CN114877975A - A method of correcting flow error of ultrasonic water meter based on Reynolds number of pipeline inlet - Google Patents

Abstract

The invention discloses an ultrasonic water meter flow error correction method based on a reynolds number of a pipeline inlet. Calculating to obtain a flow correction coefficient through the Reynolds number of the pipeline inlet, the standard instantaneous flow and the instantaneous flow of the ultrasonic water meter to be measured at different flow points, and establishing a nonlinear correction model of the flow correction coefficient and the Reynolds number of the pipeline inlet in different flow intervals, wherein each flow interval comprises 30% of flow points in two adjacent intervals. Calculating a flow correction coefficient by using calibration flow points with large error values at 30% -70% and relatively concentrated in each flow interval to calibrate the flow in the interval; after two corrections, the error of the flow point in the flow interval is greatly reduced. The error correction method of the invention ensures that the correction models of each flow interval are mutually independent, the flow points of different flow intervals are not influenced mutually, the correction difficulty is reduced, and the method is suitable for the ultrasonic water meter with wide range ratio and high accuracy.

Description

A method of correcting flow error of ultrasonic water meter based on Reynolds number of pipeline inlet

technical field

The invention belongs to the technical field of flow detection, and relates to a flow error correction method of an ultrasonic water meter based on the Reynolds number of a pipeline inlet.

Background technique

Error is a key indicator for evaluating the quality of ultrasonic water meters. 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, ultrasonic water meters need to carry out cumulative flow experiments on the verification device, and carry out error correction according to the experimental results, so as to meet the accuracy level, so the flow correction results determine whether the product is qualified or not.

The ultrasonic water meter mostly adopts the measurement principle of the time transmission method, which mainly calculates the water velocity by calculating the time difference between the forward and reverse propagation of ultrasonic waves in the water, and finally converts it into the flow through the water meter pipeline. The velocity of ultrasonic propagation measurement is the linear velocity _VL in the pipeline, and the standard flow Q is equal to the product of the cross-sectional area S and the average velocity of the cross-section V _F , and the correction coefficient is usually calculated using an empirical formula. However, the empirical formulas are all corrected and compensated under ideal conditions, but in practice, the fluid motion state in the tube of the ultrasonic water meter is complex (see Figure 1-4 in the specification), and the influence of environmental factors such as fluid temperature and viscosity coefficient leads to the linear velocity _VL There is a certain difference with the average velocity V _F of the section, and the empirical formula is difficult to correctly reflect the actual flow conditions. Usually, the piecewise linear interpolation of the standard flow Q and the time difference T is used to correct the error to improve the accuracy of flow measurement. However, in the measurement of small-diameter ultrasonic water meters, in order to improve the sound path, inserts, uprights, and brackets are often used to increase the propagation path of ultrasonic waves, which causes the actual flow field inside the pipeline to deviate from the ideal state and become more disordered. Error correction methods are no longer suitable. Especially in small flow measurement, the interval between calibration points is small, and the nonlinearity is more obvious. The correction of flow points will not only affect each other, but also increase the difficulty of correction, and the calibration efficiency is low.

SUMMARY OF THE INVENTION

Aiming at the problems existing in the error correction of the ultrasonic water meter, the present invention proposes a flow error correction method of the ultrasonic water meter based on the Reynolds number of the pipeline inlet.

The technical scheme adopted in the present invention is:

Through the pipeline inlet Reynolds number, the standard instantaneous flow rate and the instantaneous flow rate of the ultrasonic water meter under different flow points, the flow correction coefficient is calculated to obtain the flow correction coefficient, and the establishment of Q _I ~ Q _II , Q _II ~ Q _III , Q _III ~ Q _IV , Q _IV ～Q _Ⅴ ... and other flow correction coefficients and nonlinear correction models of pipeline inlet Reynolds number in different flow intervals (Q _Ⅰ , Q _Ⅱ , Q _Ⅲ , Q _Ⅳ , Q _Ⅴ are the flow rates within the measured ultrasonic water meter range points), and each flow interval contains 30% of the flow points in each of the two adjacent intervals. In each flow interval, the calibration flow point with a relatively large error value at 30% to 70% is used to calculate the flow correction coefficient to calibrate the flow in the interval; after two corrections, the error of the flow point in the flow interval is greatly increased. Zoom out. The error correction method of the present invention makes the correction models of each flow interval independent of each other, and the flow points of different flow intervals do not affect each other.

The beneficial effects of the present invention are:

1. The current ultrasonic water meter error correction method is to correct the linear formula of flow rate and time difference, and the method of the present invention introduces the Reynolds number of the pipeline inlet into the correction model. The Reynolds number is a dimensionless number that can be used to characterize fluid flow. The fluid condition of the small-diameter ultrasonic water meter 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 rate, and viscosity coefficient. These variables are related to the fluid state. The pipeline inlet Reynolds number is introduced into the correction. The model makes the correction error from a single time difference to a multi-faceted comprehensive correction of the fluid state.

2. The present invention makes the correction model of each flow interval independent, so that the correction of a single flow point does not affect other flow points, thereby reducing the difficulty of correction for operators. Because the ultrasonic water meter is in the small flow measurement, the error correction of one calibrated flow point will affect the error of the adjacent calibrated flow points. After the correction, the error of the surrounding calibrated flow points needs to be verified. When the flow error exceeds the accuracy requirements, it needs to be repeatedly confirmed. Correction coefficient, repeated experiments, which not only increases the difficulty of correction but also increases the time for calibrating the ultrasonic water meter. Using the correction method of the invention, an independent correction model for each flow interval is established, and the error correction of overlapping intervals is not affected, which is convenient for correcting and calibrating the flow point, and is more suitable for ultrasonic water meters with wide range ratio and high accuracy.

Description of drawings

Figure 1 is the simulated velocity cloud diagram of the vertical section of the Q3 flow of the ultrasonic water meter pipeline;

Figure 2 is the simulation velocity cloud diagram of the Q3 flow horizontal section of the ultrasonic water meter pipeline;

Figure 3 is the simulated velocity cloud diagram of the vertical section of the Q1 flow of the ultrasonic water meter pipeline;

Fig. 4 is the simulation velocity cloud diagram of the Q1 flow horizontal section of the ultrasonic water meter pipeline;

Figure 5 is a schematic diagram of flow interval division;

Fig. 6 is the flow chart of the ultrasonic water meter error correction method based on pipeline inlet Reynolds number of the present invention;

FIG. 7 is a flow correction model diagram of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings.

The technical scheme adopted in the present invention is: to establish Q _I ~ Q _II , Q _II ~ _{Q III , Q III ~} Q _Ⅳ , Q _Ⅳ ～Q _Ⅴ ... and other nonlinear correction models in several different flow intervals (where Q _Ⅰ , Q _Ⅱ , Q _Ⅲ , Q _Ⅳ , Q _Ⅴ ... are the flow points within the range of the ultrasonic water meter ), where the interval division is shown in Figure 5. Considering that the flow field in the pipeline is affected by the secondary flow and pulsating flow, and the systematic error of the experimental calibration device itself, the flow point is not stable at a fixed value, so each flow interval needs to include 30 points of each adjacent interval. % of the flow points, so that the flow points in the critical interval are included in both correction models. Then in each flow interval, the flow point with large error value and relatively concentrated at 30% to 70% is used to calculate the flow correction coefficient to calibrate the flow in the interval; after two corrections, the flow interval is The error of the inner flow point is greatly reduced.

Figure 6 shows the flowchart of the method for correcting errors of ultrasonic water meters based on the Reynolds number at the inlet of the pipeline. The steps of the method are as follows:

Step 1: Install the ultrasonic water meter to be tested on the water flow standard verification device, and set different flow points within the range through the upper computer of the water flow standard verification device. After waiting for the flow to stabilize, record the standard instantaneous flow Q _S of the standard meter under each flow point, the instantaneous flow Q _m of the ultrasonic water meter under test, and collect the time difference T measured by the ultrasonic water meter under test in real time.

In order to reduce the influence of random errors and obtain an accurate correction model, under the same standard instantaneous flow rate Q _S , the time difference value T measured by the ultrasonic water meter to be measured is obtained by multiple acquisitions, and the average time difference value T is calculated.

According to the standard instantaneous flow Q _S , calculate the average flow velocity V _F of the pipeline inlet section, see formula (1); calculate the Reynolds number Re at the pipeline inlet through formula (2).

where ρ, v, and μ are the density, 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 _S is the standard instantaneous flow rate.

According to formula (3), the linear velocity _VL measured by the ultrasonic water meter under test is calculated, and the instantaneous flow rate Q _m of the ultrasonic water meter under test is calculated according to formula (4). Then, the flow correction coefficient Y is calculated according to formula (5), which is used to establish the correction model of the Reynolds number and flow correction coefficient of the pipeline inlet in each flow interval.

为采样得到的平均时差值，K为理想状态下面平均速度和线平均速度的比值，Q_m为被测超声水表瞬时流量值，Y为流量修正系数，L为声程，θ为超声波路径和管道中轴线的夹角。where C is the propagation speed of ultrasonic waves in water,

is the average time difference value obtained by sampling, K is the ratio of the average speed to the linear average speed under ideal conditions, Q _m is the instantaneous flow value of the ultrasonic water meter under test, Y is the flow correction coefficient, L is the sound path, θ is the ultrasonic path and The included angle of the central axis of the pipe.

Step 2: Establish a correction model of the flow correction coefficient Y and the Reynolds number Re of the pipeline inlet. Based on a large number of experimental data collected and calculated in step 1, a nonlinear correction in several different flow intervals, such as Q _I ~ Q _II , Q _II ~ Q _III , Q _III ~ Q _IV , Q _IV ~ Q _V ... and so on, is established Model (wherein Q _Ⅰ , Q _Ⅱ , Q _Ⅲ , Q _Ⅳ , Q _Ⅴ ... are the flow points within the range of the ultrasonic water meter to be tested), with the Reynolds number Re and flow correction coefficient Y at the pipeline inlet as independent variables and functions, The flow correction model of each flow interval is obtained by 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, n is the polynomial variable Reynolds number Re degree, and the flow interval can directly overlap each 30% flow point of the two adjacent intervals.

In this embodiment, according to the national metrological verification regulations of "JJG-162-2009-Cold Water Meter", the minimum flow point Q1 of the cold water water meter, the boundary flow point Q2, the common flow point Q3, the overload flow point Q4 and 0.33 (Q1+Q3) , 0.67(Q1+Q3),, five flow intervals connected in sequence are obtained by dividing the ultrasonic water meter under test, namely Q1～Q2, Q2～0.33(Q1+Q3), 0.33(Q1+Q3)～0.67(Q1+ Q3), 0.67(Q1+Q3)~Q3, Q3~Q4, establish the flow correction model diagram of the corresponding flow interval, as shown in Figure 7, the dotted line in the figure is drawn from the collected and calculated experimental data; The curve is the source of the correction model polynomial. By adjusting the degree of n, the consistency of the trend line and the broken line can be improved. Taking into account the operational efficiency after the correction model is added to the single-chip microcomputer and the polynomial coefficient cannot be too small, n is generally taken between 2-4.

Step 3: After establishing the correction model for each flow interval, substitute the pipeline inlet Reynolds number of each calibrated flow point into the corresponding correction model, and calculate the corresponding flow correction coefficient Y _i for each flow interval, and according to formula (6) Calculate the corrected instantaneous flow rate _Q'm of the ultrasonic water meter under test. The correction model can realize the initial correction of the ultrasonic water meter, but because the pipe size, transducer characteristics, hardware circuit, etc. of each ultrasonic water meter cannot be completely consistent. The protruding structures such as column brackets in the pipeline have a great influence on the flow field. In order to improve the measurement accuracy of the ultrasonic water meter again, the flow needs to be corrected twice. The present invention calculates the secondary correction coefficient Z _i (see formula 7) by correcting the instantaneous flow rate _Q'm and the standard instantaneous flow rate Q _S , and uses the method of secondary correction to further make the measured flow value close to the true value.

Q′ _m =Y _i ×Q _m (6)

Substitute the calculated secondary correction coefficient Z _i into formula (8), and calculate the secondary corrected instantaneous flow rate Q″ _m :

Q″ _m =Z _i ×Q′ _m (8)

Finally, the error value between the second corrected instantaneous flow rate Q″ _m and the standard instantaneous flow rate Q _S is calculated.

Table 1 is the experimental data obtained by the method of the present invention, and Table 2 is the experimental data obtained by using the traditional method, and the errors of the two methods meet the requirements of the secondary accuracy of the ultrasonic water meter. However, using the traditional method, the error correction of one flow point will affect the error of the adjacent flow point. After the correction, the error of the surrounding flow points needs to be verified. When the flow error exceeds the accuracy requirement, the correction coefficient needs to be repeatedly confirmed and experiments are repeated. Comparing the two methods, the traditional method has poor error repeatability at small flow rates, and the minimum flow rate is 0.01m ³ /h. Using the method of the present invention, the gap between the instantaneous flow rate Q″ _m after the secondary correction 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 0.0063m ³ /h.

Table 1 Experimental data based on the Reynolds number error correction method at the pipe inlet

Table 2 Experimental data of traditional error correction method

In the actual flow calibration process, it is not necessary to calculate all the flow correction coefficients and secondary correction coefficients in the range, but to take a calibration flow point Q _iuse ( It can be selected between 30% and 70% of the flow range), calculate its flow correction coefficient Y _iuse and secondary flow correction coefficient Z _iuse , and substitute the flow point _Yi and Z _iuse into formula (6) and formula ( 8) As the only value of the correction coefficient in the flow range.

Claims (5)

1. An ultrasonic water meter flow error correction method based on a reynolds number of a pipeline inlet is characterized by comprising the following steps:

the method comprises the following steps: setting the flow point in the range of the ultrasonic water meter to be measured by an upper computer of the water flow standard calibrating device, and collecting the standard instantaneous flow Q of the standard meter under different flow points _S And the instantaneous flow Q of the ultrasonic water meter to be measured _m Calculating to obtain a reynolds number of a pipeline inlet and a flow correction coefficient according to the time difference value measured by the ultrasonic water meter to be measured;

step two: establishing a plurality of different flow intervals based on the data acquired and calculated in the step one, and fitting to obtain a flow correction coefficient Y of each flow interval _i A modified model of the Reynolds number of the pipeline inlet;

step three: substituting the Reynolds number of the pipeline inlet of the calibration flow point in each flow interval into the correction model in the step two to obtain a flow correction coefficient Y corresponding to each flow interval _i And calculating the corrected instantaneous flow Q 'of the ultrasonic water meter to be measured according to the formula (6)' _m ：

Q′ _m ＝Y _i ×Q _m (6)

Then, a quadratic correction coefficient Z is calculated according to the formula (7) _i ：

The calculated quadratic correction coefficient Z _i Substituting into formula (8), calculating to obtain secondary corrected instantaneous flow Q ″) _m ：

Q″ _m ＝Z _i ×Q′ _m (8)

Step four: calculating the secondary corrected instantaneous flow Q _m And standard instantaneous flow rate Q _S To an error value therebetween.

2. The ultrasonic water meter flow error correction method based on the reynolds number of the inlet of the pipeline as claimed in claim 1, wherein:

in the second step, each flow interval comprises 30% of flow points of adjacent intervals.

3. The ultrasonic water meter flow error correction method based on the reynolds number of the inlet of the pipeline as claimed in claim 1, wherein:

and in each flow interval in the third step, the flow points with larger error values and relatively concentrated at the positions of 30-70% are used as calibration flow points to calculate a flow correction coefficient for calibrating the flow in the interval.

4. The ultrasonic water meter flow error correction method based on the reynolds number of the inlet of the pipeline as claimed in claim 1, wherein:

in the first step, the time difference value measured by the ultrasonic water meter to be measured is the average time difference value measured by the ultrasonic water meter to be measured for many times.

5. The ultrasonic water meter flow error correction method based on the reynolds number of the inlet of the pipeline as claimed in claim 1, wherein:

in the second step, the flow point Q of the ultrasonic water meter to be measured is set according to the upper computer _Ⅰ 、Q _Ⅱ 、Q _Ⅲ 、Q _Ⅳ 、Q _Ⅴ .., establishing Q _Ⅰ ～Q _Ⅱ ,Q _Ⅱ ～Q _Ⅲ ,Q _Ⅲ ～Q _Ⅳ ,Q _Ⅳ ～Q _Ⅴ ... different flow intervals.

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