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How to correctly select and ultrasonic flowmeter is used to measure the air flow

by:KAIDI     2020-10-02
The measurement of air conditioning water there are many different kinds choice of flowmeter, ultrasonic flowmeter is one type of one of the use of more how to correctly select ultrasonic flowmeter, select ultrasonic flow timing need to focus on what are the main points of the? What is its working principle? Installation and use, maintenance, and need to pay attention to what? Is worth our attention. This article introduces the air conditioning and the principle of the application of the ultrasonic flowmeter in flow measurement, the principle of measurement point selection, key points of clip mounted sensor installation and measurement steps, and air conditioning water flow test practice for many years, puts forward the technical measures to ensure that the results of measurement accuracy. 1. Working principle of the ultrasonic flowmeter closed pipe is classified by measuring principle are: time transmission method, the doppler effect method, beam deflection method, correlation method, and the method of noise. The time propagation method and can be divided into the time difference, phase difference, frequency difference method. Is currently used in air conditioning water system of main measurement principle of time difference method and doppler method. Embellish of RZ - meter technology export 1158 series flow meter is also belong to the time difference ultrasonic flowmeter, by the use of the broad masses of users, stability and measuring effect is very good, is to choose the ultrasonic flowmeter products recommended products. 1. 1 time is measuring principle flowmeter information network content images of ultrasonic propagation in the liquid, due to the different fluid flow changes will make the ultrasonic wave propagation velocity. As shown in figure 1, take ultrasonic sound velocity in static fluid for c, the fluid velocity v, the installation of the upstream and downstream sensors distance L. When the ultrasonic wave propagation direction and fluid in the same direction, the ultrasonic transmission speed for ( c + v) , when the ultrasonic wave propagation direction and fluid flow in the opposite direction, the ultrasonic transmission speed for ( c-v) ; The downstream direction propagation time tl = L/( c + v) , counter-current direction propagation time t2 = L/( c-v) Information network, there are: flowmeter pictures content is constant, c, L measured time delta t can calculate the fluid velocity v, then the fluid flow. 1. 2 doppler doppler is measuring principle is based on using the doppler effect principle to measure fluid flow. As shown in figure 2, the sensor 1 transmitting frequency ultrasonic signal for f1, suspended particles or bubbles in the liquid through the pipe after the frequency offset, with 2 f2 reflect the frequency of the sensor, this is called the doppler effect, f2 and the difference between the f1 for doppler frequency offset fd. Fluid velocity v, ultrasonic sound velocity for c, doppler frequency shift fd is proportional to the fluid velocity v, i. e. , the meter information network content pictures when pipeline conditions, determine the sensor installation location, transmission frequency, sound, c, f1, & theta; Is constant, the fluid velocity and doppler frequency shift is proportional to the, fluid flow rate can be obtained by measuring the frequency shift, then the fluid flow. 1. 3 1 use main difference. 3. 1 is the current body of different water quality requirements. Jet lag type is suitable for relatively clean fluid measurement, doppler is mainly used for measuring amount can give a strong reflected signal particle or bubbles in the liquid. Jet lag type suspended particles can be measured is less fluid, doppler is than time type is applicable suspended material content limit is much higher, and can measure of bubbles is continuously mixed with liquid. 1. 3. 2 measuring precision is different. Jet lag type is higher than doppler is accuracy, time type is measurement precision can reach & plusmn; ( 0. 5 to 1) %, repeatability error is 0. 1% ~ 0. 3%; Doppler is measuring accuracy is commonly & plusmn; ( 1 ~ 2) %, repeatability error is 0. 5% ~ 1%. 2 points selection principles in order to ensure the air conditioning water flow measurement precision, selection of points when asked to choose the fluid flow field uniformity of parts, generally should follow the following principles: 2. 1 fluid being measured the pipe must be full tube. 2. 2 choose tested the material of pipe should be even and compact, easy to ultrasonic transmission, such as vertical section ( Fluid from down to up) Or horizontal section ( The whole line below as well) 。 2. 3 installation distance should choose more than 10 times the pipe diameter, upstream downstream straight pipe diameter (greater than 5 times Note: different instrument's distance will be different, specific distance to use instrument specifications shall prevail) Within any valve, elbow, reducer, such as uniform straight pipe, the measurement point should take away from the valve, pump, high voltage, frequency converter and other interference sources. 2. 4 give full consideration to tube fouling condition, as far as possible choose no scaling section measurement. 3 the main points three clamp type flow sensor installation. The determination of flow sensor installation 1 3. 1. 1 there are three kinds of jet lag is sensor installation, V, Z and W method, as shown in figure 3. Meter information network content image what installation, measurement instrument specifications have rules, but in boundaries blurred. Such as TFX1020P time difference ultrasonic flowmeter: V installation method for measuring diameter of 25 ~ 400 ㎜, Z installation method for measuring diameter of 100 ~ 2540 ㎜, W installation method for measuring diameter less than 65 ㎜ small tube. 'V' type and Z type, V and W in the applicable measuring diameter have overlap, in case of the situation, choosing a good installation according to the following principles: V installation in general is a standard installation, easy to use, accurate measurement. When the pipeline to be measured is coarse or is due to the current body high turbidity, pipe wall lining or scale is too thick, causing V installation of weak signal, instrument can not work normally, select Z type installation. Reason is the use of Z when installation, direct transmission of ultrasound in the pipe, without refraction, small signal attenuation.
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