Inductive sensor and metal proximity detection method based on multi-frequency synchronous excitation

Abstract

The application discloses a multi-frequency synchronous excitation-based inductive sensor and a metal proximity detection method, and relates to the technical field of sensors, in particular to a method for detecting the proximity of a metal target. The first excitation signal is used for sensing whether the metal target exists or not, the second excitation signal is used for extracting the environmental noise characteristics, and the third excitation signal is used for extracting the antenna DC resistance change characteristics. The three response components are extracted by the detection circuit respectively, and the voltage amplitudes are detected. The core controller independently measures the linear attenuation coefficient corresponding to the antenna DC resistance change based on the third response component, independently measures the environmental noise component based on the second response component, and substitutes the two as known quantities into the inverse solution calculation of the spatial attenuation factor to obtain the pure spatial attenuation factor which is only related to the target spatial distance. The target is determined to reach the induction distance by comparing the pure spatial attenuation factor with the calibration spatial attenuation factor. Thus, the induction distance is greatly expanded, and the long-term precision is stable and reliable.

Description

Technical Field

[0001] This application relates to the field of inductive proximity sensor technology, and in particular to an inductive sensor based on multi-frequency synchronous excitation and a metal proximity detection method. Background Technology

[0002] Metal position detection devices (such as inductive proximity switches) are used to perform non-contact detection of the presence of metal targets within a target area. They are widely used in industrial automation scenarios such as position detection, limit control, and speed measurement.

[0003] Currently, most inductive sensors widely used in industrial settings employ a single-frequency excitation principle. Their output signal amplitude is simultaneously modulated by three factors: the distance to the metal target, ambient electromagnetic noise, and the antenna's DC resistance (temperature drift). The voltage change ultimately detected by the sensor is a mixture of the eddy current losses caused by the target distance, environmental noise disturbances, and temperature-induced internal resistance drift.

[0004] To suppress environmental electromagnetic noise interference, existing technologies generally employ a dual-coil differential structure, setting up a main detection coil and a secondary compensation coil. The two response signals are subtracted, utilizing the common-mode nature of environmental noise to cancel it out. However, the practical effectiveness of this approach is limited by a key physical premise—the environmental noise sensed by the two coils must be completely identical. However, the main and secondary coils differ in spatial position, meaning the noise amplitude and phase they pick up are inevitably not entirely the same. Residual noise components remain after differential processing, and this residual noise, when superimposed on the target signal, cannot be further distinguished or eliminated, thus limiting the sensing distance. Regarding temperature drift, existing technologies use a static fitting curve compensation method. Before leaving the factory, the sensor is placed in a high-low temperature chamber to measure and store the temperature-response signal amplitude curve. During use, compensation is made by looking up a table based on the current temperature. However, the electrical performance of the sensor antenna ages with accumulated use and storage time, causing the curve to become invalid, and the compensation accuracy significantly decreases over time. Ultimately, whether it's the hardware subtraction method of dual-coil differential or the pre-stored static curve lookup method, existing technologies cannot reconstruct pure distance information from mixed signals.

[0005] Therefore, how to provide a metal position detection device that can decouple and separate pure distance information from mixed response signals is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In a first aspect, this application provides an inductive sensor based on multi-frequency synchronous excitation, characterized in that it includes: a signal excitation circuit for generating a first excitation signal, a second excitation signal, and a third excitation signal, and determining a mixed excitation signal to be applied to a transmitting antenna based on the first excitation signal, the second excitation signal, and the third excitation signal; wherein, the frequency of the first excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is less than the thickness of the metal target, so that the first excitation signal can generate an eddy current effect on the metal target for sensing the presence of the target; the frequency of the second excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is greater than the thickness of the metal target, so that the second excitation signal cannot generate an eddy current effect on the metal target, but can sense spatial electromagnetic noise for extracting environmental noise features; the third excitation signal is a DC signal used to extract the change characteristics of the DC resistance of the transmitting antenna; a transmitting antenna used to radiate the mixed excitation signal into free space in the form of electromagnetic waves; and a signal detection circuit used to... The system receives the direct response signal from the transmitting antenna, extracts the first response component, the second response component, and the third response component corresponding to the first excitation signal, the second excitation signal, and the third excitation signal, respectively, and detects the voltage amplitude of each response component. The core controller is configured to determine a linear attenuation coefficient characterizing the change in DC resistance of the transmitting antenna based on the voltage amplitude of the third response component, determine the current ambient noise component based on the voltage amplitude of the second response component, determine the current spatial attenuation factor based on the voltage amplitude of the first response component, the linear attenuation coefficient of the current antenna DC resistance, and the current ambient noise component, and compare the current spatial attenuation factor with the factory-configured calibrated spatial attenuation factor, determining whether the metal target has reached the sensing distance based on the comparison result. The spatial attenuation factor characterizes the degree of loss caused by the eddy current effect of the metal target on the electromagnetic waves radiated by the transmitting antenna, and the value of the spatial attenuation factor decreases as the distance between the metal target and the transmitting antenna decreases.

[0007] The inductive sensor based on multi-frequency synchronous excitation provided in this application applies three different frequency / type excitation signals to the same transmitting antenna simultaneously. Frequency diversity is used to sense and extract three different physical effects on three independent channels: the first excitation signal (high frequency) carries target distance information, the second excitation signal (low frequency) carries environmental noise information, and the third excitation signal (DC) carries antenna internal resistance temperature drift information. This fundamentally achieves independent sensing and decoupling of different physical effects on the same physical structure.

[0008] Compared to the existing technology that uses a dual-coil differential structure for noise cancellation, this application replaces spatial diversity with frequency diversity, simultaneously sensing target signals and environmental noise at the same spatial location, completely avoiding the residual noise problem caused by the spatial position difference of the dual coils. Compared to the existing technology that uses static fitting curve compensation method for temperature drift correction, this application senses the current state of the antenna internal resistance in real time through a third excitation signal (DC), without relying on the temperature-response signal amplitude curve pre-stored at the factory, and without setting up a temperature measurement circuit inside the sensor. This fundamentally avoids the problem of curve failure caused by the cumulative use or storage time of the sensor, making the long-term accuracy of the sensor more stable and reliable.

[0009] Based on this, the core controller uses the linear attenuation coefficient (characterizing the temperature drift of the antenna's internal resistance) independently measured by the third response component and the environmental noise component independently measured by the second response component as known quantities, and substitutes them into the inverse calculation of the spatial attenuation factor. This makes the calculated current spatial attenuation factor a pure physical quantity that is only related to the spatial distance to the target. Since the interference of temperature drift and environmental noise has been accurately subtracted, even if the signal change generated by the distant target is extremely weak, it can be stably identified after eliminating the influence of interference, thereby significantly extending the sensor's sensing range.

[0010] In some possible implementations, the signal excitation circuit includes a sensitive excitation signal generator, a reference excitation signal generator, a third excitation signal generator, a sensitive excitation anti-aliasing filter, a reference excitation anti-aliasing filter, and an adder. The sensitive excitation signal generator generates an original sensitive excitation signal, which includes a first target frequency component and a first aliasing frequency component. The sensitive excitation anti-aliasing filter attenuates the first aliasing frequency component in the original sensitive excitation signal to obtain a smoothed sensitive excitation signal, and uses the smoothed sensitive excitation signal as the first excitation signal. The reference excitation signal generator generates an original reference excitation signal, which includes a second target frequency component and a second aliasing frequency component. The reference excitation anti-aliasing filter attenuates the second aliasing frequency component in the original reference excitation signal to obtain a smoothed reference excitation signal, and uses the smoothed reference excitation signal as the second excitation signal. The third excitation signal generator generates a third excitation signal. The adder adds the smoothed sensitive excitation signal, the smoothed reference excitation signal, and the third excitation signal to obtain the mixed excitation signal.

[0011] By using this method and setting an anti-aliasing filter, the aliasing frequency components carried by the non-ideal characteristics in the signal generator output can be effectively attenuated, avoiding interference from aliasing components to subsequent signal processing and improving the purity of the excitation signal.

[0012] In some possible implementations, the signal detection circuit includes a sensitive bandpass filter, a reference bandpass filter, a third bandpass filter, a sensitive amplitude detector, a reference amplitude detector, and a third amplitude detector. The sensitive bandpass filter is used to extract the passband component corresponding to the frequency of the first excitation signal from the direct response signal to obtain a sensitive response signal. The reference bandpass filter is used to extract the passband component corresponding to the frequency of the second excitation signal from the direct response signal to obtain a reference response signal. The third bandpass filter is used to extract the DC component from the direct response signal to obtain a third response signal. The sensitive amplitude detector is used to detect the voltage amplitude of the sensitive response signal. The reference amplitude detector is used to detect the voltage amplitude of the reference response signal. The third amplitude detector is used to detect the voltage amplitude of the third response signal.

[0013] Using this method, the three frequency components mixed in the direct response signal are extracted separately through the frequency separation effect of three bandpass filters, enabling the subsequent core controller to perform independent amplitude detection and mathematical processing on each component.

[0014] In some possible implementations, the signal detection circuit is used to acquire, under calibration conditions, the voltage amplitude of the third response signal, the voltage amplitude of the reference response signal, and the voltage amplitude of the sensitive response signal when a standard metal target is fixed at a desired sensing distance, and output them to the core controller; the core controller is used to: calculate the linear attenuation coefficient under calibration conditions based on the voltage amplitude of the third response signal and the amplitude of the third excitation signal under calibration conditions; control the signal excitation circuit to output the second excitation signal with at least two different amplitude configurations, and acquire the corresponding reference response signal voltage amplitude, and simultaneously solve for the environmental noise component under calibration conditions; determine the spatial attenuation factor under calibration conditions based on the voltage amplitude of the sensitive response signal, the linear attenuation coefficient, and the environmental noise component under calibration conditions, and obtain the calibration spatial attenuation factor.

[0015] Using this method, through calibration, the core controller establishes a reference value—the calibration space attenuation factor—corresponding to the desired sensing distance at the factory. During the calibration calculation, the third response signal independently measures the linear attenuation coefficient corresponding to the change in the DC resistance of the transmitting antenna at the calibration moment, and the second response signal solves for the environmental noise component at the calibration moment by combining two measurements with different amplitude configurations. Both are used as known quantities in the inverse calculation of the calibration space attenuation factor.

[0016] Therefore, the calibration spatial attenuation factor does not include temperature or noise information at the calibration time. This value corresponds one-to-one with the spatial position of the target (desired sensing distance) and is unaffected by the calibration environment conditions. In subsequent use, regardless of changes in ambient temperature and electromagnetic noise, this reference value remains constant, providing a stable and reliable reference for accurate judgment.

[0017] In some possible implementations, the signal detection circuit is used to acquire the current third response signal voltage amplitude, reference response signal voltage amplitude, and sensitive response signal voltage amplitude in the current usage state, and output them to the core controller; the core controller is used to: calculate the linear attenuation coefficient in the current usage state based on the voltage amplitude of the current third response signal and the amplitude of the third excitation signal; control the signal excitation circuit to output the second excitation signal with at least two different amplitude configurations, and acquire the corresponding reference response signal voltage amplitude, and solve the environmental noise component in the current usage state simultaneously; determine the spatial attenuation factor in the current usage state based on the sensitive response signal voltage amplitude, linear attenuation coefficient, and environmental noise component in the current usage state; compare the spatial attenuation factor in the current usage state with the calibrated spatial attenuation factor, and drive the response signal circuit to output the corresponding switching signal based on the comparison result.

[0018] Using this method, the determination of the spatial attenuation factor during the normal use phase corresponds to the operation process during the calibration phase. The core controller dynamically obtains the current antenna internal resistance state and environmental noise state by measuring the current third response signal and second response signal in real time, and separates the two from the sensitive response signal to obtain the current pure spatial attenuation factor, thereby achieving accurate metal proximity detection.

[0019] In some possible implementations, the frequency of the first excitation signal is greater than or equal to 300 kHz and less than or equal to 500 kHz, and the frequency of the second excitation signal is greater than or equal to 1 kHz and less than or equal to 3 kHz.

[0020] Using this method, an appropriate frequency range is selected based on theoretical calculations and engineering practice summaries of the skin depth of common industrial metal targets. This ensures that the first excitation signal can produce a significant eddy current effect on common metal targets, while the second excitation signal produces almost no eddy current effect on common metal targets.

[0021] In some possible implementations, the core controller calculates the current spatial decay factor based on the following steps: The linear attenuation coefficient under current usage conditions is calculated based on the following formula. :

[0022] in, and These are the voltage amplitude of the third response signal and the amplitude of the third excitation signal, respectively, under the current usage state; By controlling the signal excitation circuit to output a second excitation signal with at least two different amplitude configurations in the current operating state, the corresponding calibration reference response signal voltage amplitude is obtained. and The environmental noise components under calibration conditions are solved by simultaneously solving the following formulas, wherein the environmental noise components include... and , and These represent the in-phase and quadrature components of the narrowband Gaussian noise falling within the passband of the reference bandpass filter in the current operating state: = = in, and These are the amplitude configuration values ​​of the second excitation signal under two different amplitude configurations; Voltage amplitude based on the sensitive response signal under calibration conditions Linear attenuation coefficient Environmental noise components and and the amplitude configuration value of the sensitive excitation signal. Substitute into the following formula to calculate the calibration space attenuation factor. : = .

[0023] Using this method, through the above calculation steps, the core controller can accurately isolate the effects of temperature drift and environmental noise from the voltage amplitudes of the three response components, restoring the pure spatial attenuation factor that is only related to spatial distance. This isolation is manifested in: , and By transforming the unknown disturbance variable in the formula into a known measured value, the core controller uses the known disturbance value to inversely solve for the pure disturbance variable. The basis for the final judgment It is only related to the target distance; the effects of temperature drift and environmental noise have been accurately subtracted.

[0024] In some possible implementations, the original sensitive excitation signal It conforms to the following signal model: ; in, Indicates the first target frequency component. Indicates the first aliasing frequency component; This represents the amplitude of the first target frequency component. Let t represent the frequency of the first target frequency component, and t represent time. The initial phase of the first target frequency component is represented by N, and N represents the number of aliased frequency components. This represents the amplitude of the i-th aliasing frequency component. This represents the frequency of the i-th aliasing frequency component. This represents the initial phase of the i-th aliasing frequency component; The sensitive excitation anti-aliasing filter conforms to the following response characteristic equation: ; The sensitive excitation signal is smoothed after being attenuated by the sensitive excitation anti-aliasing filter. Satisfy the following formula: ; The original reference excitation signal conforms to the following signal model: ; in, The second target frequency component, This is the second aliasing frequency component; This represents the amplitude of the second target frequency component. This represents the frequency of the second target frequency component. This indicates the initial phase of the second target frequency component. This represents the amplitude of the i-th aliasing frequency component. This represents the frequency of the i-th aliasing frequency component. This represents the initial phase of the i-th aliasing frequency component; The reference excitation anti-aliasing filter conforms to the following response characteristic equation: ; in, This represents the cutoff frequency of the reference excitation anti-aliasing filter; after attenuation by the reference excitation anti-aliasing filter, the reference excitation signal is smoothed. Satisfy the following formula: ; The signal model for the third excitation signal is: , This indicates the amplitude of the third excitation signal; The signal model for the hybrid excitation signal is: ; The hybrid excitation signal After being subjected to the combined effects of eddy current loss from the metallic target, environmental electromagnetic noise, and changes in the antenna's DC resistance within the transmitting antenna, it transforms into a direct response signal. The direct response signal The signal model satisfies the following: ; in, The spatial attenuation factor caused by eddy current loss in the metal target; The linear attenuation coefficient caused by the change in DC resistance of the transmitting antenna. r is the equivalent series resistance of the transmitting antenna; Environmental electromagnetic noise; The direct response signal The sensitive response signal obtained after extraction by the sensitive bandpass filter The signal model is:

[0025] in, and For environmental noise The in-phase and quadrature components of narrowband Gaussian noise falling within the passband of the sensitive bandpass filter; The direct response signal The reference response signal obtained after extraction by the reference bandpass filter The signal model is:

[0026] in, and For environmental noise The in-phase and quadrature components of the narrowband Gaussian noise that fall into the reference bandpass filter; The direct response signal The third response signal obtained after extraction by the third bandpass filter The signal model is: ; The voltage amplitude of the sensitive response signal detected by the sensitive amplitude detector It conforms to the following mathematical model: ; The voltage amplitude of the reference response signal detected by the reference amplitude detector It conforms to the following mathematical model: ; The voltage amplitude of the third response signal detected by the third amplitude detector It conforms to the following mathematical model: .

[0027] Secondly, this application also provides a metal proximity detection method based on multi-frequency synchronous excitation, comprising: generating a first excitation signal, a second excitation signal, and a third excitation signal, and determining a mixed excitation signal to be applied to a transmitting antenna based on the first excitation signal, the second excitation signal, and the third excitation signal; wherein, the frequency of the first excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is less than the thickness of the metal target, so that the first excitation signal can generate an eddy current effect on the metal target for sensing the presence of the target; the frequency of the second excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is greater than the thickness of the metal target, so that the second excitation signal cannot generate an eddy current effect on the metal target, but can sense spatial electromagnetic noise for extracting environmental noise features; the third excitation signal is a DC signal used to extract the change characteristics of the DC resistance of the transmitting antenna; radiating the mixed excitation signal into free space in the form of electromagnetic waves based on the transmitting antenna; and receiving the signal. The direct response signal of the transmitting antenna is used to extract the first response component, the second response component, and the third response component corresponding to the first excitation signal, the second excitation signal, and the third excitation signal, respectively, and the voltage amplitude of each response component is detected. Based on the voltage amplitude of the third response component, a linear attenuation coefficient characterizing the change in the DC resistance of the transmitting antenna is determined. Based on the voltage amplitude of the second response component, the current ambient noise component is determined. Based on the voltage amplitude of the first response component, the linear attenuation coefficient of the current antenna DC resistance, and the current ambient noise component, a current spatial attenuation factor is determined. The spatial attenuation factor characterizes the degree of loss of electromagnetic waves radiated by the transmitting antenna due to the eddy current effect of the metal target. The value of the spatial attenuation factor decreases as the distance between the metal target and the transmitting antenna decreases. The current spatial attenuation factor is compared with the factory-configured calibrated spatial attenuation factor, and based on the comparison result, it is determined whether the metal target has reached the sensing distance.

[0028] It is understandable that the metal proximity detection method based on multi-frequency synchronous excitation described above is different from that of an inductive sensor based on multi-frequency synchronous excitation. Therefore, the beneficial effects it can achieve can be referred to the beneficial effects of the first aspect and its related implementation methods described above, and will not be elaborated here. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of an inductive sensor based on multi-frequency synchronous excitation provided in an embodiment of this application; Figure 2This is a schematic diagram of another inductive sensor based on multi-frequency synchronous excitation provided in the embodiments of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described below in conjunction with the accompanying drawings.

[0031] It should be noted that this application embodiment uses an inductive sensor as an example to illustrate the execution subject of the metal proximity detection method based on multi-frequency synchronous excitation provided in this application. In this application embodiment, the inductive sensor may include, but is not limited to, components such as a signal excitation circuit, a transmitting antenna, a signal detection circuit, and a core controller, etc., and this application embodiment does not limit these components. This sensor can be applied to scenarios such as position detection, limit control, and speed measurement in industrial automation.

[0032] Please see Figure 1 , Figure 1 This is a functional module topology block diagram of an inductive sensor based on multi-frequency synchronous excitation, provided as an embodiment of this application. (See diagram below.) Figure 1 As shown, the inductive sensor based on multi-frequency synchronous excitation includes a signal excitation circuit, a transmitting antenna, a signal detection circuit, and a core controller.

[0033] It should be noted that, Figure 1 The use of the core controller as a component in the signal detection circuit is merely an example. The core controller can be included in the signal detection circuit or it can be a component independent of the signal detection circuit. This article does not impose any restrictions on this.

[0034] The signal excitation circuit is used to generate a first excitation signal, a second excitation signal, and a third excitation signal, and to determine a mixed excitation signal to be applied to the transmitting antenna based on the first excitation signal, the second excitation signal, and the third excitation signal.

[0035] In this embodiment, the frequency of the first excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is less than the thickness of the metal target, enabling the first excitation signal to generate an eddy current effect on the metal target for detecting the target's presence. For example, for common metal target materials such as steel, iron, aluminum, and copper in conventional industrial environments, the frequency of the first excitation signal can be selected as '300kHz to 500kHz' (inclusive), where electromagnetic waves in this frequency band can generate a relatively significant eddy current effect on common metal targets.

[0036] The frequency of the second excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is greater than the thickness of the metal target, so that the second excitation signal cannot induce eddy current effects on the metal target, but can sense spatial electromagnetic noise for extracting environmental noise characteristics. For example, in a typical industrial environment, the frequency of the second excitation signal can be selected as '1kHz to 3kHz' (inclusive), a frequency band in which electromagnetic waves hardly induce eddy current effects on common metal targets.

[0037] The third excitation signal is a DC signal, used to extract the variation characteristics of the DC resistance of the transmitting antenna. For a conventional inductive sensor transmitting antenna, the response model generated by the DC signal applied to the transmitting antenna is equivalent to the DC effect model. This signal should not radiate outward or leak very little energy in the near field of the transmitting antenna, and is not affected by metal targets and environmental noise. It is only sensitive to the variation of the DC resistance of the transmitting antenna.

[0038] In this embodiment, the hybrid excitation signal is obtained by adding the first excitation signal, the second excitation signal, and the third excitation signal. If it is necessary to attenuate the aliasing frequency components in the first and second excitation signals, the hybrid excitation signal is obtained by adding the first excitation signal after aliasing frequency attenuation, the attenuated second excitation signal, and the third excitation signal. The addition process refers to a linear superposition operation, where the instantaneous voltage values ​​of the three signals are added after time alignment to form a hybrid excitation signal containing three independent frequency components in the frequency domain, without frequency shifting or cross-modulation between the three frequency components.

[0039] A transmitting antenna is used to radiate the mixed excitation signal into free space in the form of electromagnetic waves.

[0040] Understandably, the hybrid excitation signal is affected by the combined effects of eddy current loss from the metal target, environmental electromagnetic noise, and changes in the antenna's DC resistance in the transmitting antenna. This alters the signal characteristics of the hybrid excitation signal, causing it to transform into a direct response signal within the antenna.

[0041] The signal detection circuit is used to receive the direct response signal of the transmitting antenna, extract the first response component, the second response component, and the third response component corresponding to the first excitation signal, the second excitation signal, and the third excitation signal, and detect the voltage amplitude of each response component.

[0042] The core controller is used to determine the linear attenuation coefficient characterizing the change in DC resistance of the current transmitting antenna based on the voltage amplitude of the third response component, determine the current ambient noise component based on the voltage amplitude of the second response component, determine the current spatial attenuation factor based on the voltage amplitude of the first response component, the linear attenuation coefficient of the current antenna DC resistance, and the current ambient noise component, and compare the current spatial attenuation factor with the factory-configured calibrated spatial attenuation factor, and determine whether the metal target has reached the sensing distance based on the comparison result.

[0043] In this embodiment, the spatial attenuation factor is used to characterize the degree of loss of electromagnetic waves radiated by the transmitting antenna due to the eddy current effect of the metal target, and its value decreases as the distance between the metal target and the transmitting antenna decreases.

[0044] In some possible implementations, such as Figure 2 As shown, the aforementioned inductive sensor also includes a response signal circuit, which is used to output a switching signal in response to the judgment result of the core controller.

[0045] Using the inductive sensor based on multi-frequency synchronous excitation provided in this application, on the one hand, the core controller can quantitatively measure the specific value of the current ambient noise in real time through the reference channel of the second excitation signal (low-frequency signal). Compared with the noise cancellation method using a dual-coil differential structure in the prior art, the sensitive excitation signal and the reference excitation signal of this application share the same transmitting antenna and the same spatial location, and the sensed ambient noise is completely consistent, eliminating the problem of residual noise caused by differences in the spatial position of the coils. At the same time, by performing two measurements and solving the equations simultaneously using the reference excitation signals with at least two different amplitude configurations, a unique solution for the current ambient noise component can be accurately obtained, realizing quantitative measurement and accurate subtraction of noise.

[0046] On the other hand, by measuring the change in DC resistance of the transmitting antenna in real time through the third excitation signal (DC signal), the core controller can dynamically obtain the current internal resistance state of the antenna and substitute it into the calculation. Compared with the static fitting curve compensation method used in the existing technology, it does not need to rely on the temperature-response signal amplitude curve pre-stored at the factory, nor does it need to set up a temperature measurement circuit inside the sensor. It effectively avoids the problem of curve failure caused by the accumulation of sensor use or storage time, making the accuracy of the compensated sensor more stable and reliable.

[0047] On another front, it also allows for a significant extension of the sensing range. Specifically, by removing temperature drift and environmental noise from the sensitive response signal, the calculated current spatial attenuation factor is compared with the factory-calibrated spatial attenuation factor, making the decision criterion a pure physical quantity that is only related to the spatial distance to the target. Since the interference of temperature drift and environmental noise has been accurately subtracted, even if the signal change generated by a distant target is extremely weak, it can be stably identified in a zero-interference background, thereby significantly extending the sensor's sensing range.

[0048] On the other hand, by simultaneously applying three different frequency / type excitation signals to the same transmitting antenna and separating the frequencies at the receiving end using a bandpass filter, independent sensing and decoupling of different physical effects (eddy current loss, spatial electromagnetic noise, and antenna internal resistance temperature drift) are achieved on the same physical structure. This solution does not require additional compensation coils or temperature sensing elements, and achieves a comprehensive technical effect of increased sensing distance, improved switching frequency, and reduced temperature drift by comprehensively balancing manufacturing costs, mechanical size, and mass production feasibility.

[0049] In some possible implementations, the signal excitation circuit includes a sensitive excitation signal generator, a reference excitation signal generator, a third excitation signal generator, a sensitive excitation anti-aliasing filter, a reference excitation anti-aliasing filter, and an adder.

[0050] The sensitive excitation signal generator is used to generate the original sensitive excitation signal, which includes a first target frequency component and a first aliasing frequency component. It should be noted that, ideally, the sensitive excitation signal generator should output only a pure single-frequency sine wave signal. However, in actual physical implementation, due to the non-ideal characteristics of the signal source, its output signal inevitably carries aliasing frequency components.

[0051] The sensitive excitation anti-aliasing filter is used to attenuate the first aliasing frequency component in the original sensitive excitation signal to obtain a smoothed sensitive excitation signal, and outputs the smoothed sensitive excitation signal as the first excitation signal to the adder.

[0052] A reference excitation signal generator is used to generate a raw reference excitation signal, which includes a second target frequency component and a second aliasing frequency component.

[0053] The reference excitation anti-aliasing filter is used to attenuate the second aliasing frequency component in the original reference excitation signal to obtain a smoothed reference excitation signal, and the smoothed reference excitation signal is output as the second excitation signal to the adder.

[0054] The third excitation signal generator is used to generate the third excitation signal.

[0055] The adder is used to add the smooth sensitive excitation signal (first excitation signal), the smooth reference excitation signal (second excitation signal), and the third excitation signal to obtain a mixed excitation signal.

[0056] By setting the anti-aliasing filter as described above, the aliasing frequency components carried by the non-ideal characteristics in the signal generator output can be effectively attenuated, avoiding interference from aliasing components to subsequent signal processing and improving the purity of the excitation signal.

[0057] It should be noted that those skilled in the art can also use any equivalent method, such as passive LC filter, active RC filter, crystal filter, notch filter, or oversampling combined with digital filtering, to replace the above-mentioned anti-aliasing filter according to actual design requirements, as long as it can attenuate the aliasing frequency components in the original excitation signal. This article does not limit this.

[0058] In some possible implementations, the signal detection circuit includes a sensitive bandpass filter, a reference bandpass filter, a third bandpass filter, a sensitive amplitude detector, a reference amplitude detector, and a third amplitude detector.

[0059] The sensitive bandpass filter is used to extract the passband component corresponding to the frequency of the first excitation signal from the direct response signal to obtain the sensitive response signal.

[0060] A reference bandpass filter is used to extract the passband component corresponding to the frequency of the second excitation signal from the direct response signal to obtain the reference response signal.

[0061] A third bandpass filter is used to extract the DC component from the direct response signal to obtain the third response signal. It should be noted that the third bandpass filter is actually a low-pass filter or a DC extraction filter, used to extract the DC component from the direct response signal. Its specific implementation can be an analog low-pass filter or a DC component extraction algorithm from digital signal processing; this application does not limit this implementation.

[0062] A sensitive amplitude detector is used to detect the voltage amplitude of a sensitive response signal.

[0063] A reference amplitude detector is used to detect the voltage amplitude of a reference response signal.

[0064] The third amplitude detector is used to detect the voltage amplitude of the third response signal.

[0065] Through the frequency separation effect of the three bandpass filters mentioned above, the three frequency components mixed in the direct response signal are extracted separately, enabling the subsequent core controller to perform independent amplitude detection and mathematical processing on each component.

[0066] It should be noted that using three different bandpass filters to extract the frequency components of the three signals is a preferred implementation, but there are other equivalent separation and extraction methods, such as synchronous demodulation, digital Fourier transform, switched capacitor filters, and quadrature demodulation. This article does not limit these methods. Those skilled in the art can extract the response signals corresponding to the three frequency components from the direct response signal according to actual design requirements.

[0067] To facilitate understanding of the technical principles of this application, the mathematical models upon which each signal is based are explained below. It should be understood that the following mathematical expressions describe the actual physical composition of the signal generator's output signal and the filter's signal processing behavior; they are objective descriptions of the physical signal, rather than the computational steps executed by the core controller.

[0068] Specifically, the original sensitive stimulus signal It conforms to the following signal model: ; in, Indicates the first target frequency component. Indicates the first aliasing frequency component; This represents the amplitude of the first target frequency component. The frequency of the first target frequency component is represented by t, and time is represented by t. The initial phase of the first target frequency component is represented by N, and N represents the number of aliased frequency components. This represents the amplitude of the i-th aliasing frequency component. This represents the frequency of the i-th aliasing frequency component. This represents the initial phase of the i-th aliasing frequency component; The sensitive excitation anti-aliasing filter conforms to the following response characteristic equation: ; The sensitive excitation signal is smoothed after attenuation by the sensitive excitation anti-aliasing filter. Satisfy the following formula: ; The original reference excitation signal conforms to the following signal model: ; in, The second target frequency component, This is the second aliasing frequency component; This represents the amplitude of the second target frequency component. This represents the frequency of the second target frequency component. This indicates the initial phase of the second target frequency component. This represents the amplitude of the i-th aliasing frequency component. This represents the frequency of the i-th aliasing frequency component. This represents the initial phase of the i-th aliasing frequency component; The reference-excited anti-aliasing filter conforms to the following response characteristic equation: ; in, This indicates the cutoff frequency of the reference excitation anti-aliasing filter; after attenuation by the reference excitation anti-aliasing filter, the reference excitation signal is smoothed. Satisfy the following formula: ; The signal model for the third excitation signal is: , Indicates the amplitude of the third excitation signal; The signal model for the hybrid excitation signal is: .

[0069] In some possible implementations, hybrid excitation signals are used. After being subjected to the combined effects of eddy current loss from the metallic target, environmental electromagnetic noise, and changes in the antenna's DC resistance within the transmitting antenna, it transforms into a direct response signal. .

[0070] Among them, the hybrid excitation signal The mechanism of near-field conductor (eddy current loss) in the transmitting antenna can be described using an equivalent model of linear signal attenuation, i.e. , .

[0071] Hybrid excitation signal The mechanism of electromagnetic noise interference in the transmitting antenna from the near-field environment can be described using a broadband Gaussian white noise interference model, i.e. ,in For example, environmental electromagnetic noise. It has a mean of 0 and a power spectral density of Gaussian white noise.

[0072] Hybrid excitation signal The mechanism by which the transmitting antenna is affected by the antenna's DC resistance (temperature drift) can be described using a linear attenuation model based on the equivalent series resistance, i.e. ( ); The linear attenuation coefficient caused by the change in DC resistance of the transmitting antenna. Let r be the equivalent series resistance of the transmitting antenna. In practice, the equivalent series resistance of the transmitting antenna is... The value will change with the temperature of the sensor (the ambient temperature).

[0073] In summary, the direct response signal The signal model satisfies the following: ; Among them, direct response signal Sensitive response signal obtained after extraction by sensitive bandpass filter The signal model is:

[0074] in, and For environmental noise The in-phase and quadrature components of narrowband Gaussian noise falling within the passband of a sensitive bandpass filter; It should be noted that the direct response signal In This represents the electromagnetic noise entering the original broadband environment of the transmitting antenna. Among them, when After passing through a sensitive bandpass filter (center frequency: After that, the broadband white noise is compressed into... Narrowband Gaussian noise centered on the sphere. This refers to the in-phase component (cosine component) of the narrowband Gaussian noise. These are the orthogonal components (sine components) of the narrowband Gaussian noise. Both are zero-mean Gaussian low-pass random processes and are independent of each other. Together, they describe the original broadband noise. The portion of energy that falls within the passband of the sensitive bandpass filter.

[0075] Direct response signal The reference response signal obtained after extraction by the reference bandpass filter The signal model is:

[0076] in, and For environmental noise The in-phase and quadrature components of narrowband Gaussian noise that fall into the reference bandpass filter; Direct response signal The third response signal obtained after extraction by the third bandpass filter The signal model is: ; The voltage amplitude of the sensitive response signal detected by the sensitive amplitude detector It conforms to the following mathematical model:

[0077] The voltage amplitude of the reference response signal detected by the reference amplitude detector It conforms to the following mathematical model:

[0078] The voltage amplitude of the third response signal detected by the third amplitude detector It conforms to the following mathematical model: .

[0079] Specifically, the core controller is used to configure the sensitive excitation signal generator to generate the original sensitive excitation signal. amplitude ,frequency and phase Parameters are used to configure the reference excitation signal generator to generate the original reference excitation signal. amplitude ,frequency and phase Parameters are configured for the third excitation signal generator to generate the original third excitation signal. amplitude Parameters, receive sensitive response signal Voltage amplitude data Detection reference response signal Voltage amplitude data and third response signal Voltage amplitude data And determine whether the metal target has reached the sensing distance.

[0080] In some possible implementations, the core controller performs the following operations during the factory calibration phase: In the calibrated state, the signal detection circuit acquires the voltage amplitude of the third response signal, the voltage amplitude of the reference response signal, and the voltage amplitude of the sensitive response signal when the standard metal target is fixed at the desired sensing distance, and outputs them to the core controller.

[0081] The core controller calculates the linear attenuation coefficient under calibration conditions based on the voltage amplitude of the third response signal and the amplitude of the third excitation signal under calibration conditions.

[0082] The core controller control signal excitation circuit outputs the second excitation signal with at least two different amplitude configurations, and obtains the corresponding reference response signal voltage amplitude, and solves the environmental noise component under the calibration state simultaneously.

[0083] The core controller determines the spatial attenuation factor under the calibration state based on the voltage amplitude, linear attenuation coefficient, and environmental noise component of the sensitive response signal under the calibration state, thus obtaining the calibration spatial attenuation factor.

[0084] Through the above calibration operations, the core controller can establish a reference value (calibration space attenuation factor) corresponding to the desired sensing distance at the factory. In this embodiment, the reference value is not affected by subsequent changes in ambient temperature and electromagnetic noise interference, because the influence of antenna internal resistance and environmental noise has been eliminated during the calibration process through the third response signal and the second response signal, respectively.

[0085] For example, the core controller calculates the calibration space attenuation factor based on the following steps: The linear attenuation coefficient under calibration conditions is calculated using the following formula. :

[0086] in, and These are the voltage amplitude of the third response signal and the amplitude of the third excitation signal under the calibration state, respectively. By controlling the excitation circuit to output a second excitation signal with at least two different amplitude configurations under calibration conditions, the corresponding calibration reference response signal voltage amplitude is obtained. and The environmental noise components under calibration conditions are solved by simultaneously solving the following formulas. The environmental noise components include... and , and These represent the in-phase and quadrature components of the narrowband Gaussian noise falling within the passband of the reference bandpass filter in the ambient noise under calibration conditions:

[0087]

[0088] in, and These are the amplitude configuration values ​​of the second excitation signal under two different amplitude configurations; Voltage amplitude based on the sensitive response signal under calibration conditions Linear attenuation coefficient Environmental noise components and and the amplitude configuration value of the sensitive excitation signal. Substitute into the following formula to calculate the calibration space attenuation factor. : .

[0089] Through the above calibration calculation steps, the core controller stores the spatial attenuation factor corresponding to the expected sensing distance in non-volatile memory in numerical form, as a decision criterion for subsequent normal use.

[0090] In some possible implementations, the core controller performs the following operations during normal use: Under the current operating conditions, the signal detection circuit acquires the current voltage amplitude of the third response signal, the voltage amplitude of the reference response signal, and the voltage amplitude of the sensitive response signal, and outputs them to the core controller.

[0091] The core controller calculates the linear attenuation coefficient under the current operating conditions based on the voltage amplitude of the current third response signal and the amplitude of the third excitation signal.

[0092] The core controller control signal excitation circuit outputs the second excitation signal with at least two different amplitude configurations, and obtains the corresponding reference response signal voltage amplitude, and solves the environmental noise component under the current operating state simultaneously.

[0093] The core controller determines the spatial attenuation factor under the current operating conditions based on the voltage amplitude of the sensitive response signal, the linear attenuation coefficient, and the environmental noise component.

[0094] The core controller compares the space attenuation factor under the current operating state with the calibrated space attenuation factor, and drives the response signal circuit to output the corresponding switching signal based on the comparison result.

[0095] The operation during the routine use phase corresponds to the operation during the calibration phase. The core controller dynamically acquires the current antenna internal resistance state and environmental noise state by measuring the current third and second response signals in real time, and separates these two from the sensitive response signal to obtain the current pure spatial attenuation factor. The comparison between the current spatial attenuation factor and the calibrated spatial attenuation factor reflects whether the metal target is currently within the sensing distance.

[0096] For example, the core controller calculates the current space decay factor based on the following steps: First, calculate the linear attenuation coefficient under the current usage state based on the following formula. :

[0097] in, and These are the voltage amplitude of the third response signal and the amplitude of the third excitation signal, respectively, under the current usage state; Then, by controlling the excitation circuit to output the second excitation signal with at least two different amplitude configurations in the current operating state, the corresponding calibration reference response signal voltage amplitude is obtained. and The environmental noise components under calibration conditions are solved by simultaneously solving the following formulas. The environmental noise components include... and , and These represent the in-phase and quadrature components of the narrowband Gaussian noise falling within the passband of the reference bandpass filter in the current operating state: = = in, and These are the amplitude configuration values ​​of the second excitation signal under two different amplitude configurations; Finally, the voltage amplitude of the sensitive response signal under calibration conditions. Linear attenuation coefficient Environmental noise components and and the amplitude configuration value of the sensitive excitation signal. Substitute into the following formula to calculate the calibration space attenuation factor. : = .

[0098] In the embodiments of this application, the signal model described above... , , These are the mathematical expressions for the sensitive response signal, reference response signal, and third response signal, respectively, used to describe the physical composition of each response component under ideal conditions. Based on this, the core controller obtains the measured voltage amplitude values ​​of each response component through an amplitude detector. , , Based on the specific calculation formulas for calculating the linear attenuation coefficient and environmental noise components derived from the above model inversion, the calibration space attenuation factor and the current space attenuation factor are determined.

[0099] Through the above calculation steps, the core controller can accurately separate the effects of temperature drift and environmental noise from the voltage amplitude of the three response components, and restore the pure spatial attenuation factor that is only related to spatial distance.

[0100] In practical applications, after the core controller determines the current space attenuation factor, it compares the current space attenuation factor with the factory-configured calibrated space attenuation factor. Based on the comparison result, it determines whether the metal target has reached the sensing distance and outputs the corresponding switching signal based on the response signal circuit.

[0101] For example, core controller comparison Value and Value, when: 1) When the metal target is not moved into the near field of the transmitting antenna or is moved into the near field of the transmitting antenna but still has not reached the sensing distance, the core controller drives the response signal circuit to output an invalid signal. 2) When the metal target moves into the near field of the transmitting antenna and just reaches the sensing distance, the core controller drives the response signal circuit to output a valid signal. 3) When the metal target moves into the near field of the transmitting antenna and has crossed the sensing distance, the core controller drives the response signal circuit to continue outputting a valid signal.

[0102] This application also provides a metal proximity detection method based on multi-frequency synchronous excitation, including: A first excitation signal, a second excitation signal, and a third excitation signal are generated, and a mixed excitation signal is determined to be applied to the transmitting antenna based on the first excitation signal, the second excitation signal, and the third excitation signal; The hybrid excitation signal is radiated into free space in the form of electromagnetic waves using a transmitting antenna. The system receives the direct response signal from the transmitting antenna, extracts the first response component, the second response component, and the third response component corresponding to the first excitation signal, the second excitation signal, and the third excitation signal, and detects the voltage amplitude of each response component. The linear attenuation coefficient characterizing the change in DC resistance of the current transmitting antenna is determined based on the voltage amplitude of the third response component. The current ambient noise component is determined based on the voltage amplitude of the second response component; Based on the voltage amplitude of the first response component, the linear attenuation coefficient of the current antenna DC resistance, and the current environmental noise component, the current spatial attenuation factor is determined. The current spatial attenuation factor is compared with the factory-configured calibrated spatial attenuation factor, and the comparison result is used to determine whether the metal target has reached the sensing distance.

[0103] The above method and steps correspond to the functions of each component of the sensor, and their specific implementation details have been explained in detail in the preceding descriptions of each component of the sensor, and will not be repeated here. The beneficial effects that can be achieved are also described in the preceding text, and will not be repeated here.

[0104] The term "at least one" in this application refers to one or more items. "More than one item" means two or more items. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship. Furthermore, it should be understood that although the terms "first," "second," etc., may be used to describe objects in this application, these objects should not be limited to these terms. These terms are only used to distinguish the objects from each other.

[0105] The terms “including” and “having” mentioned above, and any variations thereof, are intended to cover non-exclusive inclusion.

[0106] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An inductive sensor based on multi-frequency synchronous excitation, characterized in that, include: A signal excitation circuit is used to generate a first excitation signal, a second excitation signal, and a third excitation signal, and to determine a mixed excitation signal to be applied to the transmitting antenna based on the first excitation signal, the second excitation signal, and the third excitation signal; The frequency of the first excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is less than the thickness of the metal target, enabling the first excitation signal to generate an eddy current effect on the metal target for sensing the target's presence; the frequency of the second excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is greater than the thickness of the metal target, enabling the second excitation signal to fail to generate an eddy current effect on the metal target but to sense spatial electromagnetic noise for extracting environmental noise features; the third excitation signal is a DC signal used to extract the change characteristics of the DC resistance of the transmitting antenna. A transmitting antenna is used to radiate the hybrid excitation signal into free space in the form of electromagnetic waves. A signal detection circuit is used to receive the direct response signal of the transmitting antenna, extract the first response component, the second response component, and the third response component corresponding to the first excitation signal, the second excitation signal, and the third excitation signal, respectively, and detect the voltage amplitude of each response component. The core controller is configured to: determine a linear attenuation coefficient characterizing the change in DC resistance of the transmitting antenna based on the voltage amplitude of the third response component; determine a current ambient noise component based on the voltage amplitude of the second response component; determine a current spatial attenuation factor based on the voltage amplitude of the first response component, the linear attenuation coefficient of the current antenna DC resistance, and the current ambient noise component; and compare the current spatial attenuation factor with a factory-configured calibrated spatial attenuation factor, and determine whether the metal target has reached the sensing distance based on the comparison result; the spatial attenuation factor characterizes the degree of loss of electromagnetic waves radiated by the transmitting antenna due to the eddy current effect of the metal target, and the value of the spatial attenuation factor decreases as the distance between the metal target and the transmitting antenna decreases; The response signal circuit is used to output a switching signal in response to the judgment result of the core controller; The core controller is specifically configured to, when comparing the current spatial attenuation factor with the calibrated attenuation factor, determine that if the current spatial attenuation factor is less than the calibrated attenuation factor, the metal target has not reached the sensing distance, and the response signal circuit outputs an invalid signal; if the current spatial attenuation factor is equal to the calibrated attenuation factor, the metal target has just reached the sensing distance, and the response signal circuit outputs a valid signal; if the current spatial attenuation factor is greater than the calibrated attenuation factor, the metal target has crossed the sensing distance, and the response signal circuit continues to output a valid signal.

2. The inductive sensor based on multi-frequency synchronous excitation as described in claim 1, characterized in that, The signal excitation circuit includes a sensitive excitation signal generator, a reference excitation signal generator, a third excitation signal generator, a sensitive excitation anti-aliasing filter, a reference excitation anti-aliasing filter, and an adder. The sensitive excitation signal generator is used to generate an original sensitive excitation signal, which includes a first target frequency component and a first aliasing frequency component; the sensitive excitation anti-aliasing filter is used to attenuate the first aliasing frequency component in the original sensitive excitation signal to obtain a smoothed sensitive excitation signal, and the smoothed sensitive excitation signal is used as the first excitation signal. The reference excitation signal generator is used to generate an original reference excitation signal, which includes a second target frequency component and a second aliasing frequency component. The reference excitation anti-aliasing filter is used to attenuate the second aliasing frequency component in the original reference excitation signal to obtain a smoothed reference excitation signal, and the smoothed reference excitation signal is used as the second excitation signal. The third excitation signal generator is used to generate a third excitation signal; The adder is used to add the smooth sensitive excitation signal, the smooth reference excitation signal, and the third excitation signal to obtain the mixed excitation signal.

3. The inductive sensor based on multi-frequency synchronous excitation as described in claim 1 or 2, characterized in that, The signal detection circuit includes a sensitive bandpass filter, a reference bandpass filter, a third bandpass filter, a sensitive amplitude detector, a reference amplitude detector, and a third amplitude detector. The sensitive bandpass filter is used to extract the passband component corresponding to the frequency of the first excitation signal from the direct response signal to obtain the sensitive response signal; The reference bandpass filter is used to extract the passband component corresponding to the frequency of the second excitation signal from the direct response signal to obtain the reference response signal; The third bandpass filter is used to extract the DC component from the direct response signal to obtain the third response signal; The sensitive amplitude detector is used to detect the voltage amplitude of the sensitive response signal; The reference amplitude detector is used to detect the voltage amplitude of the reference response signal; The third amplitude detector is used to detect the voltage amplitude of the third response signal.

4. The inductive sensor based on multi-frequency synchronous excitation as described in claim 3, characterized in that, The signal detection circuit is used to acquire, under calibrated conditions, the voltage amplitude of the third response signal, the voltage amplitude of the reference response signal, and the voltage amplitude of the sensitive response signal when the standard metal target is fixed at the desired sensing distance, and output them to the core controller. The core controller is used for: Based on the voltage amplitude of the third response signal and the amplitude of the third excitation signal under the calibration state, the linear attenuation coefficient under the calibration state is calculated. The signal excitation circuit is controlled to output a second excitation signal with at least two different amplitude configurations, and the corresponding reference response signal voltage amplitude is obtained. The environmental noise component under the calibration state is solved simultaneously. The spatial attenuation factor under calibration is determined based on the voltage amplitude, linear attenuation coefficient, and environmental noise component of the sensitive response signal under calibration conditions, thus obtaining the calibration spatial attenuation factor.

5. The inductive sensor based on multi-frequency synchronous excitation as described in claim 4, characterized in that, The signal detection circuit is used to acquire the current third response signal voltage amplitude, reference response signal voltage amplitude, and sensitive response signal voltage amplitude under the current operating state, and output them to the core controller. The core controller is used for: Based on the voltage amplitude of the current third response signal and the amplitude of the third excitation signal, calculate the linear attenuation coefficient under the current usage state; The signal excitation circuit is controlled to output a second excitation signal with at least two different amplitude configurations, and the corresponding reference response signal voltage amplitude is obtained. The environmental noise component under the current usage state is solved simultaneously. Based on the voltage amplitude of the sensitive response signal, the linear attenuation coefficient, and the environmental noise component under the current usage condition, determine the spatial attenuation factor under the current usage condition; The space attenuation factor under the current usage state is compared with the calibrated space attenuation factor, and the response signal circuit is driven to output the corresponding switching signal based on the comparison result.

6. The inductive sensor based on multi-frequency synchronous excitation as described in claim 3, characterized in that, The core controller calculates the current spatial decay factor based on the following steps: The linear attenuation coefficient under current usage conditions is calculated based on the following formula. : in, and These are the voltage amplitude of the third response signal and the amplitude of the third excitation signal, respectively, under the current usage state; By controlling the signal excitation circuit to output a second excitation signal with at least two different amplitude configurations in the current operating state, the corresponding calibration reference response signal voltage amplitude is obtained. and The environmental noise components under calibration conditions are solved by simultaneously solving the following formulas, wherein the environmental noise components include... and , and These represent the in-phase and quadrature components of the narrowband Gaussian noise falling within the passband of the reference bandpass filter in the current operating state: = = in, and These are the amplitude configuration values ​​of the second excitation signal under two different amplitude configurations; Voltage amplitude based on the sensitive response signal under calibration conditions Linear attenuation coefficient Environmental noise components and and the amplitude configuration value of the sensitive excitation signal. Substitute into the following formula to calculate the calibration space attenuation factor. : = 。 7. The inductive sensor based on multi-frequency synchronous excitation as described in claim 6, characterized in that, The core controller calculates the calibration space attenuation factor based on the following steps: The linear attenuation coefficient under calibration conditions is calculated using the following formula. : in, and These are the voltage amplitude of the third response signal and the amplitude of the third excitation signal under the calibration state, respectively. By controlling the signal excitation circuit to output a second excitation signal with at least two different amplitude configurations under calibration conditions, the corresponding calibration reference response signal voltage amplitude can be obtained. and The environmental noise components under calibration conditions are solved by simultaneously solving the following formulas, wherein the environmental noise components include... and , and These represent the in-phase and quadrature components of the narrowband Gaussian noise falling within the passband of the reference bandpass filter in the ambient noise under calibration conditions: in, and These are the amplitude configuration values ​​of the second excitation signal under two different amplitude configurations; Voltage amplitude based on the sensitive response signal under calibration conditions Linear attenuation coefficient Environmental noise components and and the amplitude configuration value of the sensitive excitation signal. Substitute into the following formula to calculate the calibration space attenuation factor. : 。 8. The inductive sensor based on multi-frequency synchronous excitation as described in any one of claims 1, 2, 4, 5, 6, and 7, characterized in that, The frequency of the first excitation signal is greater than or equal to 300 kHz and less than or equal to 500 kHz, and the frequency of the second excitation signal is greater than or equal to 1 kHz and less than or equal to 3 kHz.

9. A metal proximity detection method based on multi-frequency synchronous excitation, characterized in that, The method, applied to the inductive sensor based on multi-frequency synchronous excitation as described in any one of claims 1 to 8, comprises: A first excitation signal, a second excitation signal, and a third excitation signal are generated, and a mixed excitation signal is determined to be applied to the transmitting antenna based on the first excitation signal, the second excitation signal, and the third excitation signal; The frequency of the first excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is less than the thickness of the metal target, enabling the first excitation signal to generate an eddy current effect on the metal target for sensing the target's presence; the frequency of the second excitation signal is configured such that the skin depth of the electromagnetic wave in the metal target is greater than the thickness of the metal target, enabling the second excitation signal to fail to generate an eddy current effect on the metal target but to sense spatial electromagnetic noise for extracting environmental noise features; the third excitation signal is a DC signal used to extract the change characteristics of the DC resistance of the transmitting antenna. The hybrid excitation signal is radiated into free space in the form of electromagnetic waves using a transmitting antenna. The system receives the direct response signal from the transmitting antenna, extracts the first response component, the second response component, and the third response component corresponding to the first excitation signal, the second excitation signal, and the third excitation signal, and detects the voltage amplitude of each response component. The linear attenuation coefficient characterizing the change in DC resistance of the current transmitting antenna is determined based on the voltage amplitude of the third response component. The current ambient noise component is determined based on the voltage amplitude of the second response component; Based on the voltage amplitude of the first response component, the linear attenuation coefficient of the current antenna DC resistance, and the current environmental noise component, the current spatial attenuation factor is determined. The spatial attenuation factor is used to characterize the degree of loss of electromagnetic waves radiated by the transmitting antenna due to the eddy current effect of the metal target. The value of the spatial attenuation factor decreases as the distance between the metal target and the transmitting antenna decreases. The current spatial attenuation factor is compared with the factory-configured calibrated spatial attenuation factor, and the comparison result is used to determine whether the metal target has reached the sensing distance.

Images