Digital signal processing circuit and method and eddy current displacement sensor device

Abstract

The invention relates to the technical field of eddy current sensors, and provides a digital signal processing circuit and method, an eddy current displacement sensor device and a device for reducing temperature drift of a differential eddy current sensor in a wide temperature range by adopting the signal processing method. Specifically, temperature drifts of measured metal, coils and cables in the system are counteracted through the design of a differential probe, a traditional amplitude demodulation method is replaced with a symmetric high-speed analog-digital sampling circuit and a dual-correlation demodulation algorithm, digital demodulation is carried out on signals output by a displacement sensor, and noise is reduced. The influence of the temperature characteristic of an analog device on a demodulation result is avoided, the temperature stability of the eddy current sensor can be greatly improved, and the temperature drift of the eddy current sensor is effectively inhibited.

Description

Technical Field

[0001] The present invention belongs to the technical field of eddy current sensors, and particularly relates to a digital signal processing circuit, a digital signal processing method, and an eddy current displacement sensor device including the digital signal processing circuit. Background Art

[0002] Eddy current sensors are one type of non-contact sensors. When a high-frequency alternating current signal flows through the coil of the sensor, an alternating magnetic field will be generated around the coil. Eddy currents are generated in the nearby conductor by the alternating magnetic field, and it generates another magnetic field in the direction opposite to the coil. The interaction between the magnetic field of the coil and the eddy current changes the AC impedance of the sensor coil. The distance between the detector coil and the measured metal is proportional to the coupling strength of the magnetic field. Therefore, the displacement of the target conductor can be obtained by measuring the AC impedance.

[0003] However, the disadvantage of eddy current sensors is the large temperature drift. This is because an eddy current sensor is essentially an impedance measurement circuit, and the impedance and resistivity of the sensor coil and the measured metal will change with temperature, thus affecting the measurement. The probe coil of an eddy current sensor is generally wound with enameled wires of metals with high conductivity such as copper and silver. However, while these two metals have high conductivity, they also have a high temperature drift coefficient, and the error caused by this temperature drift cannot be eliminated from the production of the sensor coil. The resistivity of the measured metal will increase with the increase of temperature, and the resistivity will affect the coupling strength, thus affecting the output strength of the detector signal. This temperature drift is also a principle error and cannot be completely eliminated. The same is true for the cable impedance drift. Finally, in the signal processing circuit, the change of temperature will cause the parameter change of semiconductor devices, resulting in zero drift and temperature drift of the amplifier, thus affecting the output of the sensor.

[0004] Generally, two methods are adopted to overcome the temperature drift of eddy current sensors. The first method is the data processing method, that is, using prior knowledge and algorithms to post-calibrate the output data of the sensor to improve its accuracy. For example, the temperature compensation method based on the binary regression method, the external compensation method using mathematical fitting to achieve temperature drift compensation, etc. The second method is to add a self-compensation module in the design of the eddy current sensor and use circuit design to achieve temperature compensation. For example, the method of using a wireless coil to compensate for temperature drift, the method of self-calibration combined with a bridge circuit, the method of designing a mechanical mechanism and a compensation circuit to reduce temperature drift, the temperature compensation displacement sensor based on a constant current circuit and a temperature coefficient parameter method, etc. However, these methods ignore the influence of the temperature drift of devices in the analog processing circuit on the system output, and the temperature characteristics of each electronic component in the demodulation circuit have not been fully analyzed and compensated. Summary of the Invention

[0005] In view of this, the present invention provides a digital signal processing circuit, a digital signal processing method, and an eddy current displacement sensor device using such a digital signal processing circuit and processing method, which is suitable for reducing the temperature drift of a sensor in a wide temperature environment, significantly improving the temperature stability of the eddy current displacement sensor, and effectively suppressing the temperature drift of the eddy current sensor.

[0006] To achieve the above object, the technical solution of the present invention is realized as follows: The present invention provides a digital signal processing circuit, which includes a demodulation circuit, an FPGA processor, and a processing computer; The demodulation circuit includes a crystal oscillator, a frequency division circuit, a resonant network, an emitter follower circuit, a differential amplifier circuit, and a high-speed digital sampling circuit; The crystal oscillator outputs a driving signal, and after the driving signal is input to the frequency division circuit to change the frequency, it is divided into a first path signal and a second path signal; The first path signal enters the resonant network to drive the displacement signal; the second path signal is input to the FPGA processor as a trigger signal; After the displacement signal is input to the resonant network, it is amplified by the emitter follower circuit to form a first emitter follower circuit and a second emitter follower circuit; the first emitter follower circuit and the second emitter follower circuit are subtracted by the subtractor to obtain a differential mode signal; the differential mode signal is input to the high-speed digital sampling circuit after passing through the differential amplifier circuit to realize digital acquisition; The input signal after digital acquisition enters the FPGA processor; the FPGA processor and the processing computer are used to run a double-correlation demodulation algorithm to process the input signal.

[0007] Furthermore, the crystal oscillator is a temperature-compensated crystal oscillator, and the temperature-compensated crystal oscillator outputs a driving signal of 500 kHz.

[0008] The present invention also provides a digital signal processing method, which is realized by the digital signal processing circuit of the present invention.

[0009] The present invention also provides an eddy current displacement sensor device, which includes a laser collimator, a differential sensing system, a one-dimensional linear displacement platform, and a digital signal processing circuit; the digital signal processing circuit is the above digital signal processing circuit; The one-dimensional linear displacement platform is fixedly connected to the object to be measured, and when the one-dimensional linear displacement platform moves, it drives the object to be measured to move; The laser collimator is used to adjust the position between the object to be measured and the differential sensing system; The differential sensing system is used to generate a displacement signal when the object to be measured is moved; The differential sensing system includes a first coil sensor probe and a second coil sensor probe; the first coil sensor probe and the second coil sensor probe are the same; The first coil sensor probe and the second coil sensor probe are respectively located on both sides of the object to be measured; the first coil sensor probe is fixed by a first probe fixing device, and the second coil sensor probe is fixed by a second probe fixing device; The first displacement signal generated by the first coil sensor probe, after being input into the resonant network and passing through the emitter follower circuit, forms the first emitter follower circuit; the second displacement signal generated by the second coil sensor probe, after being input into the resonant network and passing through the emitter follower circuit, forms the second emitter follower circuit.

[0010] Further, the input signal is: ; Wherein, is the signal to be demodulated, is the noise signal; The FPGA processor generates two reference signals with the same frequency, and the reference signals include a sine signal and a cosine signal; the reference signals are: .

[0011] Further, the process of the FPGA processor and the processing computer running the double-correlation demodulation algorithm includes: If the signal to be demodulated has a correlation with the reference signal, and the reference signal has no correlation with the noise signal, then the cross-correlation function of the eddy current displacement sensor device is: ; Wherein, is the product of the signal to be demodulated and the reference signal, is the product of the noise signal and the reference signal.

[0012] Further, if the signal to be demodulated has a correlation with the reference signal, and the reference signal has no correlation with the noise signal, and the noise of the eddy current displacement sensor device is Gaussian white noise conforming to a normal distribution; then the cross-correlation function of the eddy current displacement sensor device is: .

[0013] Further, when the reference signals are a sine signal and a cosine signal with the same frequency as the signal to be demodulated respectively, the output expression of the amplitude of the signal to be demodulated is: ; wherein, and are the amplitude of the signal to be demodulated and the amplitude of the reference signal respectively; is the phase difference between the signal to be demodulated and the reference signal.

[0014] Further, the discrete expression of the signal to be demodulated is: ; The discrete expression of the reference signal being a sine signal is: ; The discrete expression of the reference signal being a cosine signal is: ; wherein, is the number of sampling points per period, is a constant; The cross-correlation function between the signal to be demodulated and the sine signal is: ; The cross-correlation function between the signal to be demodulated and the cosine signal is: ; wherein, is the amplitude of the signal to be demodulated, is the amplitude of the sine signal, is the amplitude of the cosine signal.

[0015] Further, the output expression of the amplitude after demodulating the signal to be demodulated is: ; wherein, is the amplitude of the reference signal, is the cross-correlation function between the signal to be demodulated and the sine signal; is the cross-correlation function between the signal to be demodulated and the cosine signal.

[0016] Compared with the prior art, the present invention can achieve the following beneficial effects: The present invention provides a novel-structured digital signal processing circuit, a digital signal processing method, and a device for reducing the temperature drift of a differential eddy current sensor in a wide temperature range using the signal processing method of the present invention. Specifically, the design of a differential probe is utilized to cancel the temperature drift of the measured metal, coil, and cable in the system, and a symmetric high-speed analog-to-digital sampling circuit and a double-correlation demodulation algorithm are used to replace the traditional amplitude demodulation method to digitally demodulate the signal output by the displacement sensor and reduce noise, avoiding the influence of the temperature characteristics of analog devices on the demodulation result, which can greatly improve the temperature stability of the eddy current sensor and effectively suppress the temperature drift of the eddy current sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 is a schematic structural diagram of the differential sensing system described in the embodiment of the present invention; Figure 2 is a schematic structural diagram of the eddy current displacement sensor device described in the embodiment of the present invention; Figure 3 is a schematic structural diagram of the digital signal processing circuit framework described in the embodiment of the present invention.

[0018] Description of the reference numerals: 1. First coil sensor probe; 2. Measured object; 3. Second coil sensor probe; 4. First probe fixing device; 5. Second probe fixing device; 6. Laser collimator; 7. One-dimensional linear displacement platform; 8. Demodulation circuit; 9. FPGA processor; 10. Processing computer; 11. Processing platform. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following further details the present invention in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation on the present invention.

[0020] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0021] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0022] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0023] A digital signal processing circuit is provided in a specific embodiment of the present invention. The digital signal processing circuit includes a demodulation circuit, an FPGA processor, and a processing computer. The demodulation circuit includes a crystal oscillator, a frequency division circuit, a resonant network, an emitter follower circuit, a differential amplification circuit, and a high-speed digital sampling circuit. The crystal oscillator outputs a driving signal. After the driving signal is input to the frequency division circuit to change the frequency, it is divided into a first path signal and a second path signal. Specifically, the crystal oscillator is a temperature-compensated crystal oscillator, and the temperature-compensated crystal oscillator outputs a driving signal of 500 kHz. The first path signal enters the resonant network to drive a displacement signal; the second path signal is input to the FPGA processor as a trigger signal. After the displacement signal is input to the resonant network, it is amplified by the emitter follower circuit to form a first emitter follower circuit and a second emitter follower circuit; the first emitter follower circuit and the second emitter follower circuit are subtracted by the subtractor to obtain a differential mode signal; the differential mode signal is input to the high-speed digital sampling circuit after passing through the differential amplification circuit to achieve digital acquisition. The input signal after digital acquisition enters the FPGA processor; the FPGA processor and the processing computer are used to run the double-correlation demodulation algorithm to process the input signal.

[0024] In a specific embodiment of the present invention, a digital signal processing method is further provided, and the digital signal processing method is implemented by the digital signal processing circuit of the present invention.

[0025] In a specific embodiment of the present invention, an eddy current displacement sensor device is further provided, and the eddy current displacement sensor device includes a laser collimator, a differential sensing system, a one-dimensional linear displacement platform, and a digital signal processing circuit.

[0026] In a specific embodiment, the one-dimensional linear displacement platform is fixedly connected to the object to be measured, and when the one-dimensional linear displacement platform moves, it drives the object to be measured to move; the laser collimator is used to adjust the position between the object to be measured and the differential sensing system; the differential sensing system is used to generate a displacement signal when the object to be measured is moved; the differential sensing system includes a first coil sensor probe and a second coil sensor probe; the first coil sensor probe and the second coil sensor probe are the same; the first coil sensor probe and the second coil sensor probe are respectively located on both sides of the object to be measured; the first coil sensor probe is fixed by a first probe fixing device, and the second coil sensor probe is fixed by a second probe fixing device.

[0027] In a specific embodiment, the digital signal processing circuit includes a demodulation circuit, an FPGA processor, and a processing computer; the demodulation circuit includes a crystal oscillator, a frequency division circuit, a resonant network, an emitter follower circuit, a differential amplification circuit, and a high-speed digital sampling circuit; the crystal oscillator outputs a drive signal, and after the drive signal is input to the frequency division circuit to change the frequency, it is divided into a first path signal and a second path signal; the first path signal enters the resonant network to drive a displacement signal; the second path signal is input to the FPGA processor as a trigger signal; after the displacement signal is input to the resonant network, it is amplified by the emitter follower circuit to form a first emitter follower circuit and a second emitter follower circuit; the first displacement signal generated by the first coil sensor probe, after being input to the resonant network, passes through the emitter follower circuit to form the first emitter follower circuit; the second displacement signal generated by the second coil sensor probe, after being input to the resonant network, passes through the emitter follower circuit to form the second emitter follower circuit; the first emitter follower circuit and the second emitter follower circuit perform subtraction through the subtractor to obtain a differential mode signal; the differential mode signal passes through the differential amplification circuit and then is input to the high-speed digital sampling circuit to achieve digital acquisition; the input signal after digital acquisition enters the FPGA processor.

[0028] In a specific embodiment, the FPGA processor and the processing computer are used to run a double-correlation demodulation algorithm to process the input signal; the input signal is: ; wherein, is the signal to be demodulated, is the noise signal; The FPGA processor generates two reference signals with the same frequency, and the reference signals include a sine signal and a cosine signal; the reference signals are: .

[0029] The process of the FPGA processor and the processing computer running the double-correlation demodulation algorithm includes: If the signal to be demodulated has a correlation with the reference signal and the reference signal has no correlation with the noise signal, the cross-correlation function of the eddy current displacement sensor device is: ; wherein, is the product of the signal to be demodulated and the reference signal, is the product of the noise signal and the reference signal.

[0030] If the signal to be demodulated is correlated with the reference signal, and the reference signal is uncorrelated with the noise signal, and the noise of the eddy current displacement sensor device is Gaussian white noise that conforms to a normal distribution; then the cross-correlation function of the eddy current displacement sensor device is: .

[0031] When the reference signal is a sine signal and a cosine signal with the same frequency as the signal to be demodulated respectively, the output expression of the amplitude of the signal to be demodulated is: ; where and are the amplitude of the signal to be demodulated and the amplitude of the reference signal respectively; is the phase difference between the signal to be demodulated and the reference signal.

[0032] The discrete expression of the signal to be demodulated is: ; The discrete expression of the reference signal as a sine signal is: ; The discrete expression of the reference signal as a cosine signal is: ; where is the number of sampling points per period, is a constant; The cross-correlation function between the signal to be demodulated and the sine signal is: ; The cross-correlation function between the signal to be demodulated and the cosine signal is: ; where is the amplitude of the signal to be demodulated, is the amplitude of the sine signal, is the amplitude of the cosine signal.

[0033] The output expression of the amplitude after demodulating the signal to be demodulated is: ; where is the amplitude of the reference signal, is the cross-correlation function between the signal to be demodulated and the sine signal; is the cross-correlation function between the signal to be demodulated and the cosine signal.

[0034] In a specific embodiment of the present invention, a novel-structured digital signal processing circuit, a digital signal processing method, and a device for reducing the temperature drift of a differential eddy current sensor in a wide temperature range using the signal processing method of the present invention are proposed. Specifically, the design of a differential probe is utilized to cancel the temperature drift of the measured metal, coil, and cable in the system. A symmetric high-speed analog-to-digital sampling circuit and a double-correlation demodulation algorithm are used to replace the traditional amplitude demodulation method to digitally demodulate the signal output by the displacement sensor and reduce noise, avoiding the influence of the temperature characteristics of analog devices on the demodulation result, which can greatly improve the temperature stability of the eddy current sensor and effectively suppress the temperature drift of the eddy current sensor.

[0035] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0036] As Figure 1 shown, it is a schematic structural diagram of the differential sensing system described in the embodiment of the present invention. It can be seen from the figure that the differential sensing system of the present invention includes a first coil sensor probe 1 and a second coil sensor probe 3. The two coil sensor probes are respectively placed on both sides of the measured object 2. At this time, the basic structure of the eddy current sensor constitutes a parallel resonant LC circuit. A driving signal Ui with a constant frequency and a constant amplitude is input into the parallel resonant circuit composed of the first coil sensor probe 1 and a capacitor. When the distance between the first coil sensor probe 1 and the measured object 2 changes, the mutual inductance coefficient M between the first coil sensor probe 1 and the second coil sensor probe 3 will change, and thus the output signal will also change accordingly. The distance information between the first coil sensor probe 1 and the second coil sensor probe 3 and the measured object 2 is approximately linearly related to the amplitude of the output signal. When the circuit parameters of the two coil sensor probes are equal, the two coil sensor probes and the output differential voltage signal The linear function can be expressed as: ; is a constant input signal, and are respectively the equivalent impedance parameters of the two coil sensor probes when the eddy current displacement sensor device is at the current position. Selecting two coil sensor probes with the same structure as Figure 1 shown to form a differential sensing system can effectively eliminate the common-mode interference caused by coil temperature drift, the temperature drift caused by the resistivity of the target metal, and the temperature drift caused by cable impedance.

[0037] Figure 2Schematic structural diagram of the eddy current displacement sensor device according to the embodiment of the present invention. As can be seen from the figure, the eddy current displacement sensor device includes a laser collimator 6, a first coil sensor probe 1, a second coil sensor probe 3, a first probe fixing device 4, a second probe fixing device 5, a one-dimensional linear displacement platform 7, a demodulation circuit 8, an FPGA processor 9, and a processing computer 10 disposed on a processing platform 11.

[0038] Specifically, the laser collimator 6 is used to adjust the position of the object to be measured 2 relative to the two coil sensor probes. The one-dimensional linear displacement platform 7 is fixedly connected to the object to be measured 2, and their positions are relatively stationary. The movement of the one-dimensional linear displacement platform 7 drives the movement of the object to be measured 2. The two coil sensor probes are fixed on the probe fixing devices. The first coil sensor probe 1 is fixed on the first probe fixing device 4, and the second coil sensor probe 3 is fixed on the second probe fixing device 5, which are used to generate displacement signals when the object to be measured 2 moves. The demodulation circuit 8 is used to convert the displacement information detected by the two coil sensor probes into voltage signals. The high-speed digital sampling circuit (symmetrical high-speed ADC circuit) in the demodulation circuit 8 is used to digitally demodulate the displacement signals. The FPGA processor 9 and the processing computer 10 are used to run the double-correlation demodulation algorithm and reduce signal noise.

[0039] The setup process of the eddy current displacement sensor device test is as follows: Fix the first coil sensor probe 1 on the first probe fixing device 4. Starting from the position of the first coil sensor probe 1, use the laser collimator 6 to adjust the position of the object to be measured 2 relative to the first coil sensor probe 1. When the designed measurement range is reached, fix the position of the second coil sensor probe 3 through the second probe fixing device 5, and the object to be measured 2 returns to the middle position between the two coil sensor probes.

[0040] Figure 3 Schematic structural diagram of the digital signal processing circuit framework according to the embodiment of the present invention. As can be seen from the figure, when the object to be measured generates displacement, the two coil sensor probes placed on both sides of the object to be measured will detect displacement signals. The temperature compensation crystal oscillator outputs a driving signal. After the driving signal is input to the frequency division circuit to change the frequency, it is divided into two paths of signals. One path of signal enters the resonant network to drive the displacement signals of the two coil sensor probes, and the other path of signal is input to the FPGA processor as a trigger signal. After the displacement signals of the two coil sensor probes are input to the resonant network, they respectively enter the emitter follower circuit for amplification. After amplification, the first emitter follower circuit ( Figure 3 the middle emitter follower circuit 1) and the second emitter follower circuit ( Figure 3In the injection following circuit 2), two signals are subtracted by a subtractor at the next stage to obtain the differential mode signal measured by the differential sensing system; the differential mode signal is input to the high-speed digital sampling circuit after passing through the differential amplification circuit to realize the digital acquisition of the signal. After the digital signal is acquired, in order to further reduce the system noise and improve the temperature stability of the displacement sensor system, the digital demodulation method is used to replace the traditional amplitude demodulation method to realize the digital calculation of the displacement signal to be measured.

[0041] Specifically, when the eddy current displacement sensor device is used Figure 3 the digital signal processing circuit shown, after the signal completed digital acquisition enters the FPGA processor, the input signal at this time is: , where is the signal to be demodulated, is the noise signal in the system. The FPGA processor generates two reference signals with the same frequency, one is a sine signal and the other is a cosine signal, and the reference signal is .

[0042] If there is a correlation between the signal to be demodulated and the reference signal in the eddy current displacement sensor device, and there is no correlation between the reference signal and the noise signal, after the input signal undergoes delay, multiplication, integration and averaging operations, the cross-correlation function of the eddy current displacement sensor device can be obtained : .

[0043] Among them, is the product of the signal to be demodulated and the reference signal, is the product of the noise signal and the reference signal. From the assumption, it can be seen that the reference signal has a correlation with the signal to be demodulated, while the reference signal has no correlation with the noise signal, and the system noise of the eddy current displacement sensor device is Gaussian white noise that conforms to a normal distribution with a mean of 0. Therefore, the cross-correlation function of the eddy current displacement sensor device can be simplified as: .

[0044] When the reference signals are a sine signal and a cosine signal with the same frequency as the signal to be demodulated respectively, combined with the simplified cross-correlation function obtained above, the output of the correlation demodulator can be expressed as: and , where and are the amplitudes of the signal to be demodulated and the reference signal respectively, and is the phase difference between the two signals of the signal to be demodulated and the reference signal. At this time, the output expression of the amplitude of the signal to be demodulated can be obtained as: .

[0045] In a digital system, by setting the sampling frequency and sampling period for an analog signal, a discrete expression of the analog signal can be obtained. Both the signal to be demodulated and the reference signal are discretely expressed. The discrete expression of the signal to be demodulated is , and the discrete expression of the reference signal as a sine signal is , and the discrete expression of the reference signal as a cosine signal is: , where is the number of sampling points per period, is a constant. The cross-correlation function between the signal to be demodulated and the sine signal can be obtained as: ; The cross-correlation function between the signal to be demodulated and the cosine signal is: ; where is the amplitude of the signal to be demodulated, is the amplitude of the sine signal, is the amplitude of the cosine signal.

[0046] At this time, the output expression of the amplitude after demodulating the signal to be demodulated can be obtained as: .

[0047] In the embodiment of the present invention in the eddy current displacement sensor device, the process of the FPGA processor and the processing computer running the double-correlation demodulation algorithm is realized through the above calculation formula, effectively reducing the signal noise and achieving the technical effect of reducing the low temperature drift of the eddy current displacement sensor device in a wide temperature range.

[0048] It should be understood that various forms of the processes shown above can be used, reordering, adding or deleting steps. For example, the steps recorded in the disclosure of the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solutions disclosed in the present invention can be achieved. This is not limited herein.

[0049] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A digital signal processing circuit, characterized in that: The digital signal processing circuit includes a demodulation circuit, an FPGA processor, and a processing computer; The demodulation circuit includes a crystal oscillator, a frequency division circuit, a resonant network, an emitter follower circuit, a differential amplifier circuit, and a high-speed digital sampling circuit; The crystal oscillator outputs a drive signal, which is input to the frequency division circuit to change the frequency and then divided into a first path signal and a second path signal; The first path signal enters the resonant network to drive a displacement signal; the second path signal is input to the FPGA processor as a trigger signal; After the displacement signal is input to the resonant network, it is amplified by the emitter follower circuit to form a first emitter follower circuit and a second emitter follower circuit; The first emitter follower circuit and the second emitter follower circuit perform subtraction through a subtractor to obtain a differential mode signal; The differential mode signal is input to the high-speed digital sampling circuit after passing through the differential amplifier circuit to achieve digital acquisition; The input signal after digital acquisition enters the FPGA processor; the FPGA processor and the processing computer are used to run a double-correlation demodulation algorithm to process the input signal.

2. The digital signal processing circuit according to claim 1, wherein: The crystal oscillator is a temperature-compensated crystal oscillator, and the temperature-compensated crystal oscillator outputs a drive signal of 500 kHz.

3. A digital signal processing method, characterized in that: The digital signal processing method is implemented by the digital signal processing circuit according to any one of claims 1 or 2.

4. An eddy current displacement sensor device, characterized in that: The eddy current displacement sensor device includes a laser collimator, a differential sensing system, a one-dimensional linear displacement platform, and a digital signal processing circuit; the digital signal processing circuit is the digital signal processing circuit according to any one of claims 1 or 2; The one-dimensional linear displacement platform is fixedly connected to the object to be measured, and drives the object to be measured to move when the one-dimensional linear displacement platform moves; The laser collimator is used to adjust the position between the object to be measured and the differential sensing system; The differential sensing system is used to generate a displacement signal when the object to be measured is moved; The differential sensing system includes a first coil sensor probe and a second coil sensor probe; the first coil sensor probe and the second coil sensor probe are the same; The first coil sensor probe and the second coil sensor probe are respectively located on both sides of the object to be measured; the first coil sensor probe is fixed by a first probe fixing device, and the second coil sensor probe is fixed by a second probe fixing device; The first displacement signal generated by the first coil sensor probe, after being input to the resonant network, passes through the emitter follower circuit to form the first emitter follower circuit; the second displacement signal generated by the second coil sensor probe, after being input to the resonant network, passes through the emitter follower circuit to form the second emitter follower circuit.

5. The eddy current displacement sensor device according to claim 4, characterized in that: The input signal is as follows: ; Among them, is the signal to be demodulated, is the noise signal; The FPGA processor generates two reference signals with the same frequency, and the reference signals include a sine signal and a cosine signal; the reference signals are: .

6. The eddy current displacement sensor device according to claim 5, characterized in that: The process of the FPGA processor and the processing computer running the double-correlation demodulation algorithm includes: If the signal to be demodulated is correlated with the reference signal and the reference signal is uncorrelated with the noise signal, the cross-correlation function of the eddy current displacement sensor device is as follows: ； wherein, is the product of the signal to be demodulated and the reference signal, is the product of the noise signal and the reference signal.

7. The eddy current displacement sensor device according to claim 6, characterized in that: If the signal to be demodulated is correlated with the reference signal, the reference signal is uncorrelated with the noise signal, and the noise of the eddy current displacement sensor device is Gaussian white noise that conforms to a normal distribution; then the cross-correlation function of the eddy current displacement sensor device is: .

8. The eddy current displacement sensor device according to claim 7, wherein: When the reference signals are a sine signal and a cosine signal with the same frequency as the signal to be demodulated respectively, the output expression of the amplitude of the signal to be demodulated is: ； wherein, and are the amplitude of the signal to be demodulated and the amplitude of the reference signal, respectively; is the phase difference between the signal to be demodulated and the reference signal.

9. The eddy current displacement sensor device according to claim 8, wherein The discrete expression of the signal to be demodulated is as follows: ; The discrete expression of the reference signal as a sine signal is: ； The discrete expression of the reference signal as a cosine signal is: ； wherein, is the number of sampling points for each period, is a constant; The cross-correlation function of the signal to be demodulated and the sine signal is: ； The cross-correlation function of the signal to be demodulated and the cosine signal is as follows: ; Among them, is the amplitude of the signal to be demodulated, is the amplitude of the sine signal, is the amplitude of the cosine signal.

10. The eddy current displacement sensor device according to claim 9, characterized in that, The output expression of the amplitude of the signal to be demodulated after demodulation is: ； wherein, is the amplitude of the reference signal, is the cross-correlation function between the signal to be demodulated and the sine signal; is the cross-correlation function between the signal to be demodulated and the cosine signal.

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