CN114460505A - Low-noise induction type magnetometer for weak alternating magnetic field magnitude transmission - Google Patents
Low-noise induction type magnetometer for weak alternating magnetic field magnitude transmission Download PDFInfo
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Abstract
The invention relates to a low-noise induction type magnetometer for transmitting a weak alternating magnetic field magnitude, and belongs to the technical field of magnetic field metering. The extraction circuit is optimally designed to ensure that the background noise of the probe of the induction type magnetometer reaches 50fT/Hz1/2@10Hz, the uncertainty of the whole induction type magnetometer measurement reaches 1pT (k is 2), and the problem of insufficient weak magnetic signal detection capability of the current metering level induction type magnetometer is solved. The novel induction type magnetometer can improve the sensitivity of the original metering level induction type magnetometer probe, reduce background noise, and obviously improve the signal-to-noise ratio of the induction type magnetometer host, and has the characteristics of good temperature stability, wide probe frequency response range and the like, thereby being more favorable for realizing the waveform fidelity, time domain analysis and spectral domain analysis of magnetic signals.
Description
Technical Field
The invention relates to a low-noise induction type magnetometer for weak alternating magnetic field magnitude transmission, which belongs to the technical field of magnetic field measurement, wherein weak means that the alternating magnetic field magnitude is below 1nT, and low noise means that the background noise of an induction type magnetometer probe is not more than 50fT/Hz1/2@10Hz。
Background
In many fields such as resource exploration, deep structure detection, earthquake prediction, military target detection, cardio-cerebral-magnetic measurement, active magnetic shielding, and research on origin evolution of planetary magnetic field, instruments such as an alternating current teslameter and an alternating magnetic sensor are widely used for measuring weak alternating magnetic field, and in order to ensure that characterization units of the alternating magnetic field are uniform and the magnitude is accurate and reliable, an alternating weak magnetic field standard device or a calibration device is required to regularly carry out laboratory verification/calibration or field verification/calibration equivalent value transfer work.
The alternating weak magnetic standard device generally adopts a standard measuring coil magnetometer and an induction type magnetometer as main standard devices or main matched equipment for comparison and zero detection. The standard measuring coil magnetometer is an air-core coil structure, has no amplification function on magnetic flux, has very weak induced voltage signals even submerged in noise under a low-frequency weak magnetic field, has larger measurement uncertainty, and is generally only used for magnitude transmission work of more than 1 nT. The induction type magnetometer is composed of a probe (namely an induction coil bar or an induction type magnetic sensor) and a host, wherein the induction type magnetic sensor adopts an induction coil structure filled with a strip-shaped soft magnetic core, has a remarkable amplification effect on magnetic flux, is usually dozens of times of magnitude, is remarkably improved in signal-to-noise ratio, and is mainly used for transmitting alternating magnetic field magnitude below 1 nT. In recent years, with the rapid development of related application research, the alternating weak magnetic metering technology needs to be developed in the direction of extremely weak quantity, so that for a metering level induction magnetometer for comparison and zero detection, the weak magnetic signal detection capability of the magnetometer must be improved, and the measurement lower limit of the magnetometer must be expanded.
However, the weak magnetic signal detection capability of the existing metering-level induction type magnetometer does not meet the future development requirement whether from the probe or the host, and the background noise of the probe is mainly 500fT/Hz1/2The @10Hz frequency is still larger, the host machine converts the induced alternating magnetic field analog voltage signal into a numerical value based on the data acquisition quantification and FFT principle, the FFT cannot change the signal-to-noise ratio theoretically, in fact, due to the fact that the FFT has the problems of frequency spectrum aliasing, leakage, barrier effect and the like, the weak magnetic signal detection capability is reduced practically, the signal-to-noise ratio can be deteriorated properly in a data acquisition circuit in theory or in practice, and the situation that the future alternating magnetic field measurement is sent to the extremely weak quantity cannot be metThe need for exhibition.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the defects of the prior art are overcome, and a low-noise induction type magnetometer for weak alternating magnetic field magnitude transfer is provided, wherein the background noise of the probe of the induction type magnetometer is reduced by at least one order of magnitude to 50fT/Hz1/2@10Hz, the uncertainty of measurement of the induction type magnetometer complete machine is 1pT (k ═ 2).
The technical solution of the invention is as follows:
a low-noise induction type magnetometer used for the magnitude transmission of a weak alternating magnetic field comprises a probe, a host and a shielding cable, wherein the probe is connected with the host through the shielding cable;
the probe comprises a magnetic core, a coil framework, an induction winding, a feedback compensation winding, an electromagnetic shielding film, a preamplifier, a non-magnetic shell and a non-magnetic connector;
the coil framework is sleeved outside the magnetic core;
the induction winding is wound on the outer surface of the coil skeleton, an electric shielding film is coated on the induction winding, a feedback compensation winding is wound on the electric shielding film, an electric shielding film is coated on the feedback compensation winding, one end of the induction winding is connected with a signal ground, the other end of the induction winding is connected with the input end of the preamplifier circuit, one end of the feedback compensation winding is connected with the signal ground, the other end of the feedback compensation winding is connected with the output end of the preamplifier circuit, the output end of the preamplifier is connected with a non-magnetic connector, the magnetic core, the coil skeleton, the induction winding, the feedback compensation winding and the preamplifier are all installed in a non-magnetic shell, and the non-magnetic connector is installed outside the non-magnetic shell;
the host comprises a biphase lock-in amplifier module, a reference signal module, an algorithm implementation module and a data processing and control module;
the biphase lock-in amplifier module comprises a 50Hz wave trap, an amplifier, an anti-aliasing filter and a 24-bit analog-to-digital conversion circuit, wherein a signal output by a nonmagnetic connector of the probe is connected with the input end of the 50Hz wave trap and passes throughAfter passing through the trapped wave of the 50Hz trap, the trapped wave is output to an amplifier for amplification and output to an anti-aliasing filter for filtering, and then output to a 24-bit analog-to-digital conversion circuit for analog-to-digital conversion and then output to SI(t) providing an algorithm implementation module;
the reference signal module adopts two paths of orthogonal reference signals S generated by an internal reference sourceR0(t) and SR1(t) providing an algorithm implementation module;
the algorithm implementation module is used for receiving two paths of orthogonal reference signals S output by the reference signal moduleR0(t) and SR1(t) also used for receiving S output after the analog-to-digital conversion of the 24-bit analog-to-digital conversion circuitI(t) and according to the received SR0(t)、SR1(t) and SI(t) calculating the real part X and the imaginary part Y of the signal to be measured, then calculating the amplitude R and the phase theta,
theta is tan (Y/X), and the amplitude R and the phase theta are output to the data processing and control module;
the data processing and control module is used for receiving the amplitude R and the phase theta output by the algorithm realization module, and calibrating the received amplitude R and the received phase theta through the calibrated probe sensitivity and zero offset to obtain the amplitude and the phase of the magnetic induction intensity.
Preferably, the magnetic core is in a dumbbell-shaped structure, the dumbbell-shaped structure comprises a middle waist part and two end parts, the middle waist part is a soft magnetic alloy bundle which is formed by soft magnetic alloy wires and has a circular cross section, and the two end parts are truncated cone-shaped magnetic flux collectors made of soft magnetic alloy materials;
the soft magnetic alloy beam penetrates through the coil framework, two ends of the soft magnetic alloy beam are fixedly connected to the inner surface of the coil framework, and the magnetic flux collectors at two ends of the magnetic core are positioned outside the coil framework.
Preferably, the soft magnetic alloy is selected from a NiFe alloy or amorphous alloy soft magnetic material with low Barkhausen noise, high initial permeability, low coercive force, high resistivity and high Curie temperature (more than 150 ℃);
the coil skeleton is made of non-magnetic non-metallic materials with high stability and low linear expansion coefficient, including but not limited to polysulfone, ceramic and epoxy;
the induction winding and the feedback compensation winding are both made of oxygen-free copper enameled wires.
Preferably, the diameter of the soft magnetic alloy beam is consistent with the inner diameter of the coil framework.
Preferably, the preamplifier adopts a magnetic flux negative feedback compensation circuit based on V/I conversion, and a low-temperature drift resistor is used in the V/I conversion circuit;
the preamplifier adopts a modulation-demodulation circuit, when a low-frequency signal is detected, the low-frequency magnetic signal in a 1/f frequency band is modulated to a high-frequency band with lower noise and then demodulated, the 1/f noise is reduced, and the modulation-demodulation circuit is started only when the low-frequency magnetic field is measured.
Preferably, the induction winding is several thousands to several tens of thousands of turns and is wound on the outer surface of the coil framework in sections;
the number of turns of the feedback compensation winding is 5-10.
Preferably, the host further comprises a display module, a battery pack and a power conversion module;
the display module is used for displaying the amplitude and the phase of the weak magnetic signal to be detected sent by the data processing and control module;
the battery pack and the power supply conversion module are used for providing electric energy for all circuits of the induction type magnetometer, and comprise a probe.
Preferably, the battery pack selects to charge the lithium ion battery pack, and the power conversion module converts and stabilizes the output voltage of the battery pack through DC/DC conversion and LDO (low dropout regulator) to generate various positive and negative voltages required by the host.
Preferably, the host further comprises a case, the case is used for installing the lock-in amplifier module, the data processing and control module, the display module, the battery pack and the power conversion module, and the case is made of a nonmagnetic aluminum alloy case.
A method of magnetic field strength testing using a low noise inductive magnetometer, comprising the steps of:
firstly, placing an induction type magnetometer probe in a magnetic field uniform area of an alternating weak magnetic standard device, and enabling a sensitive axis of the probe to be parallel to the direction of a magnetic field to be measured;
secondly, placing the host machine of the induction type magnetometer at a position more than 3 meters away from the probe;
thirdly, connecting the probe of the induction type magnetometer with the host of the induction type magnetometer by using a shielded cable;
fourthly, turning on a main machine power supply of the induction type magnetometer, electrifying the induction type magnetometer, and preheating for 10-30 minutes;
and fifthly, setting calibration parameters, and reading and recording the magnetic field indication value displayed by the induction type magnetometer host according to verification or calibration requirements.
The invention has the following beneficial effects:
the invention adopts an inductive magnetic sensor probe of a magnetic flux negative feedback and magnetic flux gathering technology to detect an alternating magnetic field to obtain an analog signal, and then data processing is carried out through a host based on a biphase phase locking technology to finally obtain an indication value of the intensity of the alternating magnetic field; the problem of insufficient weak magnetic signal detection capability of the current metering-level induction type magnetometer is solved; the sensitivity of the original metering-level induction type intensity meter probe is improved, the background noise is reduced, the signal-to-noise ratio of the induction type intensity meter host is obviously improved, and the method has the characteristics of good temperature stability, wide probe frequency response range and the like, and is more favorable for realizing the waveform fidelity, time domain analysis and spectral domain analysis of magnetic signals; the method has high application value in the test and calibration of the alternating magnetometer, and has good application value in the fields of deep space magnetic field detection, mineral resource exploration, earthquake precursor disturbance magnetic field observation, magnetic shielding device test and the like.
Drawings
FIG. 1 is a block diagram of the overall composition of the novel low noise induction magnetometer;
FIG. 2 is a block diagram of an inductive magnetometer probe;
FIG. 3 is a schematic diagram of a magnetic flux negative feedback compensation preamplifier based on V/I conversion;
FIG. 4 is a diagram of the structure of the induction type magnetometer host;
FIG. 5 is a schematic diagram of the detection principle of alternating weak magnetic signals based on the two-phase locking amplification technology.
Detailed Description
In order to make the technical solution and advantages of the present invention more apparent, the present invention will be described in detail below with reference to the accompanying drawings. The specific embodiments described herein are merely illustrative of the invention and do not delimit the invention.
A low-noise induction type magnetometer used for the magnitude transmission of a weak alternating magnetic field comprises a probe, a host and a shielding cable, wherein the probe is connected with the host through the shielding cable and is used for signal transmission and power supply;
the probe comprises a magnetic core, a coil framework, an induction winding, a feedback compensation winding, an electromagnetic shielding film, a preamplifier, a non-magnetic shell and a non-magnetic connector;
the magnetic core is of a dumbbell-shaped structure, the dumbbell-shaped structure comprises a middle waist part and two end parts, the middle waist part is a soft magnetic alloy bundle which is formed by soft magnetic alloy wires and has a circular section shape, and the two end parts are truncated cone-shaped magnetic flux collectors made of soft magnetic alloy materials;
the soft magnetic alloy is made of NiFe alloy or amorphous alloy and other soft magnetic materials with low Barkhausen noise, high initial permeability, low coercive force, high resistivity and high Curie temperature (more than 150 ℃);
the diameter of the soft magnetic alloy beam is consistent with the inner diameter of the coil framework;
the soft magnetic alloy beam penetrates through the coil framework, two ends of the soft magnetic alloy beam are fixedly connected to the inner surface of the coil framework, and magnetic flux collectors at two ends of the magnetic core are positioned outside the coil framework;
the induction winding and the feedback compensation winding are both coated with a layer of electromagnetic shielding film;
the coil skeleton is made of non-magnetic non-metallic materials with high stability and low linear expansion coefficient, including but not limited to polysulfone, ceramic and epoxy;
the induction winding and the feedback compensation winding are both oxygen-free copper enameled wires;
the preamplifier adopts a magnetic flux negative feedback compensation circuit based on V/I conversion, and a low-temperature drift resistor is used in the V/I conversion circuit;
the induction winding is wound on the outer surface of the coil skeleton in sections, a layer of electric shielding film is coated on the induction winding, a feedback compensation winding is wound on the electric shielding film, a layer of electric shielding film is coated on the feedback compensation winding, one end of the induction winding is connected with a signal ground, the other end of the induction winding is connected with the input end of a preamplifier circuit, one end of the feedback compensation winding is connected with the signal ground, the other end of the feedback compensation winding is connected with the output end of the preamplifier circuit, the output end of the preamplifier is connected with a nonmagnetic connector, the magnetic core, the coil skeleton, the induction winding, the feedback compensation winding and the preamplifier are all installed in a nonmagnetic shell, and the nonmagnetic connector is installed outside the nonmagnetic shell;
the number of turns of the feedback compensation winding is 5-10, and the feedback compensation winding is used for compensating and offsetting an induced magnetic field in the magnetic core, so that the probe always works near zero magnetic flux, and the linearity of the probe can be obviously improved;
the preamplifier adopts a magnetic flux negative feedback compensation circuit based on V/I conversion and is used for inhibiting noise and flattening a middle-section resonance peak of a frequency characteristic curve, compensation current and an output magnetic field signal can have a better linear relation based on V/I conversion, and a low-temperature drift resistor is used in the V/I conversion circuit, so that the sensitivity and the temperature stability of the probe are better;
the preamplifier adopts a modulation-demodulation circuit, when a low-frequency signal is detected, the low-frequency magnetic signal in a 1/f frequency band is modulated to a high-frequency band with lower noise and then demodulated, so that the 1/f noise is reduced, and the modulation-demodulation circuit is started only when the low-frequency magnetic field is measured;
the induction type magnetometer host comprises a double-phase lock-in amplifier module, a data processing and control module, a display module, a battery pack and power supply conversion module, an algorithm realization module and a reference signal module;
the two-phase lock-in amplifier module comprises a 50Hz wave trap, an amplifier, an anti-aliasing filter, a 24-bit analog-to-digital conversion circuit and a probeThe signal output by the nonmagnetic connector is connected with the input end of the 50Hz wave trap, is output to the amplifier after being trapped by the 50Hz wave trap, is amplified and output to the anti-aliasing filter for filtering, and is output to the 24-bit analog-to-digital conversion circuit for analog-to-digital conversion and then is output to SI(t) providing an algorithm implementation module;
the reference signal module adopts an internal reference source to generate two paths of orthogonal reference signals SR0(t) and SR1(t) providing an algorithm implementation module;
the algorithm implementation module is based on a high-speed operation platform such as a DSP (digital Signal processor) or an ARM (advanced RISC machine) machine and mainly realizes dual-channel digital phase-sensitive detection, and is used for receiving two paths of orthogonal reference signals S output by the reference signal moduleR0(t) and SR1(t) also used for receiving the output of the 24-bit analog-to-digital conversion circuit after analog-to-digital conversion and according to the received SR0(t)、SR1(t) and SI(t) calculating the real part X of the signal to be measured (corresponding to S in FIG. 5)out0(t)) and an imaginary part Y (corresponding to S in FIG. 5)out1(t)), then the amplitude R and phase theta are calculated,
theta is tan (Y/X), and the amplitude R and the phase theta are output to the data processing and control module;
the data processing and control module is used for receiving the amplitude R and the phase theta output by the algorithm realization module, calibrating the received amplitude R and the received phase theta through the calibrated probe sensitivity and zero offset to obtain the amplitude and the phase of the magnetic induction intensity, and sending the amplitude and the phase to the display module for displaying;
the display module is used for displaying the amplitude and the phase of the weak magnetic signal to be detected;
the battery pack and the power supply conversion module are used for providing electric energy for all circuits of the induction type magnetometer, the battery pack comprises a probe and a selectively rechargeable lithium ion battery pack of the battery pack, the probe and the battery pack are convenient to recycle, and the power supply conversion module converts and stabilizes the output voltage of the battery pack through DC/DC conversion and LDO (low dropout regulator) to generate various positive and negative voltages required by a host;
the induction type magnetometer host machine also comprises a case, wherein the case is used for installing and fixing all functional modules of the induction type magnetometer host machine and adopts a non-magnetic aluminum alloy case.
The background noise of the probe of the induction type magnetometer and the measurement uncertainty of the whole machine are obviously reduced by optimizing and improving the probe of the induction type magnetometer and the weak signal detection and extraction circuit of the main machine of the induction type magnetometer at the same time.
The locking amplification module is a two-phase digital locking amplifier and can simultaneously measure the amplitude and the phase of a weak alternating magnetic field.
The reference signal module adopts an internal reference source.
The algorithm implementation module adopts a high-speed operation platform such as a DSP or an ARM and the like to implement double-channel digital phase-sensitive detection and calculate the amplitude R and the phase theta.
And the data processing and control module corrects the data output by the double-phase lock-in amplifier module by using the calibrated probe sensitivity and zero-offset parameters to obtain the amplitude and the phase of the magnetic induction intensity to be detected.
The invention discloses a low-noise induction type magnetometer for transmitting weak alternating magnetic field magnitude, which optimally designs a probe magnetic core, a probe preamplification circuit and an induction type magnetometer host weak signal detection extraction circuit of the induction type magnetometer so that the background noise of the probe of the induction type magnetometer reaches 50fT/Hz1/2@10Hz, the uncertainty of the whole induction type magnetometer in measurement reaches 1pT (k is 2), and the problem of insufficient weak magnetic signal detection capability of the current metering level induction type magnetometer is solved. The novel induction type magnetometer can improve the sensitivity of the probe of the original metering level induction type magnetometer, reduce background noise, obviously improve the signal-to-noise ratio of the induction type magnetometer host, has the characteristics of good temperature stability, wide probe frequency response range and the like, and is more favorable for realizing magnetic signal waveform fidelity, time domain analysis and spectral domain analysis.
The inductive magnetometer is made by optimizing and improving the probe magnetic core, the probe preamplification circuit and the weak signal detection and extraction circuit of the host machine of the inductive magnetometer
The invention adopts the modes of optimizing the soft magnetic material of the magnetic core, the shape structure of the magnetic core, the magnetic flux negative feedback of the preamplifier based on V/I conversion, 1/f modulation and demodulation, selecting a low equivalent input noise amplifier and the like to reduce the background noise of the probe on the basis of the optimization of the probe of the induction magnetometer, improves the sensitivity temperature characteristic of the probe by selecting a low temperature drift feedback resistor, and detects the amplitude and the phase of the magnetic signal output by the probe by adopting a two-phase locking amplifier based on the principle of a two-channel related demodulator. Since the weak alternating magnetic field magnitude transmission generally generates sinusoidal signals, and the frequency in the process can be obtained from a signal excitation source, the method is very suitable for being used in magnitude transmission of the alternating quantity.
The improved strategy adopted by the novel induction type magnetometer can improve the sensitivity of the probe of the original induction type magnetometer, reduce background noise and obviously improve the signal-to-noise ratio of the host of the induction type magnetometer, and the novel induction type magnetometer has the characteristics of good temperature stability and wide probe frequency response range, and is more favorable for realizing the waveform fidelity, time domain analysis and spectral domain analysis of magnetic signals.
The induction type magnetometer for transferring the magnitude of the weak alternating magnetic field comprises an induction type magnetometer probe, an induction type magnetometer host and a shielding cable, and is shown in figure 1.
The induction type magnetometer probe is composed of a magnetic core, a coil framework, an induction winding, a compensation winding, an electromagnetic shielding film, a preamplifier, a non-magnetic shell and a connector, and is shown in figure 2.
The magnetic core structure of the probe is dumbbell-shaped, the middle part of the magnetic core structure is a soft magnetic alloy bundle which is composed of soft magnetic alloy wires and has a circular cross section and the diameter of the soft magnetic alloy bundle is the inner diameter of the coil framework, and the structure is beneficial to reducing demagnetization factors and improving the effective sectional area. The two head parts of the magnetic core are truncated cone-shaped magnetic flux collectors made of the same material as the waist part, and are used for further reducing the demagnetization factor of the magnetic core and improving the effective magnetic conductivity and the effective sectional area of the magnetic core, and the magnetic core is qualified after being detected by an authentication mechanism before use, as shown in fig. 2.
The soft magnetic alloy beam of the magnetic core of the induction type magnetometer probe penetrates through the coil framework, and the two ends of the soft magnetic alloy beam are symmetrically fixed. The induction coil is generally wound on the bottom layer of the coil framework in sections, a layer of electric shielding film is coated on the induction winding, the film is wound on the compensation winding, and a layer of electric shielding film is coated on the compensation winding. One end of the induction winding is connected with a signal ground, the other end of the induction winding is connected with the input end of the preamplifier circuit, one end of the compensation winding is connected with the signal ground, the other end of the compensation winding is connected with the output end of the preamplifier circuit, the output end of the preamplifier circuit is connected with the nonmagnetic connector, the nonmagnetic connector is arranged on the end face of the cylindrical probe, and the rest of the nonmagnetic connector is arranged in the nonmagnetic shell, as shown in figure 2.
The induction type magnetometer probe magnetic core material is made of soft magnetic materials such as NiFe alloy or amorphous alloy with low Barkhausen noise, high initial permeability, low coercive force, high resistivity and high Curie temperature (more than 150 ℃).
The probe coil skeleton is made of non-magnetic non-metallic materials with high stability and low linear expansion coefficient, and the non-magnetic non-metallic materials include but are not limited to polysulfone, ceramic, epoxy and the like.
The probe induction winding adopts an oxygen-free copper enameled wire, and induces the change of magnetic flux to generate induction voltage related to the number of turns of the winding, the effective sectional area, the effective magnetic conductivity, the amplitude of magnetic induction intensity and the alternating current frequency.
The number of turns of the probe compensation winding is 5-10, and the probe compensation winding is used for compensating and offsetting an induced magnetic field in the magnetic core, so that the magnetic probe always works near zero magnetic flux, and the linearity of the probe can be obviously improved.
The probe preamplifier adopts a magnetic flux negative feedback compensation circuit based on V/I conversion for inhibiting noise and flattening a middle-section resonance peak of a frequency characteristic curve, compensation current and an output magnetic field signal have a better linear relation based on V/I conversion, a low-temperature drift resistor is used in the V/I conversion circuit, the sensitivity and temperature stability of the probe are better, and a feedback compensation schematic diagram is shown in figure 3.
The probe preamplifier adopts a modulation-demodulation technology, and when a low-frequency signal is detected, the low-frequency magnetic signal in the 1/f frequency band is modulated to a high-frequency band with lower noise and then demodulated, so that the 1/f noise is reduced. Only when measuring a low frequency magnetic field.
The host machine of the induction type magnetometer is composed of a two-phase lock-in amplifier module, a data processing and control module, a display module, a battery pack, a power supply conversion module and a case, and the composition and connection relation is shown in figure 4.
The double-phase lock-in amplifier module is of a digital structure, is beneficial to reducing temperature drift and improving dynamic reserve compared with an analog phase-sensitive detector, and is easy to debug and convenient to use. The main circuit components include: the device comprises a signal conditioning module, a reference signal processing module, an algorithm realization module and an interface circuit module. The working principle is shown in fig. 4.
The signal conditioning module comprises a wave trap, an amplifier, an anti-aliasing filter, a 24-bit analog-to-digital conversion circuit and the like, an input signal is sequentially connected in series through the four parts, and finally the output S of the analog-to-digital conversion circuitI(t) connecting the algorithm implementation modules.
The reference signal module adopts an internal reference source, needs to measure the output frequency of a signal generator of an excitation magnetic field by using a frequency technology, and then is input by the display module to generate two paths of orthogonal reference signals SR0(t) and SR1(t)。
The algorithm implementation module is based on a high-speed operation platform such as a DSP (digital signal processor) or an ARM (advanced RISC machines) and the like, mainly realizes dual-channel digital phase-sensitive detection, and calculates a real part X (corresponding to S in figure 5) of a signal to be detectedout0(t)) and an imaginary part Y (corresponding to S in FIG. 5)out1(t)), then the amplitude R and phase theta, etc. are calculated,
θ＝tan(Y/X)。
the input of the data processing and control module is connected with the output of the double-phase lock-in amplifier module, the data output by the double-phase lock-in amplifier module is processed through the calibrated probe sensitivity and zero offset to obtain the magnetic induction intensity amplitude and phase, and the magnetic induction intensity amplitude and phase are sent to the display module for display.
The display module is used for setting the detection parameters of the digital phase-locked amplifier and displaying the amplitude and the phase of the weak magnetic signal to be detected.
The battery pack and the power supply conversion module are used for providing electric energy for all circuits of the induction type magnetometer, the battery pack and the power supply conversion module comprise probes and selectively rechargeable lithium ion battery packs of the battery packs, recycling is facilitated, and the power supply conversion module converts and stabilizes the output voltage of the battery packs through DC/DC conversion and LDO (low dropout regulator) to generate various positive and negative voltages required by a host.
The case is used for installing and fixing all functional modules of the induction type magnetometer host, and a non-magnetic aluminum alloy case is adopted.
Examples
Firstly, placing an induction type magnetometer probe in a magnetic field uniform area of an alternating weak magnetic standard device, and enabling a sensitive axis of the probe to be parallel to the direction of a magnetic field to be measured;
secondly, placing the host machine of the induction type magnetometer at a position more than 3 meters away from the probe;
thirdly, connecting the probe of the induction type magnetometer with the host of the induction type magnetometer by using a shielded cable;
fourthly, turning on a main machine power supply of the induction type magnetometer, electrifying the induction type magnetometer, and preheating for 10-30 minutes;
fifthly, setting calibration parameters, reading and recording the magnetic field indication value displayed by the induction type magnetometer host according to verification or calibration requirements, and forming a measurement data sequence with not less than 10 points;
sixthly, calculating the standard uncertainty of the data sequence to be 0.4pT by a Bessel formula method, and calculating by a degree of freedom method to obtain a factor of 2.31 and an expansion uncertainty of 0.9 pT;
seventhly, placing the probe of the induction type magnetometer in a magnetic shielding cylinder, connecting an analog signal output by the probe of the induction type magnetometer with a dynamic signal analyzer, carrying out power spectral density analysis on a noise signal, averaging 10 frames of data, and obtaining the noise power density of 43fT/Hz at 10Hz1/2And low-noise measurement is realized.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A low noise inductive magnetometer for the transfer of weak alternating magnetic field magnitudes, characterized by:
the low-noise induction type magnetometer comprises a probe, a host and a shielding cable, wherein the probe is connected with the host through the shielding cable;
the probe comprises a magnetic core, a coil framework, an induction winding, a feedback compensation winding, an electromagnetic shielding film, a preamplifier, a non-magnetic shell and a non-magnetic connector;
the coil framework is sleeved outside the magnetic core;
the induction winding is wound on the outer surface of the coil skeleton, an electric shielding film is coated on the induction winding, a feedback compensation winding is wound on the electric shielding film, an electric shielding film is coated on the feedback compensation winding, one end of the induction winding is connected with a signal ground, the other end of the induction winding is connected with the input end of the preamplifier circuit, one end of the feedback compensation winding is connected with the signal ground, the other end of the feedback compensation winding is connected with the output end of the preamplifier circuit, the output end of the preamplifier is connected with a non-magnetic connector, the magnetic core, the coil skeleton, the induction winding, the feedback compensation winding and the preamplifier are all installed in a non-magnetic shell, and the non-magnetic connector is installed outside the non-magnetic shell;
the host comprises a biphase lock-in amplifier module, a reference signal module, an algorithm implementation module and a data processing and control module;
the biphase lock-in amplifier module comprises a 50Hz wave trap, an amplifier, an anti-aliasing filter and a 24-bit analog-to-digital conversion circuit, wherein a signal output by a non-magnetic connector of the probe is connected with the input end of the 50Hz wave trap, is output to the amplifier after being trapped by the 50Hz wave trap, is amplified and output to the anti-aliasing filter for filtering, and is output to the 24-bit analog-to-digital conversion circuit for analog-to-digital conversion and then is output to the SI(t) providing an algorithm implementation module;
the reference signal module adopts two paths of orthogonal reference signals S generated by an internal reference sourceR0(t) and SR1(t) providing an algorithm implementation module;
the algorithm implementation module is used for receiving the reference messageTwo paths of orthogonal reference signals S output by the signal moduleR0(t) and SR1(t) also used for receiving S output after the analog-to-digital conversion of the 24-bit analog-to-digital conversion circuitI(t) and according to the received SR0(t)、SR1(t) and SI(t) calculating the real part X and the imaginary part Y of the signal to be measured, then calculating the amplitude R and the phase theta,
theta is tan (Y/X), and the amplitude R and the phase theta are output to the data processing and control module;
the data processing and control module is used for receiving the amplitude R and the phase theta output by the algorithm realization module, and calibrating the received amplitude R and the received phase theta through the calibrated probe sensitivity and zero offset to obtain the amplitude and the phase of the magnetic induction intensity.
2. A low noise inductive magnetometer for weak alternating magnetic field magnitude transmission according to claim 1 wherein:
the magnetic core is of a dumbbell-shaped structure, the dumbbell-shaped structure comprises a middle waist part and two end parts, the middle waist part is a soft magnetic alloy bundle which is formed by soft magnetic alloy wires and has a circular section shape, and the two end parts are truncated cone-shaped magnetic flux collectors made of soft magnetic alloy materials;
the soft magnetic alloy beam penetrates through the coil framework, two ends of the soft magnetic alloy beam are fixedly connected to the inner surface of the coil framework, and the magnetic flux collectors at two ends of the magnetic core are positioned outside the coil framework.
3. A low noise inductive magnetometer for weak alternating magnetic field magnitude transmission according to claim 2 wherein:
the soft magnetic alloy is made of NiFe alloy or amorphous alloy soft magnetic material with low Barkhausen noise, high initial permeability, low coercive force, high resistivity and high Curie temperature (more than 150 ℃);
the coil skeleton is made of non-magnetic non-metallic materials with high stability and low linear expansion coefficient, including but not limited to polysulfone, ceramic and epoxy;
the induction winding and the feedback compensation winding are both made of oxygen-free copper enameled wires.
4. A low noise inductive magnetometer according to any one of claims 1 to 3 for use in the transfer of the magnitude of a weak alternating magnetic field, said magnetometer being characterized in that:
the diameter of the soft magnetic alloy bundle is consistent with the inner diameter of the coil framework.
5. A low noise inductive magnetometer according to any one of claims 1 to 3 for use in the transfer of the magnitude of a weak alternating magnetic field, said magnetometer being characterized in that:
the preamplifier adopts a magnetic flux negative feedback compensation circuit based on V/I conversion, and a low-temperature drift resistor is used in the V/I conversion circuit;
the preamplifier adopts a modulation-demodulation circuit, when a low-frequency signal is detected, the low-frequency magnetic signal in a 1/f frequency band is modulated to a high-frequency band with lower noise and then demodulated, the 1/f noise is reduced, and the modulation-demodulation circuit is started only when the low-frequency magnetic field is measured.
6. A low noise inductive magnetometer according to any one of claims 1 to 3 for use in the transfer of the magnitude of a weak alternating magnetic field, said magnetometer being characterized in that:
the induction winding is formed by winding thousands to tens of thousands of turns on the outer surface of the coil framework in sections;
the number of turns of the feedback compensation winding is 5-10.
7. A low noise inductive magnetometer according to any one of claims 1 to 3 for use in the transfer of the magnitude of a weak alternating magnetic field, said magnetometer being characterized in that:
the host machine also comprises a display module, a battery pack and a power supply conversion module;
the display module is used for displaying the amplitude and the phase of the weak magnetic signal to be detected sent by the data processing and control module;
the battery pack and the power supply conversion module are used for providing electric energy for all circuits of the induction type magnetometer, and comprise a probe.
8. A low noise inductive magnetometer for weak alternating magnetic field magnitude transmission according to claim 7 wherein:
the battery pack selects a rechargeable lithium ion battery pack, and the power supply conversion module converts and stabilizes the output voltage of the battery pack through DC/DC conversion and LDO (low dropout regulator) to generate various positive and negative voltages required by a host.
9. A low noise inductive magnetometer for weak alternating magnetic field magnitude transfer according to claim 7 wherein:
the host machine also comprises a case, wherein the case is used for installing the locking amplifier module, the data processing and control module, the display module, the battery pack and the power supply conversion module, and the case adopts a nonmagnetic aluminum alloy case.
10. A method of performing a magnetic field strength test using the low noise inductive magnetometer of any of claims 1-9, the method comprising the steps of:
firstly, placing an induction type magnetometer probe in a magnetic field uniform area of an alternating weak magnetic standard device, and enabling a sensitive axis of the probe to be parallel to the direction of a magnetic field to be measured;
secondly, placing the host machine of the induction type magnetometer at a set position away from the probe;
thirdly, connecting the probe of the induction type magnetometer with the host of the induction type magnetometer by using a shielded cable;
fourthly, turning on a main machine power supply of the induction type magnetometer, electrifying the induction type magnetometer, and preheating for 10-30 minutes;
and fifthly, setting calibration parameters, and reading and recording the magnetic field indication value displayed by the induction type magnetometer host according to verification or calibration requirements.
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| CN117970196A (en) * | 2024-04-01 | 2024-05-03 | 中国科学院地质与地球物理研究所 | Superaudio induction type magnetic field sensor and application thereof in high-resolution mineral exploration |
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| CN117970196A (en) * | 2024-04-01 | 2024-05-03 | 中国科学院地质与地球物理研究所 | Superaudio induction type magnetic field sensor and application thereof in high-resolution mineral exploration |
| CN117970196B (en) * | 2024-04-01 | 2024-05-28 | 中国科学院地质与地球物理研究所 | Superaudio induction type magnetic field sensor and application thereof in high-resolution mineral exploration |
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