CN113359070B - Low-frequency magnetic field frequency spectrum measuring method and system - Google Patents
Low-frequency magnetic field frequency spectrum measuring method and system Download PDFInfo
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- CN113359070B CN113359070B CN202110673013.5A CN202110673013A CN113359070B CN 113359070 B CN113359070 B CN 113359070B CN 202110673013 A CN202110673013 A CN 202110673013A CN 113359070 B CN113359070 B CN 113359070B
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Abstract
A low-frequency magnetic field frequency spectrum measuring method and system belong to the technical field of low-frequency magnetic field measurement. The method comprises the following steps of: generating a periodic sinusoidal signal through a signal generator, amplifying a signal current through a power amplifier, introducing the signal current into a standard coil to generate a standard magnetic field, measuring the magnetic field at the central point of the standard coil by using a measuring coil, and collecting and processing an induced voltage waveform by using an oscilloscope to finally obtain an experimental result of a sensing coefficient frequency response curve of the measuring coil; theoretical calculation simulation step: comparing and analyzing the experimental result with a theoretical calculation result and a simulation result, and determining a final relation curve by adopting a sectional splicing mode; and (3) actual measurement: and obtaining a voltage frequency spectrum, and obtaining a magnetic field frequency spectrum through a relation curve.
Description
Technical Field
The invention relates to a low-frequency magnetic field frequency spectrum measuring method and system, and belongs to the technical field of low-frequency magnetic field measurement.
Background
With the development of science and technology, various physical phenomena such as electromagnetic induction and the like are continuously discovered and researched by people, and simultaneously, the rapid development and the continuous expansion of the application range of the magnetic field measurement technology are also driven. At present, magnetic field measurement technology has been studied and applied in various fields, including biomedicine, geophysics, space science, etc., and has very important application in industrial flaw detection. Magnetic field test systems, typically consist of a magnetic field sensor that converts a magnetic field into a voltage and a voltage measurement device. Among the magnetic field sensors designed and generated based on different physical effects and electronic sensing devices are mainly: superconducting SQUID magnetometer, induction coil magnetometer, fluxgate magnetometer, hall sensor, anisotropic magnetoresistive sensor, giant magnetoresistive sensor, nuclear magnetic resonance field tester, and the like. They have their own advantages and disadvantages and are suitable for use in different fields. For a voltage measuring device, a simple voltmeter can be used if the integrated magnetic field is measured; if the magnetic field spectrum is measured, it is typically a spectrometer and a receiver. The low-frequency magnetic field is an alternating magnetic field having a frequency of not higher than 0.3 MHz. The low-frequency magnetic field generated by the electronic and electrical equipment in the using process not only can influence the normal using condition of other electronic equipment, but also can cause more or less influence on the health of human bodies. Therefore, accurate measurement of the low frequency magnetic field is required.
At present, two common methods for measuring the low-frequency magnetic field are available: one method uses a combination of a magnetic field sensor and a voltmeter, such as a gauss meter, which uses the hall effect to convert a magnetic field into a voltage, either a direct current magnetic field or an alternating current magnetic field.
Another method uses a coil in combination with a spectrometer or receiver, which can efficiently obtain the spectrum of the magnetic field.
The main drawbacks of the two methods currently in use for low frequency magnetic field measurements are: the disadvantage of the gauss meter is that the measurement results are the superposition of magnetic fields of different frequencies and the spectrum of the magnetic field cannot be displayed. The disadvantage of this method is the high cost and difficulty in low frequency measurements using a coil in combination with a spectrometer or receiver.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a low-frequency magnetic field spectrum measuring method and system.
A low-frequency magnetic field spectrum measuring method comprises the following steps: the method comprises an experiment calibration and measurement step, a theoretical calculation simulation step and an actual measurement step.
The method comprises the following steps of: the method comprises the steps of generating periodic sinusoidal signals through a signal generator, amplifying signal current through a power amplifier, introducing the signal current into a standard coil to generate a standard magnetic field, measuring the magnetic field at the central point of the standard coil by using a measuring coil, and collecting and processing induced voltage waveform by using an oscilloscope to finally obtain an experimental result of the sensing coefficient frequency response curve of the measuring coil.
Theoretical calculation simulation: and comparing and analyzing the experimental result with a theoretical calculation result and a simulation result, and determining a final relation curve by adopting a segmented splicing mode.
And actual measurement: and obtaining a voltage frequency spectrum, and obtaining a magnetic field frequency spectrum through a relation curve.
A low-frequency magnetic field spectrum measurement system comprises a communication module, an acquisition module, a storage module and a fast Fourier transform module, wherein the communication module is connected with the acquisition module, the acquisition module is connected with the storage module and the fast Fourier transform module, the communication module comprises a communication function, a data connection of a PC system and an oscilloscope, a USB interface, a VISA driver and a write/output function of VISA, the acquisition module comprises signal acquisition, oscilloscope initialization and oscilloscope parameter setting, the storage module comprises a depth storage and data storage mode file naming format and writes data into an EXCEL file in a row mode, the time naming is used, the fast Fourier transform module comprises a signal analysis module, a high-level technology calculation language for acquiring a voltage spectrum and calling a program MATLAB for algorithm development, data visualization, data analysis and numerical calculation and a fast algorithm for realizing FFT discrete Fourier transform by commercial mathematical software in an interactive environment.
The communication module establishes data connection between the PC and the oscilloscope, the acquisition module realizes acquisition of waveform data, sets or inquires related parameters of the oscilloscope as required, including a trigger mode, a vertical resolution, a horizontal time base and an edge trigger level, realizes the functions of monitoring and reading signals of the digital oscilloscope by a system through an opening function and a reading function in a VISA library, sends related code instructions compiled by the PC to the digital oscilloscope by using a write-in function of the VISA, the digital oscilloscope completes setting commands of various parameters of the digital oscilloscope according to the instructions, the specific realization process of the parameter inquiry function of the oscilloscope is realized through the write-in function of the VISA, corresponding code instructions are sent to the oscilloscope by the PC, the oscilloscope performs corresponding operation after receiving the instructions, and finally, a return value is transmitted back to the PC through the read function of the VISA.
The invention has the advantages of low cost and capability of obtaining magnetic field frequency spectrum.
The invention provides a new testing method for calibrating the sensing coefficient of a coil, and the testing method is combined with theoretical calculation and simulation to realize the measurement of the frequency response curve of the sensing coefficient of the coil in a specified frequency range according to a segmented splicing mode.
The invention uses the oscilloscope to obtain the time domain waveform of the measured magnetic field and uses the upper computer and the fast Fourier transform to obtain the frequency spectrum.
Compared with a gauss meter, the system adopts the coil as the magnetic field sensor. The coil is a passive device, so that the system is more convenient in practical application, has a larger measurement range, and can calculate the frequency spectrum of the magnetic field through the obtained frequency response curve.
Compared with the mode of combining the frequency spectrograph or the receiver with the coil, the invention adopts a digital oscilloscope as a lower computer. Compared with a frequency spectrograph, the digital oscilloscope has low cost and strong waveform processing capacity, and can transform a signal from a time domain to a frequency domain through fast Fourier transform after the voltage waveform is acquired, so that the spectral characteristic of the signal is obtained.
Drawings
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein the accompanying drawings are included to provide a further understanding of the invention and form a part of this specification, and wherein the illustrated embodiments of the invention and the description thereof are intended to illustrate and not limit the invention, as illustrated in the accompanying drawings, in which:
FIG. 1 is a schematic diagram of the process and structure of the present invention.
FIG. 2 is a schematic diagram of a test arrangement for calibration of the sensor coefficients of the measurement system of the present invention.
FIG. 3 is a schematic view of the structural connection of the present invention.
Fig. 4 is a schematic diagram of a communication module according to the present invention.
The invention is further illustrated with reference to the following figures and examples.
Detailed Description
It will be apparent that those skilled in the art can make many modifications and variations based on the spirit of the present invention.
As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element, component or section is referred to as being "connected" to another element, component or section, it can be directly connected to the other element or section or intervening elements or sections may also be present. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art.
The following examples are further illustrative in combination for ease of understanding the embodiments and are not intended to limit the invention.
Example 1: as shown in fig. 1, fig. 2, fig. 3, and fig. 4, a low frequency magnetic field spectrum measurement method is mainly used for measuring a low frequency magnetic field in the industries of rail transit and the like. In the prior art, the price of the combination mode of the receiver, the frequency spectrograph and the coil is too high; the gauss meter cannot display the spectrum of the magnetic field. Therefore, the invention develops a low-frequency magnetic field spectrum measuring system, which has the characteristics of low cost and capability of obtaining a magnetic field spectrum.
The scheme design flow of the invention is shown in figure 1.
A low-frequency magnetic field spectrum measuring method comprises the following steps: the method comprises an experimental calibration and measurement step, a theoretical calculation simulation step and an actual measurement step, and is used for calibrating the coil sensing coefficient frequency response curve.
The method comprises the following steps of: the method comprises the steps of generating periodic sinusoidal signals through a signal generator, amplifying signal current through a power amplifier, introducing the signal current into a standard coil to generate a standard magnetic field, measuring the magnetic field at the central point of the standard coil by using a measuring coil, and collecting and processing induced voltage waveform by using an oscilloscope to finally obtain an experimental result of the sensing coefficient frequency response curve of the measuring coil.
The experimental calibration and measurement step comprises the following process of obtaining a frequency response curve of the sensing coefficient of the measurement coil through an experiment:
step 1, firstly, a signal generator generates a sinusoidal signal with single frequency, the signal current is amplified by a power amplifier, and the sinusoidal signal is connected into a standard coil to generate a standard magnetic field. The magnetic field at the center of the standard coil can be calculated according to the biot-savart law, namely:
wherein, mu 0 The magnetic field at the center of the standard coil is the vacuum magnetic conductivity, B is the magnetic field at the center of the standard coil, N is the number of turns of the standard coil, I is the current introduced into the standard coil, and R is the radius of the standard coil.
And 2, measuring the known magnetic field B at the center of the standard coil by using the measuring coil. Due to the electromagnetic induction, an induced voltage U can be generated in the measuring coil, and the induced voltage output by the measuring coil is measured by using an oscilloscope. And obtaining the sensing coefficient under the frequency through a coil sensing coefficient formula.
And 3, changing the frequency of the output signal of the signal generator, and repeating the step 1 and the step 1 to obtain the sensing coefficients of the measuring coil under different frequencies.
Theoretical calculation simulation step: and comparing and analyzing the experimental result with a theoretical calculation result and a simulation result, and determining a final relation curve by adopting a sectional splicing mode.
The theoretical calculation simulation step is mainly based on Faraday's law of electromagnetic induction, and combined with the simulation result, the obtained sensing coefficient frequency response curve is subjected to comprehensive comparative analysis,
in the experiment, the diameter of the standard coil is far larger than that of the measuring coil, so that the magnetic field inside the measuring coil can be approximated to the magnetic induction intensity value at the central point of the measuring coil for convenient calculation. The magnetic flux of the measuring coil is calculated as:
wherein, mu 0 The magnetic field at the center of the standard coil is the vacuum magnetic conductivity, B is the magnetic field at the center of the standard coil, S is the area of the measuring coil, N is the number of turns of the standard coil, and I is the input markThe current of the quasi-coil, R is the radius of the standard coil, and R is the radius of the measuring coil.
By combining Faraday's law of electromagnetic induction, the induced electromotive force at the two ends of the measuring coil can be obtained as follows:
where Φ is the magnetic flux through the measuring coil, μ 0 The magnetic field at the center of the standard coil, N, R, and I are vacuum permeability, B is the magnetic field at the center of the standard coil, N is the number of turns of the standard coil, N is the number of turns of the measurement coil, R is the radius of the standard coil, and R is the radius of the measurement coil A Omega is the angular velocity and t is the time for the amplitude of the alternating current to the standard coil.
And actual measurement: and obtaining a voltage frequency spectrum, and obtaining a magnetic field frequency spectrum through a relation curve.
Example 2: as shown in fig. 1, 2, 3, and 4, in the method for measuring the frequency spectrum of the low-frequency magnetic field, on the aspect of hardware model selection, a system determines that a PC is used as an upper computer, and for the selection of a lower computer, a digital oscilloscope is selected, and the oscilloscope can transform a signal from a time domain to a frequency domain by using fast fourier transform through the upper computer after collecting a voltage waveform to obtain the frequency spectrum characteristic of the signal.
For the selection of the magnetic field sensor, the system adopts a coil which is a passive device, so that the system is more convenient in practical application, and the coil has a larger measuring range.
Finally, the hardware composition of the system is determined by taking a PC as an upper computer, an oscilloscope as a lower computer and a coil as a magnetic field sensor.
A low-frequency magnetic field spectrum measuring method selects an object-oriented C # programming language, programs are written based on a Visual Studio 2015 platform, a PC (personal computer) is controlled to control an oscilloscope by writing the programs, and a complete human-computer interaction interface is provided for a user.
Example 3: as shown in fig. 1, fig. 2, fig. 3, and fig. 4, a low-frequency magnetic field spectrum measurement system includes a communication module, an acquisition module, a storage module, and a fast fourier transform module, where the communication module is connected to the acquisition module, and the acquisition module is connected to the storage module and the fast fourier transform module.
The communication module comprises a communication function, data connection between a PC system and the oscilloscope, a USB interface, a VISA driver and a VISA write/output function.
The acquisition module comprises signal acquisition, oscilloscope initialization and oscilloscope parameter setting.
The storage module comprises a deep storage mode, a data storage mode file naming format and a mode of writing data into an EXCEL file in a column mode for naming by time.
The fast Fourier transform module comprises a fast algorithm for realizing FFT DFT by using a high-level technology computing language for algorithm development, data visualization, data analysis and numerical computation and commercial mathematical software in an interactive environment, wherein the fast algorithm comprises signal analysis, voltage spectrum acquisition and program MATLAB calling.
The communication module establishes data connection between the PC and the oscilloscope.
The acquisition module realizes acquisition of waveform data, and sets or inquires relevant parameters of the oscilloscope according to requirements, wherein the relevant parameters comprise a triggering mode, a vertical resolution, a horizontal time base, an edge triggering level and the like.
The functions of monitoring and reading signals of the digital oscilloscope by the system can be realized through the opening and reading functions in the VISA library. By utilizing the write-in function of VISA, relevant code instructions written by the PC can be sent to the digital oscilloscope, and the digital oscilloscope can complete setting commands of various parameters of the digital oscilloscope according to the instructions.
The specific implementation process of the oscilloscope parameter query function is also realized through a VISA write-in function, the corresponding code instruction is sent to the oscilloscope by the PC, the oscilloscope performs corresponding operation after receiving the instruction, and finally, a return value is transmitted back to the PC through the VISA read-out function.
And the storage module is used for transmitting the read signals to the PC for storage.
The program of the reading flow of the waveform signal in the memory is as follows:
s1, setting an oscilloscope in a STOP mode;
s2, setting a channel source for reading waveform data as CH1;
s3, setting a waveform data reading mode to RAW;
s4, setting the return format of the waveform data as an ASCII code;
s5, setting the starting position of waveform data reading as a 1 st waveform point;
s6, setting the stop position of waveform data reading as a 15625 th waveform point;
and S7, acquiring data in the cache.
When the control program reads the waveform data in the memory, the maximum value of the number of the waveform points which can be read at a time is related to the currently selected waveform data. Since the waveform data is set to be returned in the form of ASCII code, the maximum number of waveform points that can be read at a time is 15625 as can be seen from the programming manual. In order to ensure the accuracy of waveform reading, the number of sampling points can be increased, and in the program, the purpose of changing the number of sampling points can be achieved by adjusting the horizontal time base. In addition, when the storage depth of the oscilloscope is less than or equal to the maximum value of the number of the current single-time readable waveform points, the memory waveform data can be ensured to be read at one time. When the storage depth of the oscilloscope is greater than the maximum value of the number of the current single-time readable waveform points, the waveform data of the memory needs to be read in batches, the waveform data of one area in the memory (the waveform data between two adjacent blocks is continuous) is read by designating a starting point and an ending point every time, and then the data read for multiple times are spliced in sequence.
The fast Fourier transform module realizes the conversion of the read voltage signal from a time domain waveform to a frequency domain.
In the design process, instructions related to FFT in a dynamic library are directly called for programming, most relevant codes in the C # object-oriented programming language are written by others, answer verification is lacked, and result accuracy cannot be guaranteed.
The experimental arrangement for the calibration of the sensor coefficients of the measurement system is shown in fig. 2.
The theoretical calculation is mainly based on Faraday's law of electromagnetic induction, and combined with the results obtained by simulation, comprehensive comparative analysis is performed on the frequency response curves of the sensing coefficients obtained by the three methods, and the final relation curve is determined by means of segmented splicing according to advantages and disadvantages of the three methods in different frequency bands.
As described above, although the embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that many modifications are possible without substantially departing from the spirit and scope of the present invention. Therefore, such modifications are also all included in the scope of protection of the present invention.
Claims (1)
1. A low-frequency magnetic field spectrum measuring method is characterized by comprising the following steps: an experiment calibration and measurement step, a theoretical calculation simulation step and an actual measurement step;
the method comprises the following steps of: generating periodic sinusoidal signals through a signal generator, amplifying signal current through a power amplifier, introducing the signal current into a standard coil to generate a standard magnetic field, measuring the magnetic field at the central point of the standard coil by using a measuring coil, and collecting and processing induced voltage waveforms by using an oscilloscope to finally obtain an experimental result of a sensing coefficient frequency response curve of the measuring coil;
theoretical calculation simulation: comparing and analyzing the experimental result with a theoretical calculation result and a simulation result, and determining a final relation curve by adopting a sectional splicing mode;
and (3) actual measurement: obtaining a voltage frequency spectrum, and obtaining a magnetic field frequency spectrum through a relation curve;
the experimental calibration and measurement step comprises the following process of obtaining a frequency response curve of the sensing coefficient of the measurement coil through an experiment:
step 1, firstly, generating a sinusoidal signal with single frequency by a signal generator, amplifying a signal current by a power amplifier, and connecting the sinusoidal signal into a standard coil to generate a standard magnetic field, wherein the magnetic field at the center of the standard coil is calculated according to the Biot-Saval law, namely:
wherein, mu 0 The magnetic field at the center of the standard coil is B, the number of turns of the standard coil is N, the current introduced into the standard coil is I, the radius of the standard coil is R,
step 2, measuring the known magnetic field B at the center of the standard coil by using the measuring coil, generating an induced voltage U in the measuring coil due to electromagnetic induction, measuring the induced voltage output by the measuring coil by using an oscilloscope, obtaining a sensing coefficient under the frequency by using a coil sensing coefficient formula,
step 3, changing the frequency of the output signal of the signal generator, and repeating the step 1 and the step 1 to obtain the sensing coefficients of the measuring coil under different frequencies;
the theoretical calculation simulation step is based on Faraday's law of electromagnetic induction, and the results obtained by simulation are combined to perform comprehensive comparative analysis on the obtained sensing coefficient frequency response curve,
approximating the magnetic field inside the measuring coil to the magnetic induction intensity value at the central point of the measuring coil, and calculating the magnetic flux of the measuring coil as follows:
wherein, mu 0 The magnetic field at the center of the standard coil is the vacuum magnetic conductivity, B is the magnetic field at the center of the standard coil, S is the area of the measuring coil, N is the number of turns of the standard coil, I is the current led into the standard coil, R is the radius of the standard coil, R is the radius of the measuring coil,
combining Faraday's law of electromagnetic induction, the magnitude of the induced electromotive force at the two ends of the measuring coil is obtained as follows:
where Φ is the magnetic flux through the measuring coil, μ 0 The magnetic field at the center of the standard coil, N, R, and I are vacuum permeability, B is the magnetic field at the center of the standard coil, N is the number of turns of the standard coil, N is the number of turns of the measurement coil, R is the radius of the standard coil, and R is the radius of the measurement coil A The amplitude of the alternating current to the standard coil is shown as ω is the angular velocity and t is the time.
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