Principle and function of ultrasonic flowmeter

Author:admin DateTime:2019-01-28
When the ultrasonic flowmeter propagates in the flowing fluid, it carries the information of the velocity of the fluid. Therefore, the flow rate of the fluid can be detected by the received ultrasound, which can be converted into flow rate. According to the detection method, it can be divided into different types of ultrasonic flowmeters, such as propagation velocity difference method, Doppler method, beam migration method, noise method and correlation method. The acoustic flowmeter is a kind of non-contact instrument which has been applied only with the rapid development of integrated circuit technology in recent ten years. It is suitable for measuring non-contact and observable fluids and large tube runoff. It can measure the flow of open water flow in conjunction with water level gauge. Ultrasound flow ratio does not need to install measuring elements in the fluid, so it does not change the flow state of the fluid, and does not produce additional resistance. The installation and maintenance of the instrument can not affect the operation of production pipelines, so it is an ideal energy-saving flowmeter. As we all know, the current industrial flow measurement generally has the problem of large diameter and large flow measurement difficulty. This is because the general flowmeter with the increase of the measurement diameter will bring difficulties in manufacturing and transportation. The cost of construction, energy loss and installation are not only these shortcomings, but also the ultrasonic flowmeter can be avoided. Because all kinds of ultrasonic flowmeters can be installed outside the tube and non-contact flow measurement, the cost of the instrument is basically independent of the diameter of the pipeline under test, while the cost of other types of flowmeters increases greatly with the increase of the caliber, so the larger the caliber, the better the function-price ratio of the ultrasonic flowmeter is than that of other types of flowmeters with the same function. It is considered to be a better instrument for measuring large pipe runoff. Doppler ultrasonic flowmeter can measure the flow of two-phase media, so it can be used to measure sewage and sewage. In power plants, it is much more convenient to use portable ultrasonic flowmeter to measure the intake of water turbine, the circulating water of steam turbine and other pipe runoff than the old peeled tube flowmeter. Ultrasound by flow juice can also be used for gas measurement. The pipe diameter can be applied from 2cm to 5m, from open channel, underground channel to river with 500m width. In addition, the flow measurement accuracy of the ultrasonic measuring instrument is almost independent of the parameters such as temperature, pressure, viscosity and density of the measured fluid. It can also be made into a non-contact and portable measuring instrument. Therefore, it can solve the flow measurement problems of strong corrosiveness, non-conductivity, radioactivity and flammable and explosive media which are difficult to be measured by other types of instruments. In addition, in view of the characteristics of non-contact measurement, coupled with a reasonable electronic circuit, an instrument can be adapted to a variety of pipe diameter measurement and a variety of flow range measurement. The adaptability of ultrasonic flowmeter is incomparable with other instruments. Ultrasound flowmeter has the advantages mentioned above, so it has been paid more and more attention and developed to serialization and generalization of products. Now it has been made into standard, high temperature, explosion-proof and wet instruments with different sound channels to adapt to flow measurement in different media, different occasions and different pipeline conditions. The main shortcomings of the ultrasonic flowmeter are that the temperature range of the measured fluid is limited by the temperature resistance of the coupling material between the transducer and the pipeline, and the original data of the sound transmission speed of the measured fluid is not complete at high temperature. At present, it can only be used to measure fluids below 200 C in our country. In addition, the measurement circuit of the ultrasonic flowmeter is more complex than that of the general flowmeter. This is because the velocity of liquid in general industrial measurement is usually several meters per second, while the velocity of sound wave in liquid is about 1500 m/s. The variation of velocity of sound brought by the change of flow rate (flow rate) of measured fluid is 10-3 order of magnitude. If the accuracy of measuring velocity is 1%, the accuracy of measuring velocity of sound must be 10-5-10-6 order of magnitude, so it must be improved. The measurement circuit can be realized, which is the reason why the ultrasonic flowmeter can be applied in practice only under the premise of the rapid development of integrated circuit technology. The ultrasonic flowmeter is composed of three parts: ultrasonic transducer, electronic circuit, flow display and accumulation system. The ultrasonic transmitting transducer converts electric energy into ultrasonic energy, and transmits it to the fluid under test. The ultrasonic signal received by the receiver is amplified by electronic circuit and converted into an electrical signal representing the flow for display and integration. In this way, the flow detection and display are realized. Piezoelectric transducers are commonly used in ultrasonic flowmeters. It uses piezoelectric effect of piezoelectric material and appropriate transmitting circuit to add electric energy to piezoelectric element of transmitting transducer to produce ultrasonic vibration persuasion. Ultrasound is injected into the fluid at a certain angle, then received by the receiving transducer, and transformed into electricity by piezoelectric elements for detection. The transmitting transducer uses the inverse piezoelectric effect of piezoelectric elements, while the receiving transducer uses the piezoelectric effect. The piezoelectric components of the transducer of the ultrasonic flowmeter are usually made into circular thin sheets, which vibrate along the thickness. The diameter of the sheet is more than 10 times of the thickness to ensure the directivity of the vibration. Lead zirconate titanate is widely used in piezoelectric components. In order to fix the piezoelectric element and make the ultrasonic wave inject into the fluid at an appropriate angle, it is necessary to form the whole transducer (also known as probe) by inserting the component into the acoustic wedge. The material of sound wedge requires not only high strength and ageing resistance, but also low energy loss of ultrasonic wave through sound wedge, i.e. transmission coefficient is close to 1. The common material of sound wedge is organic glass, because it is transparent, the assembly of piezoelectric components in sound wedge can be observed. In addition, some rubber, plastics and bakelite can also be used as sound wedge materials. Origin of this article: http://www.jc28.com counterfeit must be reproduced, please explain the relevant sources