A phase-shift fluxgate experimental instrument

Abstract

A phase-shift fluxgate tester is designed to facilitate adjustment and matching and is not easily affected by temperature changes. The invention comprises a rectangular wave generator and a multi-stage digital two-frequency division circuit, a voltage follower, an inverse integrator, an AC voltage-controlled constant current source, a fluxgate probe, a signal amplifier, a phase difference identification circuit, a pulse width measurement circuit, a digital display circuit and a fluxgate calibration device. The rectangular wave generator and the multi-stage digital two-frequency division circuit are composed of a CD4060BCM and a crystal oscillator, and a precision reference power supply is used to provide ± dual power supply for them, so that the output rectangular wave frequency is accurate, the width and amplitude of the positive and negative rectangular pulses are equal, and the waveform is stable and symmetrical. The inverse integrator is composed of an operational amplifier with high open-loop gain and small offset, and the rectangular wave is converted into a triangular wave with excellent linearity along the edge. The AC voltage-controlled constant current source converts the triangular wave voltage into a triangular wave constant current to excite the fluxgate probe, so that the H(t) waveform in the probe magnetic core is a stable and symmetrical triangular wave.

Description

Technical Field

[0001] The invention belongs to the field of weak magnetic field measuring instruments, and in particular relates to a phase-shift type fluxgate experimental instrument. Background Art

[0002] Fluxgate technology is widely used in the field of weak magnetic field measurement. New methods for measuring magnetic fields have emerged over the past few decades, but the fluxgate method still has significant advantages such as high measurement sensitivity, low power consumption, small and sturdy probes, and flexible and convenient use, making it an enduring application in the field of weak magnetic field measurement. The structure of the fluxgate measurement probe is like a transformer with a soft magnetic material such as Permalloy that has high magnetic permeability, high rectangular ratio, low saturation magnetic induction, low coercive force, and low magnetostriction coefficient as the core. When the fluxgate is working, a waveform-symmetrical alternating current is used to excite the probe core to make it bidirectionally alternately over-saturated. In the absence of an external magnetic field, the probe outputs a symmetrical pulse signal that alternates between positive and negative, and the amplitudes of the positive and negative pulses are equal; the phase difference between the pulses is π; and the output signal contains only the fundamental wave of the excitation current and its odd harmonic components. When there is an external magnetic field H x When acting simultaneously along the axial direction of the probe, the phase of the probe output pulse shifts; the amplitude of the pulse may change asymmetrically; and even harmonic components appear in the probe output signal. Detecting any of the above changes in the probe output signal caused by the external magnetic field can achieve the measurement of the external magnetic field. The "second harmonic type" fluxgate measures the external magnetic field by detecting the size of the second harmonic component in the output signal of the probe, but the fundamental component in its output signal is much larger than the even harmonic component, making it difficult to detect. The most effective way to improve its signal-to-noise ratio is to combine two probes with the same structure and performance, with the excitation coils of the two connected in reverse series and the output coils connected in the same direction, so that the fundamental components in the total output signal cancel each other out and the even harmonic components double. To achieve this goal, the structural design and manufacturing process of the probe, the performance of the magnetic core, the waveform of the excitation current, the design and manufacturing of the signal detection and processing circuits are very demanding, so that the relative uncertainty of the measurement value of such instruments mass-produced by general professional manufacturers can only be reduced to about ±2%, and only a few professional manufacturers can reduce the relative uncertainty of their measurement value to less than 0.5%. It is even more difficult for amateurs to make their own successfully, which limits the popularization and application of this fluxgate technology. Its working principle is complicated, and the process and circuit for extracting the second harmonic component are also complicated. The "second harmonic type" fluxgate is not suitable for use as an experimental teaching instrument for "College Physics Experiment".

[0003] When the probe core is excited by sinusoidal alternating current, the external magnetic field along the axial direction of the fluxgate probe causes the peak values ​​of the positive and negative pulse signals output by the probe to change asymmetrically. Detecting the change in its peak value can also measure the external magnetic field. This type of fluxgate is called "peak difference type". The probe has a simple structure, is easy to make, has low power consumption, and is highly sensitive. However, the relationship between the change in its peak value and the external magnetic field is complex, so it is only suitable for relative measurement, such as mine detection, submersible detection, and prospecting; detecting the direction of underground iron pipes, and performing non-destructive testing on damage to steel products such as steel pipes and wire ropes. It is also not suitable for use as an experimental teaching instrument for "College Physics Experiments".

[0004] The external magnetic field can also be measured by detecting the phase shift of the positive and negative pulse signals output by the probe by detecting the external magnetic field along the axial direction of the probe. This type of fluxgate is called "phase shift type". Using a stable and symmetrical AC triangular wave constant current to give the probe core bidirectional alternating oversaturation excitation can make the waveform of the magnetic field intensity H(t) in the probe core still a stable and symmetrical triangular wave, while the magnetic induction intensity B in the core 1 The waveform of (t) is approximately a clipped triangle wave, such as Figure 1 When there is no external magnetic field, the magnetic induction intensity B in the probe core is 1 The waveform of (t) is positive and negative symmetrical, the phase difference between the positive and negative pulses output by the probe is π, and the amplitudes of the pulses are equal. There is an external magnetic field H along the positive axis of the probe. x When acting simultaneously, the combined magnetic induction intensity in the probe core is B(t) = μ d H x +B 1 (t) = B 0 +B 1 The image of (t) will be shifted upward by B 0 , as attached Figure 1 As shown: B(t) rises from a negative value through zero at the time t 1 Compared with the case without external magnetic field, the phase of the positive pulse output by the probe will be relatively advanced by Δt. The moment B(t) drops from a positive value to a zero value is t 2 The relative lag is Δt, and the phase of the negative pulse output by the probe is relatively delayed. Therefore, the phase difference between the positive pulse output by the probe and the negative pulse that follows will produce a phase shift Where Δτ=2Δt; B 0 =μ d H x is the external magnetic field H x The magnetic induction intensity induced in the probe core. Figure 1 It can be seen that:

[0005]

[0006]

[0007]

[0008] From the above formula, we can know that the external magnetic field strength along the axis of the probe is proportional to the phase shift of the probe output pulse, where is the slope of the B(t) curve near zero; μ d =dB / dH is the differential magnetic permeability of the magnetic core. In the above formula, it specifically refers to the slope of the non-saturated straight line segment on the saturation magnetization curve of the probe core.

[0009] After the probe output signal passes through the amplification circuit and the phase difference recognition circuit, the width of the output rectangular pulse is proportional to the phase difference between the positive and negative pulses output by the probe. The width τ of the pulse is measured. It is known that the width of the rectangular pulse is T / 2 when there is no external magnetic field. Δτ=τ-T / 2 is obtained, then:

[0010] H x =(2H m / T)Δτ=kΔτ;B x =μ 0 H x =μ 0 (2H m / T)Δτ=μ 0 kΔτ.

[0011] Where k = 2H m / T is the fluxgate constant, if H m If , T is known, or the phase-shift fluxgate tester is calibrated to obtain the fluxgate constant k, then H can be obtained by measuring Δτ. x and B x The value of .

[0012] The measurement principle of this "phase-shift type" flux gate is simple and easy to understand, the instrument structure is simple, the calculation formula is also simple, the measurement sensitivity and accuracy are high, it is flexible and convenient to use, and it is suitable for use as a teaching instrument for university physics experiments.

[0013] The accuracy of this "phase-shifted" fluxgate measurement result mainly depends on the stability and accuracy of the frequency and amplitude of H(t) in the fluxgate probe core, as well as the symmetry of the triangular waveform of H(t) and its linearity. The fluxgate probe has a magnetic core in its excitation coil, and its AC impedance is not only related to the frequency of the current, but also to the magnitude of the current; many solutions reported in the literature use symmetrical AC voltage excitation, such as the solution disclosed in the document "Single Operational Amplifier Fluxgate Sensor Excitation Circuit" (Patent No. ZL 200920033870.3), which uses a triangular AC voltage to perform oversaturation excitation on the fluxgate probe. Because the impedance of the excitation coil changes with the magnitude of the excitation voltage, the excitation current and the waveform of H(t) will change uncontrollably when the triangular AC voltage is used for excitation, which will cause errors in the measurement results. In order to make the waveform of H(t) a stable and symmetrical triangular waveform, it is necessary to use a stable and symmetrical triangular constant current for excitation. Therefore, designing and manufacturing an excitation circuit that outputs an AC triangular wave constant current with a stable and symmetrical output waveform is the key to making a phase-shifted fluxgate experimental instrument with excellent performance.

[0014] The rectangular wave AC voltage signal is converted into a triangular wave AC voltage signal through an electronic integrator, and then passed through the "AC voltage-controlled constant current source" circuit to obtain the triangular wave constant current excitation current i(t). In order to make the waveform of H(t) a stable, symmetrical, and well-linear triangular wave, it is required that the waveform of the excitation current i(t) is a stable, symmetrical, and well-linear triangular wave, which also requires the waveform of the rectangular wave AC voltage signal to be stable and symmetrical (stable frequency, equal amplitudes of positive and negative rectangular pulses, equal and stable widths).

[0015] There are many ways to generate rectangular waves and triangular waves, but most of them cannot meet the requirements of stable symmetry. The few methods that can basically meet the above requirements have too complex circuits, expensive core components, and require careful adjustment and matching, and are easily affected by temperature changes. Therefore, it is necessary to develop new circuits. Summary of the invention

[0016] In response to the above technical problems, the present invention provides a phase-shifted fluxgate tester circuit with a simple circuit structure, inexpensive and easily available components, no need for careful adjustment and matching, and not easily affected by temperature changes, and particularly relates to an AC triangular wave constant current excitation circuit.

[0017] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0018] A phase-shift fluxgate experiment instrument comprises an AC triangular wave constant current excitation circuit and a phase difference measurement circuit; the AC triangular wave constant current excitation circuit comprises a rectangular wave generator and a multi-stage digital two-frequency division circuit, a voltage follower, an inverse integrator, an AC voltage-controlled constant current source and a fluxgate probe, the output ends of the rectangular wave generator and the multi-stage digital two-frequency division circuit are connected to the input end of the voltage follower, the output end of the voltage follower is connected to the input end of the inverse integrator, the output end of the inverse integrator is connected to the input end of the AC voltage-controlled constant current source, and the output end of the AC voltage-controlled constant current source is connected to the excitation coil input end of the fluxgate probe;

[0019] The phase difference measurement circuit includes a signal amplification circuit, a phase difference identification circuit, a pulse width measurement circuit and a digital display circuit. The output end of the induction coil of the fluxgate probe is connected to the input end of the signal amplifier, the output end of the signal amplifier is connected to the input end of the phase difference identification circuit, the output end of the phase difference identification circuit is connected to the input end of the pulse width measurement circuit, and the output end of the pulse width measurement circuit is connected to the input end of the digital display circuit.

[0020] The rectangular wave generator includes a CD4060BCM chip, a crystal oscillator, a first precision reference power supply, a second precision reference power supply, a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor and a second capacitor. The CD4060BCM chip is connected to the first precision reference power supply and the second precision reference power supply respectively. One end of the first resistor is connected to VCC1, and the other end of the first resistor is connected to VDD of the CD4060BCM chip. Terminal 3 of the second precision reference power supply is connected to GND, and terminal 2 of the second precision reference power supply is connected to VDD of the CD4060BCM chip to provide a positive power supply for the CD4060BCM chip; one end of the second resistor is connected to VEE1, and the other end of the second resistor is connected to pin 8 of the CD4060BCM chip; terminal 3 of the first precision reference power supply is connected to pin 8 of the CD4060BCM chip; Terminal 2 of a precision reference power supply is connected to GND to provide a negative power supply for the CD4060BCM chip; one end of the third resistor is connected to pin 10 of the CD4060BCM chip, and the other end of the third resistor is connected to pin 11 of the CD4060BCM chip; one end of the fourth resistor is connected to pin 10 of the CD4060BCM chip, and the other end of the fourth resistor is connected to pin 2 of the crystal oscillator, and pin 1 of the crystal oscillator is connected to pin 11 of the CD4060BCM chip; one end of the first capacitor is connected to pin 1 of the crystal oscillator, and the other end of the first capacitor is connected to pins 8 and 12 of the CD4060BCM chip; one end of the second capacitor is connected to pin 2 of the crystal oscillator, and the other end of the second capacitor is connected to pins 8 and 12 of the CD4060BCM chip; an AC rectangular wave with a frequency of 128 Hz is output from pin 14 of the CD4060BCM chip and sent to the reverse integrator through a voltage follower.

[0021] The reverse integrator includes a first operational amplifier, a second operational amplifier, a fifth resistor, a sixth resistor, a seventh resistor, and a fifth capacitor, wherein the seventh resistor is connected in parallel with the fifth capacitor; one end of the fifth capacitor is connected to pin 6 of the second operational amplifier, the other end of the fifth capacitor is connected to pin 7 of the second operational amplifier, one end of the sixth resistor is connected to pin 5 of the second operational amplifier, the other end of the sixth resistor is connected to GND, one end of the fifth resistor is connected to pin 6 of the second operational amplifier, the other end of the fifth resistor is connected to pin 1 of the first operational amplifier, and an AC triangular wave voltage signal is output from pin 7 of the second operational amplifier to the input end of the AC voltage-controlled constant current source circuit.

[0022] The excitation coil of the fluxgate probe is divided into an inner coil and an outer coil. The number of turns of the inner coil is twice that of the outer coil, and the cross-sectional area of ​​the outer coil is twice that of the inner coil. The induction coil of the fluxgate probe is wound between the inner coil and the outer coil; end 1 of the inner coil and end 3 of the outer coil are the same-name ends, which are used as the input end of the entire excitation coil, and the input end of the excitation coil is connected to the output end of the AC voltage-controlled constant current source; end 2 of the inner coil is connected to end 4 of the outer coil to form a reverse series connection; end 5 of the induction coil is grounded, and end 6 of the induction coil is connected to the input end of the signal amplification circuit.

[0023] The AC voltage-controlled constant current source circuit includes a third operational amplifier, a sixth capacitor, an eighth resistor, a ninth resistor, a tenth resistor, a seventh capacitor, an eighth capacitor, an eleventh resistor, and a twelfth resistor. One end of the sixth capacitor is connected to pin 1 of the third operational amplifier, and the other end of the sixth capacitor is connected to pin 7 of the second operational amplifier. One end of the eighth resistor is connected to pin 1 of the third operational amplifier, and the other end of the eighth resistor is connected to GND. One end of the seventh capacitor is connected to pin 2 of the third operational amplifier, and the other end of the seventh capacitor is connected to the twelfth resistor. The other end of the twelfth resistor is connected to pin 1 of the third operational amplifier. Pin 4 forms a high-frequency suppression circuit to keep the hypotenuse of the triangular wave smooth; one end of the ninth resistor is connected to pin 2 of the third operational amplifier, the other end of the ninth resistor is connected to one end of the eighth capacitor, and the other end of the eighth capacitor is connected to GND; one end of the tenth resistor is connected to the 3rd end of the fluxgate probe excitation coil, the other end of the tenth resistor is connected to pin 2 of the third operational amplifier, one end of the eleventh resistor is connected to the 3rd end of the fluxgate probe excitation coil, the other end of the eleventh resistor is connected to GND, and the output from pin 4 of the third operational amplifier is connected to end 1 of the fluxgate probe excitation coil to excite the fluxgate probe.

[0024] The phase difference identification circuit includes a high-speed precision dual voltage comparator, a third precision reference power supply, a fourth precision reference power supply, a high-speed D trigger, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, and a sixteenth resistor. The positive and negative bidirectional voltage comparison circuit includes a first high-speed precision comparator and a second high-speed precision comparator. Pin 3 of the third precision reference power supply is connected to GND, and pin 2 of the third precision reference power supply is connected to pin 4 of the first high-speed precision comparator; one end of the fourteenth resistor is connected to pin 4 of IC8, and the other end is connected to VCC1, so as to provide a positive reference voltage for the first high-speed precision comparator; pin 2 of the fourth precision reference power supply is connected to GND, and pin 3 of the fourth precision reference power supply is connected to pin 10 of the second high-speed precision comparator; one end of the thirteenth resistor is connected to pin 10 of the second high-speed precision comparator, and the other end of the thirteenth resistor is connected to VEE1, so as to provide a negative reference voltage for the second high-speed precision comparator; pin 5 of the first high-speed precision comparator is connected to pin 9 of the second high-speed precision comparator, so as to provide a positive reference voltage for the first high-speed precision comparator. It is the input end of the positive and negative bidirectional voltage comparator, and the input end of the positive and negative bidirectional voltage comparator is connected to the output end of the signal amplifier; one end of the fifteenth resistor is connected to the 12th pin of the first high-speed precision comparator, and the other end of the fifteenth resistor is connected to VCC1, and the 12th pin of the first high-speed precision comparator is connected to the 10th pin of the high-speed D flip-flop, providing a set signal for the high-speed D flip-flop; one end of the sixteenth resistor is connected to VCC1, and the other end of the sixteenth resistor is connected to the 7th pin of IC8, and the 7th pin of the second high-speed precision comparator is connected to the 13th pin of the high-speed D flip-flop, providing a reset signal for the high-speed D flip-flop; pins 11 and 12 of the high-speed D flip-flop are both connected to VCC1, and the pulse signal output from pin 9 of the high-speed D flip-flop, pin 9 of the high-speed D flip-flop is connected to pin 6 of the single-chip microcomputer 89C2051 in the digital display circuit, and the timer of the single-chip microcomputer 89C2051 in the digital display circuit is used as a pulse width measurement circuit to measure the width of the pulse signal, and the external magnetic field strength along the axis of the probe can be calculated.

[0025] The first precision reference power supply and the second precision reference power supply adopt LM4040A-25I precision reference power supply.

[0026] The first operational amplifier and the second operational amplifier adopt the same AD708JN dual operational amplifier.

[0027] The third operational amplifier is a TDA2040 operational amplifier.

[0028] The first high-speed precision comparator and the second high-speed precision comparator use the same LM319N high-speed precision dual comparator, and the high-speed D flip-flop uses a SN74HC74N high-speed D flip-flop.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The present invention designs a new rectangular wave generator circuit, which uses CD4060BCM and crystal oscillator to form a rectangular wave generator and a multi-stage digital two-frequency division circuit, and can output rectangular wave voltage signals of various frequencies. Based on the characteristics of the crystal oscillator, the frequency of the rectangular wave is accurate and stable; based on the characteristics of the digital two-frequency division circuit itself, the widths of the positive and negative pulses of the rectangular wave are accurately equal; based on the characteristics of the small working current of CD4060BCM, two precision reference power supplies can be used to provide it with an accurate and stable ±2.5V dual power supply, so that the inherent output characteristics of CD4060BCM itself can be used to make the amplitudes of the positive and negative pulses of the rectangular wave AC voltage signal it outputs equal and stable. Then, an operational amplifier is used to form a voltage follower as an output buffer of CD4060BCM to prevent the amplitude of the CD4060BCM output signal from changing due to load changes. The combined effect of the above measures is that the frequency of the rectangular wave AC voltage signal output by CD4060BCM is stable and accurate, the amplitudes of its positive and negative rectangular pulses are accurately equal and stable, the widths of its positive and negative rectangular pulses are accurately equal and stable, and the waveform is stable and symmetrical.

[0031] 2. The present invention designs and manufactures a new electronic integrator circuit: an inverting integrator is formed by using AD708JN with large open-loop gain, small offset voltage and offset current. When the input of the integrator is a step voltage U, its output u 0 =Ut. Linear deviation rate of actual output voltage Where t is the time length of the integration, here it is the width of the rectangular pulse t≈3.906×10 -3 s; RC in the circuit = 2.2 × 10 -3 s, the open-loop gain A of AD708JN is ≥5×10 6 , we get η<1.776×10 -7 , the linearity of the triangle wave edge is excellent.

[0032] 3. The present invention designs and manufactures an AC voltage-controlled constant current source circuit: an AC voltage-controlled constant current source circuit is mainly composed of a TDA2040 power amplifier, which converts the AC triangular wave voltage signal with a stable and symmetrical waveform output by the reverse integrator into an AC triangular wave constant current with a stable and symmetrical waveform to excite the fluxgate probe.

[0033] 4. The present invention designs and manufactures a new structure of the fluxgate probe excitation coil: the excitation coil is divided into two parts, an inner coil and an outer coil, and the induction coil is wound between the two excitation coils. The number of turns of the inner coil is twice that of the outer coil; the cross-sectional area of ​​the outer coil is twice that of the inner coil. The two excitation coils are connected in series in reverse order, so that the magnetic flux generated by the excitation current passing through the inner excitation coil may all return through the inside of the outer excitation coil. Experiments have shown that this excitation method can increase the amplitude of the probe output signal and improve the signal-to-noise ratio of the output signal.

[0034] 5. The present invention designs and manufactures a phase difference recognition circuit and a pulse width measurement and display circuit: a pair of positive and negative bidirectional voltage comparators are formed by using LM319N high-speed precision dual comparator and two precision reference power supplies; a bistable circuit is formed by using high-speed D flip-flop SN74HC74N, and the two are used to form a phase difference recognition circuit. The timer / counter of the single-chip microcomputer in the digital display circuit is used to measure the width τ of the rectangular pulse output by the phase difference recognition circuit. The pulse width measurement result is displayed on the digital display on the panel. This phase difference detection circuit has a simple structure and stable and reliable operation.

[0035] 6. The present invention designs and manufactures a simple device for calibrating fluxgate: a uniformly tightly wound long straight solenoid with an aspect ratio of 15 is installed on the experimental instrument chassis; a set of DC constant current power supply with continuously adjustable output current is installed in the chassis to supply power to the solenoid; the supply current is displayed on the digital ammeter on the panel. The device can be used to calibrate fluxgate with a calibration accuracy better than 0.5%; it can also be used by students to measure the axial magnetic field distribution in the current-carrying solenoid for actual measurement exercises.

[0036] 7. The present invention places the fluxgate probe in the middle of the current-carrying solenoid, and the measured magnetic field strength is H = ncosβI + H 0 , where H 0 is the axial component of the ambient magnetic field, to eliminate H 0 The influence of changing the current i of the current-carrying solenoid at equal intervals L , the width of the corresponding phase difference detection circuit output pulse is measured, which can be used to calibrate the fluxgate constant k, and the calibration accuracy can be better than 0.5%.

[0037] 8. The present invention adopts universal components to make the instrument, and uses the timer / counter of the single-chip microcomputer to measure the width of the rectangular pulse output by the phase difference recognition circuit. The circuit can achieve a measurement accuracy of a relative uncertainty of less than 0.5% without any adjustment and matching, and is not easily affected by temperature changes, which is convenient for promotion and application. The instrument is suitable for use as an experimental teaching instrument for fluxgate experiments in university physics experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0039] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0040] Figure 1 It is a schematic diagram of the phase-shift fluxgate phase modulation principle;

[0041] Figure 2 It is the principle circuit diagram of the rectangular wave generator of the present invention;

[0042] Figure 3 The voltage follower and reverse integrator principle circuit diagram of the present invention;

[0043] Figure 4 It is a schematic diagram of the connection mode between the AC voltage-controlled constant current source excitation circuit and the probe excitation coil of the present invention;

[0044] Figure 5 It is a principle circuit diagram of the phase difference identification circuit of the present invention;

[0045] Figure 6 It is a functional circuit block diagram of the phase-shift type fluxgate experimental instrument of the present invention;

[0046] Figure 7 It is a functional block diagram of the fluxgate test instrument calibration device of the present invention;

[0047] Figure 8 It is a functional effect diagram of the phase difference identification circuit of the present invention.

[0048] Among them: T1 is a fluxgate probe, T1C is an induction coil, IC1 is a CD4060BCM chip, Y1 is a crystal oscillator, IC2 is the first precision reference power supply, IC3 is the second precision reference power supply, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, C1 is the first capacitor, C2 is the second capacitor, IC4A is the first operational amplifier, IC4B is the second operational amplifier, R5 is the fifth resistor, R6 is the sixth resistor, R7 is the seventh resistor, C5 is the fifth capacitor, T1A is the inner coil, T1B is the outer coil circle, IC5 is the third operational amplifier, C6 is the sixth capacitor, R8 is the eighth resistor, R9 is the ninth resistor, R10 is the tenth resistor, C7 is the seventh capacitor, C8 is the eighth capacitor, R11 is the eleventh resistor, R12 is the twelfth resistor, IC8A is the first high-speed precision comparator, IC8B is the second high-speed precision comparator, IC6 is the third precision reference power supply, IC7 is the fourth precision reference power supply, IC9 is a high-speed D flip-flop, R13 is the thirteenth resistor, R14 is the fourteenth resistor, R15 is the fifteenth resistor, and R16 is the sixteenth resistor. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. These descriptions are only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0050] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0051] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0052] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0053] A phase-shift fluxgate experimental apparatus, such as Figure 6 and Figure 7 As shown in Figure 1, its overall structure is divided into two parts: magnetic field measurement device and fluxgate calibration device. The main circuit of the magnetic field measurement device is introduced below: The structure of the power supply circuit of the rectangular wave generator is as follows: Figure 2 As shown, one end of the first resistor R1 is connected to VCC1, the other end of the first resistor R1 is connected to VDD of CD4060BCM chip IC1, the 3 end of the second precision reference power supply IC3 is connected to GND, the 2 end of the second precision reference power supply IC3 is connected to VDD of CD4060BCM chip IC1, providing a positive power supply for CD4060BCM chip IC1; one end of the second resistor R2 is connected to VEE1, the other end of the second resistor R2 is connected to pin 8 of CD4060BCM chip IC1; the 3 end of the first precision reference power supply IC2 is connected to pin 8 of CD4060BCM chip IC1, the 2 end of the first precision reference power supply IC2 is connected to GND, providing a negative power supply for CD4060BCM chip IC1 Source; one end of the third resistor R3 is connected to the 10th pin of the CD4060BCM chip IC1, the other end of the third resistor R3 is connected to the 11th pin of the CD4060BCM chip IC1, one end of the fourth resistor R4 is connected to the 10th pin of the CD4060BCM chip IC1, the other end of the fourth resistor R4 is connected to the 2nd pin of the crystal oscillator Y1, the 1st pin of the crystal oscillator Y1 is connected to the 11th pin of the CD4060BCM chip IC1, one end of the first capacitor C1 is connected to the 1st pin of the crystal oscillator Y1, the other end of the first capacitor C1 is connected to the 8th pin and the 12th pin of the CD4060BCM chip IC1, one end of the second capacitor C2 is connected to the 2nd pin of the crystal oscillator Y1, and the other end of the second capacitor C2 is connected to the 8th pin and the 12th pin of the CD4060BCM chip IC1. A rectangular wave signal generator is formed. From the 14th pin of CD4060BCM chip IC1, a rectangular wave AC voltage signal with a stable and accurate frequency, equal amplitude of positive and negative rectangular pulses, equal and stable pulse width, good symmetry and a frequency of 128Hz can be obtained.

[0054] The structure of the output buffer circuit of the rectangular wave generator is as follows Figure 3As shown, pins 1 and 2 of the first operational amplifier IC4A are connected to form a voltage follower, and pin 3 thereof is connected to pin 14 of the CD4060BCM chip IC1, serving as an output buffer of IC1.

[0055] The structure of the electronic integrator circuit is as follows Figure 3 As shown, the seventh resistor R7 is connected in parallel with the fifth capacitor C5; one end of the fifth capacitor C5 is connected to the 6th pin of the second operational amplifier IC4B, the other end of the fifth capacitor C5 is connected to the 7th pin of the second operational amplifier IC4B, one end of the sixth resistor R6 is connected to the 5th pin of the second operational amplifier IC4B, the other end of the sixth resistor R6 is connected to GND, one end of the fifth resistor R5 is connected to the 6th pin of the second operational amplifier IC4B, and the other end of the fifth resistor R5 is connected to the 1st pin of the first operational amplifier IC4A, forming an inverse integrator. The first operational amplifier IC4A and the second operational amplifier IC4B use AD708JN, whose offset voltage is ≤50μV, and temperature drift is ≤0.4μV / ℃; its offset current is ≤1nA, and temperature drift is ≤25pA / ℃. Its open-loop gain A≥5×10 6 , when the input of the integrator is a step voltage U, its output u o =Ut, its linearity deviation rate Where t is the time length of the integrator integrating the step voltage; RC is the integration time constant of the integrator. The period of the rectangular wave is T = 1 / 128s, and the width of its positive and negative rectangular pulses is t = 3.906ms. The linearity deviation rate of its output is

[0056]

[0057] The triangular wave AC voltage signal output by the integrator after integrating the above rectangular wave AC voltage signal has stable frequency, stable amplitude, stable and symmetrical waveform and excellent linearity.

[0058] The structure of the AC voltage-controlled constant current source excitation circuit is as follows Figure 4As shown, one end of the sixth capacitor C6 is connected to pin 1 of the third operational amplifier IC5, the other end of the sixth capacitor C6 is connected to pin 7 of the second operational amplifier IC4B, one end of the eighth resistor R8 is connected to pin 1 of the third operational amplifier IC5, and the other end of the eighth resistor R8 is connected to GND; one end of the seventh capacitor C7 is connected to pin 2 of the third operational amplifier IC5, the other end of the seventh capacitor C7 is connected to the twelfth resistor R12, and the other end of the twelfth resistor R12 is connected to pin 4 of the third operational amplifier IC5, forming a high-frequency suppression circuit to keep the hypotenuse of the triangular wave smooth; one end of the ninth resistor R9 is connected to pin 2 of the third operational amplifier IC5, and the other end of the ninth resistor R9 is connected to one end of the eighth capacitor C8, The other end of the eighth capacitor C8 is connected to GND; one end of the tenth resistor R10 is connected to the 3rd end of the excitation coil of the fluxgate probe T1, the other end of the tenth resistor R10 is connected to the 2nd pin of the third operational amplifier IC5, one end of the eleventh resistor R11 is connected to the 3rd end of the excitation coil of the fluxgate probe T1, the other end of the eleventh resistor R11 is connected to GND, and the output is from the 4th pin of the third operational amplifier IC5 to the 1st end of the excitation coil of the fluxgate probe T1. Thus, based on the third operational amplifier IC5, an "AC voltage-controlled constant current source" excitation circuit is formed to excite the probe, which is characterized in that the waveform of H(t) in the probe core is not affected by the change of the excitation coil impedance, and its waveform can also be a stable and symmetrical triangular wave. Therefore, the waveform of the positive and negative pulse signals output by the fluxgate probe T1 is symmetrical, the amplitude is equal and stable, and the external magnetic field only changes the phase difference between the output pulses of the fluxgate probe T1, and does not change the amplitude of the pulse and the waveform of the pulse itself, which provides favorable conditions for phase difference recognition.

[0059] The connection method of the two excitation coils of the fluxgate probe is as follows Figure 4 As shown, the excitation coil of the fluxgate probe T1 is divided into two parts: the inner coil T1A and the outer coil T1B. Terminals 1 and 3 are the same-name terminals. Terminals 2 and 4 are connected, and terminals 1 and 3 are input terminals, forming a reverse series connection.

[0060] The structure of the phase difference recognition circuit is as follows Figure 5As shown, pin 3 of the third precision reference power supply IC6 is connected to GND, and pin 2 of the third precision reference power supply IC6 is connected to pin 4 of the first high-speed precision comparator IC8A; one end of the fourteenth resistor R14 is connected to pin 4 of IC8, and the other end is connected to VCC1, providing a positive reference voltage for the first high-speed precision comparator IC8A; pin 2 of the fourth precision reference power supply IC7 is connected to GND, and pin 3 of the fourth precision reference power supply IC7 is connected to pin 10 of the second high-speed precision comparator IC8B; one end of the thirteenth resistor R13 is connected to pin 10 of the second high-speed precision comparator IC8B, and the other end of the thirteenth resistor R13 is connected to VEE1, providing a negative reference voltage for the second high-speed precision comparator IC8B; pin 5 of the first high-speed precision comparator IC8A is connected to the second high-speed precision dual comparator IC8 The 9th pin of B is connected as the input end of the positive and negative bidirectional voltage comparison circuit, and the input end of the positive and negative bidirectional voltage comparison circuit is connected to the output end of the signal amplifier; one end of the fifteenth resistor R15 is connected to the 12th pin of the first high-speed precision dual comparator IC8A, and the other end of the fifteenth resistor R15 is connected to VCC1, and the 12th pin of the first high-speed precision comparator IC8A is connected to the 10th pin of the high-speed D flip-flop IC9, providing a set signal for the high-speed D flip-flop IC9; one end of the sixteenth resistor R16 is connected to VCC1, and the other end of the sixteenth resistor R16 is connected to the 7th pin of IC8, and the 7th pin of the second high-speed precision comparator IC8B is connected to the 13th pin of the high-speed D flip-flop IC9, providing a reset signal for the high-speed D flip-flop IC9; the 11th and 12th pins of the high-speed D flip-flop IC9 are both connected to VCC1. Thus, a phase difference recognition circuit is formed.

[0061] The rectangular pulse signal output by the phase difference recognition circuit is output from the 9th pin of the high-speed D flip-flop IC9 and connected to the 6th pin of the single-chip microcomputer 89C2051 in the display circuit. The timer / counter of the single-chip microcomputer 89C2051 is used to measure the width of the rectangular pulse output by the phase difference recognition circuit, and the pulse width measurement result is displayed on the digital display. The structure of the phase difference detection circuit is very simple, and the operation is stable and reliable.

[0062] A uniformly tightly wound long straight solenoid is installed on the chassis, with an aspect ratio of 15. The magnetic field strength generated by the excitation current in the middle axial direction of the solenoid is calculated according to the formula H=nIcosβ, cosβ=0.9978, and its relative uncertainty is <0.2%; the relative uncertainty of the n value is <0.2%; the relative uncertainty of the ammeter measurement when it is close to the full scale is <0.2%. This set of equipment is used to calibrate the flux gate, and its total relative uncertainty can be <0.5%. It can be used by students to calibrate the flux gate, and it can also be used by students to measure the axial magnetic field distribution in the current-carrying solenoid for practical measurement exercises.

[0063] In this embodiment, the fluxgate probe is placed in the middle of the current-carrying solenoid, and the measured magnetic field strength is H = n cos β I + H 0 , where H 0is the axial component of the environmental magnetic field. To eliminate the influence of H 0 , the current i of the current-carrying solenoid is changed at equal intervals L , and the width of the output pulse of the phase difference detection circuit corresponding to it is measured, and the measurement data is recorded in Table 1.

[0064] Serial No.i 1 2 3 4 5 6 7 <![CDATA[I Li / mA]]> -150.0 -100.0 -50.0 0.0 50.0 100.0 150.0 <![CDATA[τ i / μs]]> 3190 3456 3722 3989 4256 4523 4789 <![CDATA[Δτ j =t (i+4) -t i ]]> 1066 1067 1067

[0065] Table 1 Measurement data table for calibrating the fluxgate

[0066] It is known that n = 5714 m -1 , cosβ≈0.9978. Using the progressive difference method to process the data, it can be obtained that:

[0067] k = (1.069 ± 0.004) A(mμs) -1 .

[0068] As a practical measurement exercise, measure the magnetic field strength generated by the current in the middle of the solenoid: make i L = 170.0 mA, and τ = 4896 μs is measured. When i L = 0.0 mA, τ 0 = 3989 μs is measured, and Δτ = τ - τ 0 = 907 μs, then:

[0069] H 测 = kΔτ≈969.7 A / m -1 , H 理 = nIcosβ≈969.2 A / m -1 .

[0070] The deviation between the measured value and the theoretical value is very small, and the work is reliable.

[0071] In the embodiment of the present invention, the first precision reference power supply IC2 and the second precision reference power supply IC3 are used to provide accurate and stable ±2.5V dual power supply for the CD4060BCM chip IC1, and the output characteristics of the CD4060BCM chip IC1 itself are used to make the amplitudes of the positive and negative rectangular pulses of the AC rectangular wave output by the CD4060BCM chip IC1 equal and stable; the CD4060BCM chip IC1 and the crystal oscillator Y1 form a rectangular wave signal generator and a multi-stage digital two-frequency division circuit, and the characteristics of the crystal oscillator are used to make the frequency of the AC rectangular wave output by the CD4060BCM chip IC1 accurate and stable; the characteristics of the digital two-frequency division circuit itself are used to make the widths of the positive and negative pulses of the rectangular wave equal; the AD708JN operational amplifier is used to form an integrated circuit. The AD708JN operational amplifier has high open-loop gain, small offset voltage and offset current, so that the integration of the rectangular wave AC voltage signal with stable and symmetrical waveform can obtain a triangle wave with stable and symmetrical waveform and good linearity. The TDA2040 is used to form an "AC voltage-controlled constant current source" circuit for fluxgate probe excitation, so that the waveform of H(t) in the probe core is not affected by the change of the probe coil impedance and can also be a triangle wave with stable and symmetrical waveform. The LM319N high-speed precision dual comparator and the SN74HC74N high-speed D trigger are used to form a phase difference recognition circuit, and the timer / counter of the single-chip microcomputer in the display circuit is used to measure the width of the rectangular pulse output by the phase difference recognition circuit, so that the structure of the phase difference detection circuit is simple and the operation is stable and reliable. The instrument is made of general components and fully utilizes the inherent characteristics of each component. Experiments have proved that the relative uncertainty of the measured value can reach a measurement accuracy of <0.5% without any adjustment and matching. It is suitable for opening fluxgate experiments in university physics experiment courses, and can also be used as a measuring instrument for easy promotion and application.

[0072] Only the preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention, and various changes should be included in the protection scope of the present invention.

Claims

1. A phase-shift fluxgate test instrument, Features: It comprises an AC triangular wave constant current excitation circuit and a phase difference measurement circuit; the AC triangular wave constant current excitation circuit comprises a rectangular wave generator and a multi-stage digital two-frequency division circuit, a voltage follower, an inverse integrator, an AC voltage-controlled constant current source and a fluxgate probe (T1); the output ends of the rectangular wave generator and the multi-stage digital two-frequency division circuit are connected to the input end of the voltage follower, the output end of the voltage follower is connected to the input end of the inverse integrator, the output end of the inverse integrator is connected to the input end of the AC voltage-controlled constant current source, and the output end of the AC voltage-controlled constant current source is connected to the excitation coil input end of the fluxgate probe (T1); the phase difference measurement circuit comprises a signal amplification circuit, a phase difference identification circuit, a pulse width measurement circuit and a digital display circuit; the output end of the induction coil (T1C) of the fluxgate probe (T1) is connected to the input end of the signal amplification circuit, the output end of the signal amplification circuit is connected to the input end of the phase difference identification circuit, the output end of the phase difference identification circuit is connected to the input end of the pulse width measurement circuit, and the output end of the pulse width measurement circuit is connected to the input end of the digital display circuit; The rectangular wave generator comprises a CD4060BCM chip (IC1), a crystal oscillator (Y1), a first precision reference power supply (IC2), a second precision reference power supply (IC3), a first resistor (R1), a second resistor (R2), a third resistor (R3), a fourth resistor (R4), a first capacitor (C1) and a second capacitor (C2); the CD4060BCM chip (IC1) is respectively connected to the first precision reference power supply (IC2) and the second precision reference power supply (IC3); one end of the first resistor (R1) is connected to VCC1; the other end of the first resistor (R1) is connected to VCC1; One end is connected to the VDD of the CD4060BCM chip (IC1), the 2nd end of the second precision reference power supply (IC3) is connected to GND, the 1st end of the second precision reference power supply (IC3) is connected to the VDD of the CD4060BCM chip (IC1), providing a positive power supply for the CD4060BCM chip (IC1); one end of the second resistor (R2) is connected to VEE1, the other end of the second resistor (R2) is connected to the 8th pin of the CD4060BCM chip (IC1); the 2nd end of the first precision reference power supply (IC2) is connected to the CD4060BCM chip (IC1) ), the 1 end of the first precision reference power supply (IC2) is connected to GND to provide a negative power supply for the CD4060BCM chip (IC1); one end of the third resistor (R3) is connected to the 10th pin of the CD4060BCM chip (IC1), the other end of the third resistor (R3) is connected to the 11th pin of the CD4060BCM chip (IC1), one end of the fourth resistor (R4) is connected to the 10th pin of the CD4060BCM chip (IC1), the other end of the fourth resistor (R4) is connected to the 2nd pin of the crystal oscillator (Y1), and the 1st pin of the crystal oscillator (Y1) is connected to the CD40 60BCM chip (IC1), one end of the first capacitor (C1) is connected to pin 1 of the crystal oscillator (Y1), the other end of the first capacitor (C1) is connected to pins 8 and 12 of the CD4060BCM chip (IC1), one end of the second capacitor (C2) is connected to pin 2 of the crystal oscillator (Y1), the other end of the second capacitor (C2) is connected to pins 8 and 12 of the CD4060BCM chip (IC1), and an AC rectangular wave voltage signal with a frequency of 128 Hz is output from pin 14 of the CD4060BCM chip (IC1) and sent to the reverse integrator through a voltage follower; The voltage follower comprises a first operational amplifier (IC4A), and the reverse integrator comprises a second operational amplifier (IC4B), a fifth resistor (R5), a sixth resistor (R6), a seventh resistor (R7), and a fifth capacitor (C5); the seventh resistor (R7) is connected in parallel with the fifth capacitor (C5), one end of the fifth capacitor (C5) is connected to the 6th pin of the second operational amplifier (IC4B), the other end of the fifth capacitor (C5) is connected to the 7th pin of the second operational amplifier (IC4B), one end of the sixth resistor (R6) is connected to the 5th pin of the second operational amplifier (IC4B), the other end of the sixth resistor (R6) is connected to GND, one end of the fifth resistor (R5) is connected to the 6th pin of the second operational amplifier (IC4B), the other end of the fifth resistor (R5) is connected to the 1st pin of the first operational amplifier (IC4A), and an AC triangular wave voltage signal is output from the 7th pin of the second operational amplifier (IC4B) and sent to the input end of the AC voltage-controlled constant current source circuit; The first precision reference power supply (IC2) and the second precision reference power supply (IC3) adopt LM4040A-25I precision reference power supply; the first operational amplifier (IC4A) and the second operational amplifier (IC4B) adopt AD708JN dual operational amplifier.

2. A phase-shift fluxgate tester according to claim 1, Features: The excitation coil of the fluxgate probe (T1) is divided into an inner coil (T1A) and an outer coil (T1B). The number of turns of the inner coil (T1A) is twice the number of turns of the outer coil (T1B), and the cross-sectional area of ​​the outer coil (T1B) is twice the cross-sectional area of ​​the inner coil (T1A). The induction coil (T1C) of the fluxgate probe (T1) is wound between the inner coil (T1A) and the outer coil (T1B). End 1 of the inner coil (T1A) and end 3 of the outer coil (T1B) are the same-name ends, which are used as the input end of the entire excitation coil. The input end of the excitation coil is connected to the output end of the AC voltage-controlled constant current source. End 2 of the inner coil (T1A) is connected to end 4 of the outer coil (T1B) to form a reverse series connection. End 5 of the induction coil (T1C) is grounded, and end 6 of the induction coil (T1C) is connected to the input end of the signal amplification circuit.

3. A phase-shift fluxgate tester according to claim 1, Features: The AC voltage-controlled constant current source circuit comprises a third operational amplifier (IC5), a sixth capacitor (C6), an eighth resistor (R8), a ninth resistor (R9), a tenth resistor (R10), a seventh capacitor (C7), an eighth capacitor (C8), an eleventh resistor (R11), and a twelfth resistor (R12); one end of the sixth capacitor (C6) is connected to pin 1 of the third operational amplifier (IC5), the other end of the sixth capacitor (C6) is connected to pin 7 of the second operational amplifier (IC4B), one end of the eighth resistor (R8) is connected to pin 1 of the third operational amplifier (IC5), and the other end of the eighth resistor (R8) is connected to GND; one end of the seventh capacitor (C7) is connected to pin 2 of the third operational amplifier (IC5), the other end of the seventh capacitor (C7) is connected to the twelfth resistor (R12), and the other end of the twelfth resistor (R12) is connected to the third operational amplifier (IC5 ) to form a high-frequency suppression circuit so that the hypotenuse of the triangular wave can remain smooth; one end of the ninth resistor (R9) is connected to the 2nd pin of the third operational amplifier (IC5), the other end of the ninth resistor (R9) is connected to one end of the eighth capacitor (C8), and the other end of the eighth capacitor (C8) is connected to GND; one end of the tenth resistor (R10) is connected to the 3rd end of the excitation coil of the fluxgate probe (T1), the other end of the tenth resistor (R10) is connected to the 2nd pin of the third operational amplifier (IC5), one end of the eleventh resistor (R11) is connected to the 3rd end of the excitation coil of the fluxgate probe (T1), the other end of the eleventh resistor (R11) is connected to GND, and the output from the 4th pin of the third operational amplifier (IC5) is connected to the 1st end of the excitation coil of the fluxgate probe (T1) to excite the fluxgate probe (T1); the third operational amplifier (IC5) adopts the TDA2040 operational amplifier.

4. A phase-shift fluxgate tester according to claim 1, Features: The phase difference identification circuit comprises a high-speed precision dual voltage comparator, a third precision reference power supply (IC6), a fourth precision reference power supply (IC7), a high-speed D flip-flop (IC9), a thirteenth resistor (R13), a fourteenth resistor (R14), a fifteenth resistor (R15), and a sixteenth resistor (R16); the high-speed precision dual voltage comparator comprises a first high-speed precision comparator (IC8A) and a second high-speed precision comparator (IC8B); the third precision reference power supply (IC6) has its pin 3 connected to GND, and the third precision reference power supply (IC6) has its pin 2 connected to the fourth pin of the first high-speed precision comparator (IC8A); the fourteenth resistor (R14) has its pin 1 connected to the GND, and the fourth precision reference power supply (IC6) has its pin 2 connected to the fourth pin of the first high-speed precision comparator (IC8A); One end of the resistor 14 is connected to the 4th pin of the first high-speed precision comparator (IC8A), and the other end is connected to VCC1, providing a positive reference voltage for the first high-speed precision comparator (IC8A); the 2nd pin of the fourth precision reference power supply (IC7) is connected to GND, and the 3rd pin of the fourth precision reference power supply (IC7) is connected to the 10th pin of the second high-speed precision comparator (IC8B); one end of the thirteenth resistor (R13) is connected to the 10th pin of the second high-speed precision comparator (IC8B), and the other end of the thirteenth resistor (R13) is connected to VEE1, providing a negative reference voltage for the second high-speed precision comparator (IC8B); the 5th pin of the first high-speed precision comparator (IC8A) is connected to GND, and the 3rd pin of the fourth precision reference power supply (IC7) is connected to the 10th pin of the second high-speed precision comparator (IC8B); The pin 12 of the first high-speed precision comparator (IC8A) is connected to the pin 9 of the second high-speed precision comparator (IC8B) as the input end of the positive and negative bidirectional voltage comparison circuit, and the input end of the positive and negative bidirectional voltage comparison circuit is connected to the output end of the signal amplifier circuit; one end of the fifteenth resistor (R15) is connected to the pin 12 of the first high-speed precision comparator (IC8A), and the other end of the fifteenth resistor (R15) is connected to VCC1, and the pin 12 of the first high-speed precision comparator (IC8A) is connected to the pin 10 of the high-speed D flip-flop (IC9) to provide a set signal for the high-speed D flip-flop (IC9); one end of the sixteenth resistor (R16) is connected to VCC1, and the other end of the sixteenth resistor (R16) is connected to the pin 10 of the high-speed D flip-flop (IC9). Pin 7 of the second high-speed precision comparator (IC8B), the pin 7 of the second high-speed precision comparator (IC8B) is connected to pin 13 of the high-speed D flip-flop (IC9), providing a reset signal for the high-speed D flip-flop (IC9); pins 11 and 12 of the high-speed D flip-flop (IC9) are both connected to VCC1, the pulse signal output from pin 9 of the high-speed D flip-flop (IC9), the pin 9 of the high-speed D flip-flop (IC9) is connected to pin 6 of the single-chip microcomputer 89C2051 in the digital display circuit, the timer of the single-chip microcomputer 89C2051 in the digital display circuit is used as a pulse width measurement circuit, the width of the pulse signal is measured, and the external magnetic field strength along the axial direction of the probe can be calculated;The first high-speed precision comparator (IC8A) and the second high-speed precision comparator (IC8B) use LM319N high-speed precision dual comparators, the high-speed D flip-flop (IC9) uses SN74HC74N high-speed D flip-flop, and the third precision reference power supply (IC6) and the fourth precision reference power supply (IC7) use LM385Z-1.2 precision reference power supply. ;

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