CN112179259B - Method for eliminating interference magnetic field noise of eddy current displacement sensor - Google Patents
Method for eliminating interference magnetic field noise of eddy current displacement sensor Download PDFInfo
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Abstract
The invention relates to a method for eliminating interference magnetic field noise of an eddy current displacement sensor, which comprises the following steps: selecting a universal sensor probe, wherein the front end of the universal sensor probe is provided with a detection coil; selecting a general displacement measuring module, designing and manufacturing an interference magnetic field detection module andthe detection coil is respectively connected to the displacement measurement module and the interference magnetic field detection module through a coaxial cable and a cable interface, and output signals of the displacement measurement module and the interference magnetic field detection module are connected to the magnetic field noise elimination module; the output signal of the interference magnetic field detection module is an interference magnetic field signal Um(ii) a The output signal of the displacement measurement module comprises a displacement signal U to be measuredxAnd interfering magnetic field noise Nm(ii) a Output signal of magnetic field noise eliminating module for eliminating interference magnetic field noise NmTo-be-measured displacement signal Ux. The invention is suitable for various current eddy current displacement sensors, does not need to change a detection coil and a detection circuit, and has simple circuit, low cost and good universality.
Description
Technical Field
The invention relates to the technical field of eddy current displacement sensors, in particular to a method for eliminating interference magnetic field noise of an eddy current displacement sensor.
Background
With the continuous development of ultra-precise manufacturing technology, the precision measurement technology depended on by high-end manufacturing is still deficient, and the ultra-precise displacement sensor has more and more urgent requirements on the aspects of processing, assembly, detection and the like, and the measurement precision of some occasions is improved from the micro-nano level to the sub-nano level. The non-contact displacement sensor is the mainstream of displacement measurement for the current industry, and mainly comprises a capacitance type, an eddy current type and a photoelectric type, wherein the eddy current displacement sensor has the advantages of high sensitivity, good reliability, no influence of oil stains and the like, and has extremely wide application on an ultra-precise machine tool.
The main principle of the eddy current displacement sensor is electromagnetic induction, however, there are many interference magnetic field sources in the industrial field, and how to avoid the influence of the interference magnetic field is a key problem to be solved by the eddy current displacement sensor. At present, the eddy current displacement sensor mainly adopts an electromagnetic shielding measure to avoid the influence of external magnetic field interference, and patent applications CN104729544A, CN109668504A and the like also propose to improve the capacity of resisting the interference magnetic field by probe cancellation and circuit filtering. However, the existing method cannot completely eliminate the influence of the interference magnetic field, and the noise component related to the interference magnetic field remains in the output signal, which needs to be eliminated by other methods.
Disclosure of Invention
The invention aims to provide an interference magnetic field noise elimination method of an eddy current displacement sensor, which can eliminate residual interference magnetic field noise components in output signals on the basis of a general displacement measurement module by using the correlation between interference magnetic field signals and interference magnetic field noise obtained by an interference magnetic field detection module.
In order to achieve the purpose, the invention adopts the following technical scheme: a method for canceling interference magnetic field noise of an eddy current displacement sensor, the method comprising the sequential steps of:
(1) selecting a universal sensor probe, wherein the front end of the sensor probe is provided with a detection coil for measuring the distance x between the detection coil and a target conductor, and the detection coil is influenced by an interference magnetic field B in the surrounding environment;
(2) selecting a universal displacement measuring module, designing and manufacturing an interference magnetic field detection module and a magnetic field noise elimination module, respectively connecting a detection coil to the displacement measuring module and the interference magnetic field detection module sequentially through a coaxial cable and a cable interface, and connecting output signals of the displacement measuring module and the interference magnetic field detection module to the magnetic field noise elimination module;
(3) the output signal of the interference magnetic field detection module is an interference magnetic field signal Um(ii) a The output signal of the displacement measurement module comprises a displacement signal U to be measuredxAnd interfering magnetic field noise Nm；
(4) Interfering magnetic field noise NmAnd interference magnetic field signal UmThere is a correlation between them, and N is measured by using a magnetic field calibration systemmAnd UmThe frequency characteristic equation of (a) is as follows:
Nm＝H(s)·Um (1)
(5) the frequency characteristic parameter H(s) is stored in the magnetic field noise elimination module, so that the disturbing magnetic field signal U output by the disturbing magnetic field detection modulemConversion into disturbing magnetic field noise N by equation (1)mAnd is connected with the output signal U of the displacement measuring modulex+NmSubtracting, the output signal of the magnetic field noise eliminating module is the elimination of the interference magnetic field noise NmTo-be-measured displacement signal Ux。
The interference magnetic field detection module is an analog operation circuit composed of an isolation amplifier and a low-pass filter, the input end of the isolation amplifier is used as the input end of the interference magnetic field detection module and is connected with a cable interface, the output end of the isolation amplifier is connected with the input end of the low-pass filter, and the output end of the low-pass filter is used as the output end of the interference magnetic field detection module.
The magnetic field noise eliminating module is a digital operation circuit consisting of an analog-to-digital converter and a microprocessor, the analog-to-digital converter consists of a first analog-to-digital converter and a second analog-to-digital converter, the microprocessor comprises a frequency characteristic conversion module and a subtraction operation module, and the first analog-to-digital converter converts an interference magnetic field signal output by the interference magnetic field detection module into a digital signal UmThe second A/D converter converts the output signal of the displacement measuring module into digital signal Ux+Nm(ii) a The microprocessor stores frequency characteristic parameters H(s) obtained by measurement of the magnetic field calibration system, and utilizes the frequency characteristic conversion module to convert an interference magnetic field signal UmConversion into disturbing magnetic field noise NmThen, the output signal U of the subtraction module and the displacement measurement module is utilizedx+NmSubtracting, namely the microprocessor completes the following operation processes:
Ux+Nm-H(s)·Um＝Ux+Nm-Nm＝Ux (2)
the output signal of the magnetic field noise elimination module is the elimination of the interference magnetic field noise NmTo-be-measured displacement signal Ux。
The frequency characteristic parameter H(s) comprises amplitude-frequency characteristic A (omega) and phase-frequency characteristic
According to the technical scheme, the beneficial effects of the invention are as follows: firstly, the invention is suitable for various current eddy current displacement sensors, a detection coil and a detection circuit are not required to be changed, a magnetic field noise elimination module can be realized by adding a corresponding functional module on the existing microprocessor, a cable interface and an interference magnetic field detection module are analog circuits, and the circuit is simple, low in cost and good in universality; secondly, the invention adopts the digital circuit based on the analog-to-digital converter and the microprocessor to eliminate the noise of the interference magnetic field, avoids the problems of thermal noise, dynamic characteristics and the like brought by the limit design of an analog circuit, is suitable for eliminating the weak noise of the interference magnetic field in the output voltage of the existing eddy current displacement sensor, and can greatly improve the measurement precision of the existing eddy current displacement sensor in the environment of strong interference magnetic field.
Drawings
FIG. 1 is a schematic diagram of an interference magnetic field noise cancellation system according to the present invention;
FIG. 2 is a schematic view of a displacement measuring module based on amplitude modulation detection according to the present invention;
FIG. 3 is a diagram showing voltage signals at two ends of a detection coil under a magnetic field without interference according to the present invention;
FIG. 4 shows the output voltage noise of the displacement measuring module under the magnetic field without interference according to the present invention;
FIG. 5 is a graph of voltage signals across a detection coil in the presence of an interfering magnetic field according to the present invention;
FIG. 6 shows the output voltage noise of the displacement measurement module under the disturbing magnetic field according to the present invention;
FIG. 7 is a schematic diagram of an interference magnetic field detection module according to the present invention;
FIG. 8 is a graph of the output voltage of the disturbing magnetic field detecting module according to the present invention;
FIG. 9 is a schematic diagram of a magnetic field noise cancellation module according to the present invention;
FIG. 10 illustrates the output voltage noise of the magnetic field noise cancellation module of the present invention.
Detailed Description
A method for canceling interference magnetic field noise of an eddy current displacement sensor, the method comprising the sequential steps of:
(1) selecting a universal sensor probe 1, wherein the front end of the sensor probe 1 is provided with a detection coil 2 for measuring the distance x between the detection coil 2 and a target conductor 3, and the detection coil 2 is influenced by an interference magnetic field B in the surrounding environment;
(2) selecting a universal displacement measuring module, designing and manufacturing an interference magnetic field detection module and a magnetic field noise elimination module, respectively connecting a detection coil 2 to the displacement measuring module and the interference magnetic field detection module through a coaxial cable 4 and a cable interface in sequence, and connecting output signals of the displacement measuring module and the interference magnetic field detection module to the magnetic field noise elimination module;
(3) the output signal of the interference magnetic field detection module is an interference magnetic field signal Um(ii) a The output signal of the displacement measurement module comprises a displacement signal U to be measuredxAnd interfering magnetic field noise Nm；
(4) Interfering magnetic field noise NmAnd interference magnetic field signal UmThere is a correlation between them, and N is measured by using a magnetic field calibration systemmAnd UmThe frequency characteristic equation of (a) is as follows:
Nm＝H(s)·Um (1)
(5) the frequency characteristic parameter H(s) is stored in the magnetic field noise elimination module, so that the disturbing magnetic field signal U output by the disturbing magnetic field detection modulemConversion into disturbing magnetic field noise N by equation (1)mAnd is connected with the output signal U of the displacement measuring modulex+NmSubtracting, the output signal of the magnetic field noise eliminating module is the elimination of the interference magnetic field noise NmTo-be-measured displacement signal Ux。
The interference magnetic field detection module is an analog operation circuit composed of an isolation amplifier and a low-pass filter, the input end of the isolation amplifier is used as the input end of the interference magnetic field detection module and is connected with a cable interface, the output end of the isolation amplifier is connected with the input end of the low-pass filter, and the output end of the low-pass filter is used as the output end of the interference magnetic field detection module.
The magnetic field noise eliminating module is a digital operation circuit consisting of an analog-to-digital converter and a microprocessor, the analog-to-digital converter consists of a first analog-to-digital converter and a second analog-to-digital converter, the microprocessor comprises a frequency characteristic conversion module and a subtraction operation module, and the first analog-to-digital converter converts an interference magnetic field signal output by the interference magnetic field detection module into a digital signal UmThe second A/D converter converts the output signal of the displacement measuring module into digital signal Ux+Nm(ii) a The microprocessor stores frequency characteristic parameters H(s) obtained by measurement of the magnetic field calibration system, and utilizes the frequency characteristic conversion module to convert an interference magnetic field signal UmConversion into disturbing magnetic field noise NmThen, the output signal U of the subtraction module and the displacement measurement module is utilizedx+NmSubtracting, namely the microprocessor completes the following operation processes:
Ux+Nm-H(s)·Um＝Ux+Nm-Nm＝Ux (2)
the output signal of the magnetic field noise elimination module is the elimination of the interference magnetic field noise NmTo-be-measured displacement signal Ux。
The frequency characteristic parameter H(s) comprises amplitude-frequency characteristic A (omega) and phase-frequency characteristic
The present invention will be further described with reference to fig. 1 to 10.
When the eddy current displacement sensor is used, an interference magnetic field mainly comes from nearby power equipment, wires, cables and the like, the interference magnetic field is mainly distributed in a low-frequency range, namely between direct current and 100kHz, and a power frequency interference magnetic field (namely 50Hz and harmonic waves thereof) is the most main component; in environments exposed to the human body, the prescribed interfering magnetic field strength does not exceed 0.1mT, which may be higher inside the device. Based on the electromagnetic induction principle, an interference magnetic field B in the surrounding environment can couple voltage signals related to the interference magnetic field B at two ends of the detection coil 2;
the sensor probe 1 needs to be matched with a subsequent detection circuit (namely a displacement measurement module) to obtain a displacement signal U to be measuredxThe detection circuit of the eddy current displacement sensor commonly used includes a modulation and demodulation circuit based on the principles of a frequency modulation detection method, an amplitude modulation detection method, a phase modulation detection method, an alternating current bridge method and the like. No matter which eddy current displacement sensor detection circuit is adopted, the detection coil 2 is required to be connected with the detection circuit through the coaxial cable 4, high-frequency modulation voltage (generally more than 100kHz) is applied to the detection coil 22 and used for generating a high-frequency magnetic field, eddy current is formed on the surface of the target conductor 3 by the high-frequency magnetic field, the equivalent inductance of the detection coil 2 is changed, when the detection coil 2 approaches the target conductor 3 and enters a measurement range, the detection circuit demodulates the variation of the equivalent inductance, and therefore a displacement signal U to be detected is obtainedx。
As shown in fig. 2, the detection circuit based on amplitude modulation detection method is a general displacement measurement module, and mainly includes a high frequency signal source, an RLC circuit, a subsequent signal amplifier, a signal detector, and the like. The high-frequency signal source provides high-frequency modulation voltage with stable frequency and amplitude, and the output voltage U of the RLC circuit is related to the overall equivalent impedance of the LC resonance circuit. When the detection coil 2 is far away from the target conductor 3, the equivalent inductance L of the detection coil 2 and the capacitor C are in a resonance state, and the amplitude of the output voltage U of the RLC circuit is the largest; when the detection coil 2 approaches the target conductor 3, the equivalent inductance L of the detection coil 2 changes, which causes the equivalent impedance of the LC resonant tank to decrease and the output voltage U to decrease. The output voltage signal U of the RLC circuit converts the displacement into a displacement signal U to be detected through corresponding links such as amplification and detectionxThereby, the distance x between the detection coil 2 and the target conductor 3 can be accurately measured.
Under the environment without interference magnetic field, the voltage signals at the two ends of the detection coil 2 are high-frequency modulation voltage with the amplitude changing along with the displacement. If the distance x between the detection coil 2 and the target conductor 3 remains constant, the detection coil2, as shown in fig. 3, the frequency and amplitude of the voltage signal at the two ends are kept unchanged, the voltage signal is a high-frequency modulation voltage with the amplitude of 1V and the frequency of 100kHz, while the output voltage of the displacement measurement module is a direct-current voltage signal containing the noise of the circuit itself, as shown in fig. 4, the main component of the noise is randomly distributed thermal noise, and the noise level is about 6mVp-p。
Under the environment with the interference magnetic field, the voltage signal at the two ends of the detection coil 2 will superpose the interference magnetic field voltage related to the interference magnetic field on the basis of the high-frequency modulation voltage, as shown in fig. 5, superpose 2V on the basis of the high-frequency modulation voltage with the amplitude of 1V and the frequency of 100kHzp-pLow frequency (<1kHz) that will pass down with the subsequent detection circuit. The above-mentioned interference magnetic field voltage can be inhibited to a certain extent by adopting measures of electromagnetic shielding and circuit filtering, and as shown in fig. 6, the output voltage of the displacement measuring module is obtained by superposing interference magnetic field noise N related to the interference magnetic field on the basis of the self-noise of the circuitmNoise level from original 6mVp-pIncreased to 16mVp-pThe measurement accuracy of the eddy current displacement sensor is greatly affected.
As shown in fig. 7, an interference magnetic field detection module is designed and manufactured as an analog operation circuit composed of an isolation amplifier and a low-pass filter. A cable interface is arranged, the detection coil 2 is connected to the cable interface through a coaxial cable 4, and the cable interface respectively accesses signals into the displacement detection module and the interference magnetic field detection module. The interference magnetic field detection module is electrically isolated from the displacement measurement module through the isolation amplifier, so that the added interference magnetic field detection module has high input impedance and cannot influence the original displacement measurement module. The output of the isolation amplifier is connected to a low-pass filter, the voltage signal shown in FIG. 5 will filter out the high-frequency modulation voltage component, and the interference magnetic field signal U related to the interference magnetic field remainsmThe voltage waveform is shown in fig. 8, and the voltage is in the magnitude of volt.
Interfering magnetic field noise NmAnd interference magnetic field signal UmThere is a correlation between, NmAnd UmThe frequency characteristic equation of (a) is as follows:
Nm＝H(s)·Um (1)
h(s) is a frequency characteristic parameter including an amplitude-frequency characteristic A (omega) and a phase-frequency characteristic
Because the voltages at the two ends of the detection coil 2 respectively obtain the interference magnetic field noise N through the displacement amplification module and the magnetic field detection modulemAnd interference magnetic field signal UmIf the amplitude and phase of different frequency components passing through the two modules are different, the amplitude-frequency characteristic A (omega) and the phase-frequency characteristic
Is a function of frequency, and requires accurate acquisition of amplitude-frequency characteristic A (omega) and phase-frequency characteristic
Curve line.
A magnetic field calibration system, such as a magnetic field interference noise test system disclosed in CN111043946A, is adopted to measure and obtain amplitude-frequency characteristics A (omega) and phase-frequency characteristics
Curve line. The sensor probe 1 is placed in a standard magnetic field environment generated by an exciting coil, an interference magnetic field with single frequency omega 0 is applied, interference magnetic field noise Nm and interference magnetic field signals Um of a displacement amplification module and a magnetic field detection module are respectively recorded, and the amplitude relation A (omega 0) and the phase relation of two signals under the frequency omega 0 are obtained through a lock-in amplifier
By controlling frequency scanning and data calculation by a computer, the amplitude-frequency characteristic A (omega) and the phase-frequency characteristic in the frequency range of the interference magnetic field can be obtained
Curve line.
As shown in fig. 9, a magnetic field noise cancellation module is designed and manufactured as a digital operation circuit including an analog-to-digital converter and a microprocessor, where the analog-to-digital converter includes a first analog-to-digital converter and a second analog-to-digital converter, and the microprocessor includes a frequency characteristic conversion module and a subtraction operation module. The first analog-to-digital converter converts the interference magnetic field signal output by the interference magnetic field detection module into a digital signal Um, and the second analog-to-digital converter converts the output signal of the displacement measurement module into a digital signal Ux + Nm. The microprocessor stores frequency characteristic parameters H(s) obtained by measurement of the magnetic field calibration system, converts an interference magnetic field signal Um into interference magnetic field noise Nm by using the frequency characteristic conversion module, and subtracts the interference magnetic field noise Nm from an output signal Ux + Nm of the displacement measurement module by using the subtraction operation module, namely the microprocessor finishes the following operation process:
Ux+Nm-H(s)·Um＝Ux+Nm-Nm＝Ux (2)
the output signal of the magnetic field noise elimination module is the displacement signal Ux to be measured from which the interfering magnetic field noise Nm is eliminated. As shown in fig. 6 and 10, compared with the output voltage noise of the displacement measurement module (i.e. the existing sensor), the output voltage noise of the magnetic field noise elimination module (i.e. the sensor of the present application) is greatly suppressed, and the noise level is reduced from 16mVp-p to 8 mVp-p.
In summary, the invention is applicable to various current eddy current displacement sensors except for detection circuits based on amplitude modulation detection methods, the detection coil 2 and the detection circuits are not required to be changed, the magnetic field noise elimination module can be realized by adding corresponding functional modules on the existing microprocessor, and the cable interface and the interference magnetic field detection module are analog circuits, so that the circuit is simple, the cost is low, and the universality is good. The analog-to-digital converter is adopted to convert the analog signal into the digital signal, and the microprocessor is utilized to realize the frequency characteristic conversion and subtraction operation functions required by the elimination of the interference magnetic field noise, so that the problems of complex analog circuit design and thermal noise, dynamic characteristics and the like brought by limit design are avoided, the method is suitable for the elimination of weak interference magnetic field noise in the output voltage of the existing eddy current displacement sensor, and the measurement precision of the existing eddy current displacement sensor in the strong interference magnetic field environment can be greatly improved.
Claims (3)
1. A method for eliminating interference magnetic field noise of an eddy current displacement sensor is characterized by comprising the following steps: the method comprises the following steps in sequence:
(1) selecting a universal sensor probe, wherein the front end of the sensor probe is provided with a detection coil for measuring the distance x between the detection coil and a target conductor, and the detection coil is influenced by an interference magnetic field B in the surrounding environment;
(2) selecting a universal displacement measuring module, designing and manufacturing an interference magnetic field detection module and a magnetic field noise elimination module, respectively connecting a detection coil to the displacement measuring module and the interference magnetic field detection module sequentially through a coaxial cable and a cable interface, and connecting output signals of the displacement measuring module and the interference magnetic field detection module to the magnetic field noise elimination module;
(3) the output signal of the interference magnetic field detection module is an interference magnetic field signal Um(ii) a The output signal of the displacement measurement module comprises a displacement signal U to be measuredxAnd interfering magnetic field noise Nm；
(4) Interfering magnetic field noise NmAnd interference magnetic field signal UmThere is a correlation between them, and N is measured by using a magnetic field calibration systemmAnd UmThe frequency characteristic equation of (a) is as follows:
Nm＝H(s)·Um (1)
(5) the frequency characteristic parameter H(s) is stored in the magnetic field noise elimination module, so that the disturbing magnetic field signal U output by the disturbing magnetic field detection modulemConversion into disturbing magnetic field noise N by equation (1)mAnd is connected with the output signal U of the displacement measuring modulex+NmSubtracting, the output signal of the magnetic field noise eliminating module is the elimination of the interference magnetic field noise NmTo-be-measured displacement signal Ux；
The interference magnetic field detection module is an analog operation circuit composed of an isolation amplifier and a low-pass filter, the input end of the isolation amplifier is used as the input end of the interference magnetic field detection module and is connected with a cable interface, the output end of the isolation amplifier is connected with the input end of the low-pass filter, and the output end of the low-pass filter is used as the output end of the interference magnetic field detection module.
2. The method of claim 1, wherein the method comprises: the magnetic field noise eliminating module is a digital operation circuit consisting of an analog-to-digital converter and a microprocessor, the analog-to-digital converter consists of a first analog-to-digital converter and a second analog-to-digital converter, the microprocessor comprises a frequency characteristic conversion module and a subtraction operation module, and the first analog-to-digital converter converts an interference magnetic field signal output by the interference magnetic field detection module into a digital signal UmThe second A/D converter converts the output signal of the displacement measuring module into digital signal Ux+Nm(ii) a The microprocessor stores frequency characteristic parameters H(s) obtained by measurement of the magnetic field calibration system, and utilizes the frequency characteristic conversion module to convert an interference magnetic field signal UmConversion into disturbing magnetic field noise NmThen, the output signal U of the subtraction module and the displacement measurement module is utilizedx+NmSubtracting, namely the microprocessor completes the following operation processes:
Ux+Nm-H(s)·Um＝Ux+Nm-Nm＝Ux (2)
the output signal of the magnetic field noise elimination module is the elimination of the interference magnetic field noise NmTo-be-measured displacement signal Ux。
3. The method of claim 1, wherein the method comprises: the frequency characteristic parameter H(s) comprises amplitude-frequency characteristic A (omega) and phase-frequency characteristic
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