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

Abstract

The present invention relates to the technical field of eddy current sensors, and proposes a digital signal processing circuit, method, and eddy current displacement sensor device, as well as a device for reducing the temperature drift of a differential eddy current sensor over a wide temperature range using the signal processing method of the present invention. Specifically, the design of a differential probe is utilized to offset the temperature drift of the measured metal, coil, and cable in the system, and a symmetrical high-speed analog-to-digital sampling circuit and a dual-correlation demodulation algorithm are utilized to replace the traditional amplitude demodulation method to digitally demodulate the signal output by the displacement sensor and reduce noise, thereby avoiding the influence of the temperature characteristics of the analog device on the demodulation result. The device can greatly improve the temperature stability of the eddy current sensor and effectively suppress the temperature drift of the eddy current sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of eddy current sensors, and in particular 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] An eddy current sensor is a type of non-contact sensor. When a high-frequency AC signal flows through the sensor's coil, an alternating magnetic field is generated around the coil. Eddy currents are induced by the alternating magnetic field within a nearby conductor, generating another magnetic field in the opposite direction of the coil. The interaction between the coil's magnetic field and the eddy currents changes the sensor coil's AC impedance. The distance between the detector coil and the metal being measured is proportional to the coupling strength of the magnetic field. Therefore, the displacement of the target conductor can be determined by measuring the AC impedance.

[0003] However, a disadvantage of eddy current sensors is their significant temperature drift. This is because eddy current sensors are essentially impedance measurement circuits. The impedance and resistivity of the sensor coil and the metal being measured will change with temperature, affecting the measurement. The probe coil of an eddy current sensor is generally wound with highly conductive metal enameled wire, such as copper and silver. However, these two metals, while highly conductive, also have high temperature drift coefficients. The error caused by this temperature drift cannot be eliminated by manufacturing the sensor coil. The resistivity of the metal being measured increases with increasing temperature, and resistivity affects the strength of the coupling, thereby affecting the output strength of the detector signal. This temperature drift is also a fundamental error and cannot be completely eliminated. The same applies to cable impedance drift. Finally, in the signal processing circuit, temperature changes can cause parameter changes in semiconductor devices, resulting in zero drift and temperature drift in the amplifier, which in turn affects the sensor output.

[0004] There are two common approaches to overcoming temperature drift in eddy current sensors. The first involves data processing, which uses prior knowledge and algorithms to post-calibrate the sensor's output data to improve its accuracy. Examples include temperature compensation methods based on binary regression and external compensation methods that use mathematical fitting to compensate for temperature drift. The second approach involves incorporating a self-compensation module into the design of the eddy current sensor and implementing temperature compensation through circuit design. Examples include methods that use wireless coils to compensate for temperature drift, methods that combine bridge circuits for self-calibration, methods that design mechanical mechanisms and compensation circuits to reduce temperature drift, and temperature-compensated displacement sensors based on constant current circuits and temperature coefficient parameter methods. However, these methods ignore the impact of temperature drift of components in the analog processing circuit on the system output, and the temperature characteristics of each electronic component in the demodulation circuit are not fully analyzed and compensated. Summary of the Invention

[0005] In view of this, the present invention proposes 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 the sensor in a wide range of temperature environments, 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 created by the present invention is implemented as follows:

[0007] The present invention provides a digital signal processing circuit, which includes a demodulation circuit, an FPGA processor and a processing computer;

[0008] 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;

[0009] The crystal oscillator outputs a driving signal, and after the driving signal is input into the frequency dividing circuit to change the frequency, it is divided into a first signal and a second signal;

[0010] The first signal enters the resonant network to drive the displacement signal; the second signal is input into the FPGA processor as a trigger signal;

[0011] After the displacement signal is input into 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; after the differential mode signal passes through the differential amplifier circuit, it is input into the high-speed digital sampling circuit to achieve digital acquisition;

[0012] The input signal after digital collection enters the FPGA processor; the FPGA processor and the processing computer are used to run a dual-correlation demodulation algorithm to perform signal processing on the input signal.

[0013] Furthermore, the crystal oscillator is a temperature compensated crystal oscillator, and the temperature compensated crystal oscillator outputs a driving signal of 500 kHz.

[0014] The present invention also provides a digital signal processing method, which is implemented by the digital signal processing circuit of the present invention.

[0015] The present invention further provides an eddy current displacement sensor device, comprising 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-mentioned digital signal processing circuit;

[0016] The one-dimensional linear displacement platform is fixedly connected to the object to be measured, and when the one-dimensional linear displacement platform moves, the object to be measured is driven to move;

[0017] The laser collimator is used to adjust the position between the measured object and the differential sensing system;

[0018] The differential sensing system is used to generate a displacement signal when the measured object is moved;

[0019] 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 identical;

[0020] The first coil sensor probe and the second coil sensor probe are respectively located on two 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;

[0021] The first displacement signal generated by the first coil sensor probe is input into the resonant network and then passes through the emitter follower circuit to form the first emitter follower circuit; the second displacement signal generated by the second coil sensor probe is input into the resonant network and then passes through the emitter follower circuit to form the second emitter follower circuit.

[0022] Furthermore, the input signal is: ;

[0023] in, is the signal to be demodulated, is the noise signal;

[0024] The FPGA processor generates two reference signals of the same frequency, the reference signals including a sine signal and a cosine signal; the reference signals are: .

[0025] Furthermore, the process of the FPGA processor and the processing computer running the dual-correlation demodulation algorithm includes:

[0026] If the signal to be demodulated is correlated with the reference signal, and the reference signal is not correlated with the noise signal, then the cross-correlation function of the eddy current displacement sensor device is for:

[0027] ;

[0028] in, is the product of the signal to be demodulated and the reference signal, is the product of the noise signal and the reference signal.

[0029] Furthermore, if the demodulated signal is correlated with the reference signal, the reference signal is not correlated with the noise signal, and the noise of the eddy current displacement sensor device is Gaussian white noise that conforms to the normal distribution; then the cross-correlation function of the eddy current displacement sensor device is for: .

[0030] Furthermore, when the reference signals are respectively a sine signal and a cosine signal having the same frequency as the signal to be demodulated, the output expression of the amplitude of the signal to be demodulated is:

[0031] ;

[0032] in, and are respectively the amplitude of the signal to be demodulated and the amplitude of the reference signal; is the phase difference between the signal to be demodulated and the reference signal.

[0033] Furthermore, the discrete expression of the signal to be demodulated is:

[0034] ;

[0035] The discrete expression of the reference signal as a sinusoidal signal is:

[0036] ;

[0037] The discrete expression of the reference signal as cosine signal is:

[0038] ;

[0039] in, is the number of sampling points for each cycle, is a constant;

[0040] The cross-correlation function between the signal to be demodulated and the sinusoidal signal is:

[0041] ;

[0042] The cross-correlation function between the signal to be demodulated and the cosine signal is: ;

[0043] in, is the amplitude of the signal to be demodulated, is the amplitude of the sinusoidal signal, is the amplitude of the cosine signal.

[0044] Furthermore, the output expression of the demodulated amplitude of the demodulated signal is:

[0045] ;

[0046] in, is the amplitude of the reference signal, is the cross-correlation function between the signal to be demodulated and the sinusoidal signal; is the cross-correlation function between the signal to be demodulated and the cosine signal.

[0047] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0048] The present invention proposes a novel digital signal processing circuit, a digital signal processing method, and a device for reducing the temperature drift of a differential eddy current sensor over a wide temperature range using the signal processing method of the present invention. Specifically, the design of a differential probe is used to offset the temperature drift of the measured metal, coil, and cable in the system. A symmetrical high-speed analog-to-digital sampling circuit and a dual-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, thereby avoiding the influence of the temperature characteristics of the analog device on the demodulation result. The device 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

[0049] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0050] Figure 1 A schematic structural diagram of a differential sensing system according to an embodiment of the present invention;

[0051] Figure 2 A schematic structural diagram of an eddy current displacement sensor device according to an embodiment of the present invention;

[0052] Figure 3 This is a schematic diagram of the digital signal processing circuit framework structure described in an embodiment of the present invention.

[0053] Description of reference numerals:

[0054] 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

[0055] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to 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 of the present invention.

[0056] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0057] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are 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, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0058] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0059] 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;

[0060] 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;

[0061] The crystal oscillator outputs a driving signal, which is input into the frequency dividing circuit to change the frequency and is then divided into a first signal and a second signal. Specifically, the crystal oscillator is a temperature compensated crystal oscillator, which outputs a driving signal of 500 kHz.

[0062] The first signal enters the resonant network to drive the displacement signal; the second signal is input into the FPGA processor as a trigger signal;

[0063] After the displacement signal is input into 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; after the differential mode signal passes through the differential amplifier circuit, it is input into the high-speed digital sampling circuit to achieve digital acquisition;

[0064] The input signal after digital collection enters the FPGA processor; the FPGA processor and the processing computer are used to run a dual-correlation demodulation algorithm to perform signal processing on the input signal.

[0065] In a specific embodiment of the present invention, a digital signal processing method is further provided. The digital signal processing method is implemented by the digital signal processing circuit of the present invention.

[0066] In a specific embodiment of the present invention, an eddy current displacement sensor device is further provided. 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.

[0067] 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, the object to be measured is driven 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 identical; 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.

[0068] 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 amplifier circuit and a high-speed digital sampling circuit; the crystal oscillator outputs a drive signal, and the drive signal is input to the frequency division circuit to change the frequency and is divided into a first signal and a second signal; the first signal enters the resonant network to drive the displacement signal; the second 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 signal. an emitter-follower circuit and a second emitter-follower circuit; a first displacement signal generated by the first coil sensor probe is input into the resonant network and then passes through the emitter-follower circuit to form the first emitter-follower circuit; a second displacement signal generated by the second coil sensor probe is input into the resonant network and then passes through the emitter-follower circuit to form the 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 passes through the differential amplifier circuit and is input into the high-speed digital sampling circuit to realize digital acquisition; the input signal after digital acquisition enters the FPGA processor.

[0069] In a specific implementation, the FPGA processor and the processing computer are used to run a dual-correlation demodulation algorithm to perform signal processing on the input signal; the input signal is: ;

[0070] in, is the signal to be demodulated, is the noise signal;

[0071] The FPGA processor generates two reference signals of the same frequency, the reference signals including a sine signal and a cosine signal; the reference signals are: .

[0072] The process of the FPGA processor and the processing computer running the dual-correlation demodulation algorithm includes:

[0073] If the signal to be demodulated is correlated with the reference signal, and the reference signal is not correlated with the noise signal, then the cross-correlation function of the eddy current displacement sensor device is for:

[0074] ;

[0075] in, is the product of the signal to be demodulated and the reference signal, is the product of the noise signal and the reference signal.

[0076] If the demodulated signal is correlated with the reference signal, the reference signal is not correlated with the noise signal, and the noise of the eddy current displacement sensor device is Gaussian white noise that conforms to the normal distribution; then the cross-correlation function of the eddy current displacement sensor device is for: .

[0077] When the reference signals are respectively a sine signal and a cosine signal with the same frequency as the signal to be demodulated, the output expression of the amplitude of the signal to be demodulated is:

[0078] ;

[0079] in, and are respectively the amplitude of the signal to be demodulated and the amplitude of the reference signal; is the phase difference between the signal to be demodulated and the reference signal.

[0080] The discrete expression of the signal to be demodulated is:

[0081] ;

[0082] The discrete expression of the reference signal as a sinusoidal signal is:

[0083] ;

[0084] The discrete expression of the reference signal as cosine signal is:

[0085] ;

[0086] in, is the number of sampling points for each cycle, is a constant;

[0087] The cross-correlation function between the signal to be demodulated and the sinusoidal signal is:

[0088] ;

[0089] The cross-correlation function between the signal to be demodulated and the cosine signal is:

[0090] ;

[0091] in, is the amplitude of the signal to be demodulated, is the amplitude of the sinusoidal signal, is the amplitude of the cosine signal.

[0092] The output expression of the amplitude of the demodulated signal is:

[0093] ;

[0094] in, is the amplitude of the reference signal, is the cross-correlation function between the signal to be demodulated and the sinusoidal signal; is the cross-correlation function between the signal to be demodulated and the cosine signal.

[0095] In a specific embodiment of the present invention, a novel structure digital signal processing circuit, a digital signal processing method, and a device for reducing the temperature drift of a differential eddy current sensor over a wide temperature range using the signal processing method of the present invention are proposed. Specifically, the design of a differential probe is used to offset the temperature drift of the measured metal, coil, and cable in the system. A symmetrical high-speed analog-to-digital sampling circuit and a dual-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, thereby avoiding the influence of the temperature characteristics of the analog device on the demodulation result. The temperature stability of the eddy current sensor can be greatly improved, and the temperature drift of the eddy current sensor can be effectively suppressed.

[0096] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0097] like Figure 1 As shown in FIG. 1 , a schematic diagram of the structure of the differential sensing system according to an embodiment of the present invention is shown. As can be seen from the figure, 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 placed on both sides of the object to be measured 2. The basic structure of the eddy current sensor at this time constitutes a parallel resonant LC circuit. A driving signal Ui with a constant frequency and a constant amplitude is input to the parallel resonant circuit composed of the first coil sensor probe 1 and the capacitor. When the distance between the first coil sensor probe 1 and the object to be measured 2 changes, the mutual inductance coefficient M between the first coil sensor probe 1 and the second coil sensor probe 3 will change, thereby outputting a signal. The distance information between the first coil sensor probe 1 and the second coil sensor probe 3 and the 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 are The linear function can be expressed as:

[0098] ;

[0099] is a constant input signal, and are the equivalent impedance parameters of the two coil sensor probes when the eddy current displacement sensor device is at the current position. Figure 1 The two coil sensor probes with the same structure shown in the figure form a differential sensing system, which can effectively eliminate the common mode interference caused by the coil temperature drift, the temperature drift caused by the target metal resistivity, and the temperature drift caused by the cable impedance.

[0100] Figure 2 This is a schematic structural diagram of the eddy current displacement sensor device according to an 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 fixture 4, a second probe fixture 5, a one-dimensional linear displacement platform 7, a demodulation circuit 8, an FPGA processor 9 and a processing computer 10, which are arranged on a processing platform 11.

[0101] Specifically, the laser collimator 6 is used to adjust the position of the object to be measured 2 from the two coil sensor probes. The one-dimensional linear displacement platform 7 is fixedly connected to the object to be measured 2, and the two are relatively stationary. The object to be measured 2 is moved by the movement of the one-dimensional linear displacement platform 7. The two coil sensor probes are fixed on the probe fixing device, 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. They are used to generate displacement signals when the object to be measured 2 is moved. The demodulation circuit 8 is used to convert the displacement information detected by the two coil sensor probes into a voltage signal. The high-speed digital sampling circuit (symmetrical high-speed ADC circuit) in the demodulation circuit 8 is used to digitally demodulate the displacement signal. The FPGA processor 9 and the processing computer 10 are used to run the dual-correlation demodulation algorithm and reduce signal noise.

[0102] The setup process for the eddy current displacement sensor device test is as follows: fix the first coil sensor probe 1 on the first probe fixture 4. Taking the position of the first coil sensor probe 1 as the starting point, use the laser collimator 6 to adjust the position of the object under test 2 relative to the first coil sensor probe 1. When the designed measuring range is reached, fix the position of the second coil sensor probe 3 through the second probe fixture 5, and return the object under test 2 to the middle position between the two coil sensor probes.

[0103] Figure 3This is a schematic diagram of the digital signal processing circuit framework structure described in an embodiment of the present invention. As can be seen from the figure, when the object to be measured is displaced, the two coil sensor probes placed on both sides of the object to be measured will detect the displacement signal; the temperature compensated crystal oscillator outputs a drive signal, which is input to the frequency divider circuit to change the frequency and then divided into two signals. One signal enters the resonant network to drive the displacement signals of the two coil sensor probes, and the other 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, and after amplification, a first emitter follower circuit ( Figure 3 Middle emitter follower circuit 1) and second emitter follower circuit ( Figure 3 In the next stage, the two signals are subtracted by a subtractor to generate the differential mode signal measured by the differential sensing system. After passing through a differential amplifier circuit, the differential mode signal is input into a high-speed digital sampling circuit for digital signal acquisition. To further reduce system noise and improve the temperature stability of the displacement sensor system, digital demodulation replaces traditional amplitude demodulation to achieve digital resolution of the measured displacement signal.

[0104] Specifically, in the eddy current displacement sensor device Figure 3 The digital signal processing circuit shown in the figure completes the digital acquisition of the signal and enters the FPGA processor. The input signal is: ,in 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. The reference signal is .

[0105] If the demodulated signal in the eddy current displacement sensor device is correlated with the reference signal, and the reference signal is not correlated with the noise signal, the cross-correlation function of the eddy current displacement sensor device can be obtained after the input signal is delayed, multiplied, integrated and averaged. :

[0106] .

[0107] in, is the product of the demodulated signal and the reference signal, It is the product of the noise signal and the reference signal. According to the assumption, the reference signal is correlated with the signal to be demodulated, while the reference signal is not correlated with the noise signal. Moreover, the system noise of the eddy current displacement sensor device is Gaussian white noise that conforms to the normal distribution and has a mean of 0. Therefore, the cross-correlation function of the eddy current displacement sensor device can be simplified as follows: .

[0108] When the reference signals are sine and cosine signals with the same frequency as the signal to be demodulated, combined with the simplified cross-correlation function obtained above, the output of the correlation demodulator can be expressed as: and ,in, and are the amplitudes of the demodulated signal and the reference signal, respectively, and is the phase difference between the signal to be demodulated and the reference signal. At this time, the output expression of the amplitude of the signal to be demodulated is:

[0109] .

[0110] In a digital system, the sampling frequency and sampling period of the analog signal are set to obtain the discrete expression of the analog signal. The discrete expression of the demodulated signal and the reference signal are both expressed discretely. The discrete expression of the demodulated signal is: , the discrete expression of the reference signal as a sinusoidal signal is , the discrete expression of the reference signal as cosine signal is:

[0111] ,in, is the number of sampling points for each cycle, As a constant, the cross-correlation function between the demodulated signal and the sinusoidal signal can be obtained: ;

[0112] The cross-correlation function between the demodulated signal and the cosine signal is: ;

[0113] in, is the amplitude of the signal to be demodulated, is the amplitude of the sinusoidal signal, is the amplitude of the cosine signal.

[0114] At this point, the output expression of the demodulated amplitude of the demodulated signal can be obtained as:

[0115] .

[0116] In the eddy current displacement sensor device of the embodiment of the present invention, the process of the FPGA processor and the processing computer running the dual correlation demodulation algorithm is realized through the above-mentioned calculation formula, which effectively reduces signal noise and achieves the technical effect of reducing the low temperature drift of the eddy current displacement sensor device in a wide temperature range.

[0117] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0118] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection 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 driving signal, and after the driving signal is input into the frequency dividing circuit to change the frequency, it is divided into a first signal and a second signal; The first signal enters the resonant network to drive the displacement signal; the second signal is input into the FPGA processor as a trigger signal; After the displacement signal is input into 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 a subtractor to obtain a differential mode signal; After passing through the differential amplifier circuit, the differential mode signal is input into the high-speed digital sampling 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 dual-correlation demodulation algorithm to perform signal processing on the input signal; wherein the input signal is: ;in, is the signal to be demodulated, is a noise signal; the FPGA processor generates two reference signals of the same frequency, the reference signals including a sine signal and a cosine signal; the reference signals are: ; Calculate the cross-correlation functions of the signal to be demodulated and the sine signal and the cosine signal respectively, and finally solve the amplitude of the signal to be demodulated through the two cross-correlation functions.

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 driving 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 when the one-dimensional linear displacement platform moves, the object to be measured is driven to move; The laser collimator is used to adjust the position between the measured object and the differential sensing system; The differential sensing system is used to generate a displacement signal when the measured object 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 identical; The first coil sensor probe and the second coil sensor probe are respectively located on two 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 is input into the resonant network and then passes through the emitter follower circuit to form the first emitter follower circuit; the second displacement signal generated by the second coil sensor probe is input into the resonant network and then 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 process of the FPGA processor and the processing computer running the dual-correlation demodulation algorithm includes: If the signal to be demodulated is correlated with the reference signal, and the reference signal is not correlated with the noise signal, then the cross-correlation function of the eddy current displacement sensor device is for: ； in, is the product of the signal to be demodulated and the reference signal, is the product of the noise signal and the reference signal.

6. The eddy current displacement sensor device according to claim 5, characterized in that: If the demodulated signal is correlated with the reference signal, the reference signal is not correlated with the noise signal, and the noise of the eddy current displacement sensor device is Gaussian white noise that conforms to the normal distribution; then the cross-correlation function of the eddy current displacement sensor device is for: .

7. The eddy current displacement sensor device according to claim 6, characterized in that: When the reference signals are respectively a sine signal and a cosine signal with the same frequency as the signal to be demodulated, the output expression of the amplitude of the signal to be demodulated is: ； in, and are respectively the amplitude of the signal to be demodulated and the amplitude of the reference signal; is the phase difference between the signal to be demodulated and the reference signal.

8. The eddy current displacement sensor device according to claim 7, characterized in that: The discrete expression of the signal to be demodulated is: ; The discrete expression of the reference signal as a sinusoidal signal is: ； The discrete expression of the reference signal as cosine signal is: ； in, is the number of sampling points for each cycle, is a constant; The cross-correlation function between the signal to be demodulated and the sinusoidal signal is: ； The cross-correlation function between the signal to be demodulated and the cosine signal is: ; in, is the amplitude of the signal to be demodulated, is the amplitude of the sinusoidal signal, is the amplitude of the cosine signal.

9. The eddy current displacement sensor device according to claim 8, characterized in that: The output expression of the amplitude of the demodulated signal is: ； in, is the amplitude of the reference signal, is the cross-correlation function between the signal to be demodulated and the sinusoidal signal; is the cross-correlation function between the signal to be demodulated and the cosine signal.

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