CN110687962B - Device and method for compensating stray magnetic field in real time - Google Patents
Device and method for compensating stray magnetic field in real time Download PDFInfo
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Abstract
The invention discloses a device and a method for compensating stray magnetic fields in real time, and belongs to the technical field of stray magnetic field elimination in the environment. The linear power supply, the compensating coil I, the compensating coil II, the sampling resistor and the field effect transistor are connected in series in sequence, the anode of the linear power supply is connected with the compensating coil group, the negative electrode of the magnetic flux gate meter is connected with the source electrode of the field effect tube, the magnetic flux gate meter is arranged on the outer side of the compensation coil group, voltages at two ends of the sampling resistor are connected to the feedback circuit, the feedback circuit is respectively connected with the magnetic flux gate meter, the sampling resistor and the field effect tube, the dependency relationship between output voltages in the x direction and the y direction of the magnetic flux gate meter and stray magnetic fields in the z direction of the magnetic flux gate meter is measured, voltage signals obtained by multiplying the average value of the output voltages in the x direction and the y direction of the magnetic flux gate meter by a scale factor are compared with the voltages at two ends of the sampling resistor, and obtained error signals are processed by the feedback circuit with proportion and integral and input to a grid electrode-source electrode voltage port of the field effect tube.
Description
Technical Field
The invention discloses a device and a method for compensating stray magnetic fields in real time, and belongs to the technical field of stray magnetic field elimination in the environment.
Background
A homogeneous magnetic field can be generated over a local spatial range using a set of energized helmholtz coils. The precision and stability of the spatial magnetic field are very important for many scientific research and engineering applications, such as precision measurement, atomic interferometers, new product calibration, and the like. The current in the coil can be accurately controlled by adopting a feedback circuit with a Hall sensor and a field effect tube, and the accuracy and the stability of a magnetic field at the symmetrical center of the coil are improved. However, the magnetic field in the space is affected by the stray magnetic field in the environment, so that the precision and stability of the magnetic field are deteriorated. The stray magnetic field in the environment mainly comprises a geomagnetic field, non-demagnetized materials, a power supply and a weak magnetic field generated by other electrified instruments, and in addition, an elevator and a subway close to an electrified coil can generate a stray magnetic field with amplitude changing along with time at the center of the coil. Therefore, how to eliminate the influence of stray magnetic fields in the environment, especially the magnetic field that changes irregularly with time, becomes the key to improve the precision and stability of the spatial magnetic field.
Disclosure of Invention
The invention aims to eliminate the influence of stray magnetic fields in the environment on the precision and the stability of a space magnetic field, and provides a device and a method for compensating the stray magnetic fields in real time aiming at the stray magnetic fields which change irregularly along with time in practice.
The invention is realized by adopting the following technical scheme: a device for compensating stray magnetic fields in real time comprises a linear power supply, a compensation coil group, a sampling resistor, a field effect transistor, a fluxgate meter and a feedback circuit, wherein the linear power supply, the compensation coil group, the sampling resistor and the field effect transistor are sequentially connected in series through a lead to form a current loop, the positive pole of the linear power supply is connected with the compensation coil group, and the negative pole of the linear power supply is connected with the source electrode of the field effect transistor; the fluxgate meter is arranged on the outer side of the compensation coil group, the z direction of the fluxgate meter is consistent with the axial direction of the compensation coil group, and a target magnetic field along the z direction at the center of the compensation coil group has no influence on magnetic fields in the x and y directions at the fluxgate meter; the feedback circuit is connected to two ends of the sampling resistor and is also connected with the fluxgate meter and the field effect tube respectively.
Further, the linear power supply operates in a constant voltage mode.
Furthermore, the compensation coil group comprises a compensation coil I and a compensation coil II, the compensation coil I and the compensation coil II are square coils, and currents with the same direction and the same size pass through the square coils.
Further, the distance between the two coils of the compensation coil I and the compensation coil II is equal to the average side length of the coils.
Further, the dependence of the output voltage of the fluxgate meter in the x and y directions on the stray magnetic field in the z direction is measured. And comparing a voltage signal obtained by multiplying the average value of the output voltages of the fluxgate meter in the x and y directions by a scaling factor with the voltage at two ends of the sampling resistor, processing an obtained error signal by a feedback circuit with proportion and integral, and inputting the error signal into a grid-source voltage port of the field effect tube so as to realize real-time compensation of the variable stray magnetic field.
The invention also provides a method for compensating stray magnetic fields in real time, which is carried out according to the device and comprises the following steps:
(1) adjusting the distance between the compensation coil I and the compensation coil II to enable the compensation coil group to meet the requirements of Helmholtz coils and generate uniform magnetic fields with equal sizes in a smaller space range;
(2) placing the compensation coil I and the compensation coil II at spatial positions to enable the center of the compensation coil group to be superposed with the required target magnetic field position;
(3) the linear power supply works in a constant voltage mode, and the compensation coil I and the compensation coil II are supplied with currents with the same direction and the same magnitude;
(4) the sampling resistor is used for measuring the current in the compensation coil group, when the current flows through the sampling resistor, a voltage signal is generated at two ends of the sampling resistor, and the voltage signal and a compensation magnetic field generated by the compensation coil group have a determined proportional relation;
(5) the field effect transistor can change the resistance of a drain electrode-source electrode by controlling the voltage of the gate electrode-source electrode of the field effect transistor, inputs a signal output by the feedback circuit on the gate electrode-source electrode, and changes the current of the compensation coil group by adjusting the effective resistance of the drain electrode-source electrode of the field effect transistor, so that the compensation coil group generates a uniform magnetic field at the center to compensate the stray magnetic field in the environment;
(6) the fluxgate meter is placed on the outer side of the compensation coil, so that the z direction of the fluxgate meter is along the axial direction of the compensation coil group, and a target magnetic field along the z direction at the center of the compensation coil has no influence on magnetic fields in the x and y directions at the fluxgate meter; because the distribution of the spatial magnetic field meets the requirement that the divergence of Maxwell equation is zero, the magnetic fields of the fluxgate meter in the x and y directions are in direct proportion to the stray magnetic field along the axial direction at the center of the compensation coil and can change along with the change of the stray magnetic field;
(7) the dependence relationship between the output voltage of the fluxgate meter in the x and y directions and the stray magnetic field in the z direction can be obtained through measurement; and comparing a voltage signal obtained by multiplying the average value of the output voltages of the fluxgate meter in the x and y directions by a scaling factor with the voltage at two ends of the sampling resistor, processing an obtained error signal by a feedback circuit with proportion and integral, and inputting the error signal into a grid-source voltage port of the field effect tube so as to realize real-time compensation of the variable stray magnetic field.
The invention has the beneficial effects that: the method can eliminate the influence of the change of the stray magnetic field along with time on the target magnetic field in the environment, is simple, and effectively improves the precision and the stability of the space magnetic field.
Drawings
Fig. 1 is a schematic diagram of embodiment 1.
Fig. 2 is a circuit diagram of a feedback circuit in embodiment 1.
In the figure: 1. a linear power supply; 2. a compensation coil I; 3. a compensation coil II; 4. sampling a resistor; 5. a field effect transistor; 6. a fluxgate meter; 7. a feedback circuit.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer and more obvious, the following will further describe the apparatus and method for compensating stray magnetic fields in real time according to the present invention with reference to the accompanying drawings and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1:
the device for compensating stray magnetic field in real time of the present embodiment, as shown in fig. 1, includes a linear power supply 1, a compensation coil set, a sampling resistor 4, a field effect transistor 5, a fluxgate meter 6, and a feedback circuit 7, where the linear power supply 1, the compensation coil set, the sampling resistor 4, and the field effect transistor 5 are connected in series in sequence through a wire to form a current loop, the positive electrode of the linear power supply 1 is connected to the compensation coil set, the negative electrode thereof is connected to the source electrode of the field effect transistor 5, and the linear power supply 1 is in a constant voltage mode when operating; the compensation coil group comprises a compensation coil I2 and a compensation coil II 3, the compensation coil I2 and the compensation coil II 3 are square coils, the distance between the two coils of the compensation coil I2 and the compensation coil II 3 is equal to the average side length of the coils, and the directions and the sizes of currents passing through the compensation coil group during working are the same; the fluxgate meter 6 is arranged at the outer side of the compensation coil group, the z direction of the fluxgate meter 6 is consistent with the axial direction of the compensation coil group, and the target magnetic field along the z direction at the center of the compensation coil group has no influence on the magnetic fields in the x and y directions at the fluxgate meter 6; the feedback circuit 7 is connected to two ends of the sampling resistor 4, and the feedback circuit 7 is also connected with the fluxgate meter 6 and the field effect tube 5 respectively.
The dependence of the x and y directional output voltages of the fluxgate meter 6 on the z directional stray magnetic field thereof is measured. The average value of the output voltage of the fluxgate meter 6 in the x and y directions is multiplied by a scaling factor to obtain a voltage signal, the voltage signal is compared with the voltage at the two ends of the sampling resistor 4, the obtained error signal is processed by a feedback circuit 7 with proportion and integral and is input to a gate-source voltage port of the field effect tube 5, so as to realize the real-time compensation of the variable stray magnetic field.
The feedback circuit 7 comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a proportional resistor R7, a resistor R8, a proportional resistor R9, a resistor R10, a resistor R11, a resistor R12, a resistor R13, a resistor R14, a resistor R15, a resistor R16, a resistor R17, a capacitor C1, a capacitor C2, an operational amplifier U1, an operational amplifier U2, an operational amplifier U3 and an operational amplifier U4, wherein the operational amplifier U1 is an INA114, the operational amplifier U2 is an AD711, and the operational amplifiers U3 and U4 are provided by a dual-operational amplifier chip AD 712. The positive input end of an operational amplifier U1 is grounded through a resistor R2, the negative input end of an operational amplifier U1 is grounded through a resistor R1, the input end of the operational amplifier U1 is connected with a sampling resistor 4 through a BNC joint, a resistor R3 is connected between a pin 1 and a pin 8 of the operational amplifier U1, voltage drop at two ends of the sampling resistor is amplified by 10 times through the operational amplifier U1 and then is output from the output end of the sampling resistor, and the output end of the operational amplifier U1 is connected with the negative input end of the operational amplifier U3 through a resistor R4; output voltages Vx and Vy of the fluxgate meter 6 are respectively connected with input resistors R5 and R6, an adder is formed by an operational amplifier U2 and resistors R5, R6, R7 and R8, a proportional resistor R7 is half of the input resistors R5 and R6, the output voltage of the operational amplifier U2 is an average value of Vx and Vy, and the output voltage is connected with a negative input end of the operational amplifier U3 through a proportional resistor R9; the resistor R10 is a potentiometer, the output end of the resistor R10 is connected with the negative input end of the operational amplifier U3 through the resistor R11, and bias voltage is provided for constant voltage which does not change along with time in the eliminating voltage Vx and Vy; a resistor R12 is connected between the negative input end and the output end of the operational amplifier U3, the positive input end of the operational amplifier U3 is grounded through a resistor R13, the output end of the operational amplifier U3 is connected with a resistor R14, and the proportion of a feedback circuit can be adjusted through R14; the operational amplifier U4, the resistor R15, the resistor R16, the capacitor C1, and the capacitor C2 form an integrating circuit, wherein the positive input terminal of the operational amplifier U4 is grounded, and the output terminal of the operational amplifier U4 is connected to the fet 5 through the resistor R17 and then through the BNC connector. The resistors of the resistor R1, the resistor R2, the resistor R3, the resistor R4, the resistor R5, the resistor R6, the proportional resistor R7, the resistor R8, the resistor R11, the resistor R12, the resistor R13, the resistor R15 and the resistor R17 are respectively 100K Ω, 5.5K Ω, 10K Ω, 20K Ω, 10K Ω, the proportional resistor R9, the resistor R10, the resistor R14 and the resistor R16 adopt resistors with the maximum value of 50K Ω, the measuring range of the capacitor C1 is 10pF, and the capacitance of the capacitor C2 is 10 nF.
When the device works, the distance between the two coils in the compensation coil group is adjusted, the Helmholtz coil requirement is met as far as possible, and a uniform magnetic field with the same size is generated in a smaller space range. The compensation coils are placed at proper positions, the centers of the two compensation coils are overlapped with the required target magnetic field position, the direction of the magnetic field generated by the compensation coil group is consistent with that of the target magnetic field, and the magnetic field generated by the compensation coil group can be used for eliminating the influence of stray magnetic fields on the target magnetic field. Under the condition that the output voltage of the linear power supply 1 is not changed, the current of the two compensation coils can be changed by adjusting the effective resistance of the field effect transistor 5, after the current flows through the sampling resistor 4, a potential difference appears at two ends of the sampling resistor 4, namely, the voltage drop Vd at two ends of the sampling resistor 4 monitors the current in the compensation coil group, and the magnetic field generated by the compensation coil group at the center can be obtained according to the ampere law.
The voltage of the sampling resistor 4 is amplified to become Vd, the difference between the Vx and Vy output voltages in the x and y directions of the fluxgate meter 6 is taken as the average value of the output voltages in the x and y directions of the fluxgate meter, namely (Vx + Vy)/2, multiplied By a scaling factor to obtain a voltage signal Vs, the voltage of the sampling resistor 4 is amplified to become Vd, the difference between the Vx and Vy output voltages is taken as the feedback voltage of the feedback circuit 7, the feedback voltage of the feedback circuit 7 is taken as the integral voltage of the feedback circuit 7, the integral voltage of the feedback voltage is changed to be a new value after being subjected to the integral effect of a new compensation voltage, and the compensation voltage is changed to be a new value after being subjected to the integral effect of a grid electrode, so that the compensation voltage of the sampling resistor 4 is changed to a new value after being subjected to the change of the offset voltage of the source electrode and the offset voltage of the offset current of the fluxgate meter 6, and the offset voltage of the offset current of the offset circuit 6 is changed to be zero after being subjected to the change of the offset voltage of the offset transistor 5, thereby the offset voltage of the offset transistor 5.
Example 2:
the method for compensating stray magnetic field in real time of the present embodiment, which is operated according to the apparatus for compensating stray magnetic field of embodiment 1, comprises the following steps:
(1) adjusting the distance between the compensation coil I2 and the compensation coil II 3 to enable the compensation coil group to meet the requirements of Helmholtz coils and generate uniform magnetic fields with equal sizes in a smaller space range;
(2) placing the compensating coil I2 and the compensating coil II 3 at a spatial position to ensure that the center of the compensating coil group is superposed with the required target magnetic field position;
(3) the linear power supply 1 is enabled to work in a constant voltage mode, and the compensation coil I2 and the compensation coil II 3 are supplied with currents with the same direction and the same magnitude;
(4) the sampling resistor 4 is used for measuring the current in the compensation coil group, when the current flows through the sampling resistor 4, a voltage signal is generated at two ends of the sampling resistor, and the voltage signal and a compensation magnetic field generated by the compensation coil group have a determined proportional relation;
(5) the field effect transistor 5 can change the resistance of a drain electrode-source electrode by controlling the voltage of the gate electrode-source electrode thereof, inputs the signal output by the feedback circuit 7 on the gate electrode-source electrode, and changes the current of the compensation coil group by adjusting the effective resistance of the drain electrode-source electrode of the field effect transistor 5, so that the compensation coil group generates a uniform magnetic field at the center to compensate the stray magnetic field in the environment;
(6) the fluxgate meter 6 is placed outside the compensation coil, so that the z direction of the fluxgate meter 6 is along the axial direction of the compensation coil group, and the target magnetic field along the z direction at the center of the compensation coil has no influence on the magnetic fields of the fluxgate meter 6 in the x and y directions; because the distribution of the spatial magnetic field meets the requirement that the divergence of Maxwell equation is zero, the magnetic fields of the fluxgate meter in 6x and y directions are in direct proportion to the stray magnetic field along the axial direction at the center of the compensation coil and can change along with the change of the stray magnetic field;
(7) the dependence relationship between the output voltage of the fluxgate meter in the x and y directions and the stray magnetic field in the z direction can be obtained through measurement; the average value of the output voltages of the fluxgate meter 6x and y directions is multiplied by a scaling factor to obtain a voltage signal, the voltage signal is compared with the voltages at two ends of the sampling resistor 4, the obtained error signal is processed by a feedback circuit 7 with proportion and integral and is input to a grid-source voltage port of the field effect tube 5, and therefore real-time compensation of the variable stray magnetic field is achieved.
Claims (2)
1. An apparatus for compensating for stray magnetic fields in real time, comprising: the device comprises a linear power supply (1), a compensation coil group, a sampling resistor (4), a field effect transistor (5), a fluxgate meter (6) and a feedback circuit (7), wherein the linear power supply (1), the compensation coil group, the sampling resistor (4) and the field effect transistor (5) are sequentially connected in series through a lead to form a current loop, the positive electrode of the linear power supply (1) is connected with the compensation coil group, and the negative electrode of the linear power supply is connected with the source electrode of the field effect transistor (5); the fluxgate meter (6) is arranged at the outer side of the compensation coil group, the z direction of the fluxgate meter (6) is consistent with the axial direction of the compensation coil group, and a target magnetic field along the z direction at the center of the compensation coil group has no influence on magnetic fields in the x direction and the y direction at the fluxgate meter (6); the feedback circuit (7) is connected to two ends of the sampling resistor (4), and the feedback circuit (7) is respectively connected with the fluxgate meter (6) and the fluxgate meterThe field effect transistor (5) is connected, the linear power supply (1) works in a constant voltage mode, and the compensating coil group comprises a compensating coil I (2) and a compensating coil
(3) Compensator coil I (2) and compensator coil
(3) Is a square coil and is provided with currents with the same direction and the same magnitude, and the compensating coil I (2) and the compensating coil
The distance between the two coils is equal to the average side length of the coils, the dependency relationship between the output voltages of the fluxgate meter (6) in the x and y directions and the stray magnetic field in the z direction is measured, the voltage signal obtained by multiplying the average value of the output voltages of the fluxgate meter (6) in the x and y directions by a scale factor is compared with the voltage at two ends of the sampling resistor (4), and the obtained error signal is processed by a feedback circuit (7) with proportion and integral and is input to a grid electrode-source electrode voltage port of the field effect tube (5) to realize the real-time compensation of the variable stray magnetic field.
2. A method of compensating for stray magnetic fields in real time, comprising: the method comprises the following steps:
(1) adjusting the distance between the compensation coil I (2) and the compensation coil II (3) to enable the compensation coil group to meet the requirements of Helmholtz coils, so that uniform magnetic fields with the same size are generated in a smaller space range;
(2) placing a compensation coil I (2) and a compensation coil II (3) at spatial positions to enable the center of a compensation coil group to coincide with a required target magnetic field position;
(3) the linear power supply (1) works in a constant voltage mode, and the compensation coil I (2) and the compensation coil II (3) are supplied with currents with the same direction and the same magnitude;
(4) the sampling resistor (4) is used for measuring the current in the compensation coil group, when the current flows through the sampling resistor (4), two ends of the sampling resistor can generate a voltage signal, and the voltage signal and a compensation magnetic field generated by the compensation coil group have a determined proportional relation;
(5) the field effect transistor (5) can change the resistance of a drain electrode-source electrode by controlling the voltage of the gate electrode-source electrode thereof, the signal output by the feedback circuit (7) is input to the gate electrode-source electrode, and the current of the compensation coil group is changed by adjusting the effective resistance of the drain electrode-source electrode of the field effect transistor (5), so that the compensation coil group generates a uniform magnetic field at the center to compensate the stray magnetic field in the environment;
(6) the fluxgate meter (6) is placed on the outer side of the compensation coil, the z direction of the fluxgate meter (6) is along the axial direction of the compensation coil group, and a target magnetic field along the z direction at the center of the compensation coil has no influence on magnetic fields in the x direction and the y direction at the fluxgate meter (6); because the distribution of the spatial magnetic field meets the requirement that the divergence of Maxwell equation is zero, the magnetic fields of the fluxgate meter (6) in the x and y directions are in direct proportion to the stray magnetic field along the axial direction at the center of the compensation coil and can change along with the change of the stray magnetic field;
(7) the dependence of the output voltage of the fluxgate meter (6) in the x and y directions and the stray magnetic field in the z direction can be obtained through measurement; and comparing a voltage signal obtained by multiplying the average value of the output voltages of the fluxgate meter (6) in the x and y directions by a scaling factor with the voltage at two ends of the sampling resistor (4), processing an obtained error signal by a feedback circuit (7) with proportion and integral, and inputting the error signal into a grid-source voltage port of the field effect tube (5) to realize real-time compensation of the variable stray magnetic field.
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| CN103389478B (en) * | 2012-10-31 | 2015-08-26 | 中国科学院上海微系统与信息技术研究所 | A kind of digitizing real-time magnetic field compensation system of based superconductive Magnetic Sensor and method |
| CN104880683B (en) * | 2014-02-28 | 2018-02-13 | 西门子(深圳)磁共振有限公司 | A kind of detection means of the shimming piece of magnetic resonance imaging system, method and system |
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