CN100458374C - Electrical flowmeter and method thereof for improving online detecting accuracy - Google Patents

Abstract

This invention relates to one electric flow meter and its method to improve online test accuracy, which comprises sensor, magnetic excitation cable and converter and is characterized by the following: the said sensor is fixed onto magnetic coil with its chamber set with one standard coil with copper resistance near that of coil; the sensor wire case is set with relay and the converter wire case is set with relay and its driver power end; the said measurement end A, B and relay are connected; the excitation coil are orderly connected to relay J1 and J2 and the standard coil and relay constant probes are connected.

Description

A kind of electromagnetic flowmeter and improve the method for online detection degree of accuracy

Technical field

The invention belongs to flow measurement instrument electromagnetic flowmeter technical field, be specifically related to a kind of electromagnetic flowmeter and improve the method for online detection degree of accuracy.

Background technology

The heavy caliber electromagnetic flowmeter is used widely in the sewage treatment industry in plumbing.Generally, the Running-water Company in a big or middle city will be with 300～500.Regulation according to measurement Law is used for trade settlement, and the measuring instrument of environmental protection aspect must be carried out compulsory verification.Be to want periodic calibration every year, remove the heavy caliber electromagnetic flow transducer from pipeline, the demarcation of getting on of the flow standard device of delivering to factory.Do the difficulty that has many reality like this: must cut off the water, cutting off the water to have influence on urban water supply, is related to millions upon millions of common people's life; Factory's flow standard device normalization will be torn, be hung, transport, adorn, deliver to the instrument of so much quantity open, and workload is very big, and expense is also very big, and the user is difficult to bear.Therefore, nearly all Running-water Company all can't adopt this method to do periodic calibration.For solving above-mentioned difficulties, in recent years, gradually adopted the electrical quantity on-line detection method.Promptly determine that by test the precision of flowmeter has no change at the scene to every electrical property of flowmeter.This method is brought to the user and is greatly facilitated and interests, is subjected to users' welcome.But it is anxious to be solved to find that in practice following problem is arranged: 1. some electrical quantity can't detect.As: the performance of signal cable, excitation cable, the leakage of electrode; 2. there is the number of turns of the field coil of direct corresponding relation accurately to measure with flowmeter accuracy.This makes that the conclusion of online detection is not objective, and the precision of online detection is far below self precision of flowmeter.

Directly measured the copper resistance of coil in the past with the multimeter resistance grade, sensor is measured the copper resistance R of coil in process of production ₀(t ₀), and record environment temperature t ₀, these data are offered the user, as online detection foundation relatively; When the online detection of user, use with quadrat method and record coil copper resistance R ₀(t), t is an environment temperature, because environment temperature is inequality, can't compare.There is following problem in this method: coil is mounted in the airtight cavity between conduit and the shell, and the temperature of coil and environment temperature can not change synchronously; In use, the temperature of coil not only is subjected to the influence of environment temperature, also is subjected to the measured medium Temperature Influence.So, represent that with environment temperature t the temperature of coil obviously has bigger error.

For the shell protection grade is the sensor of IP67/IP68 structure, and the connection terminal in the terminal box is shut by sealing, if will measure the copper resistance of coil, must A, B in converter hold measurement, and the result who records like this is the copper resistance R of coil ₀(t) with the line resistance R of excitation cable _L(t) sum, i.e. R ₀(t) survey=R ₀(t)+R _L(t).The cable length that factory according to the contract provides, after flowmeter installed, some user can cut off unnecessary cable, and the contract length of cable and the length of actual installation are inconsistent, therefore, come modified R according to cable length _L(t) also have any problem, must produce error.And for the sensor of IP67/IP68 structure, the insulation resistance that records at converter A, B two ends is the common result of cable and coil, can't distinguish the quality of excitation cable.

Summary of the invention

The objective of the invention is: a kind of electromagnetic flowmeter is provided, and improves the degree of accuracy of the online detection of flowmeter by the method for testing of improving the cell winding copper resistance.

For achieving the above object, the technical scheme of employing is: a kind of electromagnetic flowmeter, comprise sensor, sensor terminal box, excitation cable and converter, and it is characterized in that: the cavity that field coil L is installed at described sensor is built-in with a standard coil L _b, described standard coil L _bCopper resistance R _bCopper resistance R with field coil L ₀Close; Be built-in with relay J in the sensor terminal box ₁And J ₂, be built-in with relay J at converter ₁And J ₂Driving power terminal M, N, P and measurement terminal A, B, described measurement terminal A, B and relay J ₂Be electrically connected, field coil L successively with relay J ₁And relay J ₂Normally closed contact be electrically connected standard coil L _bWith relay J ₁Normally opened contact be connected.

Described relay driving power terminal M, N energising, relay J ₁Normally closed contact becomes normally opened contact, standard coil L _bConnect with the excitation cable, field coil L and excitation cable disconnect; Described relay driving power terminal N, P energising, relay J ₂Normally closed contact becomes normally opened contact, excitation cable and field coil L, standard coil L _bAll disconnect.

Described electromagnetic flowmeter improves the method for online detection degree of accuracy, it is characterized in that comprising the steps:

1) during described electromagnetic flowmeter operate as normal, described measurement terminal A, B record resistance R ₁(t) be field resistance R ₀(t) with excitation cable resistance R _L(t) sum;

R ₁(t)＝R ₀(t)+R _L(t)

2) driving power terminal M, N energising, described measurement terminal A, B record resistance R ₂(t) be the standard coil resistance R _b(t) with excitation cable resistance R _L(t) sum;

R ₂(t)＝R _b(t)+R _L(t)

3) driving power terminal N, P energising, described measurement terminal A, B record resistance R ₃(t) be excitation cable resistance R _L(t);

R ₃(t)＝R _L(t)

Record the insulation resistance R of excitation cable from measurement terminal A, B _X(t) and excitation cable resistance R _L(t), whether differentiation excitation cable is qualified;

4) field resistance R according to the physics knowledge that concerns between copper coil resistance and the temperature as can be known, ₀(t) with the standard coil resistance R _b(t) ratio K is constant, and is temperature independent, so as long as measure R at one time ₀(t) and R _b(t) value, K (t when obtaining K (t) and dispatching from the factory ₀) be worth relatively, know that the parameter of coil has no change, and the copper resistance variation delta R behind the field coil partial short-circuit coil sections ₀(t) size;

6) sensor produces electromotive force E and field resistance R ₀(t) in direct ratio, determine that coil parameter changes the amount of the influence δ to the flowmeter degree of accuracy:

$\mathrm{\δ}=\frac{\mathrm{\ΔE}}{E}=\frac{{\mathrm{\ΔR}}_0\left(t\right)}{R_0\left(t\right)}\×100\%$

Good effect of the present invention is the degree of accuracy that has improved the online detection of electromagnetic flowmeter, brings up to 0.3% from original 2%, makes the conclusion to the online detections such as Performance Detection of excitation cable more meet objective circumstances.

Description of drawings

The invention will be further described below in conjunction with the drawings and specific embodiments:

Fig. 1 is a structural representation of the present invention.

Among the figure, the 1-sensor; 2-sensor terminal box; 3-excitation cable; The 4-converter.

Embodiment

A kind of electromagnetic flowmeter comprises sensor 1, sensor terminal box 2, excitation cable 3 and converter 4, it is characterized in that: the cavity of field coil L being installed at described sensor 1 is built-in with a standard coil L _b, described standard coil L _bCopper resistance R _bCopper resistance R with field coil L ₀Close; Be built-in with relay J in sensor terminal box 2 ₁And J ₂, be built-in with relay J at converter 4 ₁And J ₂Driving power terminal M, N, P and measurement terminal A, B, described measurement terminal A, B and relay J ₂Be electrically connected, field coil L successively with relay J ₁And relay J ₂Normally closed contact be electrically connected standard coil L _bWith relay J ₁Normally opened contact be connected.Described relay driving power terminal M, N energising, relay J ₁Normally closed contact becomes normally opened contact, standard coil L _bConnect with excitation cable 3, field coil L and excitation cable 3 disconnect; Described relay driving power terminal N, P energising, relay J ₂Normally closed contact becomes normally opened contact, excitation cable 3 and field coil L, standard coil L _bAll disconnect.

Described a kind of electromagnetic flowmeter improves the method for online detection degree of accuracy, it is characterized in that comprising the steps:

1) during described electromagnetic flowmeter operate as normal, measurement terminal A, B record resistance R ₁(t) be field resistance R ₀(t) with excitation cable resistance R _L(t) sum;

R ₁(t)＝R ₀(t)+R _L(t)

2) driving power terminal M, N energising, measurement terminal A, B record resistance R ₂(t) be the standard coil resistance R _b(t) with excitation cable resistance R _L(t) sum;

R ₂(t)＝R _b(t)+R _L(t)

3) driving power terminal N, P energising, measurement terminal A, B record resistance R ₃(t) be excitation cable resistance R _L(t);

R ₃(t)＝R _L(t)

Record the insulation resistance R of excitation cable from measurement terminal A, B _X(t) and excitation cable resistance R _LWhether (t), can differentiate the excitation cable qualified;

4) according to the physics knowledge that concerns between copper coil resistance and the temperature as can be known: the resistance of copper coil and the pass between the temperature are:

$R_0\left(t\right)=R_0\left(t_0\right)(1+\frac{t-t_0}{t_0+273})---\left(1\right)$

$R_b\left(t\right)=R_b\left(t_0\right)(1+\frac{t-t_0}{t_0+273})---\left(2\right)$

(1)/(2): $K\left(t\right)=\frac{R_0\left(t\right)}{R_b\left(t\right)}=\frac{R_0\left(t_0\right)}{R_b\left(t_0\right)}=K\left(t_0\right)=K---\left(3\right)$

From (3) formula as can be known: though the copper resistance value of field coil and standard coil is all followed the temperature variation of coil, field resistance R ₀(t) with the standard coil resistance R _b(t) ratio K is constant, and is temperature independent.So, under the plant produced condition, measure and still measure the influence of all not considering environment temperature and fluid temperature (F.T.) at the scene, as long as measure R at one time ₀(t) and R _b(t) value, the K (t when obtaining ratio K (t) and dispatching from the factory ₀) be worth relatively, know that the parameter of coil has no change, and the copper resistance variation delta R behind the field coil partial short-circuit coil sections ₀(t) size;

5) sensor produces electromotive force E and field resistance R ₀(t) in direct ratio, can determine that coil parameter changes the amount of the influence δ to the flowmeter degree of accuracy:

$\mathrm{\δ}=\frac{\mathrm{\ΔE}}{E}=\frac{{\mathrm{\ΔR}}_0\left(t\right)}{R_0\left(t\right)}\×100\%$

The present invention to the precondition of the estimation of online detection degree of accuracy is:

1) measurement of other electrical quantitys all belongs to normally, comprises converter;

2) loosening, displacement phenomenon that the sound construction of sensor, coil can not produce;

3) field coil of sensor is to concentrate the winding construction form;

4) degree of accuracy of resistance meter is better than 0.1%.

Under above precondition, online detection degree of accuracy can be better than 0.3%.

Claims (3)

1. an electromagnetic flowmeter comprises sensor (1), sensor terminal box (2), excitation cable (3) and converter (4), it is characterized in that: the cavity that field coil L is installed at described sensor (1) is built-in with a standard coil L _b, described standard coil L _bCopper resistance R _bCopper resistance R with field coil L ₀Close; Be built-in with relay J in sensor terminal box (2) ₁And J ₂, be built-in with relay J at converter (4) ₁And J ₂Driving power terminal M, N, P and measurement terminal A, B, described measurement terminal A, B and relay J ₂Be electrically connected, field coil L successively with relay J ₁And relay J ₂Normally closed contact be electrically connected standard coil L _bWith relay J ₁Normally opened contact link to each other.

2. according to the described a kind of electromagnetic flowmeter of claim 1, it is characterized in that described relay driving power terminal M, N energising, relay J ₁Normally closed contact becomes normally opened contact, standard coil L _bConnect with excitation cable (3), field coil L and excitation cable (3) disconnect; Described relay driving power terminal N, P energising, relay J ₂Normally closed contact becomes normally opened contact, excitation cable (3) and field coil L, standard coil L _bAll disconnect.

3. the described electromagnetic flowmeter of claim 1 improves the method for online detection degree of accuracy, it is characterized in that comprising:

1) during described electromagnetic flowmeter operate as normal, described measurement terminal A, B record resistance R ₁(t) be field resistance R ₀(t) with excitation cable resistance R _L(t) sum;

R ₁(t)＝R ₀(t)+R _L(t)

2) driving power terminal M, N energising, described measurement terminal A, B record resistance R ₂(t) be the standard coil resistance R _b(t) with excitation cable resistance R _L(t) sum;

R ₂(t)＝R _b(t)+R _L(t)

3) driving power terminal N, P energising, described measurement terminal A, B record resistance R ₃(t) be excitation cable resistance R _L(t);

R ₃(t)＝R _L(t)

Record the insulation resistance R of excitation cable from measurement terminal A, B _X(t) and excitation cable resistance R _L(t), whether differentiation excitation cable is qualified;

4) field resistance R according to the physics knowledge that concerns between copper coil resistance and the temperature as can be known, ₀(t) with the standard coil resistance R _b(t) ratio K is constant, and is temperature independent, so as long as measure R at one time ₀(t) and R _b(t) value, K (t0) value relatively knows that the parameter of coil has no change when obtaining when actual measurement K (t) and dispatching from the factory, and reaches the copper resistance variation delta R behind the field coil partial short-circuit coil sections ₀(t) size;

5) sensor produces electromotive force E and field resistance R ₀(t) in direct ratio, determine that coil parameter changes the amount of the influence δ to the flowmeter degree of accuracy:

$\mathrm{\δ}=\frac{\mathrm{\ΔE}}{E}=\frac{{\mathrm{\ΔR}}_0\left(t\right)}{R_0\left(t\right)}\×100\%$

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