CN103575960B - giant magnetoresistance effect current sensor - Google Patents
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Abstract
Giant magnetoresistance effect current sensor of the present invention, relate to the device for measuring electric current, it is a kind of giant magnetoresistance effect current sensor with magnetic shielding shell and bias coil, its formation comprises U-shaped magnetic shielding shell, giant magnetoresistance chip, bias coil winding, current－carrying conductor, pcb board, bias current sources and signal processing circuit, wherein, by U-shaped magnetic shielding shell, giant magnetoresistance chip, bias coil winding, current－carrying conductor and pcb board form the probe of giant magnetoresistance effect current sensor, above-mentioned signal processing circuit comprises bias magnetic field circuit for generating, giant magnetoresistance chip power supply voltage conversion circuit, generating circuit from reference voltage and modified calculus of differences amplifying circuit, the existence of magnetic shielding shell overcomes because the extremely sensitive characteristic of giant magnetoresistance on magnetic field makes them be subject to the defect of the impact of extraneous stray magnetic field simultaneously, there is provided the method for bias magnetic field to reduce hysteresis error and the accurate measurement of realization to ac and dc current by bias coil winding again simultaneously.
Description
Technical field
Technical scheme of the present invention relates to the device for measuring electric current, specifically giant magnetoresistance effect current sensor.
Background technology
Along with the development of Power Electronic Technique, the demand of compact high performance current sensor increases gradually.Traditional electric current detecting method comprises shunt, current transformer, Luo-coil and Hall element; New type of current detection technique comprises fluxgate sensor, giant magnetoresistance effect current sensor and Fibre Optical Sensor.By contrast, giant magnetoresistance effect current sensor has himself outstanding advantage performance, has unique magnetic inductive capacity.Giant magnetoresistance effect current sensor has the features such as, low-power consumption splendid to applying magnetic field high sensitivity, high workload bandwidth range, temperature stability and miniaturization.
But, because giant magnetoresistance is to the extremely sensitive characteristic in magnetic field, make them be subject to the impact of extraneous stray magnetic field simultaneously.The field source of these stray magnetic fields comprises the electric equipment such as motor and transformer, or current－carrying conductor around sensor etc.Stray magnetic field can cause sensor to produce larger output error, have impact on the accuracy of current measurement result.Meanwhile, when tested magnetic field more weak and positive and negative alternately change time, due to the coupling that giant magnetoresistance neighboring ferromagnetic interlayer is more weak, make giant magnetoresistance chip list reveal obvious hysteresis effect.Giant magnetoresistance chip used in prior art is in addition unipolar output characteristic, and when being measured as alternating current, output waveform is similar to full-wave rectification and exports, and the easy distortion of waveform exported like this, causes larger output error.
CN102043083A discloses a kind of giant magnetoresistance array current sensor, measures, and can complete Digital Transmission, the storage of information while realizing alternating current-direct current.But the weak point of this sensor is: 1. this sensor probe needs the Al-Ni-Co permanent magnet of 8 giant magnetoresistance chips and 16 bar shapeds to form, and cost is higher, and sonde configuration is comparatively complicated; 2. utilize permanent magnet to provide bias magnetic field, the magnetic field produced like this is stable not, and permanent magnet, along with the change of environment temperature, phenomenon of demagnetizing can occur, and causes output signal out of true; 3. this sensor carries out sampling maintenance and A/D conversion to the voltage signal that probe exports, then carries out spatial fourier transform through FPGA process, and signal processing circuit like this is comparatively complicated.
CN101038305B proposes a kind of array type current sensor of giant magnetic impedance (GMI) effect had based on amorphous soft magnet band, its defect has 3 points: 1. require just the same and Parallel Symmetric to two array amorphous current sensor probes, but due to reasons such as manufacturing process, to be difficult to guarantee two array amorphous current sensor probes completely the same, and consequent temperature drift phenomenon can cause certain output error; 2. sensor circuit part comprises two-way Bryant thatch oscillatory circuit and rectification circuit, and relate to the devices such as starting of oscillation electric capacity, crystal oscillator, transistor, high-frequency operational amplifier, commutation diode, electric capacity of voltage regulation and filter capacitor, circuit is comparatively complicated; 3. utilize permanent magnet provide bias magnetic field exist equally as in CN102043083A 2. as described in defect and deficiency.
Summary of the invention
Technical matters to be solved by this invention is: provide giant magnetoresistance effect current sensor, be a kind of giant magnetoresistance effect current sensor with magnetic shielding shell and bias coil, the existence of magnetic shielding shell overcomes because the extremely sensitive characteristic of giant magnetoresistance on magnetic field makes them be subject to the defect of the impact of extraneous stray magnetic field simultaneously; There is provided the method for bias magnetic field to reduce hysteresis error and the accurate measurement of realization to ac and dc current by bias coil winding again simultaneously.
The present invention solves this technical problem adopted technical scheme: giant magnetoresistance effect current sensor, it is a kind of giant magnetoresistance effect current sensor with magnetic shielding shell and bias coil, its formation comprises U-shaped magnetic shielding shell, giant magnetoresistance chip, bias coil winding, current－carrying conductor, pcb board, bias current sources and signal processing circuit, wherein, by U-shaped magnetic shielding shell, giant magnetoresistance chip, bias coil winding, current－carrying conductor and pcb board form the probe of giant magnetoresistance effect current sensor, above-mentioned signal processing circuit comprises bias magnetic field circuit for generating, giant magnetoresistance chip power supply voltage conversion circuit, generating circuit from reference voltage and modified calculus of differences amplifying circuit, pcb board is placed in U-shaped magnetic shielding shell, giant magnetoresistance chip fixed placement is above pcb board, current－carrying conductor is placed in the below of giant magnetoresistance chip, bias coil winding is wrapped on giant magnetoresistance chip uniformly, the output voltage of giant magnetoresistance chip power supply voltage conversion circuit is connected to the power pins of giant magnetoresistance chip, bias current sources is connected to bias coil winding two ends, modified calculus of differences amplifying circuit two input ends are connected to the positive output end of giant magnetoresistance chip and the negative output terminal of giant magnetoresistance chip, the output voltage Vref of generating circuit from reference voltage is connected to the positive input terminal of modified calculus of differences amplifying circuit, through the superposition of modified calculus of differences input amplifier signal, finally in the output signal of the output terminal output current sensor of modified calculus of differences amplifying circuit, form giant magnetoresistance current sensor thus.
Above-mentioned giant magnetoresistance effect current sensor, what described U-shaped magnetic shielding shell adopted is that permalloy material makes, its resistivity is 0.56 μ Ω m, and Curie point is 400 DEG C, and saturation induction density is Bs=0.7T, coercivity H under saturation induction density is not more than 1.6A/m, the magnetic permeability that DC magnetic performance meets in 0.08A/m magnetic field intensity is not less than 37.5mH/m, and thickness is 1mm, and width is 7mm, height is 10mm, and length is 13mm.
Above-mentioned giant magnetoresistance effect current sensor, described giant magnetoresistance chip and GMR chip, employing be NVE company of the U.S. produce AA002-02.
Above-mentioned giant magnetoresistance effect current sensor, described bias magnetic field circuit for generating is made up of chip LT3092 and bias coil winding L, chip LT3092 utilizes an internal current source and error amplifier and two external resistor Rset and resistor Rout to provide output current, the size of the resistance of regulating resistor Rset and resistor Rout can obtain the constant output current that is positioned at 0.5mA to 200mA, LT3092 output terminal is connected to bias coil winding L, bias coil winding L other end ground connection, the coil diameter of bias coil winding L is 0.08mm, the number of turn is 50 circles, direct current resistance is 3.487 Ω, the DC current size passed through is 50mA, resistor Rset resistance is 20k Ω, resistor Rout resistance is 4k Ω.
Above-mentioned giant magnetoresistance effect current sensor, the constituted mode of described giant magnetoresistance chip power supply voltage conversion circuit is: the input end Vin of voltage stabilizer VR7805 meets giant magnetoresistance current sensor system power supply DC power supply+15V, the filter capacitor C1 of 0.33uF is connected in parallel between the input end Vin of voltage stabilizer VR7805 and the earth terminal of voltage stabilizer VR7805, the direct current of+5V the voltage of the output end vo ut stable output of voltage stabilizer VR7805, the filter capacitor C2 of 0.1uF is connected in parallel between the output end vo ut of voltage stabilizer VR7805 and the earth terminal of voltage stabilizer VR7805, the output voltage of Vout pin is stable 5V direct current thus.
Above-mentioned giant magnetoresistance effect current sensor, the constituted mode of described generating circuit from reference voltage is: operational amplifier U1A and resistance R1 and R2 and R3 forms anti-phase input scaling circuit, the normal phase input end of the one termination U1A of resistance R1, the other end ground connection of resistance R1, the inverting input of the one termination U1A of resistance R2, the voltage source of another termination direct current 5V of resistance R2, resistance R3 receives at two ends inverting input and the output terminal of U1A respectively, and the supply voltage of U1A is+15V and-15V; The output terminal of U1A receives the normal phase input end of U1B, the inverting input of U1B and output terminal connect together formation voltage follower, the model of operational amplifier U1A and operational amplifier U1B is LF353, above-mentioned resistance R1 resistance is 8.2k Ω, resistance R2 resistance is 3.6k Ω, and resistance R3 resistance is 10k Ω.
Above-mentioned giant magnetoresistance effect current sensor, the formation of described modified calculus of differences amplifying circuit is: the inverting input of a termination operational amplifier A 1 of resistance R4, the output terminal of another termination operational amplifier A 2 of resistance R4, the inverting input of the one termination operational amplifier A 2 of resistance R5, the output terminal of another termination operational amplifier A 1 of resistance R5, the positive input terminal of operational amplifier A 2 is connected to the output terminal of operational amplifier A 1, the two ends of resistance R6 receive inverting input and the output terminal of operational amplifier A 2 respectively, the one termination voltage U 1 of resistance R1, the inverting input of another termination operational amplifier A 1 of resistance R1, the one termination voltage U 2 of resistance R2, the normal phase input end of another termination operational amplifier A 1 of resistance R2, the normal phase input end of the one termination operational amplifier A 1 of resistance R3, the other end ground connection of resistance R3, the model of operational amplifier A 1 and operational amplifier A 2 is LF356, above-mentioned resistance R1 resistance is 27k Ω, resistance R2 resistance is 27k Ω, resistance R3 resistance is 270k Ω, resistance R4 resistance is 270k Ω, resistance R5 resistance is 1k Ω, resistance R6 resistance is 10k Ω.
Above-mentioned giant magnetoresistance effect current sensor, involved device and parts are all that known approach obtains, and the installation method of all parts is that those skilled in the art grasped.
The invention has the beneficial effects as follows: compared with prior art, outstanding substantive distinguishing features of the present invention is:
(1) giant magnetoresistance current sensor principle of work is the magnetic field produced based on current－carrying conductor, increase to make the magnetic field at chip place as far as possible and ensure that the interference that extraneous stray magnetic field causes chip place is minimum simultaneously, effective method is application shielding techniques, i.e. magnetic shielding shell of the present invention and be designed to U-shaped structure.Magnetic shielding is used to isolate the measure of magnetic Field Coupling, be utilize magnetic flux to circulate along low reluctance path principle to change the direction of extraneous stray magnetic field, thus the magnetic line of force is gathered in shield.From magnetic resistance formula Rm=l/ μ S, the magnetic permeability of magnetic resistance and material is inversely proportional to, and therefore generally will select high-permeability material.In order to increase the range of sensing range, the permeability magnetic material of high saturation magnetic induction should being selected, simultaneously in order to obtain accurate testing result in real time, low magnetic hysteresis, low-coercivity material be selected.Conventional magnetic shielding material comprises: electromagnetic soft iron, siliconized plate, permalloy, non-crystaline amorphous metal etc.Wherein non-crystaline amorphous metal magnetic permeability is the highest, but price costly, electromagnetic soft iron and siliconized plate low price, but magnetic permeability is lower.From the viewpoint of performance and cost, the present invention have selected permalloy material as shielding case.
(2) although the magnetic shielding shell be made up of the permalloy magnetic material of high magnetic permeability, effectively can assemble wanted signal, reduce the impact of extraneous stray magnetic field simultaneously, but detection probe giant magnetoresistance chip used is unipolar output characteristic, when being measured as alternating current, output waveform is similar to full-wave rectification and exports, and the easy distortion of waveform exported like this, causes larger output error.In addition, be magnetic element with the current sensor based on giant magnetoresistance effect of magnetic shielding shell and bias coil due to giant magnetoresistance chip due to the present invention, therefore there is typical magnetic characteristic, namely there is hysteresis and saturated phenomenon.When tested magnetic field exceedes certain value, giant magnetoresistance chip reaches capacity, and exports and no longer increases.When tested magnetic field is more weak and when changing between positive and negative zero crossing, due to the coupling that giant magnetoresistance neighboring ferromagnetic interlayer is more weak, make giant magnetoresistance chip list reveal obvious hysteresis effect.Meanwhile, giant magnetoresistance chip used is unipolar output characteristic, and when being measured as alternating current, output waveform is similar to full-wave rectification and exports, and the easy distortion of waveform exported like this, causes larger output error.The present invention devises unique bias magnetic field structure for this reason, makes the magnetic field acting on giant magnetoresistance chip and GMR chip all bring up to linear zone by the superposition in magnetic field.Like this when without tested magnetic field, giant magnetoresistance chip exports a DC offset voltage, when there being tested electric current, the output voltage of giant magnetoresistance chip is the voltage having superposed again the magnetic field produced by tested electric current and produce on the basis of former bias voltage, provides DC bias magnetic field effectively can improve the linearity and the hysteresis error of sensor.
(3) due to the differential signal that giant magnetoresistance chip signal output is faint, application calculus of differences amplifying circuit is therefore needed to amplify signal.General calculus of differences amplifying circuit is made up of an integrated operational amplifier and external resistor network, and this structure causes input and output phase differential also to increase along with the increase of measured signal frequency, have impact on the bandwidth range of measured signal.In order to reduce phase error, the present invention proposes a kind of modified calculus of differences amplifying circuit, its structure introduces amplifier resistor network in the backfeed loop of general calculus of differences amplifying circuit, can effective compensation phase error, has higher common-mode rejection ratio simultaneously.The reference voltage Vref of this modified calculus of differences amplifying circuit positive input terminal is for eliminating the bias voltage of bias magnetic field generation, make giant magnetoresistance current sensor of the present invention finally export the voltage obtaining a bipolar output, also namely exporting to have just has negative voltage.
Compared with prior art, marked improvement of the present invention is:
(1) the present invention is 0.8% with the maximum error of the current sensor based on giant magnetoresistance effect in full range of magnetic shielding shell and bias coil, and has higher sensitivity and precision;
(2) the present invention adopts permalloy material with the magnetic shielding shell of the current sensor based on giant magnetoresistance effect of magnetic shielding shell and bias coil, it has high magnetic permeability, low-coercivity, high squareness ratio, core loss is low and high-temperature stability is good advantage, and saturation induction density is higher, wearing quality and corrosion stability are all strong.Add the sensitivity that magnetic shielding shell not only makes sensor export to be greatly improved, the linearity has also had improvement to a certain extent simultaneously.
(3) the present invention effectively have accumulated wanted signal with the current sensor based on giant magnetoresistance effect of magnetic shielding shell and bias coil, reduces the impact of extraneous stray magnetic field simultaneously.When there is the extraneous stray magnetic field of 2mT, the output error signal that the present invention has the giant magnetoresistance current sensor of shielding case is about 4mV, compared with being about 400mV with the output error signal of the current sensor of unshielded shell, the impact by extraneous stray magnetic field reduces and is about 100 times.
Accompanying drawing explanation
Below in conjunction with drawings and Examples, the present invention is further described.
Fig. 1 is the sonde configuration figure of giant magnetoresistance current sensor of the present invention.
Fig. 2 is the interphase interaction schematic diagram of each component part in giant magnetoresistance current sensor of the present invention.
Fig. 3 is the structural representation of giant magnetoresistance current sensor of the present invention.
Fig. 4 is the giant magnetoresistance chip power supply voltage conversion circuit schematic diagram of giant magnetoresistance current sensor of the present invention.
Fig. 5 is the bias magnetic field circuit for generating schematic diagram of giant magnetoresistance current sensor of the present invention.
Fig. 6 is the generating circuit from reference voltage schematic diagram of giant magnetoresistance current sensor of the present invention.
Fig. 7 is the circuit diagram of general type calculus of differences amplifying circuit.
Fig. 8 is the modified calculus of differences amplifying circuit schematic diagram of giant magnetoresistance current sensor of the present invention.
Fig. 9 is the B-H loop of giant magnetoresistance current sensor of the present invention in being and not being bias magnetic field two kinds of situations.
Figure 10 is the input-output characteristic curve of giant magnetoresistance current sensor of the present invention in being and not being magnetic shielding shell two kinds of situations.
Figure 11 is giant magnetoresistance current sensor of the present invention current sensor relative error curve map when adding magnetic shielding shell.
In figure, 1. magnetic shielding shell, 2. bias coil winding, 3. giant magnetoresistance chip, 4. current－carrying conductor, 5.PCB plate, 6. bias current sources, 7. modified calculus of differences amplifying circuit, 8. generating circuit from reference voltage, 9. giant magnetoresistance chip positive output end, 10. giant magnetoresistance chip negative output terminal.
Embodiment
Embodiment illustrated in fig. 1ly to show, the probe of giant magnetoresistance current sensor of the present invention comprises magnetic shielding shell 1, bias coil winding 2, giant magnetoresistance chip 3, current－carrying conductor 4 and pcb board 5, magnetic shielding shell 1 is U-shaped structure, from the viewpoint of performance and cost, have selected the material of permalloy as shielding case, the magnetic field at giant magnetoresistance chip 3 place is increased as far as possible, ensures that the interference that extraneous stray magnetic field causes giant magnetoresistance chip 3 place is minimum simultaneously.Because giant magnetoresistance chip 3 has the characteristic of unipolar output, therefore DC bias magnetic field is provided by bias coil winding 2, bias coil winding 2 is wrapped on giant magnetoresistance chip 3 uniformly, makes the magnetic field acting on giant magnetoresistance chip 3 all bring up to linear zone by the superposition in magnetic field.Giant magnetoresistance chip 3 is fixed on pcb board 5.Current－carrying conductor 4 is placed between giant magnetoresistance chip 3 and pcb board 5, passes into current induced magnetic field in current－carrying conductor 4, and giant magnetoresistance chip 3 is output difference divided voltage signal under the effect in tested magnetic field.Owing to having linear variability law between output signal and tested magnetic field, the voltage proportional of output in tested electric current, thus realizes the measurement function of current signal.
Embodiment illustrated in fig. 2ly show, in giant magnetoresistance current sensor of the present invention, the interphase interaction of each component part is: giant magnetoresistance chip is placed in magnetic shielding shell; Bias magnetic field circuit for generating acts on giant magnetoresistance chip, makes the magnetic field acting on giant magnetoresistance chip all bring up to linear zone; The magnetic field that tested electric current produces is gathered after magnetic through magnetic shielding shell and is acted on giant magnetoresistance chip, and giant magnetoresistance chip output voltage signal enters the general type calculus of differences amplifying circuit in figure in the amplifying circuit of modified calculus of differences shown in dotted line frame; In order to eliminate the DC offset voltage that bias magnetic field circuit for generating causes, shown in dotted line frame, modified calculus of differences input amplifier adds the reference voltage that generating circuit from reference voltage produces, superposing of the bias voltage produced with bias magnetic field circuit for generating by this reference voltage, plays the effect of bias compensation.Because general type calculus of differences amplifying circuit causes input and output phase differential also to increase along with the increase of measured signal frequency, therefore in the backfeed loop of general type calculus of differences amplifying circuit, amplifier resistor network is introduced, so effect of phase compensation is played to general type calculus of differences amplifying circuit, form the modified calculus of differences amplifying circuit shown in dotted line frame thus, output signal and the tested electric current of final modified calculus of differences amplifying circuit are forward proportionate relationship.
Embodiment illustrated in fig. 3ly to show, the structure of giant magnetoresistance current sensor of the present invention is: giant magnetoresistance chip 3 is placed in magnetic shielding shell 1, current－carrying conductor 4 is placed in the below of giant magnetoresistance chip 3, bias coil winding 2 is wrapped on giant magnetoresistance chip 3 uniformly, bias current sources 6 is connected to bias coil winding 2 two ends, for giant magnetoresistance chip 3 provides bias magnetic field.The magnetic fields that current－carrying conductor 4 produces is in giant magnetoresistance chip 3 output voltage signal, output signal enters modified calculus of differences amplifying circuit 7 and amplifies, generating circuit from reference voltage 8 is added to the input end of modified calculus of differences amplifying circuit 7, so through the bias voltage superposition that generating circuit from reference voltage 8 produces with the bias magnetic field produced by bias coil winding, make modified calculus of differences amplifying circuit 7 export one with the voltage signal of tested electric current proportional.
Embodiment illustrated in fig. 4ly to show, the constituted mode of the giant magnetoresistance chip power supply voltage conversion circuit of giant magnetoresistance current sensor of the present invention is: the input end Vin of voltage stabilizer VR7805 meets giant magnetoresistance current sensor system power supply DC power supply+15V, the filter capacitor C1 of 0.33uF is connected in parallel between the input end Vin of voltage stabilizer VR7805 and the earth terminal of voltage stabilizer VR7805, the direct current of+5V the voltage of the output end vo ut stable output of voltage stabilizer VR7805, the filter capacitor C2 of 0.1uF is connected in parallel between the output end vo ut of voltage stabilizer VR7805 and the earth terminal of voltage stabilizer VR7805, the output voltage of Vout pin is stable 5V direct current thus.Because the supply voltage needed for giant magnetoresistance chip is positive 5V, and giant magnetoresistance current sensor system power supply power supply is positive and negative 15V, therefore produced the supply voltage needed for stable DC voltage supply giant magnetoresistance chip of 5V by the effect of voltage stabilizer VR7805.
Embodiment shown in Fig. 5 shows, the bias magnetic field circuit for generating of giant magnetoresistance current sensor of the present invention is made up of chip LT3092 and bias coil winding L.The inner structure of the DC current source of the power voltage supply of display 5V in Fig. 5 square frame, its chips LT3092 utilizes an internal current source and error amplifier and two external resistor Rset and resistor Rout to provide output current, the size of the resistance of regulating resistor Rset and resistor Rout can obtain the constant output current that is positioned at 0.5mA to 200mA, IN is the input end pin of LT3092 chip, and this pin is the power supply input end of chip.OUT is the output terminal of chip, SET be chip end is set, SET is connected to the in-phase input end of chip internal error amplifier, can arrange the offset operation point of electric current simultaneously.10 μ A are LT3092 chip internal reference current source, and this reference current source flows through resistor Rset and produces a voltage, and this voltage is applied to another resistor Rout and produces output current, and resistor Rout is connected to chip OUT output terminal and resistor Rset two ends.LT3092 output terminal is connected to bias coil winding L, bias coil winding L other end ground connection, and the coil diameter of bias coil winding L is 0.08mm, and the number of turn is 50 circles, and direct current resistance is 3.487 Ω, and the DC current size passed through is 50mA.In figure, resistor Rset resistance is 20k Ω, and resistor Rout resistance is 4k Ω.
Embodiment shown in Fig. 6 shows, the constituted mode of the generating circuit from reference voltage of giant magnetoresistance current sensor of the present invention is: operational amplifier U1A and resistance R1 and R2 and R3 forms anti-phase input scaling circuit, the other end ground connection of the normal phase input end c of the one termination U1A of resistance R1, resistance R1.The voltage source of another termination direct current 5V of the inverting input b of the one termination U1A of resistance R2, resistance R2, the supply voltage of inverting input b and output terminal a, U1A that resistance R3 receives at two ends U1A is respectively that+15V holds h and-15V to hold d; The output terminal a of U1A receives the normal phase input end e of U1B, and the inverting input f of U1B and output terminal g connects together formation voltage follower.Because voltage follower has, input impedance is high, output impedance is low, is equivalent to a constant pressure source to late-class circuit, its output voltage not by load impedance influence, so obtain a constant reference voltage Vref.The model of operational amplifier U1A and operational amplifier U1B is LF353.In figure, resistance R1 resistance is 8.2k Ω, and resistance R2 resistance is 3.6k Ω, and resistance R3 resistance is 10k Ω.
Embodiment shown in Fig. 7 shows, the formation of the circuit of general type calculus of differences amplifying circuit is: be made up of an integrated operational amplifier and external resistor network, the one termination voltage U 1 of resistance R1, the inverting input of another termination operational amplifier of resistance R1, the one termination voltage U 2 of resistance R2, the normal phase input end of another termination operational amplifier of resistance R2, resistance R4 receives at two ends inverting input and the output terminal of operational amplifier respectively, the normal phase input end of the one termination operational amplifier of resistance R3, the other end ground connection of resistance R3.Operational amplifier model is LF356.This structure causes input and output phase differential also to increase along with the increase of measured signal frequency, have impact on the bandwidth range of measured signal.In figure, resistance R1 resistance is 27k Ω, and resistance R2 resistance is 27k Ω, and resistance R3 resistance is 270k Ω, and resistance R4 resistance is 270k Ω.
Embodiment shown in Fig. 8 shows, the formation of the modified calculus of differences amplifying circuit of giant magnetoresistance current sensor of the present invention is: the inverting input of a termination operational amplifier A 1 of resistance R4, the output terminal of another termination operational amplifier A 2 of resistance R4, the inverting input of the one termination operational amplifier A 2 of resistance R5, the output terminal Uo of another termination operational amplifier A 1 of resistance R5 and the output terminal of modified calculus of differences amplifying circuit, the positive input terminal of operational amplifier A 2 is connected to the output terminal Uo of operational amplifier A 1, the two ends of resistance R6 receive inverting input and the output terminal of operational amplifier A 2 respectively, the one termination voltage U 1 of resistance R1, the inverting input of another termination operational amplifier A 1 of resistance R1, the one termination voltage U 2 of resistance R2, the normal phase input end of another termination operational amplifier A 1 of resistance R2, the normal phase input end of the one termination operational amplifier A 1 of resistance R3, the other end ground connection of resistance R3, the model of operational amplifier A 1 and operational amplifier A 2 is LF356.In figure, resistance R1 resistance is 27k Ω, and resistance R2 resistance is 27k Ω, and resistance R3 resistance is 270k Ω, and resistance R4 resistance is 270k Ω, and resistance R5 resistance is 1k Ω, and resistance R6 resistance is 10k Ω.
In order to reduce phase error, the present invention proposes a kind of modified calculus of differences amplifying circuit.Compared with the general type calculus of differences amplifying circuit shown in Fig. 7, the improvement of modified calculus of differences amplifying circuit of the present invention is exactly the output terminal of the inverting input one termination amplifier A2 of resistance R4 mono-termination amplifier A1, the inverting input of the one termination amplifier A2 of resistance R5, the output terminal Uo of another termination amplifier A1 of resistance R5, the positive input terminal of amplifier A2 is also connected to the output terminal Uo of amplifier A1, and the two ends of resistance R6 receive inverting input and the output terminal of amplifier A2 respectively.Modified calculus of differences amplifying circuit of the present invention introduces amplifier resistor network in the backfeed loop of general type calculus of differences amplifying circuit, can effective compensation phase error, has higher common-mode rejection ratio simultaneously.
Embodiment shown in Fig. 9 shows, in being and not being bias magnetic field two kinds of situations, when tested electric current in certain range in positive stroke and revesal process current sensor export and the relation of input, test result improves current sensor hysteresis error after showing to add bias magnetic field significantly reduces, and the linearity has had raising to a certain degree simultaneously.
Embodiment shown in Figure 10 shows, in being and not being magnetic shielding shell two kinds of situations, the data obtained by tested for difference electric current lower sensor output voltage to be carried out curve fitting the figure obtained by matlab software, test result shows to compare without magnet shielding structure, has the sensitivity of the giant magnetoresistance current sensor of the present invention of magnetic shielding shell to be greatly improved.
Embodiment shown in Figure 11 shows giant magnetoresistance current sensor of the present invention current sensor relative error curve map when adding magnetic shielding shell.Deduct actual value by the theoretical value of output voltage, more just can obtain the relative error within the scope of this current sensor measurement divided by actual value.When can show that range of current is-20A ~+20A based on experimental data, relative error has been restricted to 0.8%.
Embodiment
With above-mentioned Fig. 1, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 and all parts embodiment illustrated in fig. 8, device becomes to have the current sensor based on giant magnetoresistance effect of magnetic shielding shell and bias coil, and wherein the planform of magnetic shielding shell 1 and the shape of bias coil winding 2 and position are expressed all in FIG.Giant magnetoresistance chip 3 i.e. GMR chip, employing be NVE company of the U.S. produce AA002-02; What U-shaped magnetic shielding shell adopted is that permalloy material makes, its resistivity is 0.56 μ Ω m, Curie point is 400 DEG C, saturation induction density is Bs=0.7T, and the coercivity H under saturation induction density is not more than 1.6A/m, and the magnetic permeability that DC magnetic performance meets in 0.08A/m magnetic field intensity is not less than 37.5mH/m, thickness is 1mm, width is 7mm, and height is 10mm, and length is 13mm.
The giant magnetoresistance current sensor that said apparatus becomes is carried out the experiments of measuring of DC current, tested electric current, from-20A ~ 20A, measures the output voltage of modified calculus of differences amplifying circuit.The data obtained are inputted international business software matlab and carries out least square curve fitting, obtain the relation of the output voltage of current sensor shown in Figure 10 and tested electric current.The fit equation of this curve is respectively: when there is magnetic shielding shell, the pass of sensor output voltage and tested electric current is as shown in Figure 10: Uout=119.96*I+4.1659, this formula represents the quantitative relation between tested electric current and current sensor output voltage, can obtain, the sensitivity of this current sensor is 119.96, drift is 4.1659mV, and output voltage is limited in ± 3V.Carry out test when not having magnetic shielding shell again, equally also with the pass that least square curve fitting obtains sensor output voltage as shown in Figure 10 and tested electric current be: Uout=47.289*I+5.7122, analyzing the sensitivity obtaining current sensor is 47.289, and drift is 5.7122mV.Can find out and add the sensitivity that magnetic shielding shell effectively can increase current sensor, the drift of current sensor can be reduced simultaneously.Actual value is deducted by the theoretical value of output voltage, just relative error when can to obtain this current sensor measurement scope be-20A ~ 20A divided by actual value again, embodiment as shown in figure 11 shows giant magnetoresistance current sensor of the present invention current sensor relative error curve map when adding magnetic shielding shell, visible in the range of-20A to 20A, relative error is limited in ± 0.8% in.
Device involved in above-described embodiment and parts are all that known approach obtains, and the installation method of all parts is that those skilled in the art grasped.
Claims (4)
1. giant magnetoresistance effect current sensor, it is characterized in that: be a kind of giant magnetoresistance effect current sensor with magnetic shielding shell and bias coil, its formation comprises U-shaped magnetic shielding shell, giant magnetoresistance chip, bias coil winding, current－carrying conductor, pcb board, bias current sources and signal processing circuit, wherein, by U-shaped magnetic shielding shell, giant magnetoresistance chip, bias coil winding, current－carrying conductor and pcb board form the probe of giant magnetoresistance effect current sensor, above-mentioned signal processing circuit comprises bias magnetic field circuit for generating, giant magnetoresistance chip power supply voltage conversion circuit, generating circuit from reference voltage and modified calculus of differences amplifying circuit, pcb board is placed in U-shaped magnetic shielding shell, giant magnetoresistance chip fixed placement is above pcb board, current－carrying conductor is placed in the below of giant magnetoresistance chip, bias coil winding is wrapped on giant magnetoresistance chip uniformly, the output voltage of giant magnetoresistance chip power supply voltage conversion circuit is connected to the power pins of giant magnetoresistance chip, bias current sources is connected to bias coil winding two ends, modified calculus of differences amplifying circuit two input ends are connected to the positive output end of giant magnetoresistance chip and the negative output terminal of giant magnetoresistance chip, the output voltage Vref of generating circuit from reference voltage is connected to the positive input terminal of modified calculus of differences amplifying circuit, through the superposition of modified calculus of differences input amplifier signal, finally in the output signal of the output terminal output current sensor of modified calculus of differences amplifying circuit, form giant magnetoresistance current sensor thus, described giant magnetoresistance chip and GMR chip, that adopt is the AA002-02 that NVE company of the U.S. produces.
2. according to the said giant magnetoresistance effect current sensor of claim 1, it is characterized in that: what described U-shaped magnetic shielding shell adopted is that permalloy material makes, its resistivity is 0.56 μ Ω m, and Curie point is 400 DEG C, and saturation induction density is Bs=0.7T, coercivity H under saturation induction density is not more than 1.6A/m, the magnetic permeability that DC magnetic performance meets in 0.08A/m magnetic field intensity is not less than 37.5mH/m, and thickness is 1mm, and width is 7mm, height is 10mm, and length is 13mm.
3. according to the said giant magnetoresistance effect current sensor of claim 1, it is characterized in that: described bias magnetic field circuit for generating is made up of chip LT3092 and bias coil winding L, chip LT3092 utilizes an internal current source and error amplifier and two external resistor Rset and resistor Rout to provide output current, the size of the resistance of regulating resistor Rset and resistor Rout can obtain the constant output current that is positioned at 0.5mA to 200mA, LT3092 output terminal is connected to bias coil winding L, bias coil winding L other end ground connection, the coil diameter of bias coil winding L is 0.08mm, the number of turn is 50 circles, direct current resistance is 3.487 Ω, the DC current size passed through is 50mA, resistor Rset resistance is 20k Ω, resistor Rout resistance is 4k Ω.
4. according to the said giant magnetoresistance effect current sensor of claim 1, it is characterized in that: the formation of described modified calculus of differences amplifying circuit is: the inverting input of a termination operational amplifier A 1 of resistance R4, the output terminal of another termination operational amplifier A 2 of resistance R4, the inverting input of the one termination operational amplifier A 2 of resistance R5, the output terminal of another termination operational amplifier A 1 of resistance R5, the positive input terminal of operational amplifier A 2 is connected to the output terminal of operational amplifier A 1, the two ends of resistance R6 receive inverting input and the output terminal of operational amplifier A 2 respectively, the one termination voltage U 1 of resistance R1, the inverting input of another termination operational amplifier A 1 of resistance R1, the one termination voltage U 2 of resistance R2, the normal phase input end of another termination operational amplifier A 1 of resistance R2, the normal phase input end of the one termination operational amplifier A 1 of resistance R3, the other end ground connection of resistance R3, the model of operational amplifier A 1 and operational amplifier A 2 is LF356, above-mentioned resistance R1 resistance is 27k Ω, resistance R2 resistance is 27k Ω, resistance R3 resistance is 270k Ω, resistance R4 resistance is 270k Ω, resistance R5 resistance is 1k Ω, resistance R6 resistance is 10k Ω.
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