CN117562543A - An active magnetic compensation method and system - Google Patents

Abstract

The invention discloses an active magnetic compensation system, which includes: a reference magnetometer and a magnetic compensation coil located in a magnetic shielding barrel. The output end of the reference magnetometer is connected to the input end of a signal processor. The output end of the signal processor It is connected to the compensation coil through a voltage-controlled current source; among them, the reference magnetometer regularly collects the magnetic field intensity T ₁ in the magnetic shielding tube environment, and sends the magnetic field intensity T ₁ to the signal processor, and the signal processor outputs the compensation voltage to the voltage-controlled The current source, the voltage-controlled current source converts the compensation voltage into the compensation current of the compensation coil, so that the magnetic field intensity T ₁ in the magnetic shielding cylinder environment is close to or reaches the target magnetic field intensity T ₀ . The active magnetic compensation system of the present invention has a compensation accuracy of up to pT level, can also produce a good suppression effect on low-frequency magnetic noise in the environment, and is suitable for magnetocardiograph systems that require higher accuracy.

Description

An active magnetic compensation method and system

Technical field

The present invention belongs to the technical field of magnetic compensation, and more specifically, the present invention relates to an active magnetic compensation method and system.

Background technique

The human heart is accompanied by the generation of extremely weak biological magnetic fields during electrophysiological activities. In the process of diagnosing heart-related diseases, cardiomagnetic detection is already an indispensable part. As a non-invasive functional testing technology, magnetocardiography (MCG) has been widely used in clinical medicine, such as the localization of myocardial ischemia, the judgment of arrhythmia, and the diagnosis of cardiac load. The typical strength of the MCG signal is about tens of pT (10 ^-12 Tesla), while the geomagnetic field strength is 30μT ~ 50μT (10 ^-6 Tesla), which means that the collection of MCG signals is often affected by the environmental magnetic field.

In order to suppress the interference of environmental magnetic noise, passive magnetic shielding technology is usually used, such as magnetic shielding chambers and magnetic shielding buckets. However, magnetic shielding chambers have the disadvantages of high cost and large volume. The shielding performance of magnetic shielding buckets is also affected by its material properties. Impact. These shortcomings of passive shielding technology limit the measurement range of high-precision measuring instruments and cannot bring a stable magnetic field environment to high-precision magnetic detection sensors. In order to ensure the quality of MCG signals while controlling costs, the current mainstream solution is to build an active magnetic compensation system. Further suppress environmental magnetic noise.

The compensation algorithms currently used in active magnetic compensation systems have the characteristics of simple parameter adjustment and convenient operation. In a stable magnetic field environment, the corresponding magnetic compensation amount can be generated. However, when sudden magnetic field changes and electronic magnetic noise appear in the environment, the compensation effect will be reduced. Greatly reduced, the compensation accuracy is also unsatisfactory.

Contents of the invention

The present invention provides an active magnetic compensation method, aiming to improve the above problems.

The present invention is implemented as follows: an active magnetic compensation system, which includes:

A reference magnetometer and a magnetic compensation coil are installed in the magnetic shielding barrel. The output end of the reference magnetometer is connected to the input end of the signal processor, and the output end of the signal processor is connected to the compensation coil through a voltage-controlled current source;

Among them, the reference magnetometer regularly collects the magnetic field intensity T ₁ in the magnetic shielding tube environment, and sends the magnetic field intensity T ₁ to the signal processor. The signal processor outputs the compensation voltage to the voltage-controlled current source, and the voltage-controlled current source will compensate the voltage. The compensation current is converted into the compensation coil so that the magnetic field intensity T ₁ in the magnetic shielding cylinder environment is close to or reaches the target magnetic field intensity T ₀ .

Further, the signal processor includes:

Magnetic noise monitoring module, desired signal tracking module and magnetic compensation processing module, wherein the magnetic noise monitoring module, desired signal tracking module and magnetic compensation processing module are connected, where,

The magnetic noise monitoring module uses the magnetic field strength T ₁ collected by the reference magnetometer as the feedback signal y, and outputs the feedback signal y, the differential signal monitoring values y ₁ and y ₂ of the feedback signal y, and the total monitoring value y ₃ ;

The expected signal tracking module takes the set target magnetic field intensity T ₀ as the expected signal v, and outputs the expected signal v and its differential signal monitoring values v ₁ and v ₂ ;

The magnetic compensation processing module is based on the difference between the differential signal monitoring values y ₁ and y ₂ of the feedback signal y and the differential signal monitoring values v ₁ and v ₂ of the desired signal v To calculate the voltage compensation component u ₀ , and then compensate the voltage compensation component u ₀ based on the total monitoring value of magnetic noise y ₃ to obtain the total voltage compensation amount U, that is, the signal processor output compensation voltage.

Further, the calculation formula of the voltage compensation component u ₀ is as follows:

Among them, k _p is the proportional coefficient, k _d is the differential coefficient, is a nonlinear function, α ₁ and α ₂ are constants ranging from 0 to 1, and β is a constant.

Further, the calculation formula of the total voltage compensation amount U is as follows:

U＝u ₀ -y ₃ /c

Among them, c is a constant.

Further, the tracking formulas of the differential signal monitoring values y ₁ , y ₂ and the total monitoring value y ₃ of the feedback signal y are as follows:

y ₁ =y′ ₁ +q(y′ ₂ -K ₀₁ z′ ₁ );

Among them, K ₀₁ , K ₀₂ , and K ₀₃ are three adjustable parameters; z′ ₁ , z′ ₂ , and z′ ₃ are respectively the feedback signal monitoring values y′ ₁ , y′ ₂ , y′ ₃ and the feedback signal at the previous moment. The difference of signal y; q is the filter factor, which is an adjustable parameter, c is a constant, U′ is the compensation voltage output by the signal processor at the last moment, is a nonlinear function.

Furthermore, nonlinear functions The expression is specifically as follows:

Among them, z is the difference between the monitoring value of the feedback signal and the feedback signal, α is an adjustable parameter, ranging from 0 to 1, β is the parameter factor, and sign(*) is the sign function.

Furthermore, the tracking formulas of the differential signals v ₁ and v ₂ of the desired signal v are as follows:

v ₁ =v′ ₁ +qv′ ₂ ;

v ₂ =v′ ₂ qf(x ₁ ,x ₂ ,p,q);

Among them, v′ ₁ and v′ ₂ respectively represent the differential signal monitoring value of the desired signal v at the previous moment, and f (x ₁ , x ₂ , p, q) is the discrete domain control function.

Further, the discrete control function f(x ₁ , x ₂ , p, q) is as follows:

y＝x ₁ +qx ₂ ;

m=pq, m ₀ =mq

Among them, x ₁ , x ₂ , m, n ₀ , and m ₀ are intermediate parameters, and p and q are the set tracking speed factors and filter factors respectively.

The present invention is implemented in this way. An active magnetic compensation method based on an active magnetic compensation system is specifically as follows:

(1) Read the set expected signal v;

(2) When the sampling time is reached, the expected signal v enters the expected signal tracking module, and the feedback signal y enters the magnetic noise monitoring module;

(3) After receiving the expected signal v, the expected signal tracking module tracks the expected signal v and its differential signal, and then uses v ₁ =v′ ₁ +qv′ ₂ , v ₂ =v′ ₂ +qf(x ₁ , x ₂ , p, q) output tracking values v ₁ and v ₂ ;

(4) After receiving the feedback signal y, the magnetic noise monitoring module will track the feedback signal y and its differential signal, and then use y ₁ =y′ ₁ +q(y′ ₂ -K ₀₁ z′ ₁ ) and Output the monitoring values y ₁ and y ₂ , and at the same time /> Output the total monitoring value of magnetic noise y ₃ ;

(5) with and/> Calculate the deviation/> and/> The voltage compensation component u ₀ is output through the magnetic compensation amount processing module, and then the low-voltage compensation component and the total monitoring value of the magnetic noise are extracted to compensate the magnetic noise, and finally the compensation voltage U is output as U=u ₀ -y ₃ /c;

(6) The voltage-controlled current source converts the compensation voltage into the compensation current of the compensation coil, so that the magnetic field intensity T ₁ in the magnetic shielding cylinder environment is close to or reaches the target magnetic field intensity T ₀ .

The active magnetic compensation system provided by the present invention has the following beneficial technical effects:

(1) There is no need to wait until magnetic noise is generated before performing compensation control. It can accurately track the differential of the expected magnetic field value through the expected signal tracking module and magnetic noise detection module, and at the same time compensate the monitored magnetic noise to the control output end immediately. The response speed is faster than the general compensation algorithm.

(2) The three modules in the compensation algorithm can form a complete closed loop. The magnetic compensation amount can be calculated only based on the expected magnetic field value and magnetic noise monitoring value. It can be applied to various magnetic fields without knowing the model of the controlled object. The compensation system has better adaptability than the general magnetic compensation algorithm;

(3) The compensation accuracy of this compensation algorithm can reach pT level, and it can also produce a good suppression effect on low-frequency magnetic noise in the environment. It is suitable for magnetocardiograph systems with high accuracy requirements.

Description of the drawings

Figure 1 is a schematic structural diagram of an active magnetic compensation system provided by an embodiment of the present invention;

Figure 2 is a schematic diagram of signal feedback of the active magnetic compensation system provided by an embodiment of the present invention;

Figure 3 is a flow chart of an active magnetic compensation method provided by an embodiment of the present invention.

Detailed ways

The specific implementation modes of the present invention will be further described in detail below by describing the embodiments with reference to the accompanying drawings, so as to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concepts and technical solutions of the present invention.

Figure 1 is a schematic structural diagram of an active magnetic compensation system provided by an embodiment of the present invention. For ease of explanation, only the parts related to the embodiment of the present invention are shown. The system includes:

A reference magnetometer and a magnetic compensation coil are installed in the magnetic shielding barrel. The output end of the reference magnetometer is connected to the input end of the signal processor, and the output end of the signal processor is connected to the compensation coil through a voltage-controlled current source;

Among them, the reference magnetometer regularly collects the magnetic field intensity T ₁ in the magnetic shielding tube environment, and sends the magnetic field intensity T ₁ to the signal processor. The signal processor outputs the compensation voltage to the voltage-controlled current source, and the voltage-controlled current source will compensate the voltage. The compensation current is converted into the compensation coil so that the magnetic field intensity T ₁ in the magnetic shielding cylinder environment is close to or reaches the target magnetic field intensity T ₀ .

In the embodiment of the present invention, the reference magnetometer is designed at the center of the magnetic shielding cylinder to mainly monitor the magnetic field intensity of the environment of the magnetic shielding cylinder, and the compensation coil is mainly used to generate a uniform compensation magnetic field in the magnetic shielding cylinder. Compensate the magnetic field strength to offset the fluctuation of the environmental magnetic field strength. In addition, the magnetic shielding cylinder is also equipped with an induction magnetometer. The position of the induction magnetometer is different from that of the reference magnetometer. It is mainly used to verify the compensated magnetic field. Check whether the magnetic field intensity at other locations in the shielding tube is close to the target magnetic field intensity T ₀ .

In this embodiment of the present invention, the signal processor includes:

Magnetic noise detection module, desired signal tracking module and magnetic compensation processing module. The magnetic noise detection module, desired signal tracking module and magnetic compensation processing module are connected, as shown in Figure 2.

(1) The magnetic noise monitoring module uses the magnetic field intensity T ₁ collected by the reference magnetometer as the feedback signal y, and outputs the feedback signal y, the differential signal monitoring values y ₁ and y ₂ of the feedback signal y, and the total monitoring value y ₃ .

The magnetic noise monitoring module is used to monitor the actual magnetic noise and the total noise in the system. The magnetic noise monitoring module does not require too many information sources. It can obtain the status variables of each state variable in the system based only on the input and output of the system. monitoring value. Not only that, using the magnetic noise monitoring module does not need to consider the noise conditions inside and outside the system. Even in the face of uncertain noise models, the magnetic noise monitoring module can obtain the monitoring value of the overall magnetic noise in real time, and at the same time add magnetic compensation in the feedback. .

After receiving the feedback signal y, the magnetic noise monitoring module will track the feedback signal y and its differential signals y ₁ , y ₂ , y ₃ , where:

y ₁ =y′ ₁ +q(y′ ₂ -K ₀₁ z′ ₁ );

Among them, K ₀₁ , K ₀₂ , and K ₀₃ are three adjustable parameters; z′ ₁ , z′ ₂ , and z′ ₃ are respectively the feedback signal monitoring values y′ ₁ , y′ ₂ , y′ ₃ and the feedback signal at the previous moment. The difference of signal y; q is the filter factor, which is an adjustable parameter, c is a constant, U′ is the compensation voltage output by the signal processor at the last moment, is a nonlinear function, and its expression is as follows:

Among them, z is the difference between the monitoring value of the feedback signal and the feedback signal, α is an adjustable parameter with a value range of 0 to 1, β is a parameter factor with adjustable parameters, and sign(*) is a sign function. Increasing the value of β can improve The monitoring effect of the function, but will reduce its monitoring speed; reducing the value of α can improve/> The monitoring speed of the function will reduce its monitoring effect, so choosing appropriate α and β values according to different magnetic noise conditions can achieve complementary effects.

When magnetic noise occurs inside and outside the system, the magnetic noise monitoring module can transform the state of these noises so that they are in a first-order state, and then use the nonlinear function defined above and parameters K ₀₁ , K ₀₂ , K ₀₃ , the monitoring values of all noise states inside and outside the system can be obtained.

(2) The expected signal tracking module takes the set target magnetic field intensity T ₀ as the expected signal v, and outputs the expected signal v and its differential signal monitoring values v ₁ and v ₂ ;

The desired signal tracking module extracts the required magnetic signal based on the input characteristics of the magnetic field, while reducing the jump of the magnetic field input to facilitate real-time tracking of the magnetic compensation system. The expected signal tracking module can obtain the differential signal of magnetic noise through feedback and perform transition processing on the response of the magnetic field signal, so that the system can quickly obtain the compensation expectation while ensuring a smaller overshoot. Finally, the range of object parameters adapted to the magnetic field feedback gain and magnetic noise differential gain can be expanded, thereby improving the robustness of the magnetic compensation system.

After the expected signal tracking module receives the expected signal v, it will perform the above tracking processing on the expected signal v and its differential signals v ₁ and v ₂ , where:

v ₁ =v′ ₁ +qv′ ₂ ;

v ₂ =v′ ₂ +qf(x ₁ ,x ₂ ,p,q);

Among them, v′ ₁ and v′ ₂ respectively represent the differential signal monitoring value of the desired signal v at the previous moment, f (x ₁ , x ₂ , p, q) is the discrete domain control function, and two parameters are set, namely the tracking speed. Factor p and filter factor q, in a second-order system For example, the discrete control function is:

y＝x ₁ +qx ₂ ;

m=pq, m ₀ =mq

Among them, x ₁ and x ₂ are the intermediate parameters in the second-order system.

(3) The magnetic compensation processing module is based on the difference between the differential signal monitoring values y ₁ and y ₂ of the feedback signal y and the differential signal monitoring values v ₁ and v ₂ of the desired signal v To calculate the voltage compensation component u ₀ , and then compensate the voltage compensation component u ₀ based on the total monitoring value of magnetic noise y ₃ to obtain the total voltage compensation amount U, that is, the signal processor output compensation voltage.

The magnetic compensation processing module adopts a nonlinear controller structure that is independent of the object model. It can automatically detect magnetic noise and provide a voltage compensation component. As long as the speed of the magnetic noise monitoring module is fast enough, then this voltage compensation component can be It accurately reflects the changes in magnetic noise. After integrating the magnetic field variables in series, the magnetic compensation processing module can achieve the ideal control effect. In general, the magnetic compensation processing module is a nonlinear combination of the magnetic field state variable error generated by the desired signal tracking module and the magnetic noise monitoring module. It is combined with the voltage compensation component of the overall magnetic noise (total monitoring value) of the magnetic noise monitoring module. Together they form a compensation voltage; among them, the calculation formula of the voltage compensation component u ₀ is as follows:

Among them, k _p is the proportional coefficient, k _d is the differential coefficient, in,

The monitoring values y ₁ and y ₂ in the magnetic noise monitoring module will be fed back to the expected signal tracking module to generate the expected signal tracking values v ₁ and v ₂ , and the magnetic compensation processing module calculates the compensation component u ₀ through the expected signal tracking value, and The total monitoring value y ₃ will also be combined with the system coefficient c to give the compensation component u ₀ in the form of negative feedback. Therefore, it can be seen that the output of the total magnetic compensation U and the compensation component u ₀ , constant c and the total monitoring of the magnetic noise monitoring module The value y ₃ is related and its expression is:

U=u ₀ -y ₃ /c.

Figure 3 is a flow chart of an active magnetic compensation method provided by an embodiment of the present invention. The method specifically includes the following steps:

(1) At the beginning, the set expected signal v is read, and the feedback signal y of the previous moment is also read. The initial value of the feedback signal y defaults to zero.

(2) Wait for the sampling time. The sampling time can be set to different values as needed. When the sampling time is reached, the expected signal v will enter the expected signal tracking module, and the feedback signal y will enter the magnetic noise monitoring module. When the sampling time is not reached, the expected signal and feedback signal will continue to wait.

(3) After receiving the expected signal v, the expected signal tracking module tracks the expected signal v and its differential signal, and then uses v ₁ =v′ ₁ +qv′ ₂ , v ₂ =v′ ₂ +qf(x ₁ , x ₂ , p, q) output tracking values v ₁ and v ₂ ;

(4) After receiving the feedback signal y, the magnetic noise monitoring module will track the feedback signal y and its differential signal, and then use y ₁ =y′ ₁ +q(y′ ₂ -K ₀₁ z′ ₁ ) and Output the monitoring values y ₁ and y ₂ , and at the same time /> Output the total monitoring value of magnetic noise y ₃ ;

(5) followed by and/> Calculate the deviation/> and/> The magnetic compensation processing module outputs the voltage compensation component u ₀ , then extracts the low-voltage compensation component and the total monitoring value of magnetic noise to compensate for the magnetic noise, and finally outputs the compensation voltage U as U=u ₀ -y ₃ /c.

(6) The voltage-controlled current source converts the compensation voltage into the compensation current of the compensation coil, so that the magnetic field intensity T ₁ in the magnetic shielding cylinder environment approaches or reaches the target magnetic field intensity T ₀

The active magnetic compensation system is placed in a passive magnetic shielding environment. The magnetic compensation method can be integrated into the signal processor after parameter setting, or real-time parameter adjustment can be performed directly in the host computer. The desired signal tracking module and magnetic noise monitoring module in this invention will receive the digital signal from the analog-to-digital converter ADC. The digital signal represents the magnetic field measurement value in the real environment, and is called the actual feedback signal in the feedback process. The magnetic noise monitoring module needs to track the differential signal monitoring values y ₁ , y ₂ and the total monitoring value y ₃ based on the actual feedback signal. The expected signal tracking module tracks the differential signals v ₁ and v ₂ of the expected signal v. The magnetic compensation amount processing module is based on differential amount The magnetic compensation amount is calculated and output through the digital-to-analog converter. The principle block diagram of the compensation algorithm in the active magnetic compensation system is shown in Figure 2.

Among them, the magnetometer is responsible for collecting the magnetic field signal B _OUT and converting the magnetic field signal B _OUT into a voltage signal V _OUT and inputting it into the signal processor. The magnetic compensation algorithm embedded in the signal processor will calculate the value based on the set expected value. The signal processor then outputs the magnetic compensation amount U to the voltage-controlled current source in the form of a voltage signal V _COMP . The voltage-controlled current source inputs the corresponding current signal I _COMP into the magnetic compensation coil. Finally, the magnetic compensation coil Generate a magnetic field B _COMP with the same magnitude and opposite direction as the magnetic noise, thereby achieving the purpose of magnetic compensation.

The present invention has been described exemplarily. It is obvious that the specific implementation of the present invention is not limited by the above-mentioned manner. As long as various non-substantive improvements are made using the method concepts and technical solutions of the present invention, or the present invention is modified without improvement. If the ideas and technical solutions are directly applied to other situations, they are all within the protection scope of the present invention.

Claims (9)

1. An active magnetic compensation system, the system comprising:

the output end of the reference magnetometer is connected with the input end of the signal processor, and the output end of the signal processor is connected with the compensation coil through a voltage-controlled current source;

wherein, the reference magnetometer collects the magnetic field intensity T in the magnetic shielding barrel environment at regular time ₁ And the magnetic field intensity T ₁ Send to signalThe processor outputs the compensation voltage to the voltage-controlled current source, and the voltage-controlled current source converts the compensation voltage into the compensation current of the compensation coil so as to ensure that the magnetic field intensity T in the magnetic shielding barrel environment ₁ Near or reaching target magnetic field strength T ₀ 。

2. The active magnetic compensation system of claim 1, wherein the signal processor comprises:

the magnetic noise monitoring module, the expected signal tracking module and the magnetic compensation processing module are connected with each other,

the magnetic noise monitoring module refers to the magnetic field intensity T acquired by the magnetometer ₁ As feedback signal y, differential signal monitoring value y of feedback signal y is output ₁ 、y ₂ Monitoring the total value y ₃ ；

The expected signal tracking module sets the target magnetic field intensity T ₀ As the desired signal v, the desired signal v and the differential signal monitoring value v thereof are output ₁ 、v ₂ ；

Differential signal monitoring value y of magnetic compensation quantity processing module based on feedback signal y ₁ 、y ₂ Differential signal monitoring value v from desired signal v ₁ 、v ₂ Is the difference of (2)To calculate the voltage compensation component u ₀ And then based on the total monitored value y of magnetic noise ₃ For the voltage compensation component u ₀ And compensating to obtain the total compensation quantity U of the voltage, namely outputting the compensation voltage by the signal processor.

3. The active magnetic compensation system of claim 1, wherein the voltage compensation component u ₀ The calculation formula of (2) is specifically as follows:

wherein k is _p Is a proportionality coefficient, k _d As a result of the differential coefficient,as a nonlinear function, alpha ₁ 、α ₂ The value of β is a constant which is 0 to 1.

4. The active magnetic compensation system of claim 4, wherein the total compensation amount U is calculated by the following formula:

U＝u ₀ -y ₃ /c

wherein c is a constant.

5. The active magnetic compensation system of claim 1, wherein the differential signal monitor value y of the feedback signal y ₁ 、y ₂ Monitoring the total value y ₃ The tracking formula of (2) is as follows:

y ₁ ＝y′ ₁ +q(y′ ₂ -K ₀₁ z′ ₁ )；

wherein K is ₀₁ 、K ₀₂ 、K ₀₃ Three adjustable parameters; z'. ₁ 、z′ ₂ 、z′ ₃ Respectively the monitoring value y 'of the feedback signal at the last moment' ₁ 、y′ ₂ 、y′ ₃ A difference from the feedback signal y; q is a filtering factor, c is a constant, U' is a compensation voltage output by the signal processor at the previous moment,as a nonlinear function.

6. The active magnetic compensation system of claim 5, wherein the nonlinear functionThe expression is specifically as follows:

wherein z is the difference between the monitored value of the feedback signal and the feedback signal, alpha is an adjustable parameter, the value range is 0-1, beta is a parameter factor, and sign is a sign function.

7. The active magnetic compensation system of claim 1, wherein a differential signal v of the desired signal v ₁ 、v ₂ The tracking formula of (2) is as follows:

v ₁ ＝v′ ₁ +qv′ ₂ ；

v ₂ ＝v′ ₂ +qf(x ₁ ,x ₂ ,p,q)；

wherein v' ₁ 、v′ ₂ Differential signal monitoring values, f (x) ₁ ,x ₂ P, q) is a discrete domain control function.

8. The active magnetic compensation system of claim 1, wherein the discrete control function f (x ₁ ,x ₂ P, q) is specifically as follows:

y＝x ₁ +qx ₂ ；

m＝pq，m ₀ ＝mq

wherein x is ₁ 、x ₂ 、m、n ₀ 、m ₀ And p and q are respectively set tracking speed factors and filtering factors for intermediate parameters.

9. Active magnetic compensation method based on an active magnetic compensation system according to any of claims 1 to 8, characterized in that it comprises in particular the following steps:

(1) Reading a set expected signal v;

(2) When the sampling time is reached, the expected signal v enters an expected signal tracking module, and the feedback signal y enters a magnetic noise monitoring module;

(3) After the expected signal tracking module receives the expected signal v, the expected signal v and the differential signal thereof are tracked, and then v is respectively used for ₁ ＝v′ ₁ +qv′ ₂ 、v ₂ ＝v′ ₂ +qf(x ₁ ,x ₂ P, q) output trace value v ₁ And v ₂ ；

(4) After receiving the feedback signal y, the magnetic noise monitoring module tracks the feedback signal y and its differential signal, and then uses y ₁ ＝y′ ₁ +q(y′ ₂ -K ₀₁ z′ ₁ ) Andoutputting the monitored value y ₁ And y ₂ At the same time +.>Output of the total monitored value y of magnetic noise ₃ ；

(5) To be used forAnd->Calculating deviation +.>And->Outputting a voltage compensation component u by a magnetic compensation amount processing module ₀ Then extracting the low-voltage compensation component and the total monitored value y ₃ Compensating for magnetic noise with u=u ₀ -y ₃ C outputting a compensation voltage U;

(6) The voltage-controlled current source converts the compensation voltage into the compensation current of the compensation coil so as to lead the magnetic field intensity T in the magnetic shielding barrel environment ₁ Near or reaching target magnetic field strength T ₀ 。