A low frequency magnetic field calibration device

Abstract

The present application relates to a kind of low-frequency magnetic field calibration device, including closed-loop magnetic field coil and resonant type stabilized excitation source component, closed-loop magnetic field coil is mutually connected in series with resonant type stabilized excitation source, closed-loop magnetic field coil can be electrified to generate 10kHz~100kHz magnetic field, the magnetic field generated by its coil has 0.5% non-uniformity level magnetic field uniform area, and coil inductance parameter decreases with frequency rise;Resonant type stabilized excitation source can match the impedance parameter of closed-loop magnetic field coil on 10kHz, 30kHz, 50kHz, 70kHz, 100kHz etc. Frequency point and constitute resonant circuit, can with large current low voltage drive closed-loop magnetic field coil generates 10kHz~100kHz, 1mT order of magnitude magnetic field.The present application can be reproduced 100kHz, 1mT uniform magnetic field space by the mode of resonant operation, magnetic field uniformity is better than 0.5%, with reduce energy consumption, high uniformity magnetic field space, improve the effect of existing magnetic field calibration device operating frequency range.

Description

Technical Field

[0001] This invention belongs to the field of calibration technology for alternating magnetic field measuring instruments, and relates to a device for calibrating low-frequency magnetic fields. Background Technology

[0002] Low-frequency magnetic field measuring instruments are commonly used in fields such as power, health, environmental protection, and national defense to monitor low-frequency magnetic fields in the environment. Because these applications involve personal safety, the accuracy of low-frequency magnetic field measuring instruments in measuring environmental electromagnetic radiation has a significant impact.

[0003] Referring to the ICNIRP guidelines, "Guidelines for Limiting Exposure to Time-Varying Electric and Magnetic Fields," which require coverage of magnetic radiation above 100 kHz, the measuring instruments applicable to these guidelines primarily focus on magnetic field parameters. For example, Hioki's 3470 magnetic field detector can measure magnetic induction intensity in the frequency range of 10 Hz to 400 kHz, with a measurement error of ±3.5% of the reading and ±0.5% of the range. my country's Ministry of Housing and Urban-Rural Development is also organizing the research and development of building magnetic field radiation detection equipment to replace foreign products, with technical standards referencing the ICNIRP guidelines.

[0004] Current calibration devices either lack sufficient frequency range or measurement accuracy to calibrate low-frequency magnetic field measuring instruments. Existing domestic calibration devices with uniform field characteristics for alternating magnetic fields are insufficient to operate stably up to 100kHz at magnetic induction intensities on the order of 10mT. For example, the 10kHz alternating weak magnetic field standard device used in the defense metrology industry employs a power source to directly drive the magnetic field coil, outputting alternating magnetic fields up to 1mT, 1kHz / 0.1mT, and 10kHz. Its schematic diagram is shown below. Figure 1 As shown, when the device outputs a magnetic field above 10kHz, the magnetic induction intensity of the alternating magnetic field decreases sharply because the coil impedance increases exponentially with frequency, making it impossible to form a stable magnetic field output above 10kHz.

[0005] Another method uses a single-loop coil as the transmitting antenna to calibrate the low-frequency magnetic field measuring instrument at a given distance. This method suffers from low magnetic field strength, poor magnetic field uniformity, and positioning issues, leading to low magnetic field accuracy. Its test system block diagram is shown below. Figure 2 As shown, the principle used is Biot-Sava's law to calculate the standard magnetic field value.

[0006]

[0007] In the formula:

[0008] B – Magnetic flux density generated by the transmitting antenna at a point d / m along its axis, T; μ0 – Permeability of free space, H / m; r – Equivalent radius of the transmitting antenna, m; I – Current in the transmitting antenna, A; N – Number of turns of the transmitting antenna; d – Distance from the test point on the transmitting antenna axis to the plane of the transmitting antenna, m.

[0009] The alternating magnetic field reproduced by this method is around 300 nT. However, since the probe of the instrument being calibrated usually has a considerable volume, it is difficult to accurately locate the distance d, resulting in the uncertainty of the standard magnetic field usually being on the order of 10%.

[0010] Based on the above-mentioned shortcomings, this invention adopts a closed-loop magnetic field coil with a decreasing inductance-frequency curve and a resonant working mode to realize a low-frequency magnetic field calibration device with high accuracy and uniform magnetic field characteristics, thus solving the problem of reproducing uniform magnetic field calibration at the level of 100kHz and 1mT. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of existing technologies and to solve the problem that in the process of reproducing a uniform magnetic field above 10kHz, the power of the excitation power supply increases significantly due to the large inductance of the magnetic field coil, which makes it difficult to achieve a uniform magnetic field on the order of 100kHz and 1mT. Therefore, a low-frequency magnetic field calibration device is proposed.

[0012] The device of the present invention is achieved through the following technical solution:

[0013] A low-frequency magnetic field calibration device includes a closed-loop magnetic field coil and a resonant voltage-regulated excitation source. The closed-loop magnetic field coil and the resonant voltage-regulated excitation source are connected in series. The closed-loop magnetic field coil can generate a magnetic field of 10kHz to 100kHz when energized. The magnetic field generated by the coil has a uniform magnetic field region with a non-uniformity level of 0.5%, and the inductance parameter of the coil decreases as the frequency increases. The resonant voltage-regulated excitation source can match the impedance parameter of the closed-loop magnetic field coil at frequencies such as 10kHz, 30kHz, 50kHz, 70kHz, and 100kHz to form a resonant circuit. It can drive the closed-loop magnetic field coil with a large current and low voltage to generate a magnetic field on the order of 1mT in the range of 10kHz to 100kHz.

[0014] Furthermore, the inductance and resistance of the closed-loop magnetic field coil and the capacitance and resistance of the resonant voltage regulated excitation source are connected in series to form a resonant circuit. By changing the capacitance, the resonant frequency of the resonant circuit can be adjusted to frequencies such as 10kHz, 30kHz, 50kHz, 70kHz, and 100kHz.

[0015] Furthermore, the closed-loop magnetic field coil is formed by closing the lead wires of the solenoid coil with four parallel wires.

[0016] Furthermore, the resonant voltage-regulated excitation source includes a power source, impedance matching, and a resonant section. The power source consists of a signal generator and a 10kW power amplifier connected in series. The impedance matching uses a primary coil and a suitable matching transformer for the secondary coil to achieve the impedance relationship between the matching resonant terminal and the power amplifier. The resonant section mainly consists of a resonant capacitor and a resonant resistor connected in parallel, which are used to cancel the imaginary part of the input impedance at the operating frequency.

[0017] Furthermore, the resonant voltage regulator excitation source is equipped with five switches S1 to S5 for selecting the operating frequency range. The five switches control the change of capacitors C1 to C5 in the resonant circuit, correspondingly adjusting the resonant frequency to 10kHz, 30kHz, 50kHz, 70kHz, and 100kHz resonant frequency points.

[0018] Furthermore, the magnitude of the output voltage on the resonant regulated excitation source controls the change in magnetic induction intensity of the alternating magnetic field.

[0019] Beneficial effects

[0020] The device proposed in this invention, compared with existing technologies, can reproduce a uniform magnetic field space of 100kHz and 1mT with low energy consumption through a resonant operating mode, with a magnetic field uniformity better than 0.5%. It has the effects of reducing energy consumption, providing a high uniformity magnetic field space, and improving the operating frequency range of existing magnetic field calibration devices. Attached Figure Description

[0021] Figure 1 A block diagram of a standard 10kHz alternating weak magnetic field device for existing technology;

[0022] Figure 2 A block diagram of a current-technology single-loop coil (transmitting antenna) calibration system;

[0023] Figure 3 This is a circuit block diagram of the low-frequency magnetic field calibration device of the present invention;

[0024] Figure 4 This is a schematic diagram of a closed-loop magnetic field coil for a low-frequency magnetic field calibration device. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0026] A low-frequency magnetic field calibration device includes a closed-loop magnetic field coil and a resonant voltage-regulated excitation source. The closed-loop magnetic field coil and the resonant voltage-regulated excitation source are connected in series. The closed-loop magnetic field coil can generate a magnetic field of 10kHz to 100kHz when energized. The magnetic field generated by the coil has a uniform magnetic field region with a non-uniformity level of 0.5%, and the inductance parameter of the coil decreases as the frequency increases. The resonant voltage-regulated excitation source can match the impedance parameter of the closed-loop magnetic field coil at frequencies such as 10kHz, 30kHz, 50kHz, 70kHz, and 100kHz to form a resonant circuit. It can drive the closed-loop magnetic field coil with a large current and low voltage to generate a magnetic field on the order of 1mT in the range of 10kHz to 100kHz.

[0027] Furthermore, the inductance and resistance of the closed-loop magnetic field coil and the capacitance and resistance of the resonant voltage-regulated excitation source are connected in series to form a resonant circuit. The resonant circuit's resonant frequency can be adjusted to 10kHz, 30kHz, 50kHz, 70kHz, and 100kHz by changing the capacitance. The closed-loop magnetic field coil is formed by closing the leads of a solenoid coil with four parallel wires. The resonant voltage-regulated excitation source includes a power source, impedance matching, and a resonant section. The power source consists of a signal generator and a 10kW power amplifier connected in series. Impedance matching uses a primary coil and a suitable matching transformer for the secondary coil to achieve the impedance relationship between the resonant terminal and the power amplifier. The resonant section mainly consists of a resonant capacitor and a resonant resistor connected in parallel to cancel the imaginary part of the input impedance at the operating frequency.

[0028] Because the inductance of the closed-loop magnetic field coil does not increase with frequency, the resonant circuit can achieve a low Q value, resulting in low load impedance over a wide frequency range. This allows the regulated power source to output optimal power. The quality factor Q is primarily determined by the capacitance C at the resonant circuit. P The equivalent series impedance, and the resistance R in parallel with the resonant capacitor. P This can be used to smooth the input impedance of a magnetic field coil. The relevant calculation formula is as follows.

[0029] The input impedance of the alternating magnetic field coil is given by the following formula:

[0030] Z = (R R +R L +R N )+j2πf(L R +L N )

[0031] In the formula:

[0032] RR—DC resistance of the magnetic field coil winding;

[0033] RL – The additional resistance of the magnetic field coil winding at higher frequencies due to the skin effect;

[0034] RN – Other resistors such as those used for feeders;

[0035] LR—Inductance of the magnetic field coil winding;

[0036] LN – other inductors such as feeders.

[0037]

[0038]

[0039] The connection relationship between the above components is as follows: the two are connected in series. The resonant voltage regulated excitation source provides low-frequency AC power supply to the closed-loop magnetic field coil. The closed-loop magnetic field coil forms a uniform magnetic field space in its central region, thereby achieving the ability to reproduce a uniform magnetic field at the 100kHz and 1mT level with low energy consumption, which is used for the calibration of low-frequency magnetic field measurement equipment.

[0040] The specific working process of this device is as follows:

[0041] 1) such as Figure 3 The closed-loop magnetic field coil and the resonant voltage-regulated excitation source are connected in series.

[0042] 2) Based on the preset alternating magnetic field frequency, control the switches S1 to S5 on the resonant voltage stabilizing excitation source to select the working frequency range, change the capacitors C1 to C5 in the resonant circuit, and adjust the resonant frequency to 10kHz, 30kHz, 50kHz, 70kHz, and 100kHz resonant frequency points.

[0043] 3) Since the impedance of the closed-loop magnetic field coil does not increase significantly with frequency, the resonant circuit can achieve a low Q value (below 20), achieving low load impedance in this frequency range, allowing the voltage regulator to output optimal power.

[0044] 4) By changing the output voltage of the resonant regulated excitation source, the magnetic induction intensity of the alternating magnetic field can be changed.

[0045] In this invention, the closed-loop magnetic field coil and the resonant regulated excitation source are connected in series. The inductance and resistance of the coil, along with the capacitance and resistance of the excitation source, form a series resonant circuit. The resonant frequency is adjusted by changing the capacitance of the resonant circuit. Since the inductance of the closed-loop magnetic field coil does not increase with frequency, the resonant circuit can achieve a low Q value, resulting in low load impedance over a wide frequency range and allowing the regulated source to output optimal power. Compared to existing technologies, this invention can reproduce a uniform magnetic field space of 100kHz and 1mT with low energy consumption through resonant operation, achieving a magnetic field uniformity better than 0.5%. This results in reduced energy consumption, a high-uniformity magnetic field space, and an improved operating frequency range for existing magnetic field calibration devices.

[0046] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art will be able to make various modifications and improvements without departing from the principles of the present invention, and these modifications and improvements should also be considered to fall within the scope of protection of the present invention.

Claims

1. A low-frequency magnetic field calibration device, comprising a closed-loop magnetic field coil and a resonant regulated excitation source, characterized in that: A closed-loop magnetic field coil and a resonant regulated excitation source are connected in series. The closed-loop magnetic field coil can generate a magnetic field of 10kHz to 100kHz when energized. The magnetic field generated by the coil has a uniform magnetic field region with a non-uniformity level of 0.5%, and the coil inductance parameter decreases as the frequency increases. The resonant regulated excitation source can match the impedance parameters of the closed-loop magnetic field coil at frequencies such as 10kHz, 30kHz, 50kHz, 70kHz, and 100kHz to form a resonant circuit. It can drive the closed-loop magnetic field coil with a large current and low voltage to generate a magnetic field on the order of 1mT in the 10kHz to 100kHz range. The closed-loop magnetic field coil is formed by closing the leads of a solenoid coil with four parallel wires. The resonant regulated excitation source includes a power source, impedance matching, and a resonant section. The power source is composed of a signal generator and a 10kW power amplifier connected in series. Impedance matching uses a primary coil and a suitable matching transformer with the secondary coil to achieve the impedance relationship between the resonant terminal and the power amplifier. The resonant section mainly consists of a resonant capacitor and a resonant resistor connected in parallel to cancel the imaginary part of the input impedance at the operating frequency. The resonant voltage regulator excitation source is equipped with five switches S1 to S5 for selecting the operating frequency range. The five switches control the change of capacitors C1 to C5 in the resonant circuit, corresponding to adjusting the resonant frequency to 10kHz, 30kHz, 50kHz, 70kHz, and 100kHz resonant frequency points.

2. The low-frequency magnetic field calibration device according to claim 1, characterized in that: The inductance and resistance of the closed-loop magnetic field coil and the capacitance and resistance of the resonant voltage regulated excitation source are connected in series to form a resonant circuit. By changing the capacitance, the resonant frequency of the resonant circuit can be adjusted to 10kHz, 30kHz, 50kHz, 70kHz, and 100kHz.

3. The low-frequency magnetic field calibration device according to claim 1, characterized in that: The output voltage of the resonant regulated excitation source controls the change in magnetic induction intensity of the alternating magnetic field.

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