Discussion on Calibration of Ultrasonic Flow Meter in Sewage Flow Meter

Abstract: The discussion information of ultrasonic flow meter in the calibration of sewage flow meter is provided by excellent flow meter and flow meter manufacturers and quotation manufacturers. 1 Principle of Ultrasonic Flowmeter There are two principles of commonly used ultrasonic flowmeter: time difference method and Doppler method. 1.1 The principle of time difference method Ultrasonic signal in the fluid, the signal propagation speed is fast when the flow is downstream, and the propagation time is short; For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following is the discussion article details of ultrasonic flowmeters in sewage flowmeter calibration. 1 The principle of ultrasonic flowmeter There are two principles of ultrasonic flowmeter commonly used: the time difference method and the Doppler method. 1.1 The principle of time difference method Ultrasonic signal in the fluid, the signal propagation speed is fast and the propagation time is short when the flow is downstream; the signal propagation speed is slow and the propagation time is long when the flow is upstream. There is a difference in the propagation time of the ultrasonic signal in the fluid in the upstream and downstream directions. Instantaneous difference, fluid flow can be calculated. The time difference method is more suitable for measuring pure liquids. Liquids or suspended substances with more bubbles will hinder the normal propagation of sound pulses, resulting in abnormal measurement. 1.2 Principle of Doppler Method Ultrasonic signals are scattered when they encounter tiny floating objects (suspended substances or tiny bubbles) on the propagation path, and the ultrasonic receiver can receive the scattered ultrasonic signals. The frequency of the transmitted signal is affected by the Doppler effect and becomes a different frequency of the received signal. The difference between the two frequencies has a definite quantitative relationship with the fluid flow rate, from which the fluid flow rate can be calculated. Doppler flowmeters cannot measure clean fluids, only fluids with a turbidity above about 50 mg/L. At the same time, the measurement accuracy of the Doppler method is lower than that of the time difference method, which is generally 2.0, that is, 2% full-scale error (2% F.S.). 2 Precautions for the use of ultrasonic flow meters The flowmeter itself is the problem. 2.1 In terms of operating irregular pipelines, technicians often do not operate in accordance with standard operating procedures, such as inaccurate measurement of the outer diameter, perimeter, wall thickness, contact temperature, etc. of the pipeline. These parameters will have an important impact on the original data correction of the ultrasonic flowmeter. . In terms of installation method, technicians often do not choose the installation method according to the pipe size and signal strength, and often choose the default dual sound path mode of the flowmeter. The correct installation method is: single sound path should be used in large pipes and complex environments; multi sound paths should be selected in the case of small pipes and strong signals. In terms of installation location, technicians often place ultrasonic probes at will, and do not confirm the important measurement condition of whether the pipeline is full of sewage. The correct installation position is: the probe should be placed in the horizontal middle position of the pipeline; accurate measurement can be performed only when the pipeline is full, and the vertical pipeline with the fluid flowing upward can ensure full pipeline flow. In addition, important parameters such as the type and thickness of the pipeline lining in the field are often difficult to obtain, which also seriously affects the accuracy of the flowmeter. 2.2 The problem of ultrasonic flowmeter itself is the selection of time difference method and Doppler method flowmeter first. The time difference method flowmeter is suitable for the measurement of pure liquid, and the accuracy is better than±1.0%; Doppler flowmeter is suitable for fluids with turbidity above 50mg/L. Therefore, the selection of flowmeters with two principles is very important when calibrating sewage flowmeters. Under normal circumstances, when the sewage in the pipeline is relatively clean, the time difference method can be used; when the sewage is turbid, the Doppler method should be used. However, it is difficult to quantitatively define whether the sewage is clean or turbid in the field. Therefore, there is no general method to follow for the flowmeters using these two principles, resulting in inaccurate measurement of the flowmeter itself, let alone calibrating the sewage flowmeter. Secondly, there are also defects in ultrasonic reception. Because ultrasonic waves measure fluid flow by transmitting and receiving ultrasonic signals in pipes, the refraction of ultrasonic waves by pipe materials, the reflection and scattering of ultrasonic waves by impurities in the fluid, and the content of randomly existing bubbles and impurities in the fluid will all affect the measurement. produce unstable effects. Oilfield sewage contains a lot of crude oil, gravel, air bubbles, chemicals, etc. The environment inside the pipeline is very complex and changeable, which seriously affects the measurement accuracy. Aiming at the low accuracy of ultrasonic flowmeter in online calibration of sewage flowmeter. In the past year, using 26 qualified sewage flowmeters as reference flowmeters, 4 ultrasonic flowmeters have been calibrated on-site. role in meter calibration. 3.1 Selection of flowmeter In order to make the test representative, the portable ultrasonic flowmeter is selected from a well-known foreign manufacturer's time difference type A and Doppler type B, and one set of time difference type C and Doppler D type from a well-known domestic manufacturer. , all of which are qualified and within the verification period. The 26 sewage flow meters were used for the first time after passing the verification, and within the verification period. 3.2 Precautions for the test This test strictly follows the instructions for use with the ultrasonic flowmeter and the precautions mentioned in Chapter 3 of this article. The straight section of the pipeline where the flowmeter is installed in the test conforms to the“Top ten and last five”Provisions. In the test, the pipeline where the flowmeter is installed is a new pipeline within the past one year, and the problem of low ultrasonic signal reception quality caused by the corrosion of the inner wall of the pipeline should be avoided as much as possible. The above is the whole content of this article. You are welcome to inquire about the flowmeter selection and quotation of our factory. 'Discussion on Calibration of Ultrasonic Flow Meters in Sewage Flow Meters'

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