Inductive magnetic sensor noise calibration device

Abstract

This invention discloses a noise calibration device for an inductive magnetic sensor. Based on an existing magnetic shielding cylinder, this invention adds an active magnetic shielding device and a magnetic shielding chamber. By effectively combining these three components, a combined magnetic shielding system is formed, which effectively eliminates the influence of external environmental interference magnetic fields. Simultaneously, a dynamic signal analyzer is used to accurately measure the sensitivity and voltage-noise cross-correlation power spectral density of the inductive magnetic sensor, completing the calibration. This device can reduce the ambient magnetic field to the level required for inductive magnetic sensor calibration, eliminating the need for simultaneous calibration of multiple probes with the same frequency characteristics. Calibration can be carried out in the laboratory, facilitating the calibration process. It features low ambient magnetic field noise, a simple calibration method, and high operability.

Description

Technical Field

[0001] This invention belongs to the field of weak magnetic field measurement technology and relates to an inductive magnetic sensor noise calibration device. Background Technology

[0002] An inductive magnetometer is an instrument that uses Faraday's law of electromagnetic induction to precisely measure alternating weak magnetic fields. It typically includes an inductive magnetometer probe, a main unit, and a shielded cable. The probe usually consists of a magnetic core, a detection coil, a feedback coil, and a preamplifier circuit. Inductive magnetometers are mainly used in many fields such as Earth resource exploration, earthquake prediction, submarine ultra-low frequency communication, electromagnetic environment observation, and deep space magnetic field detection.

[0003] Background noise is a core indicator of inductive magnetometers and requires calibration. Inductive magnetometers have extremely low magnetic field noise. For example, the Metronix GMS-06e magnetometer from Germany has noise levels of 100pT / Hz¹ / ²@0.001Hz, 11pT / Hz¹ / ²@0.01Hz, 10fT / Hz¹ / ²@100Hz, and 1fT / Hz¹ / ²@1kHz. This places extremely high demands on the magnetic field of the calibration environment for background noise.

[0004] In order to achieve extremely low background noise calibration of inductive magnetometers, domestic and foreign research and user units usually use conventional magnetic shielding cylinder method and field differential method.

[0005] While conventional magnetic shielding cylinder calibration methods can reduce external environmental interference magnetic fields through shielding and enable noise calibration in the laboratory, the shielding coefficient of the magnetic shielding cylinder is relatively small at power frequency and below (generally below 30dB). The environment inside the shielding cylinder is easily affected by external low-frequency interference magnetic fields, and cannot meet the calibration requirements for extremely low noise of inductive magnetic sensors, i.e., the environmental magnetic field noise at typical frequency points should not be greater than one-third of the noise of the inductive magnetic sensor being calibrated.

[0006] The field differential method uses dual-probe differential signals to calculate and analyze magnetic field noise in field environments with low magnetic field noise. Theoretically, this method can effectively eliminate the influence of environmental interference magnetic fields and obtain accurate magnetic field noise. However, the method requires simultaneous calibration of at least two probes, and it is necessary to ensure that the sensitivity transfer functions of the two probes are highly consistent. In actual calibration, the number of objects being calibrated is mostly a single set. Even if there are multiple sets, it is difficult to ensure that the transfer functions of the magnetoelectric conversion coefficient are consistent. Therefore, this method is not very practical for metrological calibration. Summary of the Invention

[0007] In view of this, the present invention provides an inductive magnetic sensor noise calibration device that can reduce the ambient magnetic field to the level required for inductive magnetic sensor calibration. It eliminates the need for simultaneous calibration of multiple probes with the same frequency characteristics, and allows calibration work to be carried out in the laboratory, facilitating the implementation of calibration work. It has the advantages of low ambient magnetic field noise, simple calibration method, and strong operability.

[0008] An inductive magnetic sensor noise calibration device includes an alternating weak magnetic field system and a combined magnetic shielding system. The alternating weak magnetic field system uses a dynamic signal analyzer to obtain the sensitivity of the inductive magnetic sensor. The combined magnetic shielding system, used to shield environmental interference magnetic fields, includes an active magnetic shielding device, a magnetic shielding chamber, and a magnetic shielding cylinder. A triaxial active magnetic shielding coil in the active magnetic shielding device is wound outside the magnetic shielding chamber, and the magnetic shielding cylinder is nested inside the magnetic shielding chamber. The dynamic signal analyzer is used to measure the voltage-noise cross-correlation power spectral density of the inductive magnetic sensor, thereby obtaining the power spectral density of the magnetic field noise and completing the calibration.

[0009] Preferably, the active magnetic shielding device includes an active magnetic shielding controller, a triaxial magnetic sensor, and a triaxial active magnetic shielding coil; the active magnetic shielding controller is placed outside the magnetic shielding room and connected to the triaxial magnetic sensor; the three probes of the triaxial magnetic sensor are respectively arranged at the center of the outer surface of the three mutually perpendicular walls of the magnetic shielding room; the triaxial active magnetic shielding coil is wired along the 12 sides of the magnetic shielding room.

[0010] Preferably, the magnetic shielding cylinder is nested inside the magnetic shielding chamber, the working area of ​​the magnetic shielding cylinder and the working area of ​​the magnetic shielding chamber overlap, and the opening direction of the magnetic shielding cylinder is consistent with the opening direction of the magnetic shielding chamber.

[0011] Preferably, during use, the inductive magnetic sensor is placed in the working area of ​​the combined magnetic shielding system, and the dynamic signal analyzer is connected to the inductive magnetic sensor to obtain the voltage-noise cross-correlation power spectral density of the inductive magnetic sensor.

[0012] Preferably, the alternating weak magnetic field system is used to generate a standard alternating magnetic field, including an AC current source, an AC / DC shunt, and an alternating magnetic field coil connected in series, and a dynamic signal analyzer connected to the AC / DC shunt; wherein the AC current source, AC / DC shunt, and dynamic signal analyzer are placed outside the magnetic shielding chamber, the alternating magnetic field coil is located inside the magnetic shielding chamber, and the uniform region of the alternating magnetic field coil is located within the working area of ​​the magnetic shielding chamber; in use, the inductive magnetic sensor is placed in the uniform region of the alternating weak magnetic field system, the orientation of the inductive sensor is adjusted so that the sensitive axis of the probe is parallel to the magnetic axis of the alternating magnetic field coil, and the dynamic signal analyzer is connected to the inductive magnetic sensor; the measured output voltage of the AC / DC shunt and the output voltage of the inductive magnetic sensor are obtained, and finally the sensitivity of the inductive magnetic sensor is obtained.

[0013] Preferably, according to Obtain the power spectral density N of the magnetic field noise m , complete calibration; where K w For the sensitivity of the inductive magnetic sensor, N v This represents the voltage-noise cross-correlation power spectral density of the magnetic sensor.

[0014] Beneficial effects

[0015] This invention, based on existing magnetic shielding cylinders, adds an active magnetic shielding device and a magnetic shielding chamber. By effectively combining these three components, a combined magnetic shielding system is formed, which effectively eliminates the influence of external environmental interference magnetic fields. Simultaneously, a dynamic signal analyzer is used to accurately measure the sensitivity and voltage-noise cross-correlation power spectral density of the inductive magnetic sensor, completing the calibration. This device can reduce the ambient magnetic field to the level required for inductive magnetic sensor calibration, eliminating the need for simultaneous calibration of multiple probes with the same frequency characteristics. Calibration can be carried out in the laboratory, facilitating the calibration process. It features low ambient magnetic field noise, a simple calibration method, and high operability.

[0016] Active magnetic shielding devices are used to shield environmental interference magnetic fields, and magnetic shielding chambers are also used to shield environmental interference magnetic fields. However, the simple encirclement of the two cannot achieve effective superposition of shielding effects. To solve this problem, the triaxial active magnetic shielding coil in the active magnetic shielding device is wired along the 12 sides of the magnetic shielding chamber. This structure can ensure the superposition of shielding effects between the main shielding system and the magnetic shielding chamber, and also reduce the structure of the shielding coil.

[0017] Magnetic shielding cylinders are used to shield environmental interference magnetic fields, and magnetic shielding chambers are also used to shield environmental interference magnetic fields. However, simple nesting between the two cannot achieve effective superposition of shielding effects. To solve this problem, the working areas of the magnetic shielding cylinder and the magnetic shielding chamber need to overlap, and the opening direction of the magnetic shielding cylinder should be consistent with the opening direction of the magnetic shielding chamber. This structural constraint can effectively increase the shielding effect.

[0018] This invention employs a dynamic signal analyzer consisting of a high-speed, high-precision data acquisition unit and data processing and analysis software. It is capable of acquiring data at high speed and with high precision, and has functions such as amplitude spectrum, cross-correlation power spectrum, and cross-correlation power spectral density analysis, enabling direct data analysis of measurement docking. Attached Figure Description

[0019] Figure 1 Composition and connection diagram of an alternating weak magnetic field system;

[0020] Figure 2 Structural diagram of a combined magnetic shielding system;

[0021] Figure 3 Schematic diagram of noise calibration for inductive magnetic sensor Detailed Implementation

[0022] The implementation of the method of the present invention will be described below with reference to the accompanying drawings and embodiments.

[0023] This invention provides a noise calibration device for an inductive magnetic sensor. The device primarily employs a combined magnetic shielding system, adding an active magnetic shielding device and a magnetic shielding chamber to the existing magnetic shielding cylinder. This effective combination of the three components effectively eliminates the influence of external environmental interference magnetic fields. Furthermore, the device's alternating weak magnetic field system utilizes a dynamic signal analyzer, capable of measuring the sensitivity and voltage noise of the inductive magnetic sensor. Its specific structure is as follows:

[0024] The calibration device includes an alternating weak magnetic field system and a combined magnetic shielding system, wherein:

[0025] like Figure 1 As shown, the alternating weak magnetic field system is used to generate a standard alternating magnetic field, including an AC current source, an AC / DC shunt and an alternating magnetic field coil connected in series, and a dynamic signal analyzer connected to the AC / DC shunt.

[0026] The aforementioned AC current source is used to generate AC current. It is selected to output low-noise, high-precision AC current with an amplitude range of 1uA to 100mA and a frequency range of 1mHz to 100kHz, and a stability of no more than 2uA / 24h. Preferably, the Keithley 6221 AC current source is selected, with a frequency range of 0.001Hz to 100kHz.

[0027] The AC / DC shunt is used to convert AC current into AC voltage signal. Its core component is a sampling resistor with high stability and high accuracy. The current operating range is 1uA to 100mA. Preferably, the HT-8 type AC / DC shunt is selected.

[0028] The dynamic signal analyzer is connected to both the AC / DC shunt and the inductive magnetic sensor to measure their output voltages. It consists of a high-speed, high-precision data acquisition unit and data processing and analysis software. The high-speed, high-precision data acquisition unit has a sampling rate of at least 200 ks / s and a resolution of at least 24 bits. The data processing and analysis software includes functions such as amplitude spectrum, cross-correlation power spectrum, and cross-correlation power spectral density analysis.

[0029] like Figure 2 As shown, the combined magnetic shielding system, used to shield against environmental interference magnetic fields, includes an active magnetic shielding device, a magnetic shielding chamber, and a magnetic shielding cylinder. Combining these three shielding devices using a specific method enhances the shielding effect.

[0030] The main magnetic shielding system comprises an active magnetic shielding controller, a triaxial magnetic sensor, and a triaxial active magnetic shielding coil, used to shield against environmental interference magnetic fields. Specifically: the active magnetic shielding controller is placed outside the magnetic shielding chamber and connected to the triaxial magnetic sensor; the triaxial active magnetic shielding coil is wound outside the magnetic shielding chamber, arranged along the 12 sides of the magnetic shielding chamber (considered a cube). This structure ensures the superposition of shielding effects between the main shielding system and the magnetic shielding chamber while reducing the structural complexity of the shielding coil. A rectangular Helmholtz coil is preferred. The triaxial magnetic sensor is a split-probe magnetic sensor. The three probes of the triaxial magnetic sensor are respectively arranged at the center of the outer surface of three mutually perpendicular walls of the magnetic shielding chamber.

[0031] The magnetic shielding cylinder is nested within the magnetic shielding chamber, with the working areas of the cylinder and chamber coinciding, and the opening direction aligned with the door opening direction of the chamber. Preferably, the magnetic shielding cylinder uses permalloy as the magnetic conductive material, with at least five layers. The magnetic shielding chamber uses permalloy and oriented silicon steel sheets as the magnetic conductive materials, with at least three layers of permalloy and at least two layers of silicon steel. Furthermore, all magnetic shielding layers of both the magnetic shielding cylinder and the magnetic shielding chamber are connected to the grounding grid via conductors.

[0032] The alternating magnetic field coil of the alternating weak magnetic field system is located inside the magnetic shielding cylinder, and the uniform region of the alternating magnetic field coil is located within the working area of ​​the magnetic shielding cylinder. The AC current source, AC / DC shunt, and dynamic signal analyzer of the alternating weak magnetic field system are located outside the shielding chamber.

[0033] When using it, first place the inductive magnetic sensor in the uniform area of ​​the alternating weak magnetic field system, adjust the orientation of the inductive sensor so that the sensitive axis of the probe is parallel to the magnetic axis of the alternating magnetic field coil; connect the inductive magnetic sensor to the dynamic signal analyzer; then power on the inductive magnetometer and preheat for 30 minutes; select the frequency calibration point as needed, use the AC current source and the alternating magnetic field coil to reproduce the standard magnetic field, read the output voltage of the AC / DC shunt and the output voltage of the inductive magnetic sensor measured by the dynamic signal analyzer, and calculate the sensitivity of the inductive magnetic sensor according to formula (1).

[0034]

[0035] In the formula:

[0036] K Bf — Coil constant of the alternating magnetic field coil, T / A;

[0037] U i —The output voltage of the AC / DC shunt was measured by a dynamic signal analyzer, in V;

[0038] U o —The output voltage of the inductive magnetic sensor, measured by the dynamic signal analyzer, in V;

[0039] R f — The resistance of the AC / DC shunt at the calibration frequency point, in Ω.

[0040] Afterwards, the AC current source was turned off, and the inductive magnetic sensor was connected to the dynamic signal analyzer. The inductive magnetic sensor was located in the working area of ​​the combined magnetic shielding system. The voltage-noise cross-correlation power spectral density N of the inductive magnetic sensor was tested. v ,like Figure 3 As shown.

[0041] Finally, the power spectral density N of the magnetic field noise is calculated according to formula (2) based on the sensitivity of the inductive magnetic sensor and the cross-correlation power spectral density of the voltage noise. m .

[0042]

[0043] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An inductive magnetic sensor noise calibration apparatus, characterized by: The system includes an alternating weak magnetic field system and a combined magnetic shielding system. The alternating weak magnetic field system uses a dynamic signal analyzer to obtain the sensitivity of the inductive magnetic sensor. The combined magnetic shielding system is used to shield the environmental interference magnetic field and includes an active magnetic shielding device, a magnetic shielding chamber, and a magnetic shielding cylinder. The triaxial active magnetic shielding coil in the active magnetic shielding device is wound around the outside of the magnetic shielding chamber, and the magnetic shielding cylinder is nested inside the magnetic shielding chamber. The dynamic signal analyzer is used to measure the voltage noise cross-correlation power spectral density of the inductive magnetic sensor, thereby obtaining the power spectral density of the magnetic field noise and completing the calibration. The alternating weak magnetic field system is used to generate a standard alternating magnetic field. It includes an AC current source, an AC / DC shunt, and an alternating magnetic field coil connected in series, as well as a dynamic signal analyzer connected to the AC / DC shunt. The AC current source, AC / DC shunt, and dynamic signal analyzer are placed outside the magnetic shielding chamber, while the alternating magnetic field coil is located inside the magnetic shielding chamber, with the uniform region of the alternating magnetic field coil located within the working area of ​​the magnetic shielding chamber. In use, an inductive magnetic sensor is placed in the uniform region of the alternating weak magnetic field system. The orientation of the inductive sensor is adjusted so that the sensitive axis of the probe is parallel to the magnetic axis of the alternating magnetic field coil. The dynamic signal analyzer is connected to the inductive magnetic sensor. The measured output voltage of the AC / DC shunt and the output voltage of the inductive magnetic sensor are obtained, and the sensitivity of the inductive magnetic sensor is finally obtained.

2. The noise calibration apparatus of claim 1, wherein: The active magnetic shielding device includes an active magnetic shielding controller, a triaxial magnetic sensor, and a triaxial active magnetic shielding coil. The active magnetic shielding controller is placed outside the magnetic shielding room and connected to the triaxial magnetic sensor. The three probes of the triaxial magnetic sensor are respectively arranged at the center of the outer surface of the three mutually perpendicular walls of the magnetic shielding room. The triaxial active magnetic shielding coil is wired along the 12 sides of the magnetic shielding room.

3. The noise calibration apparatus of claim 1, wherein The magnetic shielding cylinder is nested inside the magnetic shielding chamber, with the working area of ​​the magnetic shielding cylinder coinciding with the working area of ​​the magnetic shielding chamber, and the opening direction of the magnetic shielding cylinder is consistent with the opening direction of the magnetic shielding chamber.

4. The noise calibration device as described in claim 3, characterized in that, In use, the inductive magnetic sensor is placed in the working area of ​​the combined magnetic shielding system, and the dynamic signal analyzer is connected to the inductive magnetic sensor to obtain the voltage-noise cross-correlation power spectral density of the inductive magnetic sensor.

5. The noise calibration apparatus of claim 1, wherein: according to Obtain the power spectral density of the magnetic field noise. Complete the calibration; among them The sensitivity of the inductive magnetic sensor, This represents the voltage-noise cross-correlation power spectral density of the magnetic sensor.

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