CN118670485B

CN118670485B - Electromagnetic flowmeter production calibration method capable of being used for non-full pipe

Info

Publication number: CN118670485B
Application number: CN202410848689.7A
Authority: CN
Inventors: 贾改革; 陈彦霖; 张俊; 焦洋; 贾伯阳; 曾雷; 张超; 李程; 王超
Original assignee: Yangtze Ecology And Environment Co ltd; Chongqing Three Gorges Ecological Environment Technology Innovation Center Co ltd
Current assignee: Yangtze Ecology And Environment Co ltd; Chongqing Three Gorges Ecological Environment Technology Innovation Center Co ltd
Priority date: 2024-06-27
Filing date: 2024-06-27
Publication date: 2025-01-14
Anticipated expiration: 2044-06-27
Also published as: CN118670485A

Abstract

A production calibration method for an electromagnetic flowmeter that can be used for a non-full pipe, assuming that n points are calibrated from low to high liquid levels; the first calibrated point is set as the instrument coefficient _k1 when the liquid level is _H1 ; the second calibrated point is set as the instrument coefficient _k2 when the liquid level is _H2 ; and so on, the nth point is calibrated as the instrument coefficient _kn when the liquid level is _Hn ; wherein n is a natural integer, and _Hn and _kn are both 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 values at each liquid point, thereby reducing the production calibration cost and achieving high-precision measurement in the full pipe and non-full pipe states.

Description

Electromagnetic flowmeter production calibration method capable of being used for non-full pipe

Technical Field

The invention belongs to the technical field of electromagnetic flow calibration, and particularly relates to a production calibration method of an electromagnetic flowmeter capable of being used for a non-full pipe.

Background

Along with the continuous acceleration of environmental management and protection in China, the requirement for effectively metering sewage discharge is also increasing. Municipal drainage pipeline is mainly in a non-full pipe state, a full pipe state can occur in a specific time period, a large amount of sundries such as dead branches and rotten leaves, household garbage and the like are often mixed in sewage, commonly used ultrasonic wave, doppler and other flowmeters need to be fixed at the bottom of the pipeline, the data inaccuracy and pipeline blockage are caused by easily mounting garbage, no protrusion exists on the inner wall of the electromagnetic flowmeter, no pressure loss exists, the metering precision is high, the stability is good, and the flowmeter is most suitable for long-term monitoring of the municipal drainage pipeline.

In conventional applications, electromagnetic flowmeters are used primarily to measure the flow of full pipe fluid. Under the condition of full pipe, the weight function is constant to be 1, and the linear relation between the induced voltage signal generated by the sensor and the average flow velocity of the fluid is maintained according to Faraday electromagnetic induction law. Therefore, the meter coefficient of the sensor (i.e., the ratio between the induced voltage signal and the flow rate) is kept constant, so that the measurement accuracy is high. The flow correction method for the full pipe flow generally performs interval correction for the flow or flow velocity point.

However, in the case of non-full pipe flow, the variation of the fluid cross-sectional shape results in the weighting function no longer remaining constant, but rather a function that varies with the level height, which complicates the relationship between the induced voltage signal of the flowmeter and the average flow rate, and is no longer a simple linear relationship, with the consequent variation of the meter coefficient of the electromagnetic flowmeter. This means that at different liquid levels, the same flow rate may produce different induced voltage signals. Therefore, the measurement accuracy of the calibration method applied to the full pipe flow is obviously reduced under the condition of non-full pipe flow, and the flow correction method applied to the full pipe flow cannot be effectively applied to the non-full pipe flow.

Current domestic patents on non-full-pipe electromagnetic flowmeters fall into two general categories. The first patent uses special mounting means such as a U-tube to ensure that the flowmeter is always in a full tube state, however, this design is prone to pipe fouling and plugging problems. The second type of patent uses the flow rate area method to calculate the flow rate by adjusting the position of the electrode and combining the liquid level measurement with the liquid level meter, but the scheme is still based on an assumption that the instrument coefficient is regarded as the same fixed value as that of the full pipe, so that the expected accuracy is often difficult to achieve in practical application.

In order to meet the requirement of accurately measuring the flow in the full pipe and the non-full pipe states at the same time, development of a novel calibration method and algorithm is needed, so that the fluid flow in the non-full pipe condition can be accurately measured and effectively corrected, and high-precision measurement results can be achieved under different liquid level conditions.

Disclosure of Invention

The invention aims to solve the technical problem of providing a production calibration method for an electromagnetic flowmeter for a non-full pipe, according to the theory that the instrument coefficient k changes along with the liquid level h in the non-full pipe state and the unique k values corresponding to different liquid levels, the invention realizes high-precision measurement in the full pipe and the non-full pipe state while reducing the production calibration cost by carrying out real-flow calibration and sectional fitting on the k values at each liquid level point.

In order to solve the technical problems, the invention adopts the following technical scheme:

the production calibration method of the electromagnetic flowmeter capable of being used for the non-full pipe assumes that the liquid level is calibrated by n points altogether from low to high;

The 1st point of the calibration is made to be the instrument coefficient k ₁ with the liquid level fullness degree of H ₁, the 2nd point of the calibration is made to be the instrument coefficient k ₂ with the liquid level fullness degree of H ₂, and the n-th point of the calibration is made to be the instrument coefficient k _n when the liquid level fullness degree of H _n, wherein n is a positive integer, H _n、k_n is a specific value of real-flow calibration, and the last 1 calibration point is a full pipe, namely, the calibration mode of the instrument coefficient k when the full pipe flow is adopted, so that the measurement when the full pipe is full is realized;

And (3) sequentially carrying out real-flow calibration on n-1 point positions according to a calibration formula of the instrument coefficient k when the pipe is not full, and obtaining a specific numerical value of the calibration coefficient k.

Preferably, the liquid level is full at full tube flowThe calculation formula is as follows:

;

wherein h is the height of the liquid level in the flowmeter tube, and D is the inner diameter of the flowmeter tube.

Preferably, real-flow calibration is sequentially carried out on n-1 points according to a calibration formula of the instrument coefficient k when the pipe is not full, and a specific numerical value of the calibration coefficient k is obtained, wherein the calibration formula of the instrument coefficient k when the pipe is not full is obtained:

;

Wherein Q is the instantaneous flow of a standard meter, U is the flow velocity signal or flow velocity display value of a flowmeter, A is the sectional area of liquid in the pipe;

Function of cross-sectional area of liquid in pipe The following are provided:

;

The real-flow calibration is carried out by adopting a sectional calibration method when the pipe is not full, and the method comprises the following three modes:

mode one: and when the pipe is not full, the real-flow calibration is carried out by adopting a sectional calibration method, and the steps are as follows:

1) Establishing a k-H scatter diagram aiming at real-flow calibration point data, and determining m sections of intervals with better linearity, namely liquid level fullness M is a positive integer, wherein X _i represents an H interval with good ith linearity.

2) Performing piecewise linear fitting on the calibration points of the X ₁~X_m section respectively, wherein the corresponding fitting functions are g ₁(H)~g_m (H);

3) In the instrument coefficient After the function fitting is completed, the fluid flow velocity V and the fluid flow Q _v in the pipe can be calculated according to a flow velocity formula and a flow formula by collecting the liquid level height h and the flow velocity signal U in the pipe measured by the flowmeter.

Preferably, the meter factor in step 2)Expression one is:

①, H<H₁;

②, H∈X_i;

③, H≥H_n;

and in the second mode, real-flow calibration is carried out by adopting a sectional calibration method when the pipe is not full, and the method comprises the following steps:

1) Aiming at real-flow calibration point position data, the piecewise linear interpolation method divides H into n-1 adjacent point position intervals, namely liquid level fullness X _j=[H_j,H_j+1), j is a positive integer, n is more than or equal to 2, and the instrument coefficientExpression two is as follows:

Wherein j is a positive integer, and j is [1, n-1], n is more than or equal to 2;

2) Instrument coefficient The expression two is:

①,H<H₁;

②,H∈[H_j,H_j+1);

③,H≥H_n。

And in a third mode, real-flow calibration is carried out by adopting a sectional calibration method when the pipe is not full, and the method comprises the following steps:

1) Aiming at real-flow calibration point position data, the cubic spline interpolation method divides H into n-1 adjacent point position intervals, namely liquid level fullness X _r=[H_r,H_r+1), r is a positive integer, n is more than or equal to 4;

respectively for the calibration points in the X ₁~X_n-1 section, obtaining the cubic spline interpolation function f ₁(H)~f_n-1 (H), preferably, the boundary condition is a natural boundary condition,

2) Instrument coefficientExpression three is:

①, H<H₁;

②, H∈[H_r,H_r+1);

③, H≥H_n。

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

wherein V is the average flow velocity in the pipe, and U is the flow velocity signal.

Preferably, the flow formula in step 3) is:

。

Preferably, the flow rate formula and the flow rate formula of step 3) are derived as follows:

in a closed circular pipeline, the working conditions of water flow are generally divided into pressureless non-full pipe flow and pressured full pipe flow, and the volume flow is calculated by adopting a flow velocity-area method, wherein the formula is as follows:

(1);

In the formula, V is the average flow velocity in the tube, A is the sectional area of the liquid in the tube of the flowmeter;

in order to realize the measurement of the flow of the non-full pipe, the average flow velocity V of the fluid in the flow meter pipe is measured by a flow velocity sensor, the liquid height h in the flow meter pipe is measured by a liquid level sensor, and the liquid sectional area A in the pipe can be calculated according to the formula (2):

(2);

Wherein D is the inner diameter of the flowmeter tube, and h is the liquid level height in the flowmeter tube;

According to Faraday's law of electromagnetic induction and J.A.Stercliff weight function theory, the induced voltage measured on the measuring electrode is a set of all flow elements in the section of the electrode, if the magnetic field intensity on the flow element i is set to be B _i, the effective length of the flow element cutting magnetic line is l _i, the flow element speed is v _i, the calculation formula (3) of the induced voltage on the measuring electrodes a and B is as follows:

(3);

from equation (3), the calculation equation (4) for the average flow velocity V can be derived:

,(4);

Defining a liquid level fullness in the flowmeter, H, formula (5):

,(5);

For each particular level, there is a uniquely determined value of the weighting function W, expressed as For each specific level, a uniquely determined value of the magnetic field strength B is present, expressed asThen there is a functionEquation (6) is satisfied, i.e. the instrument coefficient k is only related to the level fullness H:

,(6);

bringing equations (5) and (6) into equation (4) yields the flow velocity V calculation equation for U and H measured by the sensor:

,(7);

Bringing formulae (7) and (2) into formula (1) yields the flow rates for U and h measured by the sensor The calculation formula is as follows:

,(8)。

an electromagnetic flowmeter production calibration system capable of being used for a non-full pipe adopts an electromagnetic flowmeter production calibration method capable of being used for the non-full pipe.

The invention has the following beneficial effects:

(1) The high-precision measurement is performed by calibrating the liquid level fullness, so that the method is suitable for high-precision measurement in the states of non-full pipe and full pipe, and meets changeable practical application scenes.

(2) The cost is optimized, and the sectional calibration scheme reduces the calibration quantity and effectively reduces the calibration and production cost by analyzing the key liquid sites.

(3) The applicability is wide, the requirements on the structure and the position of the velocity electrode are not high, the existing product can be directly modified, and the applicability is improved.

(4) The device is clean and environment-friendly, has no pressure loss, has no influence on the metering precision by the physical properties of the fluid, and is particularly suitable for sewage metering.

(5) The maintenance is reduced, no protrusion exists on the inner wall, and the problems of pipeline blockage and instrument maintenance are reduced.

(6) The environmental monitoring is promoted, the environmental treatment requirement is met, and an effective tool is provided for pollutant emission monitoring.

(7) The universal use is not limited to municipal drainage, and is also suitable for industrial wastewater treatment and other flow measurement scenes.

Drawings

The invention is further illustrated by the following examples in conjunction with the accompanying drawings:

FIG. 1 is a graph showing the variation of the meter coefficient of the flowmeter 1 with the liquid level fullness H under the experimental verification of the invention;

FIG. 2 is a graph showing the variation of the meter coefficient of the flowmeter 2 with the liquid level fullness H under the experimental verification of the invention;

FIG. 3 is a flow error line graph in example 1 of the present invention;

fig. 4 is a flow error line diagram in example 2 of the present invention.

Detailed Description

Preferred embodiments as shown in fig. 1 to 4, a method for calibrating an electromagnetic flowmeter for non-full pipes,

1. N point positions are marked altogether under the assumption that the liquid level is from low to high;

2. The 1 st point of the calibration is made to be the instrument coefficient k ₁ with the liquid level fullness degree of H ₁, the 2 nd point of the calibration is made to be the instrument coefficient k ₂ with the liquid level fullness degree of H ₂, and the n-th point of the calibration is made to be the instrument coefficient k _n with the liquid level fullness degree of H _n by analogy, wherein n is a positive integer, H _n、k_n is a specific value of real-flow calibration, and the last 1 calibration point is a full pipe, namely, the calibration mode of the instrument coefficient k in full pipe flow is adopted, and metering in full pipe is realized.

Wherein the liquid level is fullThe calculation formula is as follows:

;

3. According to a calibration formula of the instrument coefficient k in the non-full pipe, real-flow calibration is sequentially carried out on n points, and a specific numerical value of the calibration coefficient k is obtained, wherein the calibration formula of the instrument coefficient k in the non-full pipe is as follows:

;

wherein Q is the instantaneous flow of a standard meter, U is the flow velocity signal or flow velocity display value of the flowmeter, and A is the sectional area of liquid in the pipe.

Function of cross-sectional area of liquid in pipeThe following are provided:

The method for segment calibration comprises the following steps:

1) When the subsection calibration is carried out, a k-H scatter diagram is established aiming at real-flow calibration point position data, and m sections of intervals with better linearity, namely liquid level fullness, are determined M is a positive integer;

2) Piecewise linear fitting is respectively carried out on the calibration points in the X ₁~X_m section, the corresponding fitting functions are g ₁(H)~g_m (H), and the instrument coefficients are respectively The expression one is as follows:

①, H<H₁;

②, H∈X_i;

③, H≥H_n;

3) In the instrument coefficient After the function fitting is completed, the flow velocity V and the flow Q _v of the fluid in the pipe can be calculated according to a flow velocity formula and a flow formula by collecting the liquid level height h and the flow velocity signal U in the pipe measured by the flowmeter, wherein:

the flow rate formula:

the flow formula:

in the actual production, the prototype models and specifications produced by the same manufacturer keep basic consistency in geometric dimension and instrument parameters, and the instrument coefficient values have certain differences but have similar change rules, so that real-flow calibration can be carried out only on the point positions with the critical liquid level height, and the number of calibration point positions is reduced.

To further reduce the number of calibration points and calibration costs, the instrument coefficients in step 3) may be usedExpression an alternative formula is a simplified piecewise linear interpolation based instrument coefficientExpression two:

Aiming at real-flow calibration point position data, the piecewise linear interpolation method divides H into n-1 adjacent point position intervals, namely liquid level fullness X _j=[H_j,H_j+1), j is a positive integer, n is not less than 2. Instrument coefficientExpression two is as follows:

①,H<H₁;

②,H∈[H_j,H_j+1);

③,H≥H_n。

Alternatively, to improve the smoothness and continuity of the calibration curve of the meter coefficients, to ensure smooth transition of the meter coefficients in different intervals, the meter coefficients in step 3) may be used Expression an alternative formula is that the instrument coefficient based on cubic spline interpolation is smooth and continuousExpression three:

Aiming at real-flow calibration point position data, the cubic spline interpolation method divides H into n-1 adjacent point position intervals, namely liquid level fullness X _r=[H_r,H_r+1), r is a positive integer, and n is not less than 4.

For the calibration points in the X ₁~X_n-1 section, the cubic spline interpolation function f ₁(H)~f_n-1 (H) is obtained, the preferred boundary condition is the natural boundary condition, the instrument coefficientExpression three is as follows:

①, H<H₁;

②, H∈[H_r,H_r+1);

③, H≥H_n;

The invention provides a segmentation calibration method, wherein the formula deducing process is as follows:

In a closed circular pipeline, the working conditions of water flow are generally divided into pressureless non-full pipe flow and pressured full pipe flow, the instantaneous flow is generally calculated by a flow rate-area method, and the flowmeter must have the capability of measuring two parameters of fluid flow rate and liquid level at the same time, wherein the formula is as follows:

(1);

In the formula, The instantaneous flow is V is the average flow velocity in the tube, and A is the cross-sectional area of the liquid in the tube of the flowmeter.

(2);

Wherein D is the inner diameter of the flowmeter tube, and h is the liquid level height in the flowmeter tube.

The operating principle of the electromagnetic flowmeter is based on faraday's law of electromagnetic induction, a working magnetic field with magnetic flux density B is generated by an exciting coil, and when a conductive fluid passes through a pipeline provided with a pair of measuring electrodes with a distance L at a flow velocity V, the pair of electrodes will generate induced electromotive force e=blv perpendicular to the magnetic field direction and the liquid flow direction at the same time. According to the J.A. Stercliff weight function theory, the induced voltage measured on the measuring electrode is the set of all flow elements in the section of the electrode, and the weight function W characterizes the contribution degree of the electromotive force generated by each point in the effective area to the flow velocity signal between the electrodes and reflects the attenuation coefficient caused by the geometric position. If the magnetic field intensity on the current element i is set as B _i, the effective length of the current element cutting magnetic line is set as l _i, the current element speed is set as v _i, and the induced voltages on the measuring electrodes a and B are shown as formula (3).

(3);

,(4)

Defining a liquid level fullness in the flowmeter, H, formula (5):

,(5)

The weighting function W is a spatial function related to various factors such as the size, geometry (including electrodes) of the measured tube segment, and the degree of fluid fullness within the tube. Under the condition that various hardware parameters of the sensor are unchanged, the weight function W is only related to the liquid level, and the weight function value under different fullness levels is calculated by the existing scholars through a finite element numerical analysis method, so that the weight function W is proved to change along with the liquid level. Thus, the functional relationship between the weight function W and the liquid level fullness H can be expressed as 。

The magnetic field generated by the exciting coil is directly proportional to exciting current and directly proportional to the magnetic permeability of the medium, and the magnetic permeability of different mediums can influence the propagation of the magnetic field. The permeability of air and water are not the same, and in a state of being not full, the magnetic field distribution can pass through an upper air gap and a lower water, wherein the size of the air gap area changes along with the change of the liquid level in the pipe, so that the magnetic field distribution is not constant, but changes along with the liquid level. Thus, the functional relationship between the magnetic field strength B and the liquid level fullness H can be expressed as。

In summary, there is a functional relationshipEquation (6) is satisfied, i.e. the gauge factor k is only related to the level fullness H. In practical application, due to the influence of various factors such as manufacturing process, a completely uniform magnetic field cannot be obtained, and data such as a weight function W and a magnetic field intensity B cannot be accurately obtained, and the actual flow is usually adopted for calibration, so that the approximate value of the instrument coefficient k is determined.

,(6)

,(7)

,(8)

Experiment verification

In the study, 2 electromagnetic flowmeters of different manufacturers are adopted to carry out experimental verification work, and the verification content is that each liquid level fullness H has a unique corresponding instrument coefficient k. Because the liquid level is in a non-full pipe state, the liquid level height is difficult to control in the calibration experiment to carry out multiple experiments on a certain liquid level value, the experiment is carried out in a mode of from high to low according to a certain flow difference, the standard meter flow of the full pipe section is converted by collecting the pulse output quantity within 1 minute, the data of each point is collected for 2-3 times to average, and the repeated experiment process is repeated to verify the repeatability.

In the flowmeter 1, 3 pairs of flow rate electrodes are respectively distributed at the positions of 30%, 20% and 10% of the inner diameter height of the flowmeter, the inner diameter of a pipeline of the flowmeter is 376mm, the experimental flow range is 35-365m ³/h, the water quality is sewage mixed with mud, and the experiment is carried out in a flow laboratory of Sanxia ecological environment technical innovation center Co., ltd. During the experiment, the liquid level fluctuation is large due to the overlarge deviation between the front and rear straight pipe sections and the inner diameter of the flowmeter, so that the front and rear straight pipe sections are replaced in 2 months of 2024. By varying the standard flow and the different slope values i (in percent%) of the pipe and measuring multiple times at different dates, the resulting instrument coefficients are changed with the level fullness H as shown in fig. 1 below, without normalizing the instrument coefficients.

In the flowmeter 2, the flow velocity electrodes are distributed at the position of 10% of the inner diameter height of the flowmeter, the inner diameter of a pipeline of the flowmeter is 300mm, the flow range is 14-314m ³/h, the water quality is clear water, and the experiment is carried out on a non-full pipe real flow calibration device of the Qingshian Weiindustrial intelligent instrument science and technology park. The meter coefficient was corrected at the point where h=76% at the beginning of the experiment, so that the apparent flow error at this point was 0. The experimental procedure was repeated 2 times to verify repeatability by varying the standard flow rate, and the measured meter factor as a function of the level fullness H is shown in fig. 2 below.

The experimental data of the flowmeter 2 are shown in table 1, the standard flow Q (m ³/H) is measured by adopting a standard table of full pipe sections, the flow velocity U (m/s) is measured by using a sensor, the liquid level height H is measured by using an ultrasonic liquid level meter of the flowmeter, the liquid level ratio H is obtained through H=h/D conversion, the sectional area A (m ²) is calculated by using a sectional area formula, and the instrument coefficient k is calculated by k=Q/(U×A).

TABLE 1

Through experimental verification results of the electromagnetic flowmeters of 2 different factories, the following conclusion can be obtained:

A. Under the state of non-full pipe, the instrument coefficient k changes along with the liquid level fullness H and has a unique value, and the instrument coefficient k and the liquid level fullness H are in a nonlinear relation;

B. The instrument coefficient k is irrelevant to the gradient of the pipeline;

C. The meter coefficients of the flow rate electrodes at different positions are not identical, and the higher the flow rate electrode position is, the smaller the meter coefficient value is under the condition that H is not more than 50%.

D. the meter coefficients k of different parameter flow meters do not have a consistent trend with the liquid level fullness H.

Example 1:

By analyzing the K-H scatter diagram in fig. 2, it is found that K shows a better linear relationship between two intervals of H e (13.67%, 22.5%) and (22.5%, 77.17%), and then the two intervals are divided into 2 corresponding intervals to be subjected to linear fitting, so that a fitting formula of the two intervals is divided into g ₁ =1.207×h+0.797 and g ₂ =0.1115×h+1.0848, and then the instrument coefficient K (H) is expressed as follows:

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% Substituting the k (H) expression into the flow The flow error between the flow error and the standard meter is calculated to be an error 1, the flow error between the actual measured flow of the sample machine and the standard meter is calculated to be an error 0 (the flow error of the meter is shown to be 0 only by correcting the meter coefficient at 76% of the liquid level), and as can be seen from the graph of fig. 3, the calibration method can better improve the measurement accuracy under the non-full pipe state.

Example 2:

By analyzing the k-H scatter diagram in FIG. 2, it can be considered that the key point of the flowmeter is H E {13.67%,22.5%,77.17% } and three points are total, and the same batch of products have similar change rules, in order to further reduce the calibration point number and the calibration cost, the instrument coefficients in the step 3) are calculated by the method Expression an alternative formula is a simplified piecewise linear interpolation based instrument coefficientExpression two, the expression is as follows:

a、k(H)=0.95505,H<13.67%

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

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

a、k(H)=0.98749,H≥77.17%

substituting the k (H) expression into the flow The flow error between the calculation formula and the standard table is calculated to be an error 2, and compared with the error 1 and the error 0, as can be seen from fig. 4, the calibration method can better improve the measurement accuracy under the non-full pipe state under the condition of less calibration points.

The above embodiments are only preferred embodiments of the present invention, and should not be construed as limiting the present invention, and the scope of the present invention should be defined by the claims, including the equivalents of the technical features in the claims. I.e., equivalent replacement modifications within the scope of this invention are also within the scope of the 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;

The first calibration point is set as the instrument coefficient _k1 when the liquid level is _H1 ; the second calibration point is set as the instrument coefficient _k2 when the liquid level is _H2 ; and so on, the nth calibration point is set as the instrument coefficient _kn when the liquid level is _Hn ; where n is a positive integer, and _Hn and _kn are specific values of real 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 Xi represents the i-th H interval with good linearity;

2) Perform piecewise linear fitting on the calibration points in the interval X ₁ ~X _m , and the corresponding fitting functions are g ₁ (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 _v of the fluid in the pipe can be calculated according to the flow rate formula and flow rate formula;

The instrument factor in step 2) Expression 1 is:

① , H＜H ₁ ;

② , H∈X _i ;

③ , _H≥Hn ;

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＜H ₁ ;

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 velocity signal U in the pipe measured by the flow meter, the flow velocity V and flow rate Q _v of the fluid in the pipe can be calculated according to the flow velocity formula and flow rate formula.

2. The method for calibrating an electromagnetic flowmeter for a partially full pipe according to claim 1 is 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 production calibration method of an electromagnetic flowmeter that can be used for a partially full pipe according to claim 1 is characterized in that: when the pipe is not full, a segmented calibration method is used to perform real flow calibration, and 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 the calibration points in the interval X ₁ ~X _n-1 , the cubic spline interpolation functions are obtained as f ₁ (H) ~ f _n-1 (H), respectively, and the boundary conditions are natural boundary conditions.

2) Instrument factor Expression three is:

① , H＜H ₁ ;

② , H∈[H _r ,H _r+1 );

③ , _H≥Hn ;

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 method for producing and calibrating an electromagnetic flowmeter for a partially full pipe according to claim 4, characterized in that the flow formula in step 3) is:

.

6. The method for production calibration of an electromagnetic flowmeter that can be used for a partially full pipe according to claim 5, characterized in that the flow rate formula and the flow rate formula in step 3) are derived 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 _Bi , the effective length of the magnetic line cut by the flow element is l _i , and the flow element velocity is _vi , then the calculation formula (3) for the induced voltage on the measuring 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 an electromagnetic flowmeter that can be used for a partially full pipe, characterized in that: a production calibration method for an electromagnetic flowmeter that can be used for a partially full pipe according to claim 6 is adopted.