CN101162163A - Capacitor type electromagnetic flow meter - Google Patents

Capacitor type electromagnetic flow meter Download PDF

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Publication number
CN101162163A
CN101162163A CNA2007101569128A CN200710156912A CN101162163A CN 101162163 A CN101162163 A CN 101162163A CN A2007101569128 A CNA2007101569128 A CN A2007101569128A CN 200710156912 A CN200710156912 A CN 200710156912A CN 101162163 A CN101162163 A CN 101162163A
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electronic switch
resistance
detecting electrode
signal
operational amplifier
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CN100453979C (en
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王保良
罗元国
黄志尧
李海青
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Zhejiang University ZJU
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Zhejiang University ZJU
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Abstract

The present invention discloses a capacitive electromagnetic flowmeter. The upper side and the lower side of the outer wall of a measuring tube are provided with an upper coil and a lower coil which are in series connection; the upper coil and the lower coil are connected with an exciting circuit; the left side and the right side of the outer wall of the measuring tube are provided with a left detecting electrode and a right detecting electrode; a left shielding electrode, a right shielding electrode, a left shielding ring and a right shielding ring are arranged outside the left detecting electrode and the right detecting electrode; the left detecting electrode is connected with a left preamplifier; the right detecting electrode is connected with a right preamplifier; the left preamplifier and the right preamplifier are connected with a differential amplifying circuit and a signal processing circuit. In the signal processing circuit of the invention, a rotary capacitance filter circuit has the effect close to an ideal square wave matched filter and can overcome the influence of strong noise, improve signal-to-noise ratio, detect feeble flow signals and convert the feeble flow signals to the direct current signals along flow changing, thereby achieving the measurement on fluid flow.

Description

Capacitive electromagnetic flow meter
Technical field
The present invention relates to electromagnetic flowmeter, relate in particular to a kind of capacitive electromagnetic flow meter.
Background technology
Electromagnetic flowmeter provides the square wave exciting curent to coil, forms electromagnetic field, and the fluid cutting magnetic line that flows in measuring tube can produce induction electromotive force, and its size is directly proportional with rate of flow of fluid.Because exciting curent is an alternation, the induced potential of generation also is an alternation, and its frequency is identical with the frequency of exciting curent.A pair of comb electrode plate is located at insulation measurement pipe outer wall, with the magnetizing coil quadrature, battery lead plate and fluid form with the electric capacity of measuring tube tube wall as medium, utilize the coupling effect of electric capacity that induced potential is coupled on the pole plate, by detecting the voltage difference of two pole plates, just can obtain the signal relevant with rate of flow of fluid.
Since the flow signal that the capacitive electromagnetic flow meter sensor produces very a little less than, generally in μ V level, and electrode is very little with the coupling capacitance that forms between detected fluid, be tens of pF only, make the signal internal resistance become very big, in the coupling flow signal, also can be coupled into very strong noise, and along with the decline of detected fluid conductivity, noise amplitude can be bigger, and very low signal to noise ratio (S/N ratio) makes the difficulty that flow signal is accurately detected from strong noise background increase.In order under the very poor situation of signal to noise ratio (S/N ratio), exactly flow signal to be detected, the one, on the structure of sensor, prime amplifier is pressed close to detecting electrode, it is minimum that the noise that signal is introduced because of transmission reduces to, and taked strict shielding measure.The 2nd, in signal processing circuit, use the rotation capacitor filter, converting flow signal to amplitude is directly proportional with rate of flow of fluid, the square-wave signal that frequency is identical with flow signal, simultaneously to the hydrodynamic noise of the different frequencies of signal, industrial frequency noise, circuit in random noise etc. carried out good restraining.
Summary of the invention
The purpose of this invention is to provide a kind of capacitive electromagnetic flow meter, can overcome the influence of very noisy, improve signal to noise ratio (S/N ratio), faint flow signal is detected, and convert direct current signal to, realize the measurement of fluid flow with fluctuations in discharge.
Capacitive electromagnetic flow meter is provided with coil on the serial connection, lower coil in the upper and lower both sides of measuring tube outer wall, last coil, lower coil are connected with exciting circuit, be provided with left detecting electrode, right detecting electrode in measuring tube outer wall and arranged on left and right sides, left side detecting electrode, right detecting electrode are provided with left guarded electrode, right guarded electrode and left shading ring, right shading ring outward, left side detecting electrode is connected with left prime amplifier, right detecting electrode is connected with right prime amplifier, and left prime amplifier is connected with differential amplifier circuit, signal processing circuit with right prime amplifier.
Described signal processing circuit is: the positive input terminal of first operational amplifier is connected with the 3rd resistance one end, the other end ground connection of the 3rd resistance, the negative input end of first operational amplifier and first resistance, one end, first electronic switch, one end, the 3rd electronic switch one end is connected, the other end of first resistance is connected with the output terminal of differential amplifier circuit, one end of the other end of first electronic switch and second resistance, one end of first electric capacity, one end of quadrielectron switch is connected, the other end of the other end of the 3rd electronic switch and second resistance, the other end of first electric capacity, one end of second electronic switch is connected, the other end of second electronic switch, the output terminal of the other end of quadrielectron switch and first operational amplifier, one end of the 4th resistance, the Chang Kaiduan of the electronic switch of first single-pole double-throw (SPDT) is connected, the common port of the electronic switch of first single-pole double-throw (SPDT) is connected with the positive input terminal of second operational amplifier, the normal-closed end of the electronic switch of first single-pole double-throw (SPDT) and ground connection, the other end of the 4th resistance is through the 5th resistance, the output terminal of the 6th resistance and second operational amplifier, the normal-closed end of the electronic switch of second single-pole double-throw (SPDT) is connected, the negative input end of second operational amplifier is connected with the adjustable end of the 5th resistance, the common port of the electronic switch of second single-pole double-throw (SPDT) is connected with an end of second electric capacity, the other end ground connection of second electric capacity, the positive input terminal of the Chang Kaiduan of the electronic switch of second single-pole double-throw (SPDT) and the 3rd operational amplifier, one end of the 3rd electric capacity is connected, the other end ground connection of the 3rd electric capacity, the negative input end of the 3rd operational amplifier is connected with the output terminal of the 3rd operational amplifier.
The present invention includes the insulation measurement pipe, be located at the comb electrode of measuring tube outer wall, electrode is implemented the guarded electrode and the shading ring of shielding, the coil in magnetic field is provided, the exciting circuit of exciting current is provided for this coil, carry out the prime amplifier of signal impedance conversion, suppress the differential amplifier of common mode composition in the signal and flow signal extracted from noise and amplify, convert the signal processing circuit of the DC voltage that can directly measure to.In signal processing circuit, the rotation capacitor filter has played the effect that is similar to the ideal square wave matched filter, can overcome the influence of very noisy, improve signal to noise ratio (S/N ratio), faint flow signal is detected, and convert direct current signal to, realize the measurement of fluid flow with fluctuations in discharge.
Description of drawings
Fig. 1 is the structured flowchart of capacitive electromagnetic flow meter;
Fig. 2 is that the electrode of sensor of the present invention is provided with synoptic diagram;
Fig. 3 is a comb electrode synoptic diagram of the present invention;
Fig. 4 is the schematic diagram of signal processing circuit of the present invention;
Fig. 5 is filtered flow signal V aSynoptic diagram;
Fig. 6 is signal rectification and sampling process synoptic diagram.
Specific embodiments
As shown in Figure 1, capacitive electromagnetic flow meter is on measuring tube 1 outer wall, following both sides are provided with the last coil 2A of serial connection, lower coil 2B, last coil 2A, lower coil 2B is connected with exciting circuit 7, on measuring tube 1 an outer wall left side, right both sides are provided with left detecting electrode 3A, right detecting electrode 3B, left side detecting electrode 3A, right detecting electrode 3B is provided with left guarded electrode 4A outward, right guarded electrode 4B and left shading ring 5A, right shading ring 5B, left side detecting electrode 3A is connected with left prime amplifier 6A, right detecting electrode 3B is connected left prime amplifier 6A and right prime amplifier 6B and differential amplifier circuit 8 with right prime amplifier 6B, signal processing circuit 9 is connected.
Last coil 2A, lower coil 2B are a pair of hollow magnetizing coil, be cascaded, under the 200Hz square wave current excitation that exciting circuit 7 provides, produce with work magnetic field frequently, detected fluid produces the induced potential relevant with flow velocity by measuring tube 1 cutting magnetic line, be coupled to respectively on the pole plate of left and right detecting electrode 3A, 3B through the electric capacity that forms by left detecting electrode 3A, right detecting electrode 3B and the detected fluid tube wall by measuring tube 1, under perfect condition, electromotive force equal and opposite in direction on the two-plate, direction is opposite.Because coupling capacitance only has tens of pF, therefore, capacitive reactance becomes main signal internal resistance, in order to obtain flow signal accurately, reduce signal attenuation, left and right prime amplifier 6A, 6B have adopted the high input impedance amplifying circuit to carry out impedance transformation, and left and right prime amplifier 6A, 6B placed from left and right detecting electrode 3A, the 3B near position of trying one's best, adopt the method for equipotential excitation shielding, by shielded cable and left and right guarded electrode 4A, 4B, left and right shading ring 5A, 5B constitute complete shield loop, to overcome the influence of distributed capacitance to the signal transmission.Signal after left and right prime amplifier 6A, 6B finish impedance transformation enters differential amplifier circuit 8, the core of differential amplifier circuit 8 is instrument amplifiers of high cmrr, after amplifying, it can obtain required flow signal, but wherein include stronger noise component, send in the signal processing circuit 9 and handle.The core of signal processing circuit 9 is rotation capacitor filters, it can suppress the undesired signal with the different frequencies of signal, and convert flow signal to square-wave signal that amplitude size is directly proportional with flow signal, just can be converted into amplitude with the d. c. voltage signal that flow is directly proportional through the overcommutation sample circuit again, finish flow measurement detected fluid.
As shown in Figure 2, owing to structural symmetry, only shown the situation of sensor right-half plane among the figure.In order to be suppressed at the vortes interference that produces on the high frequency pumping inferior pole piece, right detecting electrode 3A, right guarded electrode 4A use very thin Copper Foil to make, and make pectination, and its profile as shown in Figure 3.Right detecting electrode 3A is affixed on the outer wall of insulation measurement pipe 1, and right shading ring 5A links to each other with right guarded electrode 4A in right detecting electrode 3A is enclosed in, and realizes the shielding fully to right detecting electrode 3A.
As shown in Figure 4, signal processing circuit 9 is: first operational amplifier A 1Positive input terminal and the 3rd resistance R 3One end is connected, the 3rd resistance R 3Other end ground connection, first operational amplifier A 1The negative input end and first resistance R 1One end, the first electronic switch S A1One end, the 3rd electronic switch S B1One end is connected, first resistance R 1The other end be connected the first electronic switch S with the output terminal of differential amplifier circuit 8 A1The other end and second resistance R 2An end, first capacitor C 1An end, quadrielectron switch S B2An end be connected the 3rd electronic switch S B1The other end and second resistance R 2The other end, first capacitor C 1The other end, the second electronic switch S A2An end be connected the second electronic switch S A2The other end, quadrielectron switch S B2The other end and first operational amplifier A 1Output terminal, the 4th resistance R 4An end, the electronic switch S of first single-pole double-throw (SPDT) 1Chang Kaiduan be connected the electronic switch S of first single-pole double-throw (SPDT) 1The common port and second operational amplifier A 2Positive input terminal be connected the electronic switch S of first single-pole double-throw (SPDT) 1Normal-closed end and ground connection, the 4th resistance R 4The other end through the 5th resistance R 5, the 6th resistance R 6With second operational amplifier A 2Output terminal, the electronic switch S of second single-pole double-throw (SPDT) 2Normal-closed end be connected second operational amplifier A 2Negative input end and the 5th resistance R 5Adjustable end be connected the electronic switch S of second single-pole double-throw (SPDT) 2The common port and second capacitor C 2An end be connected second capacitor C 2Other end ground connection, the electronic switch S of second single-pole double-throw (SPDT) 2Chang Kaiduan and the 3rd operational amplifier A 3Positive input terminal, the 3rd capacitor C 3An end be connected the 3rd capacitor C 3Other end ground connection, the 3rd operational amplifier A 3Negative input end and the 3rd operational amplifier A 3Output terminal be connected.
Through the flow signal V after differential amplifier 8 amplifications iAt first enter the rotation capacitor filter, this circuit comprises first operational amplifier A 1, first resistance R 1, the 3rd resistance R 3, by second resistance R 2, first capacitor C 1The RC integrating circuit of forming is by the first electronic switch S A1, the second electronic switch S A2And the 3rd electronic switch S B1, quadrielectron switch S B2Two groups of electronic switches that open and close synchronously forming.Wherein, by the first electronic switch S A1, the second electronic switch S A2One group of electronic switch forming and the 3rd electronic switch S B1, quadrielectron switch S B2Another group electronic switch of forming is respectively by synchronous with excited signal, and frequency is all 200Hz, and reverse each other a pair of square wave control produces the reference signal that multiplies each other with input signal.It is fundamental frequency omega that circuit characteristic is equivalent to a repetition frequency 0The square wave matched filter, in the input signal with reference signal with frequently signal, its output can be simplified shown as:
Figure S2007101569128D00041
Owing to the character that signal is forward and reverse is just the same, only forward is discussed here.By formula (1) as seen, when test duration t＞＞during τ, the amplitude of output signal be proportional to input signal amplitude and and switching signal between the cosine of phase differential.If both strict synchronism then are directly proportional between output signal and the input signal amplitude, realized the purpose of Test input signal amplitude.
And for the even-order harmonic of signal, its output amplitude is zero, and the good restraining effect is arranged; To odd harmonic, its output response is compared little (2n+1) doubly with first-harmonic; And the signal of other frequencies, it is big more to depart from fundamental frequency, and its amplitude is more little, and is also just more little to the influence of output.Therefore, the rotation capacitor filter has the good restraining effect for the various interference beyond the signal frequency, and its equivalent noise bandwidth summation for each odd harmonic place can be expressed as:
Δ f N = π 2 8 · Δ f N 1 = π 2 8 · 1 2 R 2 C 1 - - - ( 2 )
Therefore, improve integration time constant and can reduce noise bandwidth, but consider that magnet excitation frequency is higher, R 2C 1Value should adjust as required, should not obtain excessive.
Through obtaining the ac square wave signal V that an amplitude is directly proportional with the flow size after the filtering of rotation capacitor filter a, Fig. 5 is V aSynoptic diagram.Because the rotation capacitor filtering is actually flow signal is changed, the amplitude of signal is extracted, do not flow at fluid, promptly when zero-bit, actual and non-vanishing through filtered signal amplitude, but a determined value with the structurally associated of sensor, as the V among the figure A0, but the signal amplitude V that records aWith V A0Difference but reflected the variation of rate of flow of fluid, therefore,, just zero-bit can be removed from measured value and obtained flow value accurately as long as measure zero-bit.
V aSend into rectification circuit earlier and convert direct current signal to, rectification circuit is by second operational amplifier A 2, the first single-pole double-throw switch (SPDT) S 1, the 4th resistance R 4, the 5th resistance R 5, the 6th resistance R 6Form.The first single-pole double-throw switch (SPDT) S 1By the 200Hz square wave control synchronous, by adjusting adjustable resistance R with excited signal 5, making that circuit is equivalent to follower when the positive half cycle of square wave, the signal forward passes through, and during negative half period, circuit is equivalent to phase inverter, and after rectification, signal becomes in-phase signal V b, and send into sample circuit and carry out sampling processing.Sample circuit is by the second single-pole double-throw switch (SPDT) S 2, the 3rd operational amplifier A 3With second capacitor C 2, the 3rd capacitor C 3Form.The second single-pole double-throw switch (SPDT) S 2By frequency is the sampling pulse control of 400Hz, and pulsewidth is 0.25ms, and the positive half cycle and the negative half period that can be implemented in signal are respectively adopted a value, and pass through capacitor C 2, C 3Realize on average exporting reflected signal average DC voltage V at last a
V o = 1 2 ( V a + + V a - ) - - - ( 3 )
This circuit has stronger antijamming capability, makes signal that to a certain degree skew take place if disturb, and circuit can average by the difference with signal forward and negative sense and holding signal stable.Fig. 6 is signal rectification and sampling process synoptic diagram, and wherein (A) is the signal before the rectification, and for this process is described, this signal has been sneaked into interference, (B) is the signal V after the rectification b, (C) be sampling pulse, (D) be through over-sampling and the output V after finishing on average a, as can be seen, the process signal processing circuit can obtain a stable direct-flow signal voltage signal after carrying out filtering and rectification sampling, can measure it easily.

Claims (2)

1. capacitive electromagnetic flow meter, it is characterized in that, on measuring tube 1 outer wall, following both sides are provided with the last coil 2A of serial connection, lower coil 2B, last coil 2A, lower coil 2B is connected with exciting circuit 7, on measuring tube 1 an outer wall left side, right both sides are provided with left detecting electrode 3A, right detecting electrode 3B, left side detecting electrode 3A, right detecting electrode 3B is provided with left guarded electrode 4A outward, right guarded electrode 4B and left shading ring 5A, right shading ring 5B, left side detecting electrode 3A is connected with left prime amplifier 6A, right detecting electrode 3B is connected left prime amplifier 6A and right prime amplifier 6B and differential amplifier circuit 8 with right prime amplifier 6B, signal processing circuit 9 is connected.
2. a kind of capacitive electromagnetic flow meter according to claim 1 is characterized in that described signal processing circuit 9 is: first operational amplifier A 1Positive input terminal and the 3rd resistance R 3One end is connected, the 3rd resistance R 3Other end ground connection, first operational amplifier A 1The negative input end and first resistance R 1One end, the first electronic switch S A1One end, the 3rd electronic switch S B1One end is connected, first resistance R 1The other end be connected the first electronic switch S with the output terminal of differential amplifier circuit 8 A1The other end and second resistance R 2An end, first capacitor C 1An end, quadrielectron switch S B2An end be connected the 3rd electronic switch S B1The other end and second resistance R 2The other end, first capacitor C 1The other end, the second electronic switch S A2An end be connected the second electronic switch S A2The other end, quadrielectron switch S B2The other end and first operational amplifier A 1Output terminal, the 4th resistance R 4An end, the electronic switch S of first single-pole double-throw (SPDT) 1Chang Kaiduan be connected the electronic switch S of first single-pole double-throw (SPDT) 1The common port and second operational amplifier A 2Positive input terminal be connected the electronic switch S of first single-pole double-throw (SPDT) 1Normal-closed end and ground connection, the 4th resistance R 4The other end through the 5th resistance R 5, the 6th resistance R 6With second operational amplifier A 2Output terminal, the electronic switch S of second single-pole double-throw (SPDT) 2Normal-closed end be connected second operational amplifier A 2Negative input end and the 5th resistance R 5Adjustable end be connected the electronic switch S of second single-pole double-throw (SPDT) 2The common port and second capacitor C 2An end be connected second capacitor C 2Other end ground connection, the electronic switch S of second single-pole double-throw (SPDT) 2Chang Kaiduan and the 3rd operational amplifier A 3Positive input terminal, the 3rd capacitor C 3An end be connected the 3rd capacitor C 3Other end ground connection, the 3rd operational amplifier A 3Negative input end and the 3rd operational amplifier A 3Output terminal be connected.
CNB2007101569128A 2007-11-20 2007-11-20 Capacitor type electromagnetic flow meter Expired - Fee Related CN100453979C (en)

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CN103196503A (en) * 2013-02-22 2013-07-10 孙晓君 Flow meter
CN103206990A (en) * 2013-04-15 2013-07-17 福建上润精密仪器有限公司 Capacitive electromagnetic flowmeter
CN106979804A (en) * 2015-09-21 2017-07-25 Abb有限公司 Reduce the method and apparatus of interference
CN109489747A (en) * 2018-12-24 2019-03-19 合肥工业大学 A kind of electromagnetic flowmeter signal processing method based on frequency analysis
CN110178001A (en) * 2016-12-20 2019-08-27 恩德斯+豪斯流量技术股份有限公司 For operate magnetic induction flowmeter method and this magnetic induction flowmeter
CN110207769A (en) * 2019-07-06 2019-09-06 三川智慧科技股份有限公司 A kind of detectable and amendment data error coil induction type water meter
CN110345973A (en) * 2019-07-25 2019-10-18 深圳市普颂电子有限公司 Current vortex sensor and detection method
CN111060169A (en) * 2019-12-31 2020-04-24 上海理工大学 Device and method for measuring non-full pipe flow
CN111912471A (en) * 2019-05-10 2020-11-10 阿自倍尔株式会社 Capacitance type electromagnetic flowmeter
CN111982215A (en) * 2020-08-31 2020-11-24 维沃移动通信有限公司 Flow detection device and detection method
CN112229457A (en) * 2020-11-19 2021-01-15 吉林大学 Novel electromagnetic flowmeter and measuring method thereof
CN112360429A (en) * 2020-10-30 2021-02-12 中石化石油工程技术服务有限公司 Flow logging instrument
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CN103196503A (en) * 2013-02-22 2013-07-10 孙晓君 Flow meter
WO2014127670A1 (en) * 2013-02-22 2014-08-28 Sun Xiaojun Flowmeter
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CN103206990A (en) * 2013-04-15 2013-07-17 福建上润精密仪器有限公司 Capacitive electromagnetic flowmeter
CN103206990B (en) * 2013-04-15 2015-05-20 福建上润精密仪器有限公司 Capacitive electromagnetic flowmeter
CN106979804A (en) * 2015-09-21 2017-07-25 Abb有限公司 Reduce the method and apparatus of interference
US11047719B2 (en) 2016-12-20 2021-06-29 Endress+Hauser Flowtec Ag Magneto-inductive flow meter and operating method of analyzing a voltage pulse to correct an electrode voltage profile
CN110178001A (en) * 2016-12-20 2019-08-27 恩德斯+豪斯流量技术股份有限公司 For operate magnetic induction flowmeter method and this magnetic induction flowmeter
CN110178001B (en) * 2016-12-20 2021-06-22 恩德斯+豪斯流量技术股份有限公司 Method for operating a magnetically inductive flow meter and such a magnetically inductive flow meter
CN109489747B (en) * 2018-12-24 2020-03-20 合肥工业大学 Electromagnetic flowmeter signal processing method based on harmonic analysis
CN109489747A (en) * 2018-12-24 2019-03-19 合肥工业大学 A kind of electromagnetic flowmeter signal processing method based on frequency analysis
CN111912471A (en) * 2019-05-10 2020-11-10 阿自倍尔株式会社 Capacitance type electromagnetic flowmeter
CN111912471B (en) * 2019-05-10 2023-09-22 阿自倍尔株式会社 Capacitive electromagnetic flowmeter
CN110207769B (en) * 2019-07-06 2020-10-02 三川智慧科技股份有限公司 Coil induction type water meter capable of detecting and correcting data error
CN110207769A (en) * 2019-07-06 2019-09-06 三川智慧科技股份有限公司 A kind of detectable and amendment data error coil induction type water meter
CN110345973A (en) * 2019-07-25 2019-10-18 深圳市普颂电子有限公司 Current vortex sensor and detection method
CN111060169B (en) * 2019-12-31 2022-03-25 上海理工大学 Device and method for measuring non-full pipe flow
CN111060169A (en) * 2019-12-31 2020-04-24 上海理工大学 Device and method for measuring non-full pipe flow
CN111982215A (en) * 2020-08-31 2020-11-24 维沃移动通信有限公司 Flow detection device and detection method
CN112360429A (en) * 2020-10-30 2021-02-12 中石化石油工程技术服务有限公司 Flow logging instrument
CN112229457B (en) * 2020-11-19 2021-09-21 吉林大学 Novel electromagnetic flowmeter and measuring method thereof
CN112229457A (en) * 2020-11-19 2021-01-15 吉林大学 Novel electromagnetic flowmeter and measuring method thereof
CN113473830A (en) * 2021-07-02 2021-10-01 重庆大学 Intelligent switching electromagnetic manufacturing device based on parameter perception

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