CN111913138A - Research on sensor amplifying circuit for detecting magnetic field of power equipment - Google Patents
Research on sensor amplifying circuit for detecting magnetic field of power equipment Download PDFInfo
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- 238000005259 measurement Methods 0.000 claims abstract description 6
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
- G01R1/30—Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/58—Testing of lines, cables or conductors
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
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Abstract
The invention designs an amplifying circuit based on magnetic flux negative feedback by using Multisim circuit simulation software, analyzes an amplitude-frequency characteristic curve and a phase-frequency characteristic curve of the amplifying circuit, and verifies the reliability of the amplifying circuit. The research result can be used for amplifying the induction voltage at two ends of the induction coil of the magnetic field sensor, widens the measurement frequency of the sensor, improves the sensitivity of the magnetic field sensor, and has great significance for maintaining the stable operation of the power cable, keeping the on-line detection of the cable and maintaining the safe and stable operation of the power grid in China.
Description
Technical Field
The invention relates to a design of a magnetic field sensor amplifying circuit based on Faraday's law of electromagnetic induction, wherein an amplifying circuit based on magnetic flux negative feedback is provided.
Background
The power cable has the characteristics of stable transmission performance, good insulating performance, high temperature resistance, convenience in laying, simplicity in operation and maintenance and the like, and is widely applied to a power grid. Overhead lines and oiled paper insulated cables are gradually replaced in urban power grid construction. In order to detect the operating state of the cable on line, a magnetic field sensor based on the law of electromagnetic induction is proposed. The power cable generates a weak magnetic field in the surroundings, and the alternating magnetic field passes through the magnetic core to generate a weak induced voltage in the induction coil, so that the output voltage is also weak. In order to enable the induced voltage to be collected by data or enable the sensor to have good compatibility with other electronic equipment, an amplifying circuit needs to be designed to amplify the induced signal.
At present, scholars at home and abroad have a lot of researches on the amplifying circuit and obtain a lot of stage achievements. There are many kinds of compensation circuits for the amplitude-frequency characteristic. The circuit form of the proportional amplifying circuit is simple, the frequency band of the sensor is applied to one side lower than the resonant frequency of the sensor, but the dynamic range of the output voltage of the amplifier is larger when the frequency reaches hundreds of hertz. The integral amplifier circuit also has an advantage of simple circuit form, but also has a problem that the application frequency band is lower than the resonance frequency. Besides using a compensation circuit, the amplitude-frequency characteristic at the resonance point can be improved by connecting matching resistors in parallel at two ends of the coil, so that the detection range of the frequency is increased, but the resistance thermal noise of the coil is increased, the output gain of high and low frequencies is reduced, and the improvement of the amplitude-frequency characteristic is limited. Therefore, it is very important for the detection of the magnetic field of the cable to design an amplifying circuit which can widen the measuring frequency range and has smooth amplitude-frequency characteristic curve and phase-frequency characteristic curve.
Disclosure of Invention
The invention aims to establish a model of an amplifying circuit through Multisim, briefly describe the working principle of the magnetic feedback amplifying circuit through formula derivation, and design the structure of the amplifying circuit from the aspects of reducing circuit noise and the like. The amplitude-frequency characteristic and the phase-frequency characteristic of the amplifying circuit are detected, and the amplifying circuit is verified by examples. The research result can be used for amplifying the induction voltage at two ends of the induction coil of the magnetic field sensor, the measurement accuracy of the magnetic field sensor is improved, convenience is provided for people to analyze the induction voltage, and the method has important significance for online detection of power cables and maintenance of safe electricity utilization of people.
In order to achieve the above purpose, the present invention adopts the following technical solution for research of a sensor amplification circuit for magnetic field detection of power equipment, and is characterized by comprising the following specific steps:
1. principle analysis of the magnetic flux negative feedback amplifying circuit:
the basic principle of improving the amplitude-frequency characteristic curve by magnetic feedback is as follows: the induction coil generates induction voltage in the alternating magnetic field and then amplifies the induction voltage through the amplifier, the amplified induction voltage is converted into a current signal through the feedback resistor, and the current signal generates a magnetic field in the feedback coil, wherein the direction of the magnetic field is opposite to that of the detected magnetic field, so that magnetic flux negative feedback is formed. When the magnetic field is near the resonant frequency and outputs larger voltage amplitude, the magnetic flux negative feedback weakens the magnetic field passing through the induction coil, reduces the induction voltage, and thus achieves the purpose of smoothing the amplitude-frequency characteristic curve. The principle of the flux negative feedback circuit is shown in fig. 1.
After the feedback coil is added, the magnetic induction through the induction coil should be B ═ Bj-Bf(BjFor the magnetic induction of the measured field, BfFor the magnetic induction produced by the feedback coil), the input voltage across the amplifier should be:
wherein: n is the number of turns of the induction coil, S is the cross-sectional area of the induction coil, RLIs the direct current resistance of the induction coil, C is the distributed capacitance of the induction coil, and Lp is the inductance of the induction coil.
Input voltage UiAfter the amplification of the amplifier by G times, the obtained output voltage is as follows:
Uo＝-GUi (2)
feedback resistor RfVoltage U to be output from amplifieroIs converted into a feedback current If＝Uo/RfThen, feedback magnetic induction B is generated in a feedback coilf. The number of turns of the feedback coil is NfAnd the width of the coil is d, the formula of the feedback magnetic induction intensity is as follows:
the output voltage U can be obtained by simultaneous equations (1), (2) and (3)oThe formula of (1) is:
output voltage UoWith the magnetic induction intensity B of the measured magnetic fieldjThe transfer function of (a) is:
the amplitude-frequency characteristics obtained from this are:
the phase frequency characteristics are:
2. the structure design of the amplifying circuit:
because the voltage signal that induction coil output is very little, so need amplify voltage signal through the amplifier of sufficient multiple, convenient collection. After the amplification factor is set, in order to improve the performance of the amplification circuit, the noise of the circuit is considered when the structure of the amplification circuit is designed, and the signal-to-noise ratio and the measurement accuracy of the amplification circuit are improved.
In order to screen the output signal and reduce the noise interference of high and low frequencies, a high pass filter and a low pass filter are required to be designed, so that the frequency of the output signal is in the range of 10 Hz-500 Hz. In order to obtain a sufficiently large amplification factor and simultaneously ensure that the circuit has a high signal-to-noise ratio, the following method can be adopted in the amplification link of the circuit: the integrated operational amplifier is used for realizing multi-stage amplification, and the amplification times of each stage are relatively balanced; the main amplification factor of the multi-stage amplification should be designed in the pre-amplification stage, because the common mode rejection ratio, the input impedance and the noise depend on the pre-amplification. The schematic structure of the amplifying circuit is shown in fig. 2.
The invention designs an amplifying circuit based on magnetic flux negative feedback, which has important significance on the stability and reliability of power cable measurement, and has the specific beneficial effects that:
1. the target performance of the amplifying circuit is determined according to the application environment of the inductive magnetic sensor. And designing resistance parameters of the two amplifiers according to the target amplification factor, designing resistance-capacitance parameters of the band-pass filter according to the target frequency measurement range, and setting a voltage follower in the circuit according to the requirement of reducing circuit noise. And measuring the amplitude-frequency characteristic and the phase-frequency characteristic of the amplifying circuit by using simulation software. Simulation results show that the amplitude-frequency characteristic and the phase-frequency characteristic curve of the magnetic flux negative feedback amplifying circuit are smoother in a measuring range, and the design requirements are met.
2. The voltage at the two ends of the induction coil is brought into the amplifying circuit, and the output voltage of the amplifying circuit is tested, so that the reliability of the amplifying circuit is proved. The discharge circuit can be used for a signal post-processing module of the magnetic field sensor, is used for on-line detection and fault analysis of the power cable, reduces cable accidents, provides support for mastering the operation condition of the cable in real time, and has important significance for maintaining the safe operation of a power grid.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a schematic diagram of a flux degeneration circuit;
FIG. 2 is a schematic block diagram of an amplifying circuit;
FIG. 3 is an enlarged circuit diagram;
FIG. 4 is a graph showing the amplitude-frequency characteristic curve and the phase-frequency characteristic curve of the amplifying circuit;
FIG. 5 is a graph of the voltage waveform across the induction coil at 50 Hz;
fig. 6 is a graph of the output voltage waveform of the amplifier circuit.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
1. Description of the amplifying circuit:
fig. 3 is an amplifying circuit diagram drawn in Multisim. In view of the simulated coil induced voltage of 10-1V order of magnitude, the amplification factor G of the amplification circuit is designed to be 33, the amplification is realized by a preposed amplification link and a secondary amplification link, and the two amplification links adopt cophase proportional amplifiers. The pre-amplification factor is set to 11, the pre-amplification is realized by a pre-amplifier, and the amplification factor of a secondary amplifier is 3.
A total of three voltage followers are used in the whole amplifying circuit. The first is a voltage follower between a high-pass filter and a second-stage amplifier, the third voltage follower is arranged behind the low-pass filter, the two voltage followers are used as buffer stages, consumption of signals on the output impedance of the previous stage is reduced when the input impedance of the next stage is low, and the output capacity of the circuit to the signals is improved. The second voltage follower is arranged in a negative feedback branch circuit led out from a node of the output end of the first voltage follower before the feedback voltage is transmitted to the feedback resistor, so that the noise generated by the feedback coil is prevented from entering secondary amplification, and the resolution of the sensor is improved.
The sensor is designed to measure magnetic fields of 10Hz to 500Hz, requiring the same circuit amplification in this frequency range. The resistance of the high-pass filter is set to be 30k omega, the capacitance is 10 muF, and the obtained cut-off frequency is 0.53 Hz; the resistance of the low-pass filter was 3k Ω, the capacitance was 0.01 μ F, and the obtained cutoff frequency was 5305.16 Hz. The amplification factor of the amplification circuit is 32.95 at 10Hz, the amplification factor is 32.85 at 500Hz, the amplification factors are 32.85-32.99, and the amplitude-frequency characteristic is flat. The amplitude-frequency characteristic and the phase-frequency characteristic of the amplifier circuit are shown in fig. 4.
2. Verification of the amplifying circuit:
fig. 5 is a waveform diagram of an induced voltage obtained by COMSOL simulation, and an output waveform of a voltage source of a second-order circuit of a Multisim induction coil is set to a sine wave with a peak value of 0.26V and a frequency of 50 Hz. The output voltage at the output of the amplifier circuit was measured using an oscilloscope element in Multisim to obtain an output voltage waveform, as shown in fig. 6.
The peak value of the output voltage read from the oscilloscope is 8.435V, the amplification factor is 32.44, and the design requirements are basically met. By varying the frequency of the voltage source, the resulting output voltages at 10Hz and 500Hz were 8.681V and 8.453V, respectively, with amplification factors of 33.39 and 32.51, respectively. The reliability of the amplifier circuit design can be verified by the test data and the smoothness of the output voltage waveform.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (2)
1. The research of the sensor amplifying circuit for detecting the magnetic field of the power equipment is characterized by comprising the following specific steps:
1) the principle of the magnetic flux negative feedback amplifying circuit is analyzed, and the basic principle of improving the amplitude-frequency characteristic curve by magnetic feedback is as follows: the induction coil generates induction voltage in the alternating magnetic field and then amplifies the induction voltage through the amplifier, the amplified induction voltage is converted into a current signal through the feedback resistor, and the current signal generates a magnetic field in the feedback coil, wherein the direction of the magnetic field is opposite to that of the detected magnetic field, so that magnetic flux negative feedback is formed. When the magnetic field is near the resonant frequency and outputs larger voltage amplitude, the magnetic flux negative feedback weakens the magnetic field passing through the induction coil, reduces the induction voltage, and thus achieves the purpose of smoothing the amplitude-frequency characteristic curve. Mathematical expressions of a transfer function, an amplitude-frequency characteristic, and a phase-frequency characteristic of an amplifying circuit of a magnetic flux negative feedback are described.
2) Because the voltage signal that induction coil output is very little, so need amplify voltage signal through the amplifier of sufficient multiple, convenient collection. After the amplification factor is set, in order to improve the performance of the amplification circuit, the noise of the circuit is considered when the structure of the amplification circuit is designed, and the signal-to-noise ratio and the measurement accuracy of the amplification circuit are improved.
In order to screen the output signal and reduce the noise interference of high and low frequencies, a high pass filter and a low pass filter are required to be designed, so that the frequency of the output signal is in the range of 10 Hz-500 Hz. In order to obtain a sufficiently large amplification factor and simultaneously ensure that the circuit has a high signal-to-noise ratio, the following method can be adopted in the amplification link of the circuit: the integrated operational amplifier is used for realizing multi-stage amplification, and the amplification times of each stage are relatively balanced; the main amplification factor of the multi-stage amplification should be designed in the pre-amplification stage, because the common mode rejection ratio, the input impedance and the noise depend on the pre-amplification.
2. The research of a sensor amplifying circuit for detecting the magnetic field of power equipment is mainly characterized in that:
1) a total of three voltage followers are used in the whole amplifying circuit. The first is a voltage follower between a high-pass filter and a second-stage amplifier, the third voltage follower is arranged behind the low-pass filter, the two voltage followers are used as buffer stages, consumption of signals on the output impedance of the previous stage is reduced when the input impedance of the next stage is low, and the output capacity of the circuit to the signals is improved. The second voltage follower is arranged in a negative feedback branch circuit led out from a node of the output end of the first voltage follower before the feedback voltage is transmitted to the feedback resistor, so that the noise generated by the feedback coil is prevented from entering secondary amplification, and the resolution of the sensor is improved.
2) The peak value of the output voltage read from the oscilloscope is 8.435V, the amplification factor is 32.44, and the design requirements are basically met. By varying the frequency of the voltage source, the resulting output voltages at 10Hz and 500Hz were 8.681V and 8.453V, respectively, with amplification factors of 33.39 and 32.51, respectively. The reliability of the amplifier circuit design can be verified by the test data and the smoothness of the output voltage waveform.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101807893A (en) * | 2010-04-14 | 2010-08-18 | 天津大学 | Large-bandwidth continuous time common-mode feedback circuit and design method thereof |
| CN202171648U (en) * | 2011-07-29 | 2012-03-21 | 中国地震局地球物理研究所 | Low noise induction type magnetic sensor |
| CN104748762A (en) * | 2015-03-13 | 2015-07-01 | 西北工业大学 | Designing and manufacturing method of high-performance geomagnetic field simulation device |
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- 2020-08-06 CN CN202010780523.8A patent/CN111913138A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101807893A (en) * | 2010-04-14 | 2010-08-18 | 天津大学 | Large-bandwidth continuous time common-mode feedback circuit and design method thereof |
| CN202171648U (en) * | 2011-07-29 | 2012-03-21 | 中国地震局地球物理研究所 | Low noise induction type magnetic sensor |
| CN104748762A (en) * | 2015-03-13 | 2015-07-01 | 西北工业大学 | Designing and manufacturing method of high-performance geomagnetic field simulation device |
Non-Patent Citations (1)
| Title |
|---|
| 张飞: "宽频带感应式磁传感器放大技术研究", 《中国优秀硕士学位论文全文数据库信息科技辑》 * |
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