequency interference, the meter exceeds its own filter value. Solution: Stay away from the interference source 6. Data loss in the computer. Solution: Re-enter the correct parameters. 7. The computer freezes. 故障分析,希望对所有使用超声波流量计的技术人员能有帮助。 Solution: Restart the computer. The above is a breakdown analysis of the ultrasonic flowmeter by the technicians of Dongxiang Instrument based on the actual work. I hope it will be helpful to all technicians using ultrasonic flowmeters.


的测量是以物理学中的多普勒效应为基础的。 The measurement of ultrasonic flow meters 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. In the ultrasonic Doppler flow measurement method, the ultrasonic transmitter is a fixed sound source, and the solid particles that move with the fluid play the role of an "observer" that moves relative to the sound source. Of course, it merely sends the incident light to the solid. The ultrasonic waves on the particles are reflected back to the receiving data. The frequency difference between the transmitted sound wave and the received sound wave is the ultrasonic Doppler shift produced by 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.