CN101929883B

CN101929883B - Method for measuring flow of conductive fluid in non-full pipe by using electromagnetic flow meter

Info

Publication number: CN101929883B
Application number: CN2009101550510A
Authority: CN
Inventors: 周洪亮; 饶蕾; 张宏建
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2009-12-14
Filing date: 2009-12-14
Publication date: 2011-12-07
Anticipated expiration: 2029-12-14
Also published as: CN101929883A

Abstract

The invention discloses a method for measuring flow of conductive fluid in a non-full pipe by using an electromagnetic flow meter. The adopted flow meter is provided with at least three pairs of measuring electrodes, a grounding electrode, a coil structure for generating a magnetic field and a pressure sensor; a plurality of pairs of electrodes on the inner wall of the measured pipe ensure that each pair of electrodes is contacted with the fluid under different fluid levels H; and the measuring electrode pair is reasonably selected according to the different fluid levels so as to ensure the measurement accuracy. The measurement method is characterized in that: different pairs of electrodes are selected for measuring the flow rate under the different fluid levels, a fluid level signal H is obtained by using a pressure signal P of the pressure sensor so as to overcome measurement errors of the conductive fluids of different categories due to different conductivities and dielectric constants, the equivalent sectional area S of the fluid in the non-full pipe is calculated through the fluid level signal, the signal E of an induced electromotive force measured by the flow sensor is converted into a flow rate signal V, and the corresponding flow Q of the fluid in the non-full pipe can be obtained by integrating the equivalent sectional area S and the flow rate signal.

Description

Method with electromagnetic flowmeter survey non-full pipe conductive fluid flow

Technical field

The present invention relates to a kind of method with electromagnetic flowmeter survey non-full pipe conductive fluid flow.

Background technology

The common electrical magnetic flowmeter is with the sensor section constant area, measures mean flow rate and obtains flow.Fluid cross-section area in the non-full pipe changes, and flow measurement not only will be measured the mean flow rate of flows through sensor, but also the fluid cross-section that will measure flows through sensor amasss.That is to say that what the flow measurement of non-full pipe electromagnetic flowmeter needed is flow velocity V and two variablees of liquid level H at least.

The measuring method of non-full pipe electromagnetic flowmeter mainly contains the method for the arc broad-area electrode sensor that adopts tube hub deflection bottom, the liquid level gauge method, adopt the multielectrode sensor method, use capacitance method and carry out the method for level gauging and the method that adopts different energisation modes to obtain at the extraction of liquid level and flow velocity signal, for the non-full pipe method for electromagnetic flow measurement on basis etc.

Under the constant situation of single conductive fluid, just under the constant situation of fluid conductivity, can realize the measurement of non-full pipe as condenser type and two excitation formulas etc., but when conductivity of fluid and fluid behaviour changed, measuring accuracy can be a greater impact.

Summary of the invention

The objective of the invention is to overcome the deficiencies in the prior art, a kind of method with electromagnetic flowmeter survey non-full pipe conductive fluid flow is provided.

Method with electromagnetic flowmeter survey non-full pipe conductive fluid flow comprises the steps:

1) the non-full pipe electromagnetic flowmeter is inserted fluid circuit to be measured, have field coil on the measuring tube of non-full pipe electromagnetic flowmeter is outer, field coil is connected with field circuit, the inner-walls of duct both sides three pairs of potential electrode that distributing, the every pair of potential electrode is input in the signal processing circuit in the mode of differential wave, three pairs of potential electrode insert signal processing circuit respectively, the ground-electrode of measuring tube bottom is connected with the ground wire of field circuit and signal processing circuit, and pressure transducer is connected with signal processing circuit;

2) when conductive fluid flows through the measuring tube of non-full pipe electromagnetic flowmeter, pressure transducer is measured the normalized current signal that obtains 4-20mA, the normalized current signal is by resistance of series connection, the magnitude of voltage U at resistance two ends becomes proportional relation one to one with the pairing pressure signal P of liquid level signal H, according to formula p=ρ gH, derivation draws H=k1*U, wherein the scale-up factor of coefficient k 1 pressure liquid level;

3) field circuit produces exciting current, be input in the field coil, produce magnetic field B, the current signal that collects when pressure transducer changes into corresponding voltage signal and is input to single-chip microcomputer in the signal processing circuit, calculate the liquid level H of current fluid by single-chip microcomputer, height H according to liquid level, the Single-chip Controlling multiway analog switch, select corresponding this moment potential electrode right by multiway analog switch, should interelectrode induced electromotive force signal E be derived and draw mean flow rate V:V=k2*E, coefficient k 2 wherein is to be demarcated out by actual experiment, by mean flow rate V, calculate Q=V*S; S is the cross-sectional area of conductive fluid,

S = \frac{D^{2}}{4} \arccos \frac{D - 2 H}{D} - (\frac{D}{2} - H) \sqrt{\frac{D^{2}}{4} - {(\frac{D}{2} - H)}^{2}},

Wherein D is the caliber of measuring tube.

Described potential electrode is three pairs, first pair of potential electrode, second pair of potential electrode, the 3rd pair of potential electrode, wherein first pair of electrode is arranged on the tube wall at measuring tube caliber 50% place, second pair of electrode is arranged on the tube wall at measuring tube caliber 30% place, and the 3rd pair of electrode is arranged on the tube wall at measuring tube caliber 10% place.

The present invention compared with prior art, following some conspicuous outstanding substantive distinguishing features and remarkable advantage are arranged: the one, directly obtain corresponding liquid level signal H with pressure transducer, overcome the measuring error that different types of conductive fluid may cause owing to the different of conductivity and specific inductive capacity, the 2nd, the many installation site and the logarithms of measuring tube inwall to electrode, guaranteed under the different liquid level H, every pair of electrode all contacts with fluid, and, guaranteed the accuracy of measuring according to the corresponding potential electrode of different choose reasonable of liquid level.

Description of drawings

Fig. 1 is the structural representation of non-full pipe electromagnetic flowmeter of the present invention.

Fig. 2 is measuring tube (1) and mean flow rate V of the present invention, and the graph of a relation of the liquid level H of fluid and each three-dimensional distribution plan to electrode and pressure transducer.

Embodiment

A preferred embodiment of the present invention such as following: see Fig. 1 and Fig. 2.

1) the non-full pipe electromagnetic flowmeter is inserted fluid circuit to be measured, have field coil 2 on outside the measuring tube 1 of non-full pipe electromagnetic flowmeter, field coil 2 is connected with field circuit 4, the inner-walls of duct both sides three pairs of potential electrode that distributing, the every pair of potential electrode is input in the signal processing circuit 3 in the mode of differential wave, three pairs of potential electrode insert signal processing circuit respectively, the ground-electrode 12 of measuring tube 1 bottom is connected with the ground wire of field circuit 4 with signal processing circuit 3, and pressure transducer 11 is connected with signal processing circuit 3;

2) when conductive fluid flows through the measuring tube 1 of non-full pipe electromagnetic flowmeter, pressure transducer 11 is measured the normalized current signal that obtains 4-20mA, the normalized current signal is by resistance of series connection, the magnitude of voltage U at resistance two ends becomes proportional relation one to one with the pairing pressure signal P of liquid level signal H, according to formula p=ρ gH, derivation draws H=k1*U, wherein the scale-up factor of coefficient k 1 pressure liquid level;

3) field circuit 4 produces exciting current, be input in the field coil 2, produce magnetic field B, when changing into corresponding voltage signal, current signal that pressure transducer 11 collects is input to single-chip microcomputer in the signal processing circuit 3, calculate the liquid level H of current fluid by single-chip microcomputer, height H according to liquid level, the Single-chip Controlling multiway analog switch, select corresponding this moment potential electrode right by multiway analog switch, should interelectrode induced electromotive force signal E be derived and draw mean flow rate V:V=k2*E, coefficient k 2 wherein is to be demarcated out by actual experiment, by mean flow rate V, calculate Q=V*S; S is the cross-sectional area of conductive fluid,

S = \frac{D^{2}}{4} \arccos \frac{D - 2 H}{D} - (\frac{D}{2} - H) \sqrt{\frac{D^{2}}{4} - {(\frac{D}{2} - H)}^{2}},

Wherein D is the caliber of measuring tube 1.

Described potential electrode is three pairs, the first pair of

potential electrode

5 and 6, the second pair of

potential electrode

7 and 8, the 3rd pair of

potential electrode

9 and 10, wherein first pair of electrode is arranged on the tube wall at measuring tube 1 caliber 50% place, second pair of electrode is arranged on the tube wall at measuring tube 1 caliber 30% place, and the 3rd pair of electrode is arranged on the tube wall at measuring tube 1 caliber 10% place.

When conductive fluid flows, the pressure signal P that the pressure transducer 11 of measuring tube bottom is measured is converted into liquid level signal H, field circuit produces magnetic field B simultaneously, by known liquid level signal H, select the corresponding required electrode pair of measuring by single-chip microcomputer, carry out the measurement of induced electromotive force signal E, when the liquid level of conductive fluid during greater than 50% caliber (comprising the full packages situation), selection is distributed in the

electrode pair

5 and 6 that the pipe interior both sides are positioned at high 50% place of caliber, carry out the measurement of induction electromotive force, when the liquid level of conductive fluid during greater than 30% caliber and less than 50% caliber, selection is distributed in the

electrode pair

7 and 8 that the pipe interior both sides are positioned at high 30% place of caliber, carry out the measurement of induction electromotive force, when the liquid level of conductive fluid during greater than 10% caliber and less than 30% caliber, selection is distributed in the pipe interior both sides and is positioned at high 10% electrode pair that goes out 9 of caliber and 10, carry out the measurement of induction electromotive force, value according to the induction electromotive force E that measures calculates mean flow rate V, the flow Q that derives non-full pipe flow by the liquid level H and the mean flow rate V of conductive fluid.

Above-mentioned new method with electromagnetic flowmeter survey non-full pipe conductive fluid flow requires to measure the 3 pairs of electrodes of induction electromotive force and measuring tube inwall except that the electrode place, and all the other local normal direction electric currents are zero.The electrode Material Selection is 316L, is applicable to industrial waste water, and the acid of weak erosive, alkali, salt solusion, and cheap.The corrosion resistance of electrode pair measuring media is a factor of selecting material at first to consider, can select the metal material except that 316L, as contain the molybdenum acid resisting steel, Hastelloy B, C, titanium, tantalum, platinumiridio etc.The lining of measuring tube is selected the insulation lining, is in order to prevent induced signal voltage by the metal tube short circuit, to select here to use teflon, can selecting rubber, Polyvinylchloride, urethane rubber and industrial ceramics etc. for use in addition.

Above-mentioned new method with electromagnetic flowmeter survey non-full pipe conductive fluid flow, 3 pairs of electrodes of the measurement induction electromotive force that is adopted, wherein the 1st pair of electrode is located on the tube wall at measuring tube caliber 50% place, the 2nd pair of electrode is located on the tube wall at measuring tube caliber 30% place, the 3rd pair of electrode is located on the tube wall at measuring tube caliber 10% place, the setting height(from bottom) of the point electrode of pipeline bottommost, whether the processing technology that depends on electrode size in the lower limit of measurable liquid level H and the pipeline can accomplish the duct bottom of pressing close to as far as possible, to guarantee not influence field coil simultaneously, the signal that every pair of electrode is exported promptly is the signal E of the induction electromotive force measured, becomes the relation of corresponding ratio with flow rate of fluid.

Above-mentioned new method with electromagnetic flowmeter survey non-full pipe conductive fluid flow, in order to obtain higher measuring accuracy, measure 3 pairs of electrodes of induction electromotive force, can be 3 pairs of electrode groups of being formed with top electrode, for example, the distribution of every pair of electrode can be that liquid level H is 10% of a caliber, 20%, 30%, 40%, 50%, perhaps can get thinner, the measurement of every pair of interelectrode induction electromotive force is identical with the metering system of 3 pairs of electrodes, determines certain concrete a pair of electrode by the Single-chip Controlling analog switch in the converter.

Above-mentioned new method with electromagnetic flowmeter survey non-full pipe conductive fluid flow, be based on the liquid level signal H that electric signal that pressure transducer measures is derived, and by the induced electromotive force signal E between selected corresponding with it certain a pair of electrode of liquid level signal H, the mean flow rate signal V that derivation draws, calculate corresponding fluid flow Q, wherein the position at pressure transducer place is not on many circular cross sections to the electrode place.

Concrete operation steps:

1) when conductive fluid flows through the measuring tube 1 of non-full pipe electromagnetic flowmeter, pressure transducer 11 is measured the normalized current signal that obtains 4-20mA, the normalized current signal is by resistance of series connection, the magnitude of voltage U at resistance two ends becomes proportional relation one to one with the pairing pressure signal P of liquid level signal H, according to formula p=ρ gH, derivation draws H=k1*U, wherein the scale-up factor of coefficient k 1 pressure liquid level.

2) field circuit 4 produces sinusoidal wave exciting current, be input in the field coil 2, produce alternating magnetic field B, the current signal that collects when pressure transducer 11 changes into corresponding voltage signal and is input to single-chip microcomputer in the electromagnetic flux converter, when calculating the liquid level H of current fluid by single-chip microcomputer, according to the liquid level H that calculates, the Single-chip Controlling multiway analog switch, select corresponding this moment potential electrode right by multiway analog switch, should be to interelectrode induced electromotive force signal E, the mean flow rate V of fluid is by the formula E=BLV of induction electromotive force, and derivation draws

V = \frac{E}{BL} = k 2 * E,

Coefficient

K 2 = \frac{1}{BL},

Coefficient k 2 wherein is to be demarcated out by actual tests.

The flow of fluid then equals Q=V*S, and S is the cross-sectional area of the fluid in the measuring tube 1; S is the cross-sectional area of conductive fluid.The relation of the liquid level H of it and fluid is as follows:

S = \frac{D^{2}}{4} \arccos \frac{D - 2 H}{D} - (\frac{D}{2} - H) \sqrt{\frac{D^{2}}{4} - {(\frac{D}{2} - H)}^{2}}

。

Claims

1. the method with electromagnetic flowmeter survey non-full pipe conductive fluid flow is characterized in that comprising the steps:

1) the non-full pipe electromagnetic flowmeter is inserted fluid circuit to be measured, have field coil (2) on the measuring tube of non-full pipe electromagnetic flowmeter (1) is outer, field coil (2) is connected with field circuit (4), the inner-walls of duct both sides three pairs of potential electrode that distributing, the every pair of potential electrode is input in the signal processing circuit (3) in the mode of differential wave, three pairs of potential electrode insert signal processing circuit respectively, the ground-electrode (12) of measuring tube (1) bottom is connected with the ground wire of field circuit (4) with signal processing circuit (3), and pressure transducer (11) is connected with signal processing circuit (3);

2) when conductive fluid flows through the measuring tube (1) of non-full pipe electromagnetic flowmeter, pressure transducer (11) is measured the current signal that obtains 4-20mA, current signal is by resistance of series connection, the magnitude of voltage U at resistance two ends becomes proportional relation one to one with the pairing pressure signal P of liquid level signal H, according to formula p=ρ gH, derivation draws H=k1*U, wherein the scale-up factor of coefficient k 1 pressure liquid level;

3) field circuit (4) produces exciting current, be input in the field coil (2), produce magnetic field B, when changing into corresponding voltage signal, current signal that pressure transducer (11) collects is input to single-chip microcomputer in the signal processing circuit (3), calculate the liquid level H of current fluid by single-chip microcomputer, height H according to liquid level, the Single-chip Controlling multiway analog switch, select corresponding this moment potential electrode right by multiway analog switch, should interelectrode induced electromotive force signal E be derived and draw mean flow rate V:V=k2*E, coefficient k 2 wherein is to be demarcated out by actual experiment, by mean flow rate V, calculate Q=V*S; S is the cross-sectional area of conductive fluid,

S = \frac{D^{2}}{4} \arccos \frac{D - 2 H}{D} - (\frac{D}{2} - H) \sqrt{\frac{D^{2}}{4} - {(\frac{D}{2} - H)}^{2}},

Wherein D is the caliber of measuring tube (1).

2. according to the method described in the claim 1 with electromagnetic flowmeter survey non-full pipe conductive fluid flow, it is characterized in that described potential electrode is three pairs, first pair of potential electrode (5 and 6), second pair of potential electrode (7 and 8), the 3rd pair of potential electrode (9 and 10), wherein first pair of electrode is arranged on the tube wall at measuring tube (1) caliber 50% place, second pair of electrode is arranged on the tube wall at measuring tube (1) caliber 30% place, and the 3rd pair of electrode is arranged on the tube wall at measuring tube (1) caliber 10% place.