Working principle and application of ultrasonic flowmeter

Ultrasonic flowmeter is a non-contact instrument that has appeared in recent decades with the development of integrated circuit technology. It is suitable for measuring fluids that are not easy to contact and observe and large-diameter flow. The use of ultrasonic flowmeter does not require the installation of 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 carried out without affecting the operation of the production pipeline, so it is an ideal Energy-saving flowmeter.

Measuring principle of ultrasonic flowmeter

The engineer of the technical department of Beijing Taiya Saif Technology Development Co., Ltd. introduced that the measurement of 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 change in frequency due to relative motion is proportional to the relative velocity 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 just puts the incident on 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 Doppler frequency shift of the ultrasonic wave 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. In turn, fluid flow can be obtained.

There are many types of ultrasonic flowmeters. According to different classification methods, they can be divided into different types of ultrasonic flowmeters.

As shown in the figure above, the transducer 1 emits an ultrasonic signal with a frequency of f1. After passing through suspended particles or bubbles in the liquid in the pipe, the frequency shifts and is reflected to the transducer 2 at the frequency of f2. This is Doppler Then, the difference between f2 and f1 is the Doppler frequency difference fd. After the pipeline conditions, transducer installation position, emission frequency, and sound velocity are determined, c, f1, and θ are constants, and the fluid flow rate is proportional to the Doppler frequency shift. The fluid flow rate can be obtained by measuring the frequency shift, and then obtained Fluid flow. At present, Doppler ultrasonic flowmeters on the market are mainly imported, such as a PDFM5.0 portable Doppler ultrasonic flowmeter introduced by Beijing Taiya Saifu from Canada. It can detect pipes with a diameter of 12.5 mm to 4.5 mm, and comes with stainless steel mounting components, coupling agent, and AC charger. The rugged carrying case meets the IP67 protection standard. It is suitable for monitoring the flow of most liquids containing bubbles or solid particles, such as waste water, mud, petroleum, chemical liquid, acid liquid, alkaline liquid, corrosive liquid, abrasive and viscous liquid. Easy to operate, the sensor takes less than one minute to install on the outer wall of the pipeline. Use the built-in keyboard and calibration menu to quickly set parameters. Measurable pipelines include PVC, ductile iron, carbon steel, stainless steel and other materials that can transmit ultrasonic waves.

PDFM5.0 Portable Doppler Ultrasonic Flowmeter

The time difference ultrasonic flowmeter uses the principle that the time difference between the forward propagation and the backward propagation of sound waves in the fluid is proportional to the fluid velocity to measure the fluid flow. Widely used in raw water measurement of rivers, rivers and reservoirs, process flow detection of petrochemical products, water consumption measurement in production processes and other fields. According to actual application needs, time difference ultrasonic flowmeters are divided into portable time difference ultrasonic flowmeters, fixed time difference ultrasonic flowmeters, and time difference gas ultrasonic flowmeters.

Portable time-difference ultrasonic flowmeters are convenient for mobile measurement. For example, PT878 portable time-difference ultrasonic flowmeters of Taiya Saifu belong to this category. As long as the detector is installed on the outer wall of the pipeline during installation, there is no need to cut off or stop the flow. Therefore, there is no flange necessary for general flowmeters, and there are no problems such as medium leakage and pressure loss.

Fixed time-difference ultrasonic flowmeters are mostly used in factories and workshops to conduct routine real-time measurement of fluids. Because the equipment needs long-term operation over many years, fixed ultrasonic flowmeters put forward higher requirements for stability and reliability. Taiya Saifu "PT878 fixed time difference ultrasonic flowmeter adopts large planning integrated circuit CPLD, surface mount technology, higher accuracy, and can record the accumulation of the first 64 operating days, the first 64 operating months, and the first 5 operating years. flow. High reliability, high performance and good applicability.

The time difference gas ultrasonic flowmeter is mainly used in the field of petrochemical industry for gas flow detection, and also in the field of environmental protection. For example, the PT878GC portable time-difference gas ultrasonic flowmeter introduced by Taiya Saifu from the United States can be selected according to user requirements, with standard short tubes, special short tubes, and on-site installation under pressure. Volume flow and mass flow, cumulative flow of volume or mass flow, measured and standard density, turbulence and humidity. It has the characteristics of wide measuring range, high sensitivity and precision.

PT878GC portable time difference gas ultrasonic flowmeter

According to the needs of practical applications, ultrasonic flowmeters are divided into three types: external clamp type, plug-in type and pipe section type.

(1) External clamp

The external clamp type ultrasonic flowmeter is the earliest produced, most familiar and widely used ultrasonic flowmeter. The installation of the transducer does not require pipeline interruption, and it is ready to use. It fully embodies the characteristics of the ultrasonic flowmeter that is simple to install and easy to use. . For example, the PTF-H portable external clamp ultrasonic flowmeter produced by Taiya Saif is specially designed for water measurement. The bundled probe combination is suitable for the measurement of various diameter pipes (including small diameter pipes). Line text on the same screen displays instantaneous flow, cumulative flow, flow rate, signal strength, instrument status, etc .; 256K data memory is equipped in the machine, which can record date, cumulative flow, signal strength, working time, etc .; has RS232 data interface, which can be exported to the machine Stored data; OCT outputs cumulative flow pulse signal and frequency signal.

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(2) Pipe section type

Some pipelines have poor material, poor sound guidance, or serious corrosion, and there are gaps in the lining and the space inside the pipeline, resulting in severe attenuation of the ultrasonic signal. The external ultrasonic flowmeter cannot be measured normally, so a pipe-type ultrasonic flowmeter was produced . The pipe-segment ultrasonic flowmeter integrates the transducer and the measuring tube, which solves a difficulty in the measurement of the externally attached flowmeter. And the measurement accuracy is also higher than other ultrasonic flowmeters, but at the same time it also sacrifices the advantages of continuous flow installation of externally attached ultrasonic flowmeters, which requires cutting the pipeline to install the transducer. For example, Sentinel TM metering grade natural gas ultrasonic flowmeter of GE Corporation, which is represented by Taiya Saif, is a complete ultrasonic flow measurement system that can be used for natural gas flow measurement. Downstream straight pipe section. This configuration can eliminate the influence of the uncertain factors brought by the system installation (the flow field deformation caused by valves, elbows and other system components) on the flow meter performance. The solution provides a simple and cost-effective measurement system, the user will not be affected by other measurement uncertainties, underdeveloped, unbalanced flow field is one of the main uncertainties, and the ultrasonic flowmeter system This factor has been removed in, so users can obtain guaranteed measurement accuracy.

(3) Plug-in

The plug-in ultrasonic flowmeter is somewhere in between. The installation can be continuous flow, use special tools to punch holes in the pipeline with water, insert the transducer into the pipeline to complete the installation. Because the transducer is in the pipeline, its signal transmission and reception only pass through the measured medium, but not through the pipe wall and lining, so its measurement is not limited by the quality of the pipe and the material of the pipe lining. Taking a gas flow meter as an example, such as the XGM868 ultrasonic gas flow meter of GE Corporation, which is represented by Taiya Safe, can measure most gases, including: hydrocarbon gas, exhaust gas, biogas, desulfurization tank gas, fuel gas, and waste , Incinerator gas, steam recovery, flue gas and other gases.

The unique feature of the XGM868 gas flow meter is that it combines various advantages such as wide range, easy installation, low maintenance, high precision and low price. The fully digital German XGM868 has no pressure loss, and it may not cause plugging or accumulation of residues. There are no moving parts that can be worn, and very little daily maintenance is required, providing reliable, drift-free measurements for a long time.

Ultrasonic flowmeters are high-precision and sophisticated measurement and control instruments, which have extremely strict requirements on the relevant technical parameters in the production process of the instrument, because in the actual measurement process of industrial enterprises, even if the error is even one ten thousandth, the accumulated amount will be extremely Huge, especially in some industrial fields such as nuclear power, petrochemical, and even lead to major production safety accidents, according to media reports, Want Want Group ’s branch in Jiangsu has almost caused a huge loss of more than 2 million yuan due to the quality of the purchased flowmeter. Enterprise production plays a key role in quantitative control, so the purchase of flowmeters must not be cheap, and you must choose large brands and professional agents to buy. As the leading domestic testing equipment supplier, Taiya Saif has won the trust of users