Measurement principle and development status of external clip-on ultrasonic flowmeter

Abstract: The information on the measurement principle and development status of the external clip-on ultrasonic flowmeter is provided by the excellent flowmeter and flowmeter manufacturers and quotation manufacturers. Measurement principle and development status 0 Introduction Ultrasonic flowmeter has the advantages of non-contact measurement, low pressure loss, wide measurement range, etc. It has been widely used in flow measurement in petrochemical and other industries, especially suitable for large-diameter pipelines, non-conductive flow measurement . . More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following are the details of the measurement principle and development status of the external clamp ultrasonic flowmeter. Measurement principle and development status 0 Introduction Ultrasonic flowmeter has the advantages of non-contact measurement, low pressure loss, wide measurement range, etc. It has been widely used in flow measurement in petrochemical and other industries, especially suitable for large-diameter pipelines, non-conductive flow measurement . 1 The basic measurement principle of ultrasonic flowmeter The ultrasonic flowmeter uses the different propagation velocities of ultrasonic waves in the forward and reverse flow of the fluid to measure. The measurement principle is shown in Figure 1. The most common time difference method, speed difference method and frequency difference method. Figure 1 Schematic diagram of ultrasonic flowmeter measurement principle Time difference method: speed difference method: frequency difference method: In the formula, L is the straight-line distance between A and B transducers,θis the angle between the fluid flow direction and the ultrasonic path. Because the influence of the speed of sound c is not easily ignored by the temperature, and the frequency difference in the formula (5) is proportional to the flow velocity v, and does not contain the speed of sound c, the measurement result is not affected by the temperature, so the frequency difference method is simpler and more practical. There are also ultrasonic flowmeters specially developed by utilizing the characteristics that the temperature distribution of the fluid in the pipe section changes with the fluid flow, and the temperature distribution causes the sound velocity to change. Because the time difference between the forward flow and the reverse flow depends on the size of the pipe diameter at a general flow rate, it is only a few hundred nanoseconds to a few microseconds, so the high-precision time difference and frequency difference measurement methods are closely related to the measurement accuracy of ultrasonic flowmeters. For example, the Netherlands Instroment adopts high-speed digital processing circuit technology, which can detect tiny time differences of microsecond level, and the timing precision reaches nanosecond level. 2. Selection and installation of external clip-on ultrasonic flowmeters According to the different installation methods of the transducer, ultrasonic flowmeters can be divided into: external clip-on type, pipe section type and insertion type. The clamp-on ultrasonic flowmeter refers to an ultrasonic flowmeter with the transducer attached to the outside of the pipeline. This installation method is the most convenient for installation and maintenance among the three transducer installation methods of the ultrasonic flowmeter, but the transmission and reception signal channels of the transducer signals are the most complicated, and must pass through pipes, (linings) and fluids. medium, the measurement accuracy is also relatively low. 2.1 Precautions for selection The selection of the instrument is a very important work in the application of the instrument. In the selection of the ultrasonic flowmeter, special attention should be paid to the collection of the following information: 2.1.1 Basic information The name of the measured fluid; the maximum flow, the minimum flow; the maximum temperature , minimum temperature; pipe material; pipe lining material; pipe outer diameter D (or pipe wall thickness), pipe inner diameter. 2.1.2 There are generally two types of protection grades: IP65 and IP68. IP65 is a water-proof type, which can withstand a certain pressure and water jet in use. IP68 is submersible and can work in water for a long time. 2.1.3 Selection of measurement points 1) The measurement position should be selected at a straight pipe section that is more than 10D upstream and 5D downstream and filled with liquid; 2) The selection of measurement points should be as far away as possible from pumps, valves and other equipment to avoid interference. The reason is the same as above, because it is necessary to measure the straight body as much as possible to avoid measurement errors caused by turbulent flow; 3) The selection of the measurement point should be as far away as possible from high-power radio stations, strong magnetic field interference sources, etc.; Ultrasonic propagation; 5) Fully consider the scaling condition in the pipe, and select the pipe section without scaling as much as possible for measurement. 2.2 Installation precautions 1) The surface of the metal pipe to be installed with the transducer must be polished by 3 times the probe area, remove the rust paint, make the surface of the pipe wall smooth and flat, expose the original surface of the pipe metal and maintain the original arc; 2) The signal shielding wire of the transducer can be suspended, but cannot be short-circuited with the positive and negative terminals; 3) The contact part between the transducer and the pipeline should be sealed with couplant to prevent air, sand and rust from entering; 4) The fixture should be fixed on the The center part of the transducer makes it difficult to slide. 3 Development Status of Clamp-on Ultrasonic Flowmeter One of the characteristics of ultrasonic waves is that the propagation attenuation is large, and the gas has the strongest ability to absorb ultrasonic energy, followed by liquids and solids. Therefore, in the single-body ultrasonic flowmeter, the measurement accuracy of the outer-clamp gas ultrasonic flowmeter is generally not high in practical applications. In order to improve the measurement accuracy and signal strength, some ultrasonic flowmeters adopt a multi-channel measurement method, which uses the multi-channel measurement data to calculate the average flow rate according to the weight. There are also ultrasonic flowmeters that use wide beam technology. In this technology, the transducer emits a wide frequency range of sound beam to scan and search the pipe wall, so that the pipe becomes a part of the transducer, so that the sound beam can cover the cross section of the measured medium in a larger area. Some data show that the wide beam technology can achieve high stability and repeatability with fewer channels, and the minimum measurable diameter can reach 6.35mm. The above is the whole content of this article. You are welcome to inquire about the flowmeter selection and quotation of our factory. 'Measurement principle and development status of external clip-on ultrasonic flowmeter'

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