CN113281553A - Weak direct current detection system and method based on fluxgate - Google Patents
Weak direct current detection system and method based on fluxgate Download PDFInfo
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Abstract
The invention relates to a weak direct current detection system and a method thereof based on a fluxgate, wherein the system comprises an excitation unit, a fluxgate probe and a signal processing unit which are connected in a closed loop, wherein the excitation unit is used for regulating and outputting an excitation signal to the fluxgate probe, so that an iron core is in an alternative critical saturation state, and the magnetic core always works near a zero field; the signal processing unit is used for extracting a second harmonic component from the output signal of the fluxgate probe. Compared with the prior art, the invention forms a current feedback loop by controlling the duty ratio of the excitation signal and changing the output current value, so that the annular iron core always and alternately works in a critical saturation state, and the power consumption of the excitation winding is reduced; the whole system is a closed-loop system, the main controller adjusts output signal parameters to compensate external magnetic field changes in real time, the magnetic core always works near a zero field, the linearity and the observation range of the system are improved, the double closed-loop control ensures that the fluxgate probe works in a relatively optimal state, and the detection stability and the sensitivity are improved.
Description
Technical Field
The invention relates to the technical field of weak signal detection, in particular to a weak direct current detection system and method based on a fluxgate.
Background
At present, most direct current detection modes are based on magnetic field change for measurement, such as a Hall sensor detection mode and a magnetic modulation detection mode, wherein the Hall sensor is mature in technology and is characterized by firm structure, long service life, wide current measurement range and high heavy current measurement precision, and the direct current detection mode is widely applied to various industries. However, there are some disadvantages, such as the open-loop hall sensor is greatly affected by temperature, and has low precision in places with large temperature variation, and meanwhile, the hall sensor has insufficient sensitivity, poor stability, long reaction time and poor anti-interference capability when measuring weak current.
The basic principle of the fluxgate sensor is Faraday's law of electromagnetic induction, magnetic signals are converted into electric signals for measurement by utilizing the magnetic hysteresis saturation characteristic of a magnetic core, the fluxgate sensor based on the magnetic modulation principle has the advantages of wide range of weak current detection, isolated design, small influence on original electronic power equipment, high sensitivity, high linearity and the like, and compared with a Hall current sensor, the fluxgate sensor has long working stability time, low zero drift during no input, and small influence of the ambient temperature.
However, the waveform stability and precision of the excitation signal of the traditional fluxgate current sensor are not high enough, and the prior art makes the fluxgate iron core in an oversaturated state, and the amplitude Hm of the excitation magnetic field intensity is larger than the saturation magnetic field intensity Hs of the iron core by a considerable proportion, so that the relative magnetic permeability mu is enabled to berThe value is periodically changed from the maximum value to the minimum value, so that a stronger fluxgate signal is obtained, and the sensor cannot adjust the excitation signal in real time according to the measurement result to enable the coil to work in a critical saturation state (when the coil works at a critical saturation point, the sensitivity of the fluxgate probe is highest). In addition, there is a flux gate probe outputThe transformer effect induces electromotive force, the probe is mostly designed by adopting a double-magnetic-core structure to be mutually counteracted, but because the magnetic cores can not be completely symmetrical, the transformer differential effect still exists in output signals, namely noise of output signals of the fluxgate, and noise of the circuit also exists.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a weak direct current detection system based on a fluxgate and a method thereof so as to improve the detection sensitivity and stability.
The purpose of the invention can be realized by the following technical scheme: a weak direct current detection system based on a fluxgate comprises an excitation unit, a fluxgate probe and a signal processing unit which are sequentially connected, wherein the excitation unit is also connected with the signal processing unit and is used for regulating and outputting an excitation signal to the fluxgate probe, so that an iron core is in an alternative critical saturation state and the magnetic core always works near a zero field;
the signal processing unit is used for extracting a second harmonic component from the output signal of the fluxgate probe.
Further, the excitation unit comprises a main controller, a Direct Digital Synthesis (DDS) signal generator, a driving module, a current sampling module, a high-speed data conversion module and a high-precision data conversion module, the main controller is sequentially connected with the DDS signal generator and the driving module, the driving module is connected to the fluxgate probe, the current sampling module is sequentially connected with the high-speed data conversion module and the main controller, the current sampling module is connected with the fluxgate probe, the high-precision data conversion module is connected with the signal processing unit, and the main controller controls and adjusts the excitation signal output by the DDS signal generator according to the Digital feedback signal output by the high-speed data conversion module; controlling and compensating the change of the external magnetic field according to the digital feedback signal output by the high-precision data conversion module;
the drive module is used for driving the fluxgate probe to start working;
the current sampling module is used for measuring the current of the resistor at the exciting coil of the fluxgate probe;
the high-speed data conversion module is used for converting the current analog signal output by the current sampling module into a digital signal and transmitting the digital signal to the main controller;
and the high-precision data conversion module is used for converting the second harmonic component analog signals output by the signal processing unit into digital signals and transmitting the digital signals to the main controller.
Further, the DDS signal generator is connected with the driving module through the filtering module.
Further, the DDS signal generator comprises an STM32 single chip microcomputer and an AD9833 chip, and the AD9833 chip is connected with the main controller through an SPI bus.
Further, the driving module comprises a THS4561 chip.
Further, the fluxgate probe is of a single-ring differential structure, and the ferromagnetic material selected by the fluxgate probe is permalloy.
Further, the value obtained by subtracting 0.1 from the ratio of the number of turns of the secondary winding to the number of turns of the primary winding of the fluxgate probe is within the range of the preset threshold value.
Furthermore, the signal processing unit comprises a band-pass filter, a phase-sensitive detector and an integrator which are sequentially connected, the band-pass filter is connected with the fluxgate probe, the integrator is connected with the high-precision data conversion module, and the band-pass filter is used for filtering fundamental wave and third harmonic component in signals output by the fluxgate probe so as to reserve second harmonic component;
the phase sensitive detector is used for further removing odd harmonic components in the output signals of the fluxgate probe and extracting second harmonic components;
the integrator is used for performing integration processing on the output of the phase-sensitive detector.
Furthermore, the phase sensitive detector is connected with the output end of the filtering module through a frequency doubling phase shifting module.
A weak direct current detection method based on a fluxgate comprises the following steps:
s1, the main controller controls the DDS signal generator to generate an excitation signal, wherein the excitation signal is a square wave signal;
s2, transmitting the excitation signal to the driving module, and driving the fluxgate probe to alternately work in a saturation state by the driving module;
s3, the current sampling module measures the current value of the resistor at the exciting coil of the fluxgate probe in real time and transmits the measured current value to the high-speed data conversion module, and the high-speed data conversion module transmits the converted digital signal to the main controller, so that excitation closed-loop control is formed: if the measured current value reflects that the iron core is not in the alternate critical saturation state, the main controller adjusts the duty ratio of the output excitation signal to enable the iron core to be in the alternate critical saturation state;
s4, the signal processing unit extracts a second harmonic component from the output signal of the fluxgate probe, on one hand, the extracted second harmonic component is converted into an analog signal to be directly output, on the other hand, the converted analog signal is transmitted to the high-precision data conversion module, the high-precision data conversion module converts the analog signal into a digital signal to be transmitted to the main controller to be output, and the main controller adjusts the output signal parameter according to the digital signal to compensate the external magnetic field change in real time and enable the magnetic core to work nearby a zero field all the time.
Compared with the prior art, the invention has the following advantages:
the invention relates to a magnetic flux gate detection device, which comprises an excitation unit, a magnetic flux gate probe and a signal processing unit which are sequentially connected, wherein the signal processing unit is connected to the excitation unit, an excitation signal is regulated and output to the magnetic flux gate probe by the excitation unit, and meanwhile, a double-closed-loop control is formed by combining an excitation closed loop in the excitation unit and a closed loop control between the excitation unit and the signal processing unit, so that an iron core can be in an alternative critical saturation state, and the magnetic core can always work near a zero field, thereby effectively improving the detection sensitivity, the linearity and the observation range, ensuring that the magnetic flux gate probe can work in a relatively optimal state, and greatly improving the stability and the sensitivity of the detection of weak direct current.
The fluxgate probe adopts a single-ring differential structure, can generate better noise suppression capability, and reduces the volume of the probe; in addition, the ratio of the number of turns of the secondary winding to the number of turns of the primary winding of the fluxgate probe is set to be close to 0.1, so that the noise of the fluxgate probe is further reduced; the invention also adopts a low-noise amplifier THS4561 in the driving module, which can effectively reduce the circuit noise.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention;
fig. 2 is a schematic view of the working principle of the fluxgate current sensor in the embodiment;
FIG. 3 is a schematic diagram of an AD9833 chip connection circuit in the embodiment;
FIG. 4 is a schematic diagram of a THS4561 chip connection circuit in the embodiment;
FIG. 5 is a schematic view of a fluxgate probe;
FIG. 6 shows B and μ in ferromagnetic materialrA graph showing the variation with H;
FIG. 7 is a schematic view of a ring ferromagnetic material;
the notation in the figure is: 1. the device comprises an excitation unit, 2, a fluxgate probe, 3, a signal processing unit, 4, a frequency doubling phase shifting module, 101, a main controller, 102, a DDS signal generator, 103, a driving module, 104, a current sampling module, 105, a high-speed data conversion module, 106, a high-precision data conversion module, 107, a filtering module, 301, a band-pass filter, 302, a phase sensitive detector, 303 and an integrator.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Examples
As shown in fig. 1, a weak direct current detection system based on a fluxgate comprises an excitation unit 1, a fluxgate probe 2 and a signal processing unit 3 which are connected in sequence, wherein the excitation unit 1 is further connected with the signal processing unit 3, and the excitation unit 1 is used for adjusting and outputting an excitation signal to the fluxgate probe 2, so that an iron core is in an alternative critical saturation state, and the magnetic core always works near a zero field;
the signal processing unit 3 is used for extracting a second harmonic component from the output signal of the fluxgate probe 2.
The excitation unit 1 comprises a main controller 101, a DDS signal generator 102, a driving module 103, a current sampling module 104, a high-speed data conversion module 105 and a high-precision data conversion module 106, wherein the main controller 101 is sequentially connected with the DDS signal generator 102 and the driving module 103, the driving module 103 is connected to the fluxgate probe 2, the current sampling module 104 is sequentially connected with the high-speed data conversion module 105 and the main controller 101, the current sampling module 104 is connected with the fluxgate probe 2, the high-precision data conversion module 106 is connected with a signal processing unit 3, and the main controller 101 controls and adjusts an excitation signal output by the DDS signal generator 102 according to a digital feedback signal output by the high-speed data conversion module 105; controlling and compensating the change of the external magnetic field according to the digital feedback signal output by the high-precision data conversion module 106;
the driving module 103 is used for driving the fluxgate probe 2 to start working;
the current sampling module 104 is used for measuring the current of the resistor at the exciting coil of the fluxgate probe 2;
the high-speed data conversion module 105 is configured to convert the current analog signal output by the current sampling module 104 into a digital signal and transmit the digital signal to the main controller 101;
the high-precision data conversion module 106 is configured to convert the second harmonic component analog signal output by the signal processing unit 3 into a digital signal and transmit the digital signal to the main controller 101.
In this embodiment, the DDS signal generator 102 is further connected to the driving module 103 through the filtering module 107 to ensure that the output excitation signal is more "pure".
The signal processing unit 3 comprises a band-pass filter 301, a phase sensitive detector 302 and an integrator 303 which are sequentially connected, the band-pass filter 301 is connected with the fluxgate probe 2, the integrator 303 is connected with the high-precision data conversion module 106, and the band-pass filter 301 is used for filtering fundamental wave and third harmonic component in the output signal of the fluxgate probe 2 to reserve second harmonic component; the phase sensitive detector 302 is used for further removing odd harmonic components in the output signal of the fluxgate probe 2 and extracting second harmonic components; the integrator 303 is used to integrate the output of the phase sensitive detector 302.
In order to make the reference signal of the phase-sensitive detector 302 and the excitation power supply voltage have the same source, the phase-sensitive detector 302 is further connected with the output end of the filtering module 107 through the frequency doubling phase shifting module 4.
In this embodiment, the DDS signal generator 102 includes an STM32 single chip microcomputer and an AD9833 chip, and the AD9833 chip is connected to the main controller 101 through an SPI bus; the driving module 103 includes a THS4561 chip.
In this embodiment, in order to reduce the probe noise, the fluxgate probe 2 is a single-ring differential structure, the ferromagnetic material selected by the fluxgate probe 2 is permalloy, and in addition, a value obtained by subtracting 0.1 from a ratio of the number of turns of the secondary winding to the number of turns of the primary winding of the fluxgate probe 2 is set within a preset threshold range.
The detection system is applied to practice, and the process of detecting weak direct current mainly comprises the following steps:
s1, the main controller controls the DDS signal generator to generate an excitation signal, wherein the excitation signal is a square wave signal;
s2, transmitting the excitation signal to the driving module, and driving the fluxgate probe to alternately work in a saturation state by the driving module;
s3, the current sampling module measures the current value of the resistor at the exciting coil of the fluxgate probe in real time and transmits the measured current value to the high-speed data conversion module, and the high-speed data conversion module transmits the converted digital signal to the main controller, so that excitation closed-loop control is formed: if the measured current value reflects that the iron core is not in the alternate critical saturation state, the main controller adjusts the duty ratio of the output excitation signal to enable the iron core to be in the alternate critical saturation state;
s4, the signal processing unit extracts a second harmonic component from the output signal of the fluxgate probe, on one hand, the extracted second harmonic component is converted into an analog signal to be directly output, on the other hand, the converted analog signal is transmitted to the high-precision data conversion module, the high-precision data conversion module converts the analog signal into a digital signal to be transmitted to the main controller to be output, and the main controller adjusts the output signal parameter according to the digital signal to compensate the external magnetic field change in real time and enable the magnetic core to work nearby a zero field all the time.
In this embodiment, the fluxgate current sensor shown in fig. 2 is constructed and obtained by applying the above technical solution, and the sensor mainly includes an excitation circuit, a fluxgate probe, and a signal processing circuit: the excitation circuit comprises a main controller, a DDS signal generator, a low-pass filter, a drive circuit, a current sampling circuit and a high-speed data conversion module; the fluxgate probe adopts a single annular iron core, and the iron core is made of permalloy; the signal processing circuit comprises a band-pass filter circuit, a phase-sensitive detection circuit and an integrating circuit. The main controller controls the DDS to generate an excitation signal, the excitation signal is transmitted to the driving circuit after passing through the filter circuit, and the output of the driving circuit is connected to the primary winding through the sampling resistor to drive the fluxgate probe to alternately work in a saturated state. The current sampling circuit measures the current value of the sampling resistor and transmits the current value to the high-speed data conversion module, and the high-speed data conversion module transmits the converted digital signal to the main controller. When an excitation signal is present in the primary winding, an induced potential associated with the excitation signal is generated in the secondary winding according to the faraday's principle of electromagnetic induction. When a direct current signal passes through the annular magnetic core, the induced potential in the secondary winding is changed by the magnetic field generated by the direct current signal. The fluxgate probe modulates the magnetic field to convert the magnetic field into an even harmonic fluxgate signal, and the fluxgate circuit selects a second harmonic component of the magnetic field and converts the second harmonic component into an analog signal. The fluxgate secondary winding is connected with the band-pass filter to filter out fundamental wave and other harmonic wave components except the second harmonic wave component. The phase of the filtered second harmonic component signal is adjusted by phase-sensitive detection (the reference signal is a frequency-multiplied signal that is homologous to the excitation signal). And finally, outputting an analog signal through the integrator, and transmitting the analog signal to the main controller through the high-precision data conversion module to output a digital signal.
Specifically, the excitation circuit mainly includes the following contents:
1. DDS signal generator design
The fluxgate sensor needs to be activated by a circuit to generate an alternating signal, and generally, a crystal oscillator generates a signal of a certain frequency through a frequency divider and a band-pass filter. In the embodiment, a DDS (direct digital synthesizer) signal generator formed by a single chip microcomputer STM32 and an AD9833 chip is used for providing excitation for the sensor. The main controller is connected through a serial bus, and the main control pins are configured into an SPI bus mode to be matched with the AD9833 for data transmission. The AD9833 does not need an external element, and the output frequency and the phase position can be set through software programming and are easy to adjust. The signal frequency amplitude generated by the DDS signal source is stable and high in precision, and is an ideal fluxgate sensor excitation signal source. The AD9833 circuit is connected as shown in FIG. 3, and is connected with a filter to process the square wave signal after being output in order to make the square wave excitation generated by the DDS signal generator more pure. In the design, a low-pass filter circuit is adopted to filter out high-frequency interference and stray signals of an external active crystal oscillator.
2. Driving circuit
The amplitude of the signal output by the DDS is about 0.65V, and the magnetic field generated after the coil is excited is not enough to enable the magnetic core to reach a periodic oversaturated state, so that the condition required by the work of the fluxgate cannot be reached. A driving circuit must be provided, and the driving circuit is formed by the THS4561 in the design. The circuit connection diagram is shown in fig. 4.
3. Current sampling circuit
The saturation degree of the iron core of the exciting winding is reflected by measuring the current value of the resistor at the exciting coil, and the measured current value is transmitted to the main controller through high-speed data conversion to form an exciting closed-loop control system. If the measured current value reflects that the iron core is not in the alternate critical saturation state, the main controller enables the iron core to be in the alternate critical saturation state by adjusting the duty ratio of the output signal.
4 digital controller and communication interface
As shown in fig. 1, the measured analog current signal is directly transmitted to the high-precision data conversion module by the integrator, converted into a digital signal by the high-precision data conversion module, transmitted to the main controller, and then output by the main controller, so that the digital output is conveniently interconnected with a digital system. When the digital system is interconnected, an RS485 communication mode is adopted for data transmission. RS485 employs balanced transmission and differential reception, and thus has the capability of suppressing common mode interference.
The fluxgate probe adopts a single-ring differential structure, the used magnetic core is made of permalloy, the model is 1J85, 1000 turns of primary winding wire winding and 110 turns of secondary winding wire winding are adopted, the excitation signal uses square waves, the frequency is 100Hz (square wave signals with lower frequency are selected because the permalloy magnetic ring actually used under low frequency has higher magnetic conductivity and can meet the requirement of measuring weak current), the amplitude is 5V, and the schematic diagram of the fluxgate probe is shown in figure 5.
In the signal processing circuit, when an excitation signal is taken into account in the primary winding, an induced potential associated with the excitation signal is generated in the secondary winding according to the faraday's principle of electromagnetic induction. When a direct current signal passes through the annular magnetic core, the induced potential in the secondary winding is changed by the magnetic field generated by the direct current signal. The fluxgate probe modulates the magnetic field to convert the magnetic field into an even harmonic fluxgate signal, and the fluxgate circuit selects a second harmonic component of the magnetic field and converts the second harmonic component into an analog signal.
The fluxgate probe noise has odd harmonic characteristics and its maximum harmonic components, fundamental and third, are exactly on both sides of the signal second harmonic component. A band pass filter circuit should be provided to filter out fundamental and third harmonic components and to retain the second harmonic component.
The reference signal of the phase sensitive detector must be homologous to the excitation supply voltage. The phase difference is adjusted by the frequency doubling phase shifter to improve the output of the phase sensitive detector. The invention selects a second harmonic method circuit, and the reference signal of the circuit is the frequency multiplication signal of the excitation power supply voltage. The phase sensitive detector can also completely eliminate the influence of odd harmonics.
The integrator integrates the output of the phase-sensitive detector, and outputs signals to the main controller through the high-precision data conversion module to form another closed-loop system, and the main controller adjusts output signal parameters to compensate the external magnetic field change in real time, so that the magnetic core always works near a zero field, and the linearity and the observation range of the system are improved.
The invention can lead the fluxgate exciting coil to work in a critical saturation state all the time in an alternating way, thereby improving the sensitivity of the sensor. From the curves in fig. 6, it can be seen that if the magnetic field is excited alternatelyFails to saturate the iron core, μrThe flux gate signal is very weak. To construct a fluxgate probe, mu can be achieved only by making the iron core in an oversaturated staterThe value changes periodically from a maximum value to a minimum value, and a strong fluxgate signal can be obtained. As shown in fig. 7, the ferromagnetic ring is magnetized when current is applied to the coil. When the current is I, the magnetic field intensity H in the ring is
Where N is the total number of turns of the coil on the ring and r is the average radius of the ring. The magnetic field intensity in the ring is related to the current, so that the output current value can be adjusted by changing the duty ratio of the excitation square wave signal, and the excitation coil is in a critical saturation state, thereby improving the sensitivity of the sensor.
In the signal processing circuit, the driver circuit employs a low noise device THS4561 to reduce noise in the circuit. In the aspect of probe design, a single-ring structure is adopted, the selected ferromagnetic material is permalloy, the permeability of the permalloy magnetic ring which is actually used at low frequency is high, and the requirement of measuring weak current can be met. Since the probe noise is larger when the ratio of the number of turns of the induction coil N2 to the number of turns of the exciting coil N1 is larger, the ratio of the number of turns of the induction coil N2 to the number of turns of the exciting coil N1 is close to 1/10 in order to reduce the probe noise in the invention.
In summary, the present invention utilizes the Digital signal synthesis technology to improve the stability — dds (direct Digital synthesizer), compared with the conventional frequency synthesizer, has the advantages of low cost, low power consumption, high resolution, fast conversion time, etc., is widely used in the field of telecommunications and electronic instruments, and is a key technology for realizing the digitization of equipment. The invention adopts a singlechip STM32 and an AD9833 chip to form a direct digital frequency synthesizer (DDS) to provide an excitation signal for the sensor. The frequency register of the AD9833 is 28 bits, and when the main frequency clock is 25MHz, the precision is 0.1 Hz; when the master frequency clock is l MHz, the precision can reach 0.004 Hz. The frequency stability is very high, and the accuracy of the output frequency can be improved by adopting the technology.
The invention adopts the microprocessor to automatically track the critical point and improve the sensitivity, namely adopts the digital feedback control technology to change the duty ratio of the excitation square wave signal and lead the coil iron core to work in the critical saturation state alternately, thereby improving the sensitivity of the fluxgate probe. The whole system forms a closed-loop system through high-precision analog-to-digital conversion and a main controller, the main controller adjusts output signal parameters to compensate external magnetic field changes in real time, the magnetic core always works near a zero field, and the linearity and the observation range of the system are improved. The double closed-loop system ensures that the fluxgate probe works in a relatively optimal state, and improves the stability and the sensitivity of the system.
The invention adopts a low-noise processing technology, in order to effectively filter interference signals caused by the transformer effect and improve the resolution of the system, the fluxgate sensor usually adopts a double-magnetic-core probe. The double-magnetic-core fluxgate inhibits induced voltage caused by a transformer effect through a double differential structure, and generates an induced signal related to the intensity of magnetic field to be measured. The ring-shaped fluxgate is a derivative of the double-magnetic-core fluxgate, can be regarded as a differential structure, has good symmetry and higher noise suppression capability, and reduces the volume of the probe.
The excitation supply voltage is related to the noise level of the fluxgate probe. The larger the excitation supply voltage U, the more the probe noise, but not strictly proportional. Meanwhile, the larger the number of turns of the induction coil N2 is, the larger the probe noise is. In fact, the greater the ratio of the number of turns of the induction coil N2 to the number of turns of the excitation coil N1, the greater the probe noise. Therefore, the excitation power voltage set for reducing the probe noise is 5V, and the ratio of the number of turns N2 of the induction coil to the number of turns N1 of the excitation coil is close to 1/10.
The driving circuit adopts a low noise amplifier THS4561 to reduce circuit noise. THS4561 has an ultra-low 1/f voltage noise corner frequency of 8Hz and a low total harmonic distortion of 130dB with broadband noise only
Consumes 775 muA of quiescent current at the same time, and is very suitable for power sensitiveA data acquisition system achieves an optimal signal-to-noise ratio, thereby providing high performance.
In order to reduce the influence of temperature on the weak direct current sensor, the weak direct current sensor based on the magnetic modulation principle is selected in consideration of cost factors. In the invention, a main controller, a signal generating circuit, a filter circuit, a driving circuit, a fluxgate probe, a current sampling circuit and a high-speed data conversion circuit jointly form a closed-loop system of an excitation link. The saturation degree of the iron core of the exciting winding is reflected by measuring the current value of the resistor flowing through the exciting coil, and the measured current value is transmitted to the main controller through high-speed data conversion. If the measured current value reflects that the iron core is not in the alternate critical saturation state, the main controller adjusts the output current value by adjusting the duty ratio of the output signal, so that the iron core is in the alternate critical saturation state, and the sensitivity of the sensor is improved. Meanwhile, the whole system forms a closed-loop system through high-precision data conversion and a main controller, and the main controller adjusts output signal parameters to compensate external magnetic field changes in real time, so that the magnetic core always works near a zero field, and the linearity and the observation range of the system are improved. The double closed-loop system ensures that the fluxgate probe works in a relatively optimal state, and improves the stability and the sensitivity of the system.
Claims (10)
1. The weak direct current detection system based on the fluxgate is characterized by comprising an excitation unit (1), a fluxgate probe (2) and a signal processing unit (3) which are sequentially connected, wherein the excitation unit (1) is also connected with the signal processing unit (3), and the excitation unit (1) is used for regulating and outputting an excitation signal to the fluxgate probe (2) so that an iron core is in an alternative critical saturation state and the magnetic core always works near a zero field;
the signal processing unit (3) is used for extracting a second harmonic component from the output signal of the fluxgate probe (2).
2. The fluxgate-based weak direct current detection system according to claim 1, wherein the excitation unit (1) comprises a main controller (101), a DDS signal generator (102), a driving module (103), a current sampling module (104), a high speed data conversion module (105) and a high precision data conversion module (106), the main controller (101) is sequentially connected with the DDS signal generator (102) and the driving module (103), the driving module (103) is connected to the fluxgate probe (2), the current sampling module (104) is sequentially connected with the high speed data conversion module (105) and the main controller (101), the current sampling module (104) is connected with the fluxgate probe (2), the high precision data conversion module (106) is connected with the signal processing unit (3), and the main controller (101) outputs a digital feedback signal according to the high speed data conversion module (105), controlling and adjusting an excitation signal output by a DDS signal generator (102); according to the digital feedback signal output by the high-precision data conversion module (106), the change of the external magnetic field is controlled and compensated;
the driving module (103) is used for driving the fluxgate probe (2) to start working;
the current sampling module (104) is used for measuring the current of the resistor at the exciting coil of the fluxgate probe (2);
the high-speed data conversion module (105) is used for converting the current analog signal output by the current sampling module (104) into a digital signal and transmitting the digital signal to the main controller (101);
and the high-precision data conversion module (106) is used for converting the second harmonic component analog signals output by the signal processing unit (3) into digital signals and transmitting the digital signals to the main controller (101).
3. The fluxgate-based weak direct current detection system according to claim 2, wherein the DDS signal generator (102) is connected to the driving module (103) through a filtering module (107).
4. The fluxgate-based weak direct current detection system according to claim 2, wherein the DDS signal generator (102) comprises an STM32 single chip microcomputer and an AD9833 chip, and the AD9833 chip is connected to the main controller (101) through an SPI bus.
5. The fluxgate-based weak direct current detection system according to claim 2, wherein the driving module (103) comprises a THS4561 chip.
6. The fluxgate-based weak direct current detection system according to claim 1, wherein the fluxgate probe (2) is a single-ring differential structure, and the ferromagnetic material selected by the fluxgate probe (2) is permalloy.
7. The fluxgate-based weak direct current detection system according to claim 1, wherein a value obtained by subtracting 0.1 from a ratio of a number of turns of the secondary winding to a number of turns of the primary winding of the fluxgate probe (2) is within a preset threshold range.
8. The fluxgate-based weak direct current detection system according to claim 3, wherein the signal processing unit (3) comprises a band pass filter (301), a phase sensitive detector (302) and an integrator (303) connected in sequence, the band pass filter (301) is connected to the fluxgate probe (2), the integrator (303) is connected to the high precision data conversion module (106), and the band pass filter (301) is configured to filter fundamental wave and third harmonic component in the output signal of the fluxgate probe (2) to retain second harmonic component;
the phase sensitive detector (302) is used for further removing odd harmonic components in the output signal of the fluxgate probe (2) and extracting second harmonic components;
the integrator (303) is used for performing integration processing on the output of the phase-sensitive detector (302).
9. The fluxgate-based weak direct current detection system according to claim 8, wherein the phase sensitive detector (302) is connected to the output end of the filtering module (107) through a frequency doubling phase shifting module (4).
10. A weak direct current detection method using the fluxgate-based weak direct current detection system according to claim 2, comprising the steps of:
s1, the main controller controls the DDS signal generator to generate an excitation signal, wherein the excitation signal is a square wave signal;
s2, transmitting the excitation signal to the driving module, and driving the fluxgate probe to alternately work in a saturation state by the driving module;
s3, the current sampling module measures the current value of the resistor at the exciting coil of the fluxgate probe in real time and transmits the measured current value to the high-speed data conversion module, and the high-speed data conversion module transmits the converted digital signal to the main controller, so that excitation closed-loop control is formed: if the measured current value reflects that the iron core is not in the alternate critical saturation state, the main controller adjusts the duty ratio of the output excitation signal to enable the iron core to be in the alternate critical saturation state;
s4, the signal processing unit extracts a second harmonic component from the output signal of the fluxgate probe, on one hand, the extracted second harmonic component is converted into an analog signal to be directly output, on the other hand, the converted analog signal is transmitted to the high-precision data conversion module, the high-precision data conversion module converts the analog signal into a digital signal to be transmitted to the main controller to be output, and the main controller adjusts the output signal parameter according to the digital signal to compensate the external magnetic field change in real time and enable the magnetic core to work nearby a zero field all the time.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113759288A (en) * | 2021-11-08 | 2021-12-07 | 深圳市德兰明海科技有限公司 | Leakage current detection circuit and method and leakage current detector |
| CN113945871A (en) * | 2021-10-20 | 2022-01-18 | 北京微纳星空科技有限公司 | Fluxgate signal processing method, fluxgate signal processing circuit, fluxgate signal processing device and storage medium |
| CN116754823A (en) * | 2023-06-19 | 2023-09-15 | 深圳柯力三电科技有限公司 | Control method of fluxgate vibration |
Citations (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5170566A (en) * | 1990-06-05 | 1992-12-15 | Arthur D. Little, Inc. | Means for reducing interference among magnetometer array elements |
| WO2007054602A1 (en) * | 2005-11-11 | 2007-05-18 | Consejo Superior De Investigaciones Científicas | Multifunctional sensor based on multilayer magnetic microwires with magnetoelastic coupling |
| CN203250014U (en) * | 2013-06-03 | 2013-10-23 | 杭州坞坦科技有限公司 | Novel all-digital three-component fluxgate magnetometer |
| CN105866713A (en) * | 2016-03-29 | 2016-08-17 | 吉林大学 | State feedback type self-excitation fluxgate sensor |
| US20160334473A1 (en) * | 2015-05-12 | 2016-11-17 | Texas Instruments Deutschland Gmbh | Fluxgate Magnetic Field Detection Method and Circuit |
| CN106324542A (en) * | 2016-08-30 | 2017-01-11 | 中国人民解放军海军工程大学 | Triaxial decoupling self-zero-setting fluxgate magnetometer zero point measurement circuit |
| CN107271933A (en) * | 2017-06-15 | 2017-10-20 | 成都理工大学 | A kind of axis fluxgate sensor of spherical three |
| CN207067224U (en) * | 2017-05-15 | 2018-03-02 | 宜昌市瑞磁科技有限公司 | A kind of leakage current sensor |
| CN208421051U (en) * | 2018-08-02 | 2019-01-22 | 宜昌市瑞磁科技有限公司 | A kind of leakage current sensor |
| CN111527413A (en) * | 2017-12-08 | 2020-08-11 | 莱姆国际股份有限公司 | Annular fluxgate current sensor |
| CN111650415A (en) * | 2020-06-09 | 2020-09-11 | 南京师范大学 | Self-powered current detection system and detection method for wide-current-band power transmission line |
| CN211505671U (en) * | 2019-10-25 | 2020-09-15 | 珠海多创科技有限公司 | DC large current sensor |
| CN212060398U (en) * | 2020-04-07 | 2020-12-01 | 无锡创联科技有限公司 | Non-invasive high-precision AC/DC universal current sensor |
-
2021
- 2021-04-23 CN CN202110442434.7A patent/CN113281553A/en active Pending
Patent Citations (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5170566A (en) * | 1990-06-05 | 1992-12-15 | Arthur D. Little, Inc. | Means for reducing interference among magnetometer array elements |
| WO2007054602A1 (en) * | 2005-11-11 | 2007-05-18 | Consejo Superior De Investigaciones Científicas | Multifunctional sensor based on multilayer magnetic microwires with magnetoelastic coupling |
| CN203250014U (en) * | 2013-06-03 | 2013-10-23 | 杭州坞坦科技有限公司 | Novel all-digital three-component fluxgate magnetometer |
| US20160334473A1 (en) * | 2015-05-12 | 2016-11-17 | Texas Instruments Deutschland Gmbh | Fluxgate Magnetic Field Detection Method and Circuit |
| CN105866713A (en) * | 2016-03-29 | 2016-08-17 | 吉林大学 | State feedback type self-excitation fluxgate sensor |
| CN106324542A (en) * | 2016-08-30 | 2017-01-11 | 中国人民解放军海军工程大学 | Triaxial decoupling self-zero-setting fluxgate magnetometer zero point measurement circuit |
| CN207067224U (en) * | 2017-05-15 | 2018-03-02 | 宜昌市瑞磁科技有限公司 | A kind of leakage current sensor |
| CN107271933A (en) * | 2017-06-15 | 2017-10-20 | 成都理工大学 | A kind of axis fluxgate sensor of spherical three |
| CN111527413A (en) * | 2017-12-08 | 2020-08-11 | 莱姆国际股份有限公司 | Annular fluxgate current sensor |
| CN208421051U (en) * | 2018-08-02 | 2019-01-22 | 宜昌市瑞磁科技有限公司 | A kind of leakage current sensor |
| CN211505671U (en) * | 2019-10-25 | 2020-09-15 | 珠海多创科技有限公司 | DC large current sensor |
| CN212060398U (en) * | 2020-04-07 | 2020-12-01 | 无锡创联科技有限公司 | Non-invasive high-precision AC/DC universal current sensor |
| CN111650415A (en) * | 2020-06-09 | 2020-09-11 | 南京师范大学 | Self-powered current detection system and detection method for wide-current-band power transmission line |
Non-Patent Citations (4)
| Title |
|---|
| PAVEL RIPKA: "Flugate Sensor With Pulse Feedback", 《IEEE TRANSACTIONS ON MAGNETICS》 * |
| PEI-MING WU: "Design optimization of a low-power micromachined fluxgate sensor using localized core saturation method", 《2006 12TH BIENNIAL IEEE CONFERENCE ON ELECTROMAGNETIC FIELD COMPUTATION》 * |
| 吕冰: "磁通门传感器与误差修正技术", 《中国优秀硕士学位论文全文数据库 信息科技辑》 * |
| 汪汉国: "基于STM32的三轴磁通门磁强计研究", 《中国优秀硕士学位论文全文数据库 信息科技辑》 * |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113945871A (en) * | 2021-10-20 | 2022-01-18 | 北京微纳星空科技有限公司 | Fluxgate signal processing method, fluxgate signal processing circuit, fluxgate signal processing device and storage medium |
| CN113759288A (en) * | 2021-11-08 | 2021-12-07 | 深圳市德兰明海科技有限公司 | Leakage current detection circuit and method and leakage current detector |
| CN113759288B (en) * | 2021-11-08 | 2022-03-11 | 深圳市德兰明海科技有限公司 | Leakage current detection circuit and method and leakage current detector |
| CN116754823A (en) * | 2023-06-19 | 2023-09-15 | 深圳柯力三电科技有限公司 | Control method of fluxgate vibration |
| CN116754823B (en) * | 2023-06-19 | 2024-02-02 | 深圳柯力三电科技有限公司 | Control method of fluxgate vibration |
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