An ultrasonic water meter flow error correction method based on the Reynolds number at the pipeline inlet
By using the pipeline inlet Reynolds number to establish a nonlinear correction model in an ultrasonic water meter, the flow rate in each flow interval is independently calibrated, which solves the problem that traditional error correction methods are difficult to accurately reflect the fluid motion state in small diameter and small flow measurements, and improves the accuracy and calibration efficiency of flow measurement.
Patent Information
- Application Number
- CN202210652059.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-06-09
- Publication Date
- 2025-06-24
- Estimated Expiration
- 2042-06-09
AI Technical Summary
In the measurement of small diameter and small flow, traditional error correction methods are difficult to accurately reflect the fluid motion state, resulting in large flow measurement errors and low calibration efficiency.
Through the pipeline inlet Reynolds number, standard instantaneous flow rate and measured ultrasonic water meter instantaneous flow rate at different flow points, a nonlinear correction model within different flow intervals such as QⅠ~QⅡ, QⅡ~QⅢ,... is established, the flow correction coefficient is calculated, and the flow rate in each flow interval is independently calibrated.
A comprehensive correction of the flow error of ultrasonic water meter has been achieved, reducing the impact of single flow point correction on other flow points, and improving calibration efficiency and measurement accuracy.
Smart Images
Figure CN114877975B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of flow detection, and relates to a method for correcting the flow error of an ultrasonic water meter based on the Reynolds number at the pipe inlet. Background Art
[0002] Error is a key index for evaluating the quality of an ultrasonic water meter. It is the percentage of the difference between the measured flow rate and the standard flow rate in the standard flow rate. The smaller the percentage and the smaller the repeatability, the better the performance of the ultrasonic water meter. Before leaving the factory, an ultrasonic water meter needs to conduct a cumulative flow experiment on a calibration device and perform error correction according to the experimental results to meet the accuracy level. Therefore, its flow correction result determines whether the product is qualified.
[0003] The ultrasonic water meter mostly adopts the time transmission method measurement principle, mainly calculates the flow velocity by calculating the time difference of the ultrasonic wave propagating in the water in the forward and reverse directions, and finally converts it into the flow rate flowing through the water meter pipeline. The speed measured by the ultrasonic wave propagation is the linear velocity V in the pipeline L , and the standard flow rate Q is equal to the product of the cross-sectional area S and the cross-sectional average velocity V F . Usually, an empirical calculation formula is used to calculate the correction coefficient. However, the empirical formulas are all corrected and compensated under ideal conditions. In actual situations, the fluid motion state in the pipe of the ultrasonic water meter is complex (see the attached drawings of the specification Figures 1-4 ), and the influence of environmental factors such as fluid temperature and viscosity coefficient causes a certain difference between the linear velocity V L and the cross-sectional average velocity V F . It is difficult for the empirical formula to correctly reflect the actual flow condition. Usually, the piecewise linear interpolation of the standard flow rate Q and the time difference T is used to correct the error to improve the flow measurement accuracy. However, in the measurement of small-diameter ultrasonic water meters, in order to increase the acoustic path, inserts, columns, and brackets are often used to increase the propagation path of ultrasonic waves, resulting in the actual flow field inside the pipe deviating from the ideal state and becoming more disordered. Therefore, the traditional error correction method is no longer suitable. Especially in small-flow measurements, the interval between each calibration point is small, the nonlinearity is more obvious, the correction of flow points will not only affect each other, but also increase the correction difficulty, and the calibration efficiency is low Summary of the Invention
[0004] Aiming at the problems existing in the error correction of ultrasonic water meters, the present invention proposes a method for correcting the flow error of an ultrasonic water meter based on the Reynolds number at the pipe inlet.
[0005] The technical solution adopted by the present invention is as follows:
[0006] By means of the Reynolds number at the pipe inlet, the standard instantaneous flow rate, and the instantaneous flow rate of the measured ultrasonic water meter at different flow points, the flow correction coefficient is calculated, and Q Ⅰ ~Q Ⅱ , Q Ⅱ ~QⅢ , Q Ⅲ ~Q Ⅳ , Q Ⅳ ~Q Ⅴ ... nonlinear correction models of flow correction coefficients and pipeline inlet Reynolds numbers in different flow ranges such as (Q Ⅰ , Q Ⅱ , Q Ⅲ , Q Ⅳ , Q Ⅴ are the flow points within the range of the ultrasonic water meter to be measured), and each flow range contains 30% of the flow points of the adjacent two ranges. Each flow range uses the calibration flow points with larger and relatively concentrated error values at 30% - 70% to calculate the flow correction coefficient to calibrate the flow in the corresponding range; after two corrections, the error of the flow points in this flow range is greatly reduced. The error correction method of the present invention makes the correction models of each flow range independent, and the flow points in different flow ranges do not affect each other.
[0007] The beneficial effects of the present invention are as follows:
[0008] 1. Currently, the error correction method for ultrasonic water meters is to correct the linear formula of flow and time difference, while the method of the present invention introduces the Reynolds number at the pipeline inlet into the correction model. The Reynolds number is a dimensionless number that can be used to characterize the fluid flow situation. The fluid condition of small-diameter ultrasonic water meters is complex and does not conform to the traditional flow coefficient correction formula. The Reynolds number calculation formula contains variables such as fluid density, flow velocity, and viscosity coefficient, which are related to the fluid state. Introducing the pipeline inlet Reynolds number into the correction model enables the correction error to be comprehensively corrected from a single time difference to multiple aspects of the fluid state.
[0009] 2. The present invention makes the correction models of each flow range independent, so that the correction of a single flow point does not affect other flow points, reducing the correction difficulty for operators. Because in the small-flow measurement of ultrasonic water meters, the error correction of one calibration flow point will affect the errors of adjacent calibration flow points. After correction, it is necessary to verify the errors of the surrounding calibration flow points. When the flow error exceeds the accuracy requirements, it is necessary to repeatedly confirm the correction coefficient and conduct repeated experiments, which not only increases the correction difficulty but also increases the time for calibrating the ultrasonic water meter. Using the correction method of the present invention, independent correction models for each flow range are established, and the error correction of the overlapping intervals does not affect each other, facilitating the correction of calibration flow points and being more suitable for ultrasonic water meters with a wide range ratio and high accuracy. Description of the Drawings
[0010] Figure 1 is the simulation velocity cloud diagram of the vertical cross-section of the Q3 flow in the ultrasonic water meter pipeline;
[0011] Figure 2 is the simulation velocity cloud diagram of the horizontal cross-section of the Q3 flow in the ultrasonic water meter pipeline;
[0012] Figure 3 It is the simulation velocity cloud diagram of the vertical section of the Q1 flow rate in the ultrasonic water meter pipeline;
[0013] Figure 4 It is the simulation velocity cloud diagram of the horizontal section of the Q1 flow rate in the ultrasonic water meter pipeline;
[0014] Figure 5 It is the schematic diagram of the flow rate interval division;
[0015] Figure 6 It is the flow chart of the error correction method for the ultrasonic water meter based on the Reynolds number at the pipeline inlet of the present invention;
[0016] Figure 7 It is the flow rate correction model diagram of the present invention. Specific embodiments
[0017] The present invention will be further described in detail below with reference to the accompanying drawings.
[0018] The technical solution adopted by the present invention is: by means of the Reynolds number Re at the pipeline inlet, the standard instantaneous flow rate Q S and the instantaneous flow rate Q of the ultrasonic water meter m , establish the nonlinear correction models in several different flow rate intervals such as Q Ⅰ ~Q Ⅱ , Q Ⅱ ~Q Ⅲ , Q Ⅲ ~Q Ⅳ , Q Ⅳ ~Q Ⅴ ... (where Q Ⅰ , Q Ⅱ , Q Ⅲ , Q Ⅳ , Q Ⅴ ... are the flow rate points within the range of the ultrasonic water meter). The interval division is as shown in Figure 5 . Considering that the internal flow field of the pipeline is affected by secondary flow and pulsating flow, and there are also systematic errors in the experimental calibration device itself, the flow rate points are not stable at a fixed value. Therefore, each flow rate interval needs to include 30% of the flow rate points in the adjacent intervals, so that the flow rate points in the critical interval are included in two correction models at the same time. Then, in each flow rate interval, the flow rate points with larger and relatively concentrated error values at 30% - 70% are used to calculate the flow rate correction coefficient to calibrate the flow rate in the interval. After two corrections, the error of the flow rate points in the flow rate interval is greatly reduced.
[0019] As shown in Figure 6 , it is the flow chart of the error correction method for the ultrasonic water meter based on the Reynolds number at the pipeline inlet. The steps of this method are as follows:
[0020] Step 1: Install the ultrasonic water meter under test on the water flow standard calibration device, and set different flow points within the range through the host computer of the water flow standard calibration device. After waiting for the flow to stabilize, record the standard instantaneous flow rate Q of the standard meter and the instantaneous flow rate Q of the ultrasonic water meter under test at each flow point, and collect the time difference T measured by the ultrasonic water meter under test in real time. S and the instantaneous flow rate Q of the ultrasonic water meter under test. m And collect the time difference T measured by the ultrasonic water meter under test in real time.
[0021] To reduce the influence of random errors and obtain an accurate correction model, at the same standard instantaneous flow rate Q, collect the time difference T measured by the ultrasonic water meter under test multiple times and calculate the average time difference T. S And calculate the average time difference T.
[0022] According to the standard instantaneous flow rate Q, calculate the average flow velocity V at the inlet cross-section of the pipeline, as shown in Equation (1); calculate the Reynolds number Re at the inlet of the pipeline through Equation (2). S calculate the average flow velocity V at the inlet cross-section of the pipeline, F see Equation (1); calculate the Reynolds number Re at the inlet of the pipeline through Equation (2).
[0023]
[0024]
[0025] where ρ, v, and μ are the density, flow velocity, and viscosity coefficient of the fluid respectively, d is the characteristic length, S is the cross-sectional area of the pipeline fluid domain, and Q is the standard instantaneous flow rate value. S is the standard instantaneous flow rate value.
[0026] According to Equation (3), calculate the linear velocity V measured by the ultrasonic water meter under test, L calculate the instantaneous flow rate Q of the ultrasonic water meter under test according to Equation (4), m and then calculate the flow correction coefficient Y according to Equation (5) to establish the correction model between the Reynolds number at the inlet of the pipeline and the flow correction coefficient for each flow interval.
[0027]
[0028]
[0029]
[0030] where C is the propagation speed of ultrasonic waves in water, is the average time difference obtained by sampling, K is the ratio of the average velocity in the ideal state to the linear average velocity, Q m is the instantaneous flow rate value of the ultrasonic water meter under test, Y is the flow correction coefficient, L is the acoustic path, and θ is the angle between the ultrasonic wave path and the central axis of the pipeline.
[0031] Step 2: Establish a correction model for the flow correction coefficient Y and the Reynolds number Re at the pipeline inlet. Based on the large amount of experimental data collected and calculated in Step 1, establish Q Ⅰ ~Q Ⅱ ,Q Ⅱ ~Q Ⅲ ,Q Ⅲ ~Q Ⅳ ,Q Ⅳ ~Q Ⅴ ... and several non-linear correction models in different flow rate intervals (where Q Ⅰ , Q Ⅱ , Q Ⅲ , Q Ⅳ , Q Ⅴ ... are the flow rate points within the range of the ultrasonic water meter to be measured). Taking the Reynolds number Re at the pipeline inlet and the flow correction coefficient Y as independent variables and functions, obtain the flow correction models for each flow rate interval through matlab: Y i = a i ·Re n + b i ·Re n-1 + ······ + c i , where a i , b i …c i are the coefficients of the polynomial, i is the interval number, and n is the degree of the variable Reynolds number Re of the polynomial. The flow rate intervals can directly overlap 30% of the flow rate points in adjacent intervals.
[0032] In this embodiment, according to the minimum flow rate point Q1, the demarcation flow rate point Q2, the common flow rate point Q3, the overload flow rate point Q4 of the cold water meter in the national metrological verification regulation "JJG - 162 - 2009 - Cold Water Meters" and 0.33(Q1 + Q3), 0.67(Q1 + Q3), divide the ultrasonic water meter to be measured into five consecutive flow rate intervals, namely Q1~Q2, Q2~0.33(Q1 + Q3), 0.33(Q1 + Q3)~0.67(Q1 + Q3), 0.67(Q1 + Q3)~Q3, Q3~Q4, and establish the flow correction model diagrams for the corresponding flow rate intervals, as shown in Figure 7 . In the figure, the dashed line is drawn from the experimental data collected and calculated; the solid curve is the source of the correction model polynomial. By adjusting the degree of n, the consistency between the rising trend line and the dashed line is improved. Considering the operation efficiency after the correction model is added to the single-chip microcomputer and the polynomial coefficients cannot be too small, n is generally taken between 2 and 4.
[0033] Step 3: After establishing the correction model for each flow rate interval, substitute the Reynolds number at the pipeline inlet of each calibration flow rate point into the corresponding correction model to calculate the corresponding flow correction coefficient Y for each flow rate interval i, and calculate the corrected instantaneous flow rate Q' of the ultrasonic water meter to be measured according to formula (6) m . The correction model can perform the initial correction on the ultrasonic water meter. However, since the pipe dimensions, transducer characteristics, hardware circuits, etc. of each ultrasonic water meter cannot be made completely consistent. The protruding structures such as the column brackets in the pipe have a great influence on the flow field. In order to further improve the measurement accuracy of the ultrasonic water meter, the flow rate needs to be corrected twice. The present invention calculates the secondary correction coefficient Z m by the corrected instantaneous flow rate Q' S and the standard instantaneous flow rate Q i (see formula 7), and uses the method of secondary correction to further make the measured flow rate value close to the true value.
[0034] Q' m = Y i ×Q m (6)
[0035]
[0036] Substitute the calculated secondary correction coefficient Z i into formula (8) to calculate the secondary corrected instantaneous flow rate Q'' m :
[0037] Q'' m = Z i ×Q' m (8)
[0038] Finally, calculate the error value between the secondary corrected instantaneous flow rate Q'' m and the standard instantaneous flow rate Q S .
[0039] Table 1 shows the experimental data obtained by using the method of the present invention, and Table 2 shows the experimental data obtained by using the traditional method. The errors of both methods meet the requirements of the secondary accuracy of the ultrasonic water meter. However, when using the traditional method, the error correction of one flow point will affect the errors of adjacent flow points. After correction, it is necessary to verify the errors of the surrounding flow points. When the flow error exceeds the accuracy requirements, the correction coefficient needs to be repeatedly confirmed and repeated experiments are required. By comparing the two methods, it can be seen that the repeatability of the error at small flow rates of the traditional method is poor, and the minimum flow rate is 0.01 m 3 / h. While using the method of the present invention, the gap between the secondary corrected instantaneous flow rate Q'' m and the standard instantaneous flow rate Q S is greatly reduced, and the repeatability of the measurement error of the ultrasonic water meter is better, and the minimum flow rate is 0.0063 m 3 / h.
[0040] Table 1 Experimental data of the error correction method based on the Reynolds number at the pipe inlet
[0041]
[0042] Table 2 Experimental data of traditional error correction method
[0043]
[0044] In the actual flow calibration process, it is not necessary to calculate all the flow correction coefficients and secondary correction coefficients within the range, but to take a calibration flow point Q with a relatively large and concentrated error value in each flow interval iuse (which can be selected between 30% and 70% of this flow interval), and calculate its flow correction coefficient Y iuse and secondary flow correction coefficient Z iuse , and substitute the Y iuse and Z iuse of this flow point into Formula (6) and Formula (8) as the only correction coefficient value within this flow interval.
Claims
1. A method for correcting the flow error of an ultrasonic water meter based on the Reynolds number at the pipeline inlet, characterized in that The method comprises the following steps: Step 1: Through the host computer of the water flow standard verification device, set the flow points within the range of the ultrasonic water meter under test, and collect the standard instantaneous flow rate Q of the standard meter, the instantaneous flow rate Q of the ultrasonic water meter under test, and the time difference measured by the ultrasonic water meter under test, and calculate the Reynolds number at the pipeline inlet and the flow correction coefficient; S , the instantaneous flow rate Q of the ultrasonic water meter under test m and the time difference measured by the ultrasonic water meter under test, and calculate the Reynolds number at the pipeline inlet and the flow correction coefficient; Step 2: Based on the data collected and calculated in Step 1, establish several different flow rate ranges, and fit to obtain the flow rate correction coefficient Y for each flow rate range i And the correction model of the Reynolds number at the pipeline inlet; Step 3: Substitute the pipe inlet Reynolds numbers of the calibrated flow points in each flow range into the correction model described in Step 2 to obtain the flow correction coefficient Y corresponding to each flow range i , and calculate the corrected instantaneous flow rate Q′ of the ultrasonic water meter under test according to formula (6) m :[[]]END]] Q′ m = Y i × Q m (6) Then, calculate the secondary correction coefficient Z according to formula (7). i : Substitute the calculated secondary correction coefficient Z i into formula (8) to calculate the secondary correction instantaneous flow rate Q″ m : Q″ m = Z i × Q′ m (8) Step 4: Calculate the secondary corrected instantaneous flow rate Q″ m and the standard instantaneous flow rate Q S to obtain the error value therebetween.
2. A method for correcting the flow error of an ultrasonic water meter based on the Reynolds number at the pipeline inlet according to claim 1, characterized in that: In the second step, each flow interval contains 30% of the flow points of adjacent intervals.
3. A method for correcting the flow error of an ultrasonic water meter based on the Reynolds number at the pipeline inlet according to claim 1, characterized in that: For each flow interval in the third step, the flow points with relatively large and concentrated error values at 30% - 70% are used as calibration flow points to calculate the flow correction coefficient for calibrating the flow in the interval.
4. A method for correcting the flow error of an ultrasonic water meter based on the Reynolds number at the pipeline inlet according to claim 1, characterized in that: In the first step, the time difference measured by the ultrasonic water meter under test is the average time difference of multiple measurements of the ultrasonic water meter under test.
5. A method for correcting the flow error of an ultrasonic water meter based on the Reynolds number at the pipeline inlet according to claim 1, characterized in that: In the second step, according to the flow points Q of the ultrasonic water meter under test set by the host computer Ⅰ , Q Ⅱ , Q Ⅲ , Q Ⅳ , Q Ⅴ ..., establish different flow ranges of Q Ⅰ ~Q Ⅱ , Q Ⅱ ~Q Ⅲ , Q Ⅲ ~Q Ⅳ , Q Ⅳ ~Q Ⅴ ...