A production calibration method for electromagnetic flowmeters that can be used for partially full pipes

Abstract

A production calibration method for electromagnetic flowmeters with non-full pipes is provided. Assuming that the liquid level is calibrated at n points from low to high, the first calibrated point is set as the instrument coefficient k1 with a liquid level fullness of H1; the second calibrated point is set as the instrument coefficient k2 with a liquid level fullness of H2; and so on, the nth point is calibrated as the liquid level fullness H n The instrument factor k n ; where n is a natural integer, H n , k n All of them are specific values ​​of real flow calibration; the last calibration point is a full pipe, that is, the calibration method of the instrument coefficient k when the pipe is full is adopted to achieve measurement when the pipe is full. According to the theory that the instrument coefficient k changes with the liquid level h in the non-full pipe state and different liquid levels correspond to unique k values, the present invention performs real flow calibration and segmented fitting on the k value at each liquid point, while reducing the production calibration cost, and achieving high-precision measurement in full and non-full pipe states.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic flow calibration, and in particular relates to a production calibration method for an electromagnetic flow meter that can be used for a non-full pipe. Background Art

[0002] As the pace of environmental governance and protection in my country continues to accelerate, the demand for effective measurement of sewage discharge is also increasing. Municipal drainage pipes are usually not full, and they will be full in a certain period of time. Sewage is often mixed with a large amount of dead branches, rotten leaves, domestic garbage and other debris. Commonly used ultrasonic and Doppler flow meters need to be fixed at the bottom of the pipe, which is easy to be loaded with garbage, causing inaccurate data and pipe blockage. The electromagnetic flow meter has no protrusions on the inner wall, no pressure loss, high measurement accuracy and good stability, and is the most suitable flow meter for long-term monitoring of municipal drainage pipes.

[0003] In traditional applications, electromagnetic flowmeters are mainly used to measure the flow rate of full pipe fluids. Under full pipe conditions, the weight function is constant at 1. According to Faraday's law of electromagnetic induction, the induced voltage signal generated by the sensor maintains a linear relationship with the average flow rate of the fluid. Therefore, the instrument factor of the sensor (i.e., the proportional coefficient between the induced voltage signal and the flow rate) remains constant, resulting in higher measurement accuracy. The flow correction method for full pipe flow is usually to perform interval correction on the flow or flow rate points.

[0004] However, in the case of non-full pipe flow, the change in the cross-sectional shape of the fluid causes the weight function to no longer remain constant, but to be a function that changes with the liquid level height. This makes the relationship between the induced voltage signal of the flowmeter and the average flow velocity complicated and no longer a simple linear relationship. The instrument coefficient of the electromagnetic flowmeter will also change accordingly. This means that at different liquid levels, the same flow rate may produce different induced voltage signals. Therefore, the calibration method applied to full pipe flow will significantly reduce its measurement accuracy under non-full pipe flow conditions, and the flow correction method for full pipe flow cannot be effectively applied to non-full pipe flow.

[0005] At present, domestic patents on non-full-pipe electromagnetic flowmeters can be roughly divided into two categories. The first type of patent uses special installation methods such as U-tubes to ensure that the flowmeter is always in a full-pipe state. However, this design scheme is prone to pipeline siltation and blockage. The second type of patent adjusts the position of the electrode and combines it with a liquid level meter to measure the liquid level, and uses the velocity area method to calculate the flow rate. Although this type of solution is innovative in structure, it is still based on an assumption that the instrument coefficient is regarded as a fixed value that is the same as when the pipe is full. Therefore, it is often difficult to achieve the expected accuracy in practical applications.

[0006] In order to meet the demand for accurate measurement of flow in full and part-full pipe conditions at the same time, it is urgent to develop a new calibration method and algorithm so that the fluid flow in part-full pipe conditions can be accurately measured and effectively corrected to ensure high-precision measurement results under different liquid level conditions. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a production calibration method for an electromagnetic flowmeter that can be used in a non-full pipe. According to the theory that the instrument coefficient k changes with the liquid level h in a non-full pipe state and different liquid levels correspond to unique k values, the present invention performs real-flow calibration and segmented fitting on the k value at each liquid point, thereby reducing the production calibration cost and achieving high-precision measurement in full and non-full pipe states.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A production calibration method for electromagnetic flowmeters that are not full of pipes, assuming that the liquid level is calibrated at n points from low to high;

[0010] Let the first calibration point be the instrument coefficient k1 with a liquid level fullness of H1; let the second calibration point be the instrument coefficient k2 with a liquid level fullness of H2; and so on, calibrate the nth point to the instrument coefficient k1 with a liquid level fullness of H1. n The instrument factor k n ; where n is a positive integer, H n , k n All of them are specific values ​​of actual flow calibration; the last calibration point is the full pipe, that is, the calibration method of the instrument coefficient k when the pipe is full is adopted to achieve the measurement when the pipe is full;

[0011] According to the calibration formula of the instrument coefficient k when the pipe is not full, real flow calibration is carried out on n-1 points in turn to obtain the specific value of the calibration coefficient k.

[0012] Preferably, when the pipe is full, the liquid level is full The calculation formula is as follows:

[0013] ;

[0014] Where h is the liquid level height in the flowmeter tube, and D is the inner diameter of the flowmeter tube.

[0015] Preferably, according to the calibration formula of the instrument coefficient k when the pipe is not full, real flow calibration is performed on n-1 points in sequence to obtain the specific value of the calibration coefficient k, wherein the calibration formula of the instrument coefficient k when the pipe is not full is:

[0016] ;

[0017] Where: Q is the instantaneous flow rate of the standard meter, U is the flow rate signal or flow rate display value of the flow meter, and A is the cross-sectional area of ​​the liquid in the tube;

[0018] Function of cross-sectional area of ​​liquid in tube as follows:

[0019] ;

[0020] Where h is the liquid level height in the flowmeter tube, and D is the inner diameter of the flowmeter tube.

[0021] When the pipe is not full, the real flow calibration is carried out by using the segmented calibration method, including the following three methods:

[0022] Method 1: When the pipe is not full, use the segmented calibration method to perform real flow calibration. The steps are as follows:

[0023] 1) Establish a kH scatter plot for the actual flow calibration point data and determine the m-segment interval with good linearity, i.e., the liquid level fullness , m is a positive integer; X i Represents the i-th H interval with better linearity.

[0024] 2) For X1~X m The calibration points of the interval are piecewise linearly fitted, and the corresponding fitting functions are g1(H)~g m (H);

[0025] 3) In the instrument factor After the function fitting is completed, by collecting the liquid level height h and flow rate signal U measured by the flow meter, the flow rate V and flow rate Q of the fluid in the pipe can be calculated according to the flow rate formula and flow rate formula v .

[0026] Preferably, the instrument factor in step 2) Expression 1 is:

[0027] ① , H

[0028] ② , H∈X i ;

[0029] ③ , H≥H n ;

[0030] Method 2: When the pipe is not full, use the segmented calibration method to perform real flow calibration. The steps are as follows:

[0031] 1) For the real flow calibration point data, the piecewise linear interpolation method divides H into n-1 adjacent point intervals, that is, the liquid level fullness , X​j =[H j ,H j+1 ), j is a positive integer, n≥2; instrument coefficient Expression 2 is as follows:

[0032] Where j is a positive integer, and j∈[1, n-1], n≥2;

[0033] 2) Instrument factor Expression 2 is:

[0034] ① , H

[0035] ② , H∈[H j ,H j+1 );

[0036] ③ , H≥H n .

[0037] 3) In the instrument factor After the function fitting is completed, by collecting the liquid level height h and flow rate signal U measured by the flow meter, the flow rate V and flow rate Q of the fluid in the pipe can be calculated according to the flow rate formula and flow rate formula v .

[0038] Method 3: When the pipe is not full, use the segmented calibration method to perform real flow calibration. The steps are as follows:

[0039] 1) For the real flow calibration point data, the cubic spline interpolation method divides H into n-1 adjacent point intervals, that is, the liquid level fullness , X r =[H r ,H r+1 ), r is a positive integer, n≥4;

[0040] For X1~X n-1 The calibration points of the interval are obtained to obtain the cubic spline interpolation functions f1(H)~f n-1 (H), preferably, the boundary conditions are natural boundary conditions,

[0041] 2) Instrument factor Expression three is:

[0042] ① , H

[0043] ② , H∈[H r ,H r+1 );

[0044] ③ , H≥H​​n .

[0045] 3) In the instrument factor After the function fitting is completed, by collecting the liquid level height h and flow rate signal U measured by the flow meter, the flow rate V and flow rate Q of the fluid in the pipe can be calculated according to the flow rate formula and flow rate formula v .

[0046] Preferably, the flow rate formula in step 3) is: ;

[0047] Where V is the average flow velocity in the tube and U is the flow velocity signal.

[0048] Preferably, the flow formula in step 3) is:

[0049] .

[0050] Preferably, the derivation process of the flow rate formula and the flow rate formula in step 3) is as follows:

[0051] In a closed circular pipe, the working conditions of water flow are usually divided into non-pressure non-full pipe flow and pressure full pipe flow. The volume flow rate is calculated using the velocity-area method, and the formula is:

[0052] (1);

[0053] In the formula, is the instantaneous flow rate, V is the average flow velocity in the tube, and A is the cross-sectional area of ​​the liquid in the flowmeter tube;

[0054] In order to measure the flow rate of a partially full pipe, the average flow velocity V of the partially full fluid in the flow meter pipe is measured by the flow velocity sensor, and the liquid height h in the flow meter pipe is measured by the liquid level sensor. The cross-sectional area A of the liquid in the pipe can be calculated according to formula (2):

[0055] (2);

[0056] In the formula, D is the inner diameter of the flow meter tube, and h is the liquid level height in the flow meter tube;

[0057] According to Faraday's law of electromagnetic induction and JA Shercliff's weight function theory, the induced voltage measured on the measuring electrode is the collection of all flow elements in the electrode section. If the magnetic field intensity on flow element i is B i , the effective length of the flow element cutting the magnetic field line is l i , the velocity of the stream element is v i , then the calculation formula (3) for measuring the induced voltage on electrodes a and b is:

[0058] (3);

[0059] From formula (3), the calculation formula (4) of the average flow velocity V can be derived:

[0060] , (4);

[0061] Define the liquid level filling degree H in the flow meter as formula (5):

[0062] , (5);

[0063] For each specific liquid level, there is a unique value of the weight function W, which is expressed as ; For each specific liquid level, there is a unique value of magnetic field strength B, which is expressed as ; then there exists a function Formula (6) is satisfied, that is, the instrument coefficient k is only related to the liquid level filling degree H:

[0064] , (6);

[0065] Substituting equations (5) and (6) into equation (4), we get the flow velocity V calculation formula for U and H measured by the sensor:

[0066] , (7);

[0067] Substituting equation (7) and equation (2) into equation (1) yields the flow rate of U and h measured by the sensor: Calculation formula:

[0068] , (8).

[0069] The invention discloses a production calibration system of an electromagnetic flowmeter which can be used for a partially full pipe, and adopts a production calibration method of an electromagnetic flowmeter which can be used for a partially full pipe.

[0070] The present invention can achieve the following beneficial effects:

[0071] (1) High-precision measurement: By calibrating the liquid level fullness, it can be applied to high-precision measurement in both partially full and fully filled pipe states, meeting the needs of a variety of practical application scenarios.

[0072] (2) Cost optimization: The segmented calibration scheme reduces the number of calibrations by analyzing key liquid point locations, effectively reducing calibration and production costs.

[0073] (3) Wide applicability: The requirements for the flow rate electrode structure and position are not high, and existing products can be directly modified, which improves applicability.

[0074] (4) Clean and environmentally friendly: There is no pressure loss, and the metering accuracy is not affected by the physical properties of the fluid, which is particularly suitable for sewage metering.

[0075] (5) Reduced maintenance: There are no protrusions on the inner wall, which reduces pipe blockage and instrument maintenance problems.

[0076] (6) Promote environmental monitoring: Adapt to the needs of environmental governance and provide an effective tool for pollutant emission monitoring.

[0077] (7) Versatility: Not limited to municipal drainage, but also applicable to industrial wastewater treatment and other flow measurement scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0079] Figure 1 The curve of the change of the instrument coefficient of the flow meter 1 with the liquid level filling degree H under the experimental verification of the present invention;

[0080] Figure 2 The curve of the change of the instrument coefficient of the flow meter 2 with the liquid level filling degree H under the experimental verification of the present invention;

[0081] Figure 3 It is a flow error line graph in Example 1 of the present invention;

[0082] Figure 4 This is a line graph of flow error in Example 2 of the present invention. DETAILED DESCRIPTION

[0083] The preferred solution is Figures 1 to 4 As shown, a production calibration method for electromagnetic flowmeters that can be used for non-full pipes is

[0084] 1. Assume that the liquid level is calibrated at n points from low to high;

[0085] 2. Let the first calibration point be the instrument coefficient k1 with a liquid level fullness of H1; let the second calibration point be the instrument coefficient k2 with a liquid level fullness of H2; and so on, calibrate the nth point to the instrument coefficient k1 with a liquid level fullness of H2. n The instrument factor k n ; where n is a positive integer, H n , k n All of them are specific values ​​for actual flow calibration; the last calibration point is a full pipe, that is, the calibration method of the instrument coefficient k at full pipe flow is adopted to achieve measurement when the pipe is full.

[0086] Among them, the liquid level is full The calculation formula is as follows:

[0087] ;

[0088] Where h is the liquid level height in the flowmeter tube, and D is the inner diameter of the flowmeter tube.

[0089] 3. According to the calibration formula of the instrument coefficient k when the pipe is not full, perform real flow calibration on n points in turn to obtain the specific value of the calibration coefficient k. The calibration formula of the instrument coefficient k when the pipe is not full is:

[0090] ;

[0091] In the formula: Q is the instantaneous flow rate of the standard meter, U is the flow meter flow rate signal or flow rate display value, and A is the cross-sectional area of ​​the liquid in the pipe.

[0092] Function of cross-sectional area of ​​liquid in tube as follows:

[0093]

[0094] The method of segment calibration is as follows:

[0095] 1) When performing segmented calibration, a kH scatter plot is established for the actual flow calibration point data to determine the m-segment interval with good linearity, i.e., the liquid level fullness. , m is a positive integer;

[0096] 2) For X1~X m The calibration points of the interval are piecewise linearly fitted, and the corresponding fitting functions are g1(H)~g m (H), instrument factor Expression 1 is as follows:

[0097] ① , H

[0098] ② , H∈X i ;

[0099] ③ , H≥H n ;

[0100] 3) In the instrument factor After the function fitting is completed, by collecting the liquid level height h and flow rate signal U measured by the flow meter, the flow rate V and flow rate Q of the fluid in the pipe can be calculated according to the flow rate formula and flow rate formula v :in:

[0101] Flow rate formula:

[0102] Flow formula:

[0103]

[0104] ​As an alternative solution, in actual production, prototypes of the same model and specification produced by the same manufacturer maintain basic consistency in geometric dimensions and instrument parameters. Although there are certain differences in the values ​​of their instrument coefficients, they have similar change patterns. Therefore, real-flow calibration can be performed only at key liquid level heights to reduce the number of calibration points.

[0105] In order to further reduce the number of calibration points and calibration costs, the instrument coefficient in step 3) can be Expression 1 is replaced by: Simplified instrument coefficient based on piecewise linear interpolation Expression 2:

[0106] For the real flow calibration point data, the piecewise linear interpolation method divides H into n-1 adjacent point intervals, that is, the liquid level fullness , X j =[H j ,H j+1 ), j is a positive integer, n≥2. Instrument coefficient Expression 2 is as follows:

[0107] ① , H

[0108] ② , H∈[H j ,H j+1 );

[0109] ③ , H≥H n .

[0110] As an alternative solution, in order to improve the smoothness and continuity of the instrument factor calibration curve and ensure the smooth transition of the instrument factor in different intervals, the instrument factor in step 3) can be Expression 1 is replaced by the formula: Smooth and continuous instrument coefficient based on cubic spline interpolation Expression three:

[0111] For the real flow calibration point data, the cubic spline interpolation method divides H into n-1 adjacent point intervals, that is, the liquid level fullness , X r =[H r ,H r+1 ), r is a positive integer, n≥4.

[0112] For X1~X n-1 The calibration points of the interval are obtained to obtain the cubic spline interpolation functions f1(H)~f n-1 (H), preferably, the boundary conditions are natural boundary conditions, and the instrument coefficient Expression three is as follows:

[0113] ①​ , H

[0114] ② , H∈[H r ,H r+1 );

[0115] ③ , H≥H n ;

[0116] The segmented calibration method provided by the present invention has a formula derivation process as follows:

[0117] In a closed circular pipe, the working conditions of water flow are usually divided into non-pressure non-full pipe flow and pressure full pipe flow. The velocity-area method is usually used to calculate the instantaneous flow rate. The flow meter must be able to measure both the fluid velocity and the liquid level at the same time. The formula is:

[0118] (1);

[0119] In the formula, is the instantaneous flow rate, V is the average flow velocity in the tube, and A is the cross-sectional area of ​​the liquid in the flowmeter tube.

[0120] In order to measure the flow rate of a partially full pipe, the average flow velocity V of the partially full fluid in the flow meter pipe is measured by the flow velocity sensor, and the liquid height h in the flow meter pipe is measured by the liquid level sensor. The cross-sectional area A of the liquid in the pipe can be calculated according to formula (2):

[0121] (2);

[0122] Where D is the inner diameter of the flow meter tube, and h is the liquid level height in the flow meter tube.

[0123] The working principle of the electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. The excitation coil generates a working magnetic field with a magnetic flux density of B. When the conductive fluid passes through a pipe equipped with a pair of measuring electrodes with a spacing of L at a flow rate V, the pair of electrodes will generate an induced electromotive force E=BLV that is perpendicular to both the magnetic field direction and the liquid flow direction. According to the JA Shercliff weight function theory, the induced voltage measured on the measuring electrode is the collection of all flow elements in the electrode section. The weight function W characterizes the contribution of the electromotive force generated at each point in the effective area to the flow velocity signal between the electrodes, reflecting the attenuation coefficient caused by the geometric position. If the magnetic field strength on flow element i is B i , the effective length of the flow element cutting the magnetic field line is l i , the velocity of the stream element is v i , then the induced voltage on the measuring electrodes a and b is as shown in formula (3).

[0124] (3);​

[0125] From formula (3), the calculation formula (4) of the average flow velocity V can be derived:

[0126] , (4)

[0127] Define the liquid level filling degree H in the flow meter as formula (5):

[0128] , (5)

[0129] The weight function W is a spatial function related to many factors such as the measurement pipe size, geometry (including electrodes), and the liquid filling degree in the pipe. When the hardware parameters of the sensor remain unchanged, the weight function W is only related to the liquid level. Some scholars have calculated the weight function values ​​under different filling degrees through finite element numerical analysis methods, proving that the weight function W will change with the liquid level. Therefore, the functional relationship between the weight function W and the liquid filling degree H can be expressed as .

[0130] The magnetic field generated by the excitation coil is proportional to the excitation current and the magnetic permeability of the medium. The magnetic permeabilities of different media will affect the propagation of the magnetic field. The magnetic permeabilities of air and water are different. When the tube is not full, the magnetic field distribution will pass through the air gap at the top and the water at the bottom. The size of the air gap area changes with the liquid level in the tube, resulting in the magnetic field distribution not being constant, but changing with the liquid level. Therefore, the functional relationship between the magnetic field intensity B and the liquid level fullness H can be expressed as .

[0131] In summary, there is a functional relationship Formula (6) is satisfied, that is, the instrument coefficient k is only related to the liquid level filling degree H. In practical applications, due to the influence of various factors such as the manufacturing process, it is impossible to obtain a completely uniform magnetic field, and data such as the weight function W and the magnetic field strength B cannot be accurately obtained. The actual flow rate is usually used for calibration to determine the approximate value of the instrument coefficient k.

[0132] , (6)

[0133] Substituting equations (5) and (6) into equation (4), we get the flow velocity V calculation formula for U and H measured by the sensor:

[0134] , (7)

[0135] Substituting equation (7) and equation (2) into equation (1) yields the flow rate of U and h measured by the sensor: Calculation formula:

[0136] , (8)

[0137] Experimental verification

[0138] In this study, two electromagnetic flowmeters from different manufacturers were used to carry out experimental verification. The verification content is that each liquid level fullness H has a unique corresponding instrument coefficient k. Due to the non-full pipe state, it is difficult to control the liquid level height in the calibration experiment to conduct multiple experiments on a certain liquid level value. Therefore, the experiment is carried out in a high to low manner according to a certain flow difference. The standard meter flow of the full pipe section is converted by collecting the number of pulse outputs within 1 minute. The data is collected 2-3 times at each point to calculate the average value, and the experimental process is repeated many times to verify the repeatability.

[0139] In flow meter 1, there are 3 pairs of flow rate electrodes, which are respectively distributed at 30%, 20%, and 10% of the flow meter inner diameter height. The inner diameter of the flow meter pipe is 376 mm, and the experimental flow range is 35-365 m 3 / h, the water quality is sewage mixed with mud, and the experiment was carried out in the flow laboratory of Chongqing Three Gorges Ecological Environment Technology Innovation Center Co., Ltd. During the experiment, the liquid level fluctuated greatly due to the large deviation between the front and rear straight pipe sections and the inner diameter of the flow meter, so the front and rear straight pipe sections were replaced in February 2024. By changing the standard flow rate and different slope values ​​i (in percentage %) of the pipeline, and measuring multiple times on different dates, the obtained instrument coefficient changes with the liquid level filling degree H as follows Figure 1 , the instrument coefficients are not normalized.

[0140] In flow meter 2, the velocity electrodes are located at 10% of the flow meter inner diameter height. The inner diameter of the flow meter pipe is 300 mm, and the flow range is 14-314 m 3 / h, the water quality is clean water, and the experiment was carried out on the non-full pipe real flow calibration device of Qingtian Weiye Intelligent Instrument Technology Park. At the beginning of the experiment, the instrument coefficient was corrected at the point of H=76% to make the apparent flow error of this point 0. By changing the standard flow, the experimental process was repeated twice to verify the repeatability. The measured instrument coefficient changes with the liquid level filling degree H as follows Figure 2 .

[0141] The experimental data of flow meter 2 are shown in Table 1. The standard flow rate Q (m 3 / h) is measured by a standard meter for full pipe section; the flow rate U (m / s) is the flow rate data measured by the sensor; the liquid level height h is measured by the ultrasonic level meter built into the flow meter, and the liquid level proportion H is obtained by converting H = h / D; the cross-sectional area A (m 2 ) is calculated by the cross-sectional area formula; the instrument factor k is calculated by k=Q / (U*A).

[0142]

[0143] Table 1

[0144] Through the experimental verification results of two electromagnetic flowmeters from different manufacturers, the following conclusions can be drawn:

[0145] A. In the non-full pipe state, the instrument coefficient k changes with the liquid level fullness H and has a unique value. The two are in a nonlinear relationship.

[0146] B. The instrument factor k has nothing to do with the slope of the pipeline;

[0147] C. The instrument coefficients of flow rate electrodes at different positions are not the same. When H does not exceed 50%, the higher the position of the flow rate electrode, the smaller the value of the instrument coefficient.

[0148] D. The changing trend of the instrument coefficient k of flow meters with different parameters as the liquid level filling degree H is not consistent.

[0149] Embodiment 1:

[0150] By analyzing Figure 2 From the kH scatter plot, it is found that K has a good linear relationship in the two intervals of H∈(13.67%, 22.5%) and (22.5%, 77.17%), so it is divided into two corresponding intervals for linear fitting, and the fitting formulas are obtained as g1=1.207*H + 0.797 and g2=-0.1115*H+1.0848, respectively. The expression of the instrument factor k(H) is as follows:

[0151] k(H)=0.95505,H<13.67%k(H)=1.207*H + 0.797,H∈[13.67%,22.5%)k(H)=-0.1115*H + 1.0848,H∈[22.5%,77.17%)k(H)=0.98749H≥77.17%Substitute the above k(H) expression into the flow rate Calculation formula, the flow error between the calculated flow and the standard meter is 1; the flow error between the calculated sample machine measured flow and the standard meter is 0 (only at 76% liquid level, the meter coefficient is corrected to make the meter display flow error 0), by Figure 3 It can be seen that this calibration method can effectively improve the measurement accuracy under the non-full pipe state.

[0152] Embodiment 2:

[0153] By analyzing Figure 2 From the kH scatter plot in the figure, it can be considered that the key points of the flow meter are H∈{13.67%, 22.5%, 77.17%}, a total of three points, and the products of the same batch have similar variation patterns. In order to further reduce the number of calibration points and calibration costs, the instrument coefficient in step 3) is Expression 1 is replaced by: Simplified instrument coefficient based on piecewise linear interpolation Expression 2, its expression is as follows:

[0154] a、k(H)=0.95505,H<13.67%

[0155] b. k(H)=0.95505 + (H-0.1367)*1.2016 ,H∈[13.67%, 22.5%)

[0156] c, k(H)=1.0612 - (H-0.225)*0.1348 ,H∈[22.5%,77.17%)

[0157] a, k(H)=0.98749, H≥77.17%

[0158] Substituting the above k(H) expression into the flow Calculation formula, calculate the flow error between it and the standard table as error 2, compared with the above error 1 and error 0, by Figure 4 It can be seen that this calibration method can better improve the measurement accuracy in the non-full pipe state with a smaller number of calibration points.

[0159] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A production calibration method for electromagnetic flowmeters that can be used for partially full pipes, characterized in that: Assume that the liquid level is calibrated at n points from low to high; Let the first calibration point be the instrument coefficient k1 with a liquid level fullness of H1; let the second calibration point be the instrument coefficient k2 with a liquid level fullness of H2; and so on, calibrate the nth point to the instrument coefficient k1 with a liquid level fullness of H1. n The instrument factor k n ; where n is a positive integer, H n , k n All of them are specific values ​​of actual flow calibration; the last calibration point is the full pipe, that is, the calibration method of the instrument coefficient k when the pipe is full is adopted to achieve the measurement when the pipe is full; According to the calibration formula of the instrument coefficient k when the pipe is not full, perform real flow calibration at n-1 points in turn to obtain the specific value of the calibration coefficient k; According to the calibration formula of the instrument coefficient k when the pipe is not full, the actual flow calibration is carried out at n-1 points in turn to obtain the specific value of the calibration coefficient k. The calibration formula of the instrument coefficient k when the pipe is not full is: ； Where: Q is the instantaneous flow rate of the standard meter, U is the flow rate signal or flow rate display value of the flow meter, and A is the cross-sectional area of ​​the liquid in the tube; Function of cross-sectional area of ​​liquid in tube as follows: ； In the formula, h is the liquid level height in the flow meter tube, and D is the inner diameter of the flow meter tube; When the pipe is not full, the real flow calibration is performed by segmented calibration method. The steps are as follows: 1) Establish a kH scatter plot for the actual flow calibration point data to determine the m-segment H interval with good linearity, that is, the liquid level fullness , m is a positive integer, where X i represents the i-th H interval with better linearity; 2) For X1~X m The calibration points of the interval are piecewise linearly fitted, and the corresponding fitting functions are g1(H)~g m (H); 3) In the instrument factor After the function fitting is completed, by collecting the liquid level height h and flow rate signal U measured by the flow meter, the flow rate V and flow rate Q of the fluid in the pipe can be calculated according to the flow rate formula and flow rate formula v ; The instrument factor in step 2) Expression 1 is: 1 , H<H1; ② , H∈X i ; ③ , H≥H n ; When the pipe is not full, the real flow calibration is performed by segmented calibration method. The steps are as follows: 1) For the real flow calibration point data, the piecewise linear interpolation method divides H into n-1 adjacent point intervals, that is, the liquid level fullness , X j =[H j ,H j+1 ), j is a positive integer, n≥2; instrument coefficient Expression 2 is as follows: Where j is a positive integer, and j∈[1, n-1], n≥2; 2) Instrument factor Expression 2 is: 1 ,H,H1; ② ,H∈[H j ,H j+1 ); ③ ,H≥H n ; 3) In the instrument factor After the function fitting is completed, by collecting the liquid level height h and flow rate signal U measured by the flow meter, the flow rate V and flow rate Q of the fluid in the pipe can be calculated according to the flow rate formula and flow rate formula v .

2. The method for producing and calibrating an electromagnetic flowmeter that can be used for a partially full pipe according to claim 1, characterized in that: When the pipe is full, the liquid level is full The calculation formula is as follows: ； Where h is the liquid level height in the flowmeter tube, and D is the inner diameter of the flowmeter tube.

3. The method for producing and calibrating an electromagnetic flowmeter that can be used for a partially full pipe according to claim 1, characterized in that: When the pipe is not full, the real flow calibration is performed by segmented calibration method. The steps are as follows: 1) For the real flow calibration point data, the cubic spline interpolation method divides H into n-1 adjacent point intervals, that is, the liquid level fullness , X r =[H r ,H r+1 ), r is a positive integer, n≥4; For X1~X n-1 The calibration points of the interval are obtained to obtain the cubic spline interpolation functions f1(H)~f n-1 (H), the boundary conditions are natural boundary conditions, 2) Instrument factor Expression three is: 1 , H<H1; ② , H∈[H r ,H r+1 ); ③ , H≥H n ; 3) In the instrument factor After the function fitting is completed, by collecting the liquid level height h and flow rate signal U measured by the flow meter, the flow rate V and flow rate Q of the fluid in the pipe can be calculated according to the flow rate formula and flow rate formula v .

4. The method for producing and calibrating an electromagnetic flowmeter that can be used for a partially full pipe according to claim 3, characterized in that: The flow rate formula in step 3) is: ; Where V is the average flow velocity in the tube and U is the flow velocity signal.

5. The production calibration method of an electromagnetic flowmeter applicable to a partially full pipe according to claim 4, characterized in that: The flow formula in step 3) is: 。 6. The production calibration method of an electromagnetic flowmeter applicable to a partially full pipe according to claim 5, characterized in that: The derivation process of the flow rate formula and flow rate formula in step 3) is as follows: In a closed circular pipe, the working conditions of water flow are usually divided into non-pressure non-full pipe flow and pressure full pipe flow. The volume flow rate is calculated using the velocity-area method, and the formula is: （1）； In the formula, is the instantaneous flow rate, V is the average flow velocity in the tube, and A is the cross-sectional area of ​​the liquid in the flowmeter tube; In order to measure the flow rate of a partially full pipe, the average flow velocity V of the partially full fluid in the flow meter pipe is measured by the flow velocity sensor, and the liquid height h in the flow meter pipe is measured by the liquid level sensor. The cross-sectional area A of the liquid in the pipe can be calculated according to formula (2): （2）； In the formula, D is the inner diameter of the flow meter tube, and h is the liquid level height in the flow meter tube; According to Faraday's law of electromagnetic induction and JA Shercliff's weight function theory, the induced voltage measured on the measuring electrode is the collection of all flow elements in the electrode section. If the magnetic field intensity on flow element i is B i , the effective length of the flow element cutting the magnetic field line is l i , the velocity of the stream element is v i , then the calculation formula (3) for measuring the induced voltage on electrodes a and b is: （3）； From formula (3), the calculation formula (4) of the average flow velocity V can be derived: ，（4）； Define the liquid level filling degree H in the flow meter as formula (5): ，（5）； For each specific liquid level, there is a unique value of the weight function W, which is expressed as ; For each specific liquid level, there is a unique value of magnetic field strength B, which is expressed as ; then there exists a function Formula (6) is satisfied, that is, the instrument coefficient k is only related to the liquid level filling degree H: ，（6）； Substituting equations (5) and (6) into equation (4), we get the flow velocity V calculation formula for U and H measured by the sensor: ，（7）； Substituting equation (7) and equation (2) into equation (1) yields the flow rate of U and h measured by the sensor: Calculation formula: ，(8)。 7. A production calibration system for electromagnetic flowmeters that can be used for partially full pipes, characterized in that: A production calibration method for an electromagnetic flowmeter that can be used for a partially full pipe as described in claim 6 is adopted.

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