CN103575960B - giant magnetoresistance effect current sensor - Google Patents

Abstract

The giant magnetoresistance effect current sensor of the present invention relates to a device for measuring current, which is a giant magnetoresistance effect current sensor with a magnetic shielding shell and a bias coil, and its composition includes a U-shaped magnetic shielding shell, a giant magnetoresistance chip, Bias coil winding, current-carrying conductor, PCB board, bias current source and signal processing circuit, wherein, the giant magnetoresistance is composed of U-shaped magnetic shielding shell, giant magnetoresistance chip, bias coil winding, current-carrying conductor and PCB board The probe of the effect current sensor, the above-mentioned signal processing circuit includes a bias magnetic field generation circuit, a giant magnetoresistance chip power supply voltage conversion circuit, a reference voltage generation circuit and an improved differential operational amplifier circuit. The highly sensitive nature of the magnetic field makes them susceptible to the defects of external stray magnetic fields. At the same time, the method of providing a bias magnetic field through the bias coil winding reduces the hysteresis error and realizes accurate measurement of AC and DC currents.

Description

giant magnetoresistance effect current sensor

technical field

The technical solution of the invention relates to a device for measuring current, specifically a giant magnetoresistance effect current sensor.

Background technique

With the development of power electronics technology, the demand for high-performance compact current sensors is gradually increasing. Traditional current detection methods include shunts, current transformers, Rogowski coils, and Hall sensors; new current detection technologies include fluxgate sensors, giant magnetoresistance effect current sensors, and fiber optic sensors. In contrast, the giant magnetoresistance effect current sensor has its own outstanding advantages and unique magnetic induction ability. The giant magnetoresistance effect current sensor has the characteristics of high sensitivity to applied magnetic field, high operating bandwidth range, excellent temperature stability, low power consumption and miniaturization.

However, due to the high sensitivity of giant magnetoresistance to magnetic field, they are also vulnerable to external stray magnetic fields. Sources of these stray magnetic fields include electrical equipment such as motors and transformers, or current-carrying conductors around sensors, among others. The stray magnetic field will cause a large output error of the sensor, which affects the accuracy of the current measurement result. At the same time, when the measured magnetic field is weak and alternately positive and negative, the giant magnetoresistance chip exhibits obvious hysteresis effect due to the weak coupling between the adjacent ferromagnetic layers of the giant magnetoresistance. In addition, the giant magnetoresistive chip used in the prior art has a unipolar output characteristic. When it is measured as an alternating current, the output waveform is similar to a full-wave rectified output, so the output waveform is easily distorted, causing a large output error.

CN102043083A discloses a giant magnetoresistive array current sensor to realize simultaneous measurement of AC and DC, and to complete digital transmission and storage of information. However, the disadvantages of this sensor are: ①The sensor probe needs 8 giant magnetoresistive chips and 16 bar-shaped AlNiCo permanent magnets, the cost is high, and the probe structure is relatively complicated; ②Use permanent magnets to provide a bias magnetic field , the magnetic field generated in this way is not stable enough, and the permanent magnet will demagnetize as the ambient temperature changes, resulting in inaccurate output signals; Space Fourier transform, so the signal processing circuit is more complicated.

CN101038305B proposes an array current sensor based on the giant magneto-impedance (GMI) effect of the amorphous soft magnetic strip, which has three defects: ① The probes of the two array amorphous current sensors are required to be exactly the same and parallel and symmetrical , but due to the manufacturing process and other reasons, it is difficult to ensure that the probes of the two array type amorphous current sensors are completely consistent, and the resulting temperature drift phenomenon will cause a certain output error; , involving devices such as starting capacitors, crystal oscillators, transistors, high-frequency operational amplifiers, rectifier diodes, voltage stabilizing capacitors, and filter capacitors, the circuit is relatively complicated; ③ Utilizing permanent magnets to provide bias magnetic fields also has the defects described in ② in CN102043083A and insufficient.

Contents of the invention

The technical problem to be solved by the present invention is to provide a giant magnetoresistance effect current sensor, which is a giant magnetoresistance effect current sensor with a magnetic shielding shell and a bias coil. The highly sensitive characteristics make them susceptible to the defects of external stray magnetic fields; at the same time, the method of providing a bias magnetic field through the bias coil winding reduces the hysteresis error and realizes accurate measurement of AC and DC currents.

The technical scheme adopted by the present invention to solve the technical problem is: the giant magnetoresistance effect current sensor is a giant magnetoresistance effect current sensor with a magnetic shielding shell and a bias coil, and its composition includes a U-shaped magnetic shielding shell, a giant magnetic Resistance chip, bias coil winding, current-carrying conductor, PCB board, bias current source and signal processing circuit, wherein, it is composed of U-shaped magnetic shielding shell, giant magnetoresistive chip, bias coil winding, current-carrying conductor and PCB board The probe of the giant magnetoresistance effect current sensor, the above-mentioned signal processing circuit includes a bias magnetic field generation circuit, a giant magnetoresistance chip power supply voltage conversion circuit, a reference voltage generation circuit and an improved differential operational amplifier circuit; the PCB board is placed in a U-shaped magnetic shielding shell Inside, the giant magnetoresistance chip is fixedly placed above the PCB board, the current-carrying conductor is placed under the giant magnetoresistance chip, the bias coil winding is evenly wound on the giant magnetoresistance chip, and the output of the giant magnetoresistance chip power supply voltage conversion circuit The voltage is connected to the power supply pin of the giant magnetoresistance chip, the bias current source is connected to both ends of the bias coil winding, and the two input terminals of the improved differential operational amplifier circuit are respectively connected to the positive output terminal of the giant magnetoresistance chip and the giant magnetoresistance The negative output terminal of the chip, the output voltage Vref of the reference voltage generation circuit is connected to the positive input terminal of the improved differential operational amplifier circuit, after the superposition of the signals at the input terminal of the improved differential operational amplifier circuit, and finally at the output of the improved differential operational amplifier circuit The terminal outputs the output signal of the current sensor, thus forming a giant magnetoresistive current sensor.

For the above giant magnetoresistance effect current sensor, the U-shaped magnetic shielding shell is made of permalloy material, its resistivity is 0.56μΩ·m, the Curie point is 400°C, the saturation magnetic induction is Bs=0.7T, and the saturation magnetic induction is Bs=0.7T. The coercive force Hc under the magnetic induction intensity is not more than 1.6A/m, the DC magnetic performance meets the magnetic permeability in the magnetic field intensity of 0.08A/m is not less than 37.5mH/m, the thickness is 1mm, the width is 7mm, and the height is 10mm. The length is 13mm.

The giant magnetoresistance effect current sensor mentioned above, the giant magnetoresistance chip, namely the GMR chip, adopts AA002-02 produced by NVE Company of the United States.

For the giant magnetoresistance effect current sensor mentioned above, the bias magnetic field generating circuit is composed of the chip LT3092 and the bias coil winding L, and the chip LT3092 utilizes an internal current source and an error amplifier as well as two external resistors Rset and resistor Rout to provide an output Current, adjusting the resistance value of resistor Rset and resistor Rout can get a constant output current between 0.5mA and 200mA, the output terminal of LT3092 is connected to the bias coil winding L, the other end of the bias coil winding L is grounded, and the bias The coil diameter of the coil winding L is 0.08mm, the number of turns is 50 turns, the DC resistance is 3.487Ω, the DC current passing through is 50mA, the resistance value of the resistor Rset is 20kΩ, and the resistance value of the resistor Rout is 4kΩ.

For the giant magnetoresistance effect current sensor, the configuration of the giant magnetoresistance chip power supply voltage conversion circuit is as follows: the input terminal Vin of the voltage regulator VR7805 is connected to the giant magnetoresistance current sensor system power supply DC power supply +15V, and the filter capacitor C1 of 0.33uF Connect in parallel between the input terminal Vin of the voltage regulator VR7805 and the ground terminal of the voltage regulator VR7805, the output terminal Vout of the voltage regulator VR7805 outputs a stable +5V voltage DC, and the 0.1uF filter capacitor C2 is connected in parallel with the voltage regulator VR7805 Between the output terminal Vout of the voltage regulator VR7805 and the ground terminal of the regulator VR7805, the output voltage of the Vout pin is a stable 5V direct current.

For the above giant magnetoresistance effect current sensor, the configuration of the reference voltage generating circuit is as follows: the operational amplifier U1A and the resistors R1, R2 and R3 form an inverting input proportional operation circuit, one end of the resistor R1 is connected to the positive phase input of U1A, and the resistor The other end of R1 is grounded, one end of resistor R2 is connected to the inverting input of U1A, the other end of resistor R2 is connected to a DC 5V voltage source, and the two ends of resistor R3 are respectively connected to the inverting input and output of U1A, the power supply of U1A The voltage is +15V and -15V; the output terminal of U1A is connected to the non-inverting input terminal of U1B, and the inverting input terminal and output terminal of U1B are connected together to form a voltage follower. The models of operational amplifier U1A and operational amplifier U1B are both LF353 , the resistance value of the above-mentioned resistor R1 is 8.2 kΩ, the resistance value of the resistor R2 is 3.6 kΩ, and the resistance value of the resistor R3 is 10 kΩ.

The above-mentioned giant magnetoresistance effect current sensor, the composition of the improved differential operational amplifier circuit is: one end of the resistance R4 is connected to the inverting input end of the operational amplifier A1, the other end of the resistance R4 is connected to the output end of the operational amplifier A2, and the other end of the resistance R4 is connected to the output end of the operational amplifier A2. One end is connected to the inverting input terminal of the operational amplifier A2, the other end of the resistor R5 is connected to the output terminal of the operational amplifier A1, the positive input terminal of the operational amplifier A2 is connected to the output terminal of the operational amplifier A1, and the two ends of the resistor R6 are respectively connected to the operational amplifier The inverting input terminal and output terminal of A2, one end of the resistor R1 is connected to the voltage U1, the other end of the resistor R1 is connected to the inverting input end of the operational amplifier A1, one end of the resistor R2 is connected to the voltage U2, and the other end of the resistor R2 is connected to the operational amplifier A1 One end of the resistor R3 is connected to the positive input end of the operational amplifier A1, and the other end of the resistor R3 is grounded. The models of the operational amplifier A1 and the operational amplifier A2 are both LF356. The resistance value is 27kΩ, the resistance value of the resistor R3 is 270kΩ, the resistance value of the resistor R4 is 270kΩ, the resistance value of the resistor R5 is 1kΩ, and the resistance value of the resistor R6 is 10kΩ.

The devices and parts involved in the above giant magnetoresistance effect current sensor are all obtained from known means, and the installation methods of all parts are within the grasp of those skilled in the art.

The beneficial effects of the present invention are: compared with the prior art, the outstanding substantive features of the present invention are:

(1) The working principle of the giant magnetoresistive current sensor is based on the magnetic field generated by the current-carrying conductor. In order to increase the magnetic field at the chip as much as possible and ensure the minimum interference caused by the external stray magnetic field to the chip, the effective method is to apply magnetic shielding technology. , that is, the magnetic shield used in the present invention and designed as a U-shaped structure. Magnetic shielding is a measure used to isolate magnetic field coupling. It uses the principle of magnetic flux flowing along a low reluctance path to change the direction of external stray magnetic fields, so that the magnetic field lines gather in the shielding body. It can be seen from the reluctance formula Rm=l/μS that the reluctance is inversely proportional to the magnetic permeability of the material, so generally high magnetic permeability materials should be selected. In order to increase the measuring range of the detection range, the magnetic material with high saturation magnetic density should be selected, and at the same time, in order to obtain real-time and accurate detection results, the material with low hysteresis and low coercive force should be selected. Commonly used magnetic shielding materials include: electromagnetic soft iron, silicon steel sheet, permalloy, amorphous alloy, etc. Among them, the magnetic permeability of amorphous alloy is the highest, but the price is relatively expensive, and the price of electromagnetic soft iron and silicon steel sheet is cheap, but the magnetic permeability is low. Considering performance and cost, the present invention selects permalloy material as the shielding case.

(2) Although the magnetic shielding shell composed of permalloy magnetic material with high magnetic permeability can effectively gather the desired signal and reduce the influence of external stray magnetic fields, the giant magnetoresistive chip used in the detection probe is a unipolar output Characteristics, when it is measured as an AC current, the output waveform is similar to the full-wave rectified output, so the output waveform is easily distorted, causing a large output error. In addition, since the giant magnetoresistance effect-based current sensor with a magnetic shield and a bias coil of the present invention is a magnetic element, there are typical magnetic characteristics, that is, hysteresis and saturation. When the measured magnetic field exceeds a certain value, the giant magnetoresistive chip reaches saturation, and the output will no longer increase. When the measured magnetic field is weak and changes between positive and negative zero-crossing points, the giant magnetoresistance chip exhibits obvious hysteresis effect due to the weak coupling between the adjacent ferromagnetic layers of the giant magnetoresistance. At the same time, the giant magnetoresistive chip used has unipolar output characteristics. When it is measured as an alternating current, the output waveform is similar to a full-wave rectified output, so the output waveform is easily distorted, causing a large output error. For this reason, the present invention designs a unique bias magnetic field structure, through the superposition of the magnetic field, the magnetic field acting on the giant magnetoresistive chip, that is, the GMR chip, is all increased to the linear region. In this way, when there is no measured magnetic field, the giant magnetoresistive chip outputs a DC bias voltage. When there is a measured current, the output voltage of the giant magnetoresistive chip is superimposed on the basis of the original bias voltage and a voltage generated by the measured current. The voltage generated by the magnetic field, providing a DC bias magnetic field can effectively improve the linearity and hysteresis error of the sensor.

(3) Since the output signal of the giant magnetoresistive chip is a weak differential signal, it is necessary to use a differential operational amplifier circuit to amplify the signal. A general differential operational amplifier circuit is composed of an integrated operational amplifier and an external resistor network. This structure increases the input-output phase difference with the increase of the frequency of the measured signal, which affects the bandwidth range of the measured signal. In order to reduce the phase error, the present invention proposes an improved differential operational amplifier circuit. Its structure is to introduce an operational amplifier resistor network into the feedback loop of a general differential operational amplifier circuit, which can effectively compensate the phase error and has a higher common mode suppression ratio. The reference voltage Vref at the positive input terminal of the improved differential operational amplifier circuit is used to eliminate the bias voltage generated by the bias magnetic field, so that the final output of the giant magnetoresistive current sensor of the present invention obtains a bipolar output voltage, that is, the output has positive and negative voltages. negative voltage.

Compared with prior art, remarkable progress of the present invention is:

(1) The giant magnetoresistance effect-based current sensor with a magnetic shield and a bias coil of the present invention has a maximum error of 0.8% in the full scale range, and has high sensitivity and precision;

(2) The magnetic shielding shell of the current sensor based on the giant magnetoresistance effect with a magnetic shielding shell and a bias coil in the present invention adopts permalloy material, which has high magnetic permeability, low coercive force, high squareness ratio, magnetic It has the advantages of low core loss and good high temperature stability, high saturation magnetic induction, strong wear resistance and corrosion resistance. Adding a magnetic shield not only greatly improves the sensitivity of the sensor output, but also improves the linearity to a certain extent.

(3) The giant magnetoresistance effect-based current sensor with a magnetic shield and a bias coil of the present invention effectively gathers desired signals while reducing the influence of external stray magnetic fields. When there is an external stray field of 2mT, the output error signal of the giant magnetoresistive current sensor with a shielded shell of the present invention is about 4mV, compared with the output error signal of a current sensor without a shielded shell about 400mV, it is affected by the external stray field The impact is reduced by a factor of about 100.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a structure diagram of a probe of a giant magnetoresistive current sensor of the present invention.

Fig. 2 is a schematic diagram of interaction among various components in the giant magnetoresistive current sensor of the present invention.

Fig. 3 is a schematic structural diagram of the giant magnetoresistive current sensor of the present invention.

Fig. 4 is a schematic diagram of a giant magnetoresistance chip power supply voltage conversion circuit of the giant magnetoresistance current sensor of the present invention.

FIG. 5 is a schematic diagram of a bias magnetic field generating circuit of a giant magnetoresistive current sensor of the present invention.

Fig. 6 is a schematic diagram of a reference voltage generating circuit of a giant magnetoresistive current sensor of the present invention.

FIG. 7 is a schematic circuit diagram of a differential operational amplifier circuit in a general form.

Fig. 8 is a schematic diagram of an improved differential operational amplifier circuit of the giant magnetoresistive current sensor of the present invention.

Fig. 9 is the hysteresis curves of the giant magnetoresistive current sensor of the present invention with and without a bias magnetic field.

Fig. 10 is the input and output characteristic curves of the giant magnetoresistive current sensor of the present invention with and without a magnetic shielding case.

Fig. 11 is a graph of the relative error of the current sensor when the giant magnetoresistive current sensor of the present invention is magnetically shielded.

In the figure, 1. Magnetic shielding shell, 2. Bias coil winding, 3. Giant magnetoresistive chip, 4. Current-carrying conductor, 5. PCB board, 6. Bias current source, 7. Improved differential operational amplifier circuit, 8. The reference voltage generating circuit, 9. The positive output terminal of the giant magnetoresistance chip, and 10. The negative output terminal of the giant magnetoresistance chip.

detailed description

The embodiment shown in Fig. 1 shows that the probe of the giant magnetoresistance current sensor of the present invention comprises a magnetic shield shell 1, a bias coil winding 2, a giant magnetoresistance chip 3, a current-carrying conductor 4 and a PCB board 5, and the magnetic shield shell 1 is a U In terms of performance and cost, Permalloy is selected as the material of the shielding shell, so that the magnetic field at the giant magnetoresistive chip 3 is increased as much as possible, and at the same time, the interference caused by the external stray magnetic field to the giant magnetoresistive chip 3 is guaranteed. minimum. Since the giant magnetoresistive chip 3 has the characteristics of unipolar output, a DC bias magnetic field is provided through the bias coil winding 2, and the bias coil winding 2 is evenly wound on the giant magnetoresistance chip 3, and the superposition of the magnetic field makes it act on The magnetic fields of the giant magnetoresistive chip 3 are all raised to the linear region. The giant magnetoresistance chip 3 is fixed on the PCB board 5 . The current-carrying conductor 4 is placed between the giant magnetoresistive chip 3 and the PCB board 5 , a current is passed through the current-carrying conductor 4 to generate a magnetic field, and the giant magnetoresistive chip 3 outputs a differential voltage signal under the action of the measured magnetic field. Since there is a linear change law between the output signal and the measured magnetic field, the output voltage is proportional to the measured current, thereby realizing the measurement function of the current signal.

The embodiment shown in Figure 2 shows that the interaction between the various components in the giant magnetoresistance current sensor of the present invention is: the giant magnetoresistance chip is placed in the magnetic shielding shell; the bias magnetic field generating circuit acts on the giant magnetoresistance chip, so that the effect The magnetic field of the giant magnetoresistance chip is all raised to the linear region; the magnetic field generated by the measured current acts on the giant magnetoresistance chip after being concentrated by the magnetic shielding shell, and the output voltage signal of the giant magnetoresistance chip enters the improved differential circuit shown in the dotted line box in the figure. The general form differential operational amplifier circuit in the operational amplifier circuit; in order to eliminate the DC bias voltage caused by the bias magnetic field generation circuit, the reference voltage generated by the reference voltage generation circuit is added to the input terminal of the improved differential operational amplifier circuit shown in the dotted line box, The superimposition of the reference voltage and the bias voltage generated by the bias magnetic field generating circuit plays a role of bias compensation. Since the general form of differential operational amplifier circuit increases the input and output phase difference with the increase of the frequency of the signal to be measured, an operational amplifier resistor network is introduced in the feedback loop of the general form of differential operational amplifier circuit, so the general form of differential The operational amplifier circuit plays the role of phase compensation, thereby forming the improved differential operational amplifier circuit shown in the dotted line box, and finally the output signal of the improved differential operational amplifier circuit is in a positive proportional relationship with the measured current.

The embodiment shown in Figure 3 shows that the structure of the giant magnetoresistance current sensor of the present invention is: the giant magnetoresistance chip 3 is placed in the magnetic shielding shell 1, the current-carrying conductor 4 is placed under the giant magnetoresistance chip 3, and the bias coil winding 2 is uniformly wound on the giant magnetoresistance chip 3 , and the bias current source 6 is connected to both ends of the bias coil winding 2 to provide a bias magnetic field for the giant magnetoresistance chip 3 . The magnetic field generated by the current-carrying conductor 4 acts on the output voltage signal of the giant magnetoresistive chip 3, and the output signal enters the improved differential operational amplifier circuit 7 for amplification, and the reference voltage generation circuit 8 is added to the input terminal of the improved differential operational amplifier circuit 7, so The reference voltage generation circuit 8 and the bias voltage generated by the bias magnetic field generated by the bias coil winding superimpose, so that the improved differential operational amplifier circuit 7 outputs a voltage signal that is proportional to the measured current.

The embodiment shown in Fig. 4 shows that the configuration of the giant magnetoresistance chip power supply voltage conversion circuit of the giant magnetoresistance current sensor of the present invention is: the input terminal Vin of the voltage regulator VR7805 is connected to the 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 terminal Vin of the voltage regulator VR7805 and the ground terminal of the voltage regulator VR7805, the output terminal Vout of the voltage regulator VR7805 outputs a stable +5V DC voltage, and the filter capacitor C2 of 0.1uF It is connected in parallel between the output terminal Vout of the voltage regulator VR7805 and the ground terminal of the voltage regulator VR7805, so that the output voltage of the Vout pin is a stable 5V direct current. Because the power supply voltage required by the giant magnetoresistive chip is positive 5V, and the power supply of the giant magnetoresistive current sensor system is plus or minus 15V, a stable DC voltage of 5V is generated by the function of the voltage regulator VR7805 to supply the power required by the giant magnetoresistive chip. supply voltage.

The embodiment shown in FIG. 5 shows that the bias magnetic field generating circuit of the giant magnetoresistive current sensor of the present invention is composed of a chip LT3092 and a bias coil winding L. The internal structure of a DC current source powered by a 5V voltage is shown in the box of Figure 5, in which the chip LT3092 uses an internal current source and error amplifier as well as two external resistors Rset and resistor Rout to provide output current, and adjust the resistor Rset A constant output current between 0.5mA and 200mA can be obtained according to the resistance value of the resistor Rout. IN is the input terminal pin of the LT3092 chip, and this pin is the power supply input terminal of the chip. OUT is the output terminal of the chip, SET is the setting terminal of the chip, and SET is connected to the non-inverting input terminal of the error amplifier inside the chip, and the bias operating point of the current can be set at the same time. 10μA is the internal reference current source of the LT3092 chip. This reference current source flows through the resistor Rset to generate a voltage, which is applied to another resistor Rout to generate an output current. The resistor Rout is connected between the chip OUT output terminal and the resistor Rset. The output terminal of LT3092 is connected to the bias coil winding L, and the other end of the bias coil winding L is grounded. The coil diameter of the bias coil winding L is 0.08mm, the number of turns is 50 turns, and the DC resistance is 3.487Ω. The magnitude of the DC current passing through is 50mA. In the figure, the resistance value of the resistor Rset is 20kΩ, and the resistance value of the resistor Rout is 4kΩ.

The embodiment shown in Figure 6 shows that the constitution of the reference voltage generating circuit of the giant magnetoresistive current sensor of the present invention is: operational amplifier U1A and resistors R1, R2 and R3 form an inverting input proportional operation circuit, and one end of resistor R1 is connected to U1A The non-inverting input terminal c, the other end of the resistor R1 is grounded. One end of the resistor R2 is connected to the inverting input terminal b of U1A, the other end of the resistor R2 is connected to a DC 5V voltage source, the two ends of the resistor R3 are respectively connected to the inverting input terminal b and output terminal a of U1A, and the power supply voltage of U1A is + The 15V terminal h and the -15V terminal d; the output terminal a of U1A is connected to the non-inverting input terminal e of U1B, and the inverting input terminal f of U1B is connected to the output terminal g to form a voltage follower. Since the voltage follower has the characteristics of high input impedance and low output impedance, it is equivalent to a constant voltage source for the subsequent circuit, and its output voltage is not affected by the load impedance, so a constant reference voltage Vref is obtained. Both op amp U1A and op amp U1B are LF353. In the figure, the resistance value of resistor R1 is 8.2kΩ, the resistance value of resistor R2 is 3.6kΩ, and the resistance value of resistor R3 is 10kΩ.

The embodiment shown in Fig. 7 shows that the circuit composition of the differential operational amplifier circuit in general form is: it is composed of an integrated operational amplifier and an external resistor network, one end of the resistor R1 is connected to the voltage U1, and the other end of the resistor R1 is connected to the reverse of the operational amplifier. Phase input terminal, one terminal of resistor R2 is connected to voltage U2, the other terminal of resistor R2 is connected to the positive phase input terminal of the operational amplifier, both ends of resistor R4 are respectively connected to the inverting input terminal and output terminal of the operational amplifier, and one terminal of resistor R3 is connected to the operational amplifier. The non-inverting input terminal of the amplifier, the other end of the resistor R3 is grounded. The operational amplifier model is LF356. This structure increases the input-output phase difference with the increase of the frequency of the signal under test, which affects the bandwidth range of the signal under test. In the figure, the resistance value of resistor R1 is 27kΩ, the resistance value of resistor R2 is 27kΩ, the resistance value of resistor R3 is 270kΩ, and the resistance value of resistor R4 is 270kΩ.

The embodiment shown in Figure 8 shows that the composition of the improved differential operational amplifier circuit of the giant magnetoresistive current sensor of the present invention is: one end of the resistor R4 is connected to the inverting input terminal of the operational amplifier A1, and the other end of the resistor R4 is connected to the operational amplifier A2 The output terminal of the resistor R5 is connected to the inverting input terminal of the operational amplifier A2, and the other terminal of the resistor R5 is connected to the output terminal Uo of the operational amplifier A1, which is the output terminal of the improved differential operational amplifier circuit, and the positive input terminal of the operational amplifier A2 is connected to To the output terminal Uo of the operational amplifier A1, the two ends of the resistor R6 are respectively connected to the inverting input terminal and the output terminal of the operational amplifier A2, one terminal of the resistor R1 is connected to the voltage U1, and the other terminal of the resistor R1 is connected to the inverting input terminal of the operational amplifier A1 One end of the resistor R2 is connected to the voltage U2, the other end of the resistor R2 is connected to the non-inverting input of the operational amplifier A1, one end of the resistor R3 is connected to the non-inverting input of the operational amplifier A1, the other end of the resistor R3 is grounded, and the operational amplifier A1 and The models of operational amplifier A2 are both LF356. In the figure, the resistance value of resistor R1 is 27kΩ, the resistance value of resistor R2 is 27kΩ, the resistance value of resistor R3 is 270kΩ, the resistance value of resistor R4 is 270kΩ, the resistance value of resistor R5 is 1kΩ, and the resistance value of resistor R6 is 10kΩ.

In order to reduce the phase error, the invention proposes an improved differential operational amplifier circuit. Compared with the general form differential operational amplifier circuit shown in Figure 7, the improvement of the improved differential operational amplifier circuit of the present invention is that one end of the resistor R4 is connected to the inverting input end of the amplifier A1, the other end is connected to the output end of the amplifier A2, and one end of the resistor R5 Connect the inverting input terminal of amplifier A2, the other end of resistor R5 is connected to the output terminal Uo of amplifier A1, the positive input terminal of amplifier A2 is also connected to the output terminal Uo of amplifier A1, and the two ends of resistor R6 are respectively connected to the reverse terminal of amplifier A2. phase input and output. The improved differential operational amplifier circuit of the present invention introduces an operational amplifier resistance network into the feedback loop of the general differential operational amplifier circuit, which can effectively compensate phase errors and has a higher common-mode rejection ratio.

The embodiment shown in Fig. 9 shows that under the two conditions of having or not biasing the magnetic field, when the measured current is within a certain range during the positive stroke and the reverse stroke, the relationship between the output and the input of the current sensor, the test results show that adding After the bias magnetic field is increased, the hysteresis error of the current sensor is obviously reduced, and the linearity is improved to a certain extent.

The embodiment shown in Fig. 10 shows that under the two conditions of having and not having a magnetic shielding shell, the data obtained by the output voltage of the sensor under different measured currents is obtained by the curve fitting of the matlab software, and the test results show that compared with no The sensitivity of the giant magnetoresistance current sensor of the present invention with the magnetic shielding structure and the magnetic shielding shell is greatly improved.

The embodiment shown in FIG. 11 shows the relative error curve of the current sensor when the giant magnetoresistive current sensor of the present invention is magnetically shielded. The relative error within the measurement range of the current sensor can be obtained by subtracting the actual value from the theoretical value of the output voltage and dividing by the actual value. Based on the experimental data, it can be concluded that when the current range is -20A to +20A, the relative error is limited to 0.8%.

Example

1, 3, 4, 5, 6, 7 and 8 are used to form a current sensor based on the giant magnetoresistance effect with a magnetic shield and a bias coil, The structural shape of the magnetic shielding case 1 and the shape and location of the bias coil winding 2 are clearly shown in FIG. 1 . The giant magnetoresistive chip 3 is the GMR chip, which uses AA002-02 produced by NVE Company in the United States; the U-shaped magnetic shielding shell is made of Permalloy material, with a resistivity of 0.56μΩ·m and a Curie point of 400°C , the saturation magnetic induction is Bs=0.7T, the coercive force Hc under the saturation magnetic induction is not more than 1.6A/m, the DC magnetic performance meets the magnetic permeability in the 0.08A/m magnetic field strength is not less than 37.5mH/m, the thickness It is 1mm, the width is 7mm, the height is 10mm, and the length is 13mm.

The giant magnetoresistive current sensor formed by the above device is used for the measurement experiment of direct current, the measured current is from -20A to 20A, and the output voltage of the improved differential operational amplifier circuit is measured. Input the obtained data into the internationally common commercial software matlab for least squares curve fitting, and obtain the relationship between the output voltage of the current sensor and the measured current shown in Figure 10. The fitting equations of the curve are: when there is a magnetic shield, the relationship between the output voltage of the sensor and the measured current as shown in Figure 10 is: Uout=119.96*I+4.1659, this formula represents the relationship between the measured current and the output voltage of the current sensor The quantitative relationship between them can be obtained. The sensitivity of this current sensor is 119.96, the zero drift is 4.1659mV, and the output voltage is limited to ±3V. Carry out the test without the magnetic shielding case again, and also use the least squares curve fitting to get the relationship between the sensor output voltage and the measured current as shown in Figure 10: Uout=47.289*I+5.7122, and analyze the current sensor The sensitivity is 47.289, and the zero drift is 5.7122mV. It can be seen that adding a magnetic shield can effectively increase the sensitivity of the current sensor and reduce the zero drift of the current sensor. Subtract the actual value from the theoretical value of the output voltage, and then divide by the actual value to obtain the relative error when the measurement range of the current sensor is -20A to 20A. The embodiment shown in Figure 11 shows that the giant magnetoresistive current sensor of the present invention The relative error curve of the current sensor when the magnetic shield is added, it can be seen that within the range of -20A to 20A, the relative error is limited within ±0.8%.

The devices and components involved in the above embodiments are all obtained from known channels, and the installation methods of all components are within the grasp of those skilled in the art.

Claims (4)

1. The giant magnetoresistance effect current sensor is characterized in that: it is a giant magnetoresistance effect current sensor with a magnetic shielding shell and a bias coil, and its composition includes a U-shaped magnetic shielding shell, a giant magnetoresistance chip, and a bias coil winding , current-carrying conductor, PCB board, bias current source and signal processing circuit, wherein, the U-shaped magnetic shield shell, giant magnetoresistance chip, bias coil winding, current-carrying conductor and PCB board constitute the giant magnetoresistance effect current sensor Probe, the above-mentioned signal processing circuit includes a bias magnetic field generation circuit, a giant magnetoresistance chip power supply voltage conversion circuit, a reference voltage generation circuit and an improved differential operational amplifier circuit; the PCB board is placed in a U-shaped magnetic shielding shell, and the giant magnetoresistance chip is fixed Placed on the top of the PCB board, the current-carrying conductor is placed under the giant magnetoresistance chip, the bias coil winding is evenly wound on the giant magnetoresistance chip, and the output voltage of the giant magnetoresistance chip power supply voltage conversion circuit is connected to the giant magnetoresistance chip The power pin of the power supply, the bias current source is connected to both ends of the bias coil winding, and the two input terminals of the improved differential operational amplifier circuit are respectively connected to the positive output terminal of the giant magnetoresistance chip and the negative output terminal of the giant magnetoresistance chip. Refer to The output voltage Vref of the voltage generating circuit is connected to the positive input terminal of the improved differential operational amplifier circuit, and after the superposition of the signals at the input terminal of the improved differential operational amplifier circuit, the output signal of the current sensor is finally output at the output terminal of the improved differential operational amplifier circuit , thereby forming a giant magnetoresistance current sensor, the giant magnetoresistance chip is the GMR chip, which is AA002-02 produced by NVE Corporation of the United States. 2. The giant magnetoresistance effect current sensor according to claim 1, characterized in that: the U-shaped magnetic shielding shell is made of permalloy material, its resistivity is 0.56μΩ·m, and its Curie point is 400°C , the saturation magnetic induction is Bs=0.7T, the coercive force Hc under the saturation magnetic induction is not more than 1.6A/m, the DC magnetic performance meets the magnetic permeability of not less than 37.5mH/m in the 0.08A/m magnetic field intensity, and the thickness It is 1mm, the width is 7mm, the height is 10mm, and the length is 13mm. 3. According to the said giant magnetoresistance effect current sensor of claim 1, it is characterized in that: the bias magnetic field generation circuit is made of chip LT3092 and bias coil winding L, and chip LT3092 utilizes an internal current source and error amplifier and two The external resistor Rset and resistor Rout provide the output current. Adjusting the resistance of the resistor Rset and the resistor Rout can obtain a constant output current between 0.5mA and 200mA. The output terminal of the LT3092 is connected to the bias coil winding L, The other end of the bias coil winding L is grounded, the coil diameter of the bias coil winding L is 0.08mm, the number of turns is 50 turns, the DC resistance is 3.487Ω, the DC current passing through is 50mA, the resistance value of the resistor Rset is 20kΩ, and the resistance The resistor Rout is 4kΩ. 4. according to the said giant magnetoresistive effect current sensor of claim 1, it is characterized in that: the composition of described improved differential operational amplifier circuit is: one end of resistance R4 is connected to the inverting input end of operational amplifier A1, the other end of resistance R4 Connect to the output terminal of the operational amplifier A2, one end of the resistor R5 is connected to the inverting input terminal of the operational amplifier A2, the other end of the resistor R5 is connected to the output terminal of the operational amplifier A1, and the positive input terminal of the operational amplifier A2 is connected to the output terminal of the operational amplifier A1 , the two ends of the resistor R6 are respectively connected to the inverting input and output of the operational amplifier A2, one end of the resistor R1 is connected to the voltage U1, the other end of the resistor R1 is connected to the inverting input of the operational amplifier A1, and one end of the resistor R2 is connected to the voltage U2, the other end of resistor R2 is connected to the non-inverting input of operational amplifier A1, one end of resistor R3 is connected to the positive input of operational amplifier A1, and the other end of resistor R3 is grounded. The models of operational amplifier A1 and operational amplifier A2 are both LF356 , the resistance value of the above-mentioned resistor R1 is 27kΩ, the resistance value of the resistor R2 is 27kΩ, the resistance value of the resistor R3 is 270kΩ, the resistance value of the resistor R4 is 270kΩ, the resistance value of the resistor R5 is 1kΩ, and the resistance value of the resistor R6 is 10kΩ.