CN109668504B - Eddy current displacement sensing probe and bridge circuit suitable for strong electromagnetic field interference - Google Patents
Eddy current displacement sensing probe and bridge circuit suitable for strong electromagnetic field interference Download PDFInfo
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- CN109668504B CN109668504B CN201811248906.XA CN201811248906A CN109668504B CN 109668504 B CN109668504 B CN 109668504B CN 201811248906 A CN201811248906 A CN 201811248906A CN 109668504 B CN109668504 B CN 109668504B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
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Abstract
The invention discloses a current vortex displacement sensing probe suitable for strong electromagnetic field interference and a bridge circuit design, wherein the sensing probe is composed of a detection coil, a quartz gasket and a balance coil, the difference of the vertical distances between the detection coil and the balance coil and a target conductor is utilized to enable the sensitivity of the characteristic parameter change of the two coils to the distance change of the target conductor to form difference, the induced electromotive force formed on the two coils by the environment strong electromagnetic field interference is enabled to be close by utilizing the spatial position proximity of the detection coil and the balance coil, the bridge circuit is composed of an excitation signal source, a balance bridge, a high-pass filter and an instrument amplifier, the induced electromotive force formed by the environment strong electromagnetic field interference is counteracted by utilizing the balance bridge, and the difference of the induced electromotive forces on the two coils is further attenuated by utilizing the high-pass filter. The invention designs a traditional electromagnetic shielding mode, and is suitable for realizing high-resolution displacement and vibration measurement in strong electromagnetic field interference environments such as large motors, switching equipment and the like.
Description
Technical Field
The invention relates to the field of displacement and vibration measuring equipment, in particular to an eddy current displacement sensing probe and a bridge circuit suitable for strong electromagnetic field interference.
Background
With the development of ultra-precision machining and manufacturing technologies, the requirements on displacement sensors are higher and higher, the measurement accuracy is improved from micrometer level to nanometer level, and the non-contact sensor gradually becomes the main flow of industrial application. The non-contact displacement sensor mainly comprises a capacitance type, an induction type, an eddy current type and an optical displacement sensor, wherein the eddy current displacement sensor has the advantages of high sensitivity, good reliability, low cost and the like, and is widely applied to industrial fields of ultra-precision machining and manufacturing.
The basic principle of the eddy current displacement sensor is electromagnetic induction, and displacement measurement is realized by using the eddy current effect formed on the surface of a target conductor by a high-frequency electromagnetic field generated by a detection coil, so that strong electromagnetic field interference existing in large motors and switching equipment in industrial environment is also possibly coupled to the detection coil and influences displacement measurement. At present, the eddy current displacement sensor mainly adopts an electromagnetic shielding method in an industrial environment to avoid the influence of strong electromagnetic field interference, namely, a shell made of an electromagnetic shielding material is arranged outside a sensor probe. Electromagnetic fields of different frequency bands generally need shielding materials with different physical characteristics, a high-frequency electromagnetic field is shielded by adopting a metal material with low resistivity, a low-frequency electromagnetic field is shielded by adopting a magnetic conductive material with high magnetic permeability, and the thicker the shielding shell is, the more complex the structure is, the better the shielding effect on the external electromagnetic field is. In some cases, if the sensing probe is required to have good shielding effect on high-frequency and low-frequency electromagnetic fields in the environment, a multilayer shielding body made of different shielding materials is required, and meanwhile, certain requirements are also required on the connection mode between the shielding bodies.
The traditional electromagnetic shielding technology is complex in structure, the size and the weight of a sensing probe are greatly increased, and the sensitivity of the sensor can be seriously reduced due to the existence of a shielding layer, so that the installation space and the measurement precision are difficult to meet the actual application requirements of an industrial field. Therefore, the eddy current displacement sensor suitable for strong electromagnetic field interference is designed without the traditional shielding method, and the eddy current displacement sensor has important practical significance for improving the comprehensive application capability of the sensor in a complex environment.
Disclosure of Invention
The invention aims to provide an eddy current displacement sensing probe and an electric bridge circuit suitable for strong electromagnetic field interference, which are used for solving the problems of eliminating the strong electromagnetic field interference by adopting the traditional electromagnetic shielding technology and improving the comprehensive application capability of the eddy current displacement sensing probe in the complex industrial environment on the premise of not increasing the design complexity and the manufacturing cost of the sensing probe and the electric bridge circuit.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the utility model provides an electric eddy current displacement sensing probe suitable for strong electromagnetic field interference which characterized in that: the device comprises a detection coil, a balance coil, a quartz gasket, a quartz tube seat and a quartz thin tube, wherein the detection coil is arranged at the lower part of a target conductor in parallel, the balance coil is arranged at the lower part of the detection coil in parallel through the quartz gasket, the detection coil and the balance coil have the same winding direction, wire diameter and turns, outer ring leads of the detection coil and the balance coil are connected and led out through one lead in a shielded cable, and inner ring leads of the detection coil and the balance coil are respectively led out through the other two leads in the shielded cable; the vertical distance between the detection coil and the balance coil is 2-5 times of the vertical distance between the detection coil and the target conductor; the quartz tube seat is arranged at the lower part of the balance coil in parallel, the shielding cable is led out downwards through the inside of the quartz tube seat, the detection coil, the quartz gasket, the balance coil and the quartz tube seat are bonded through epoxy glue, and the sensing probe is formed by integrally packaging a quartz thin tube.
A bridge circuit formed by eddy current displacement sensing probes suitable for strong electromagnetic field interference is characterized in that: the device comprises an excitation signal source, a balance bridge, a high-pass filter and an instrument amplifier, wherein outer ring leads of a detection coil and an outer ring lead of a balance coil are connected with the excitation signal source, inner ring leads of the detection coil and the inner ring leads of the balance coil are respectively connected with a precision resistor and then grounded, and the detection coil, the balance coil and the two precision resistors form the balance bridge; two output ends of the balance bridge are respectively connected with two input ends of the instrument amplifier, a high-pass filter composed of a filter capacitor and a filter resistor is arranged between the two output ends of the balance bridge and the two input ends of the instrument amplifier, and the excitation signal source, the balance bridge, the high-pass filter and the instrument amplifier form a bridge circuit.
The working frequency of the excitation signal source is more than 10 times of the strong electromagnetic field interference frequency, and the cut-off frequency of the high-pass filter is 5-10 times of the strong electromagnetic field interference frequency.
In the invention, the vertical distance between the balance coil and the target conductor is several times larger than the vertical distance between the detection coil and the target conductor, so that the eddy current effect formed by the balance coil on the target conductor is far smaller than the eddy current effect formed by the detection coil on the target conductor, and the sensitivity of the characteristic parameter of the balance coil to the distance of the target conductor is basically negligible compared with the sensitivity of the characteristic parameter of the detection coil to the distance of the target conductor; the positions of the detection coil and the balance coil are only a small vertical distance, namely, electromagnetic parameters of environment strong electromagnetic field interference at the positions of the detection coil and the balance coil are very close to each other, induced electromotive force formed by the environment strong electromagnetic field interference on the detection coil and the balance coil is also very close to each other, and the electromagnetic parameters can be mutually offset through the balance bridge.
In the invention, the high-pass filter is arranged between the output end of the balance bridge and the input end of the instrument amplifier, so that the common-mode voltage formed by strong electromagnetic field interference on the two input ends of the instrument amplifier is greatly reduced, the performance requirement on the instrument amplifier is reduced, and the interference noise of the output signal of the instrument amplifier is further reduced.
According to the invention, the quartz material is adopted as the main body structure of the probe, the distribution of an electromagnetic field is not influenced, the thermal expansion coefficient is low, the detection coil and the balance coil form a differential bridge mode at the same time, and the temperature stability of displacement measurement is improved.
Compared with the prior art, the invention has the advantages that: the invention abandons the traditional electromagnetic shielding mode, does not increase the design complexity and the manufacturing cost of the sensing probe and the bridge circuit, has better inhibiting effect on the strong electromagnetic field interference in a wider frequency band range, uses the material with low thermal expansion coefficient and adopts the differential bridge to improve the temperature stability of displacement measurement.
Drawings
Fig. 1 is a schematic structural diagram of an eddy current displacement sensing probe according to the present invention.
FIG. 2 is a bridge circuit diagram of the sensor of the present invention.
FIG. 3 is a graph of normalized impedance versus perpendicular distance of a target conductor for a search coil in accordance with the present invention.
Fig. 4 is a graph of the voltage waveforms at the two outputs of the balanced bridge of the present invention.
FIG. 5 is a graph of the voltage waveforms at the two inputs of the amplifier for the instrument of the present invention.
Fig. 6 is an overall block diagram of the sensor measuring circuit of the present invention.
Detailed Description
As shown in fig. 1, an eddy current displacement sensing probe suitable for strong electromagnetic field interference comprises a detection coil 1, a balance coil 2, a quartz gasket 3, a quartz tube seat 6 and a quartz thin tube 7, wherein the detection coil 1 is arranged at the lower part of a target conductor 4 in parallel, the balance coil 2 is arranged at the lower part of the detection coil 1 in parallel through the quartz gasket 3, the detection coil 1 and the balance coil 2 have the same winding direction, wire diameter and turns, outer ring leads of the detection coil 1 and the balance coil 2 are connected and lead out a point a through one lead in a shielded cable 5, and inner ring leads of the detection coil 1 and the balance coil 2 lead out a point b and a point c through the other two leads in the shielded cable 5 respectively; the vertical distance between the detection coil 1 and the balance coil 2 is 2-5 times of the vertical distance between the detection coil 1 and the target conductor 4; the quartz tube seat 6 is arranged at the lower part of the balance coil 2 in parallel, the shielding cable 5 is led out downwards through the inner part of the quartz tube seat 6, the detection coil 1, the quartz gasket 3, the balance coil 2 and the quartz tube seat 6 are bonded through epoxy glue, and the sensing probe is formed by integrally packaging a quartz thin tube 7.
As shown in figure 2, the bridge circuit formed by the eddy current displacement sensing probe suitable for strong electromagnetic field interference comprises an excitation signal source 9, a balance bridge, a high-pass filter 10 and an instrument amplifier 11, wherein equivalent circuits of a detection coil 1 and a balance coil 2 are respectively formed by connecting a resistor R and an inductor L in series, outer ring leads of the detection coil 1 and the balance coil 2 are connected with the excitation signal source 9 through a point a, and inner ring leads of the detection coil 1 and the balance coil 2 are respectively connected with a precision resistor 8 (R) through a point b and a point cS) After connection, the detection coil 1, the balance coil 2 and the two precision resistors 8 are grounded to form a balance bridge; two output ends of a point b and a point c of the balance bridge are respectively connected with two input ends of a plus and a minus of the instrument amplifier 11,a filter capacitor C is arranged between two output ends of a point b and a point C of the balance bridge and two input ends of a plus and a minus of the instrument amplifier 11HAnd a filter resistor RHThe excitation signal source 9, the balance bridge, the high-pass filter 10 and the instrument amplifier 11 form a bridge circuit.
Operating frequency f of the excitation signal source 91For the highest frequency f of strong electromagnetic field interference2More than 10 times of the cut-off frequency f of the high-pass filter3For the highest frequency f of strong electromagnetic field interference 25 to 10 times of the total weight of the composition.
The specific working process and principle are as follows:
when the sensing probe works, the detection coil 1 approaches to the target conductor 4, an eddy current is formed on the target conductor 4, so that the characteristic parameters of the detection coil 1 are changed, fig. 3 is a relation diagram of the normalized impedance of the detection coil 1 and the vertical distance of the target conductor 4, and the resistance R and the inductance L of the detection coil 1 generate the variable quantities of delta R and delta L respectively relative to the infinite positions of the resistance R and the inductance L; the vertical distance between the balance coil 2 and the target conductor 4 is several times larger than the vertical distance between the detection coil 1 and the target conductor 4, so that the eddy current effect formed by the balance coil 2 on the target conductor 4 is much smaller than the eddy current effect formed by the detection coil 1 on the target conductor 4, and the sensitivity of the characteristic parameter of the balance coil 2 to the distance of the target conductor 4 is basically negligible compared with the sensitivity of the characteristic parameter of the detection coil 1 to the distance of the target conductor 4, namely the resistance R and the inductance L of the balance coil 2 are considered to be kept unchanged; the positions of the detection coil 1 and the balance coil 2 are only a small vertical distance, that is, electromagnetic parameters of the environmental strong electromagnetic field interference at the positions of the detection coil 1 and the balance coil 2 are very close, and the induced electromotive forces E and E' formed on the detection coil 1 and the balance coil 2 by the environmental strong electromagnetic field interference are also very close, and can be mutually cancelled by the balance bridge.
The voltage of the excitation signal source 9 is U, and the voltages of the two output ends of the point b and the point c of the balance bridge are respectively:
fig. 4 is a voltage waveform diagram of two output ends of a point b and a point c of the balanced bridge. A filter capacitor C is arranged between two output ends of a point b and a point C of the balance bridge and two input ends of a plus and a minus of the instrument amplifier 11HAnd a filter resistor RHThe high-pass filter 10 is formed to attenuate the strong electromagnetic field interference component in the output signal of the balance bridge to E ', and the voltages of two input ends of the instrument amplifier 11 ' + ', and ' - ' are respectively:
fig. 5 is a voltage waveform diagram of two input terminals of the instrument amplifier 11 "+", "-", which greatly reduces the common mode voltage caused by the interference of strong electromagnetic field, reduces the performance requirement of the instrument amplifier, and further reduces the interference noise of the output signal of the instrument amplifier. The balance bridge parameters are set to satisfy that delta R is less than R and delta L is less than L, and differential mode signals of two input ends of an amplifier 11 '+' and a '-' for the instrument are as follows:
the signal is related to only the resistance change amount Δ R and the inductance change amount Δ L of the detection coil 1, and the influence of the environmental strong electromagnetic field interference is suppressed to the maximum extent.
As shown in fig. 6, in the subsequent sensor measuring circuit, the phase sensitive detector 12 demodulates the output signal of the instrumentation amplifier 11 with the excitation signal source 9 as a reference signal, and the demodulated signal outputs a sensor final measuring signal through the low pass filter 13 and the signal amplifier 14.
Claims (2)
1. The utility model provides an electric eddy current displacement sensing probe suitable for strong electromagnetic field interference which characterized in that: the detection coil is arranged at the lower part of a target conductor in parallel, the balance coil is arranged at the lower part of the detection coil in parallel through the quartz gasket, the detection coil and the balance coil have the same winding direction, wire diameter and turns, outer ring leads of the detection coil and the balance coil are connected and led out through one lead in a shielded cable, and inner ring leads of the detection coil and the balance coil are led out through the other two leads in the shielded cable respectively; the vertical distance between the detection coil and the balance coil is 2-5 times of the vertical distance between the detection coil and the target conductor; the quartz tube seat is arranged at the lower part of the balance coil in parallel, the shielding cable is led out downwards through the inside of the quartz tube seat, and the detection coil, the quartz gasket, the balance coil and the quartz tube seat are bonded through epoxy glue and are integrally packaged through a quartz thin tube to form the sensing probe;
the device comprises an excitation signal source, a balance bridge, a high-pass filter and an instrument amplifier, wherein outer ring leads of a detection coil and a balance coil are connected with the excitation signal source, inner ring leads of the detection coil and the balance coil are respectively connected with a precise resistor and then grounded, and the detection coil, the balance coil and the two precise resistors form the balance bridge; two output ends of the balance bridge are respectively connected with two input ends of the instrument amplifier, a high-pass filter composed of a filter capacitor and a filter resistor is arranged between the two output ends of the balance bridge and the two input ends of the instrument amplifier, and the excitation signal source, the balance bridge, the high-pass filter and the instrument amplifier form a bridge circuit.
2. The bridge circuit formed by the eddy current displacement sensing probe suitable for strong electromagnetic field interference according to claim 1, wherein: the working frequency of the excitation signal source is more than 10 times of the strong electromagnetic field interference frequency, and the cut-off frequency of the high-pass filter is 5-10 times of the strong electromagnetic field interference frequency.
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| CN110133318A (en) * | 2019-06-06 | 2019-08-16 | 哈尔滨工程大学 | Superhigh temperature current vortex sensor |
| CN111043946B (en) * | 2020-01-09 | 2021-05-28 | 合肥工业大学 | Magnetic field interference noise test system for eddy current displacement sensor |
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