Eddy current sensor and detection device

Abstract

The application discloses an eddy current sensor and a detection device, and relates to the technical field of sensors; the eddy current sensor comprises a probe coil and a temperature drift suppression circuit; the temperature drift suppression circuit is coupled with the probe coil; a change rate of impedance of the probe coil with temperature is a first change rate; a change rate of impedance of the temperature drift suppression circuit with temperature is a second change rate; and an absolute value of the second change rate is smaller than that of the first change rate. By arranging the temperature drift suppression circuit, the absolute value of the change rate of the equivalent impedance of the temperature drift suppression circuit and the probe coil with temperature is smaller than that of the first change rate, the interference of the temperature factor on the ranging accuracy is reduced, and the measurement accuracy of the eddy current sensor is improved.

Description

Technical Field

[0001] This application relates to the field of sensor technology, and in particular to an eddy current sensor and detection device. Background Technology

[0002] Eddy current sensors are non-contact sensors based on the principle of electromagnetic induction. Because they do not require direct contact with the target during detection, eddy current sensors offer advantages such as fast response, high reliability, resistance to oil and dust, and suitability for complex working environments. Therefore, they are widely used in industrial measurement and control scenarios such as displacement detection, vibration detection, and thickness measurement. However, their probe coils are typically made of metal wire, and their impedance has a positive temperature coefficient that changes with ambient temperature. When the ambient temperature fluctuates, the impedance corresponding to the probe coil drifts significantly, causing errors in the eddy current sensor's output signal and affecting the stability and accuracy of the measurement. Summary of the Invention

[0003] This application discloses an eddy current sensor and detection device to solve the influence of impedance drift caused by temperature change of probe coil on the detection results and improve the measurement accuracy of eddy current sensor.

[0004] In a first aspect, this application provides an eddy current sensor, comprising: a probe coil, the impedance of which changes with temperature at a first rate of change; and a temperature drift suppression circuit coupled to the probe coil, the impedance of which changes with temperature at a second rate of change, the absolute value of which is less than the absolute value of the first rate of change. As can be seen from the eddy current sensor provided in the first aspect, by coupling the temperature drift suppression circuit to the probe coil, the second rate of change of the impedance of the temperature drift suppression circuit with temperature compensates for the first rate of change of the probe coil impedance with temperature. Since the absolute value of the second rate of change corresponding to the temperature drift suppression circuit is less than the absolute value of the first rate of change corresponding to the probe coil, the absolute value of the rate of change of the total equivalent impedance of the coupled probe coil and the temperature drift suppression circuit with temperature is less than the absolute value of the first rate of change. Therefore, without adding additional temperature sensing elements or software fitting algorithms, signal drift caused by temperature can be effectively suppressed through matching hardware impedance characteristics, improving the measurement stability of the eddy current sensor in temperature fluctuation environments.

[0005] In one possible implementation, the second rate of change is greater than or equal to zero and less than a preset value; wherein the preset value is less than the absolute value of the first rate of change. Based on the above implementation, it can be seen that limiting the second rate of change of the temperature drift suppression circuit to greater than or equal to zero and less than the preset value allows the circuit to use conventional resistive elements with positive or zero temperature coefficients. Such elements are readily available on the market, inexpensive, and have high parameter consistency, facilitating large-scale selection and production of sensors; this not only effectively reduces manufacturing costs but also significantly improves the consistency of batch products, which is beneficial for the industrialization of the technology.

[0006] In one possible implementation, the second rate of change is less than zero. Based on the above implementation, it can be seen that when the temperature drift suppression circuit uses a component with a second rate of change less than zero, its impedance decreases as temperature increases, while the impedance of the probe coil typically increases with increasing temperature. Utilizing the opposite direction of these two changes, the decrease in impedance of the temperature drift suppression circuit can directly offset the increase in impedance of the probe coil, keeping the total equivalent impedance relatively stable, thereby effectively eliminating the influence of temperature changes on the ranging accuracy of the eddy current sensor.

[0007] In one possible implementation, the temperature drift suppression circuit is a universal impedance transformer, which includes multiple impedance elements, all of which have a rate of change of impedance with temperature greater than zero. The rate of change of the equivalent impedance of the universal impedance transformer with temperature is a second rate of change. Based on the above implementation, it can be seen that this solution selects impedance elements with a rate of change of impedance greater than zero with temperature when constructing the universal impedance transformer. Utilizing their topological operations, the rate of change of the equivalent impedance of the universal impedance transformer with temperature is made less than zero, thus eliminating the need for custom-designed negative temperature drift components. Since impedance elements with positive temperature coefficients are readily available, inexpensive, and have high nominal value consistency in the market, this solution not only reduces the difficulty of component selection and material costs but also effectively improves the accuracy of temperature compensation, product batch consistency, and long-term reliability by matching the temperature drift characteristics of the probe coil.

[0008] In one possible implementation, the universal impedance transformer includes multiple impedance elements, comprising a first impedance element, a second impedance element, a third impedance element, a fourth impedance element, and a fifth impedance element connected in series. A first terminal of the first impedance element is coupled to a probe coil. A first amplifier has its non-inverting input coupled to the end of the first impedance element not coupled to the second impedance element, its inverting input coupled to the node between the second and third impedance elements, and its output coupled to the node between the third and fourth impedance elements. A second amplifier has its non-inverting input coupled to the node between the fourth and fifth impedance elements, its inverting input coupled to the node between the second and third impedance elements, and its output coupled to the node between the first and second impedance elements. Any one of the first, second, third, fourth, and fifth impedance elements includes at least one of a resistor, a capacitor, or an inductor. Based on the above implementation, it can be seen that the universal impedance transformer uses a topology composed of dual operational amplifiers and five impedance elements, resulting in a simple circuit layout and eliminating the need for complex external components. This solution allows for easy setting of the required temperature compensation coefficient by adjusting parameters, enabling diverse adaptations based on actual temperature drift characteristics, thus enhancing the flexibility and engineering feasibility of circuit design.

[0009] In one possible implementation, the first impedance element is a first resistor, the second impedance element is a second resistor, the third impedance element is a third resistor, the fourth impedance element is a fourth resistor, and the fifth impedance element is a fifth resistor. Based on the above implementation, it can be seen that this solution uniformly limits the five impedance elements of the general-purpose impedance converter to resistors. Utilizing the advantages of resistors as standard components—abundant variety, low cost, and a stable supply chain—it achieves component standardization and reduces manufacturing costs. The all-resistive structure eliminates capacitors and inductors, not only removing size limitations and simplifying circuit layout and assembly difficulty, but also fully leveraging the characteristics of easily controllable temperature coefficients, good consistency, and high long-term stability of resistors. By adjusting the resistance value, temperature drift compensation requirements can be effectively matched, which is beneficial for sensor miniaturization design while significantly improving the consistency and reliability of mass production.

[0010] In one possible implementation, the ratio of the rate of change of resistance of the first, third, and fifth resistors with temperature to the rate of change of resistance of the second resistor with temperature is less than 0.1, and the ratio of the rate of change of resistance of the first, third, and fifth resistors with temperature to the rate of change of resistance of the fourth resistor with temperature is also less than 0.1. Based on the above implementation, it can be seen that by limiting the ratio of the rate of change of resistance of the first, third, and fifth resistors with temperature to the rate of change of resistance of the second and fourth resistors to less than 0.1, the circuit, when constructing the equivalent impedance, is mainly affected only by the temperature drift characteristics of the second and fourth resistors, while the temperature drift influence of the first, third, and fifth resistors is weakened to a negligible level. This parameter matching design simplifies the complex five-resistor temperature drift coupling problem into a compensation model dominated by two resistors. This not only reduces the difficulty of circuit debugging and the stringent requirements for component temperature drift consistency, but also achieves temperature compensation through the reasonable matching of conventional resistors without the need for extremely high-precision or special temperature coefficient components, effectively improving the output stability of the sensor over a wide temperature range.

[0011] In one possible implementation, the initial impedance of the temperature drift suppression circuit is 45% to 55% of the initial resistance of the probe coil, and the rate of change of the resistance of the second and fourth resistors with temperature is between 95% and 105% of the first rate of change. Based on the above implementation, it can be seen that setting the initial impedance of the temperature drift suppression circuit to 45% to 55% of the initial resistance of the probe coil, and limiting the rate of change of the resistance of the second and fourth resistors with temperature to between 95% and 105% of the first rate of change, ensures that the decrease in impedance of the temperature drift suppression circuit as temperature increases can offset the increase in resistance of the probe coil as temperature increases, thus keeping the total resistance of the two resistors connected in series essentially constant during temperature fluctuations. This scheme, based on the matching of conventional resistors, avoids the use of high-cost, highly variable dedicated thermistor elements. While simplifying the circuit structure, it effectively eliminates the influence of temperature changes on the output signal of the eddy current sensor, improving measurement accuracy over a wide temperature range.

[0012] In one possible implementation, the ratio of the rate of change of resistance of the first, second, third, and fifth resistors with temperature to the rate of change of resistance of the fourth resistor is less than 0.1. Based on the above implementation, it can be seen that by limiting the ratio of the rate of change of resistance of the first, second, third, and fifth resistors with temperature to that of the fourth resistor to less than 0.1, the overall equivalent impedance of the universal impedance transformer is primarily dominated by the fourth resistor in its temperature-dependent characteristics. This design simplifies the originally complex multi-resistor temperature drift coupling effect into a single-parameter-dominated relationship, allowing for flexible adjustment of the temperature drift slope of the equivalent impedance by simply matching the resistance ratios of conventional resistors, thus matching the temperature drift characteristics of the probe coil. This solution effectively avoids the shortcomings of traditional solutions that rely on high-cost, highly discrete dedicated thermistor components, reducing hardware costs while improving the accuracy of temperature compensation and the controllability of circuit design.

[0013] In one possible implementation, the initial impedance of the temperature drift suppression circuit is set to 95% to 105% of the initial resistance of the probe coil, and the rate of change of the resistance of the fourth resistor with temperature is between 95% and 105% of the first rate of change. Based on the above implementation, it can be seen that setting the initial impedance of the temperature drift suppression circuit to 95% to 105% of the initial resistance of the probe coil, and limiting the rate of change of the resistance of the fourth resistor with temperature to between 95% and 105% of the first rate of change, ensures that the resistance change of the temperature drift suppression circuit with temperature changes is consistent with the resistance change of the probe coil in both magnitude and trend, thus achieving mutual cancellation in the total impedance. This scheme uses conventional resistor ratios to replace traditional negative temperature coefficient thermistors with large dispersion, reducing the risk of compensation failure due to batch differences in components and improving the output stability of the sensor over a wide temperature range.

[0014] In one possible implementation, the ratio of the rate of change of resistance of the first, third, fourth, and fifth resistors with temperature to the rate of change of resistance of the second resistor with temperature is less than 0.1. Based on the above implementation, it can be seen that by limiting the ratio of the rate of change of resistance of the first, third, fourth, and fifth resistors with temperature to the rate of change of resistance of the second resistor to less than 0.1, the temperature-dependent characteristics of the overall equivalent impedance of the universal impedance transformer are primarily dominated by the second resistor. This design simplifies the originally complex multi-resistor temperature drift coupling effect into a single-parameter-dominated relationship, allowing for flexible adjustment of the temperature drift slope of the equivalent impedance by simply matching the resistance ratios of conventional resistors, thus matching the temperature drift characteristics of the probe coil. This solution effectively avoids the shortcomings of traditional solutions that rely on high-cost, highly discrete dedicated thermistor components, reducing hardware costs while improving the accuracy of temperature compensation and the controllability of circuit design.

[0015] In one possible implementation, the initial impedance of the temperature drift suppression circuit is 95% to 105% of the initial resistance of the probe coil, and the rate of change of the resistance of the second resistor with temperature is between 95% and 105% of the first rate of change. Based on the above implementation, it can be seen that by directly setting the initial impedance of the temperature drift suppression circuit to 95% to 105% of the initial resistance of the probe coil, and limiting the rate of change of the resistance of the second resistor with temperature to between 95% and 105% of the first rate of change, this parameter configuration ensures that the resistance change of the temperature drift suppression circuit with temperature changes is consistent with the resistance change of the probe coil in both amplitude and trend, thus achieving mutual cancellation in the total impedance. This scheme uses conventional resistor ratios to replace traditional negative temperature coefficient thermistors with large dispersion, reducing compensation failures caused by batch differences in components and improving the output stability of the sensor over a wide temperature range.

[0016] In one possible implementation, the eddy current sensor further includes a detection circuit; the eddy current sensor includes a detection circuit; the detection circuit is configured to: receive an excitation signal, change the phase of the excitation signal according to the total impedance change of the probe coil and the temperature drift suppression circuit connected in series, and generate a detection signal; wherein the detection signal has a phase change relative to the excitation signal corresponding to the total impedance change of the probe coil and the temperature drift suppression circuit; wherein the detection circuit includes a first capacitor and a second capacitor; a first terminal of the first capacitor is configured to receive the excitation signal, a second terminal of the first capacitor is coupled to the probe coil, a first terminal of the second capacitor is coupled to the second terminal of the first capacitor, and the second terminal of the second capacitor is grounded. Based on the above implementation, it can be seen that this solution achieves hardware-level temperature drift compensation and distance signal extraction by connecting the temperature drift suppression circuit in series with the probe coil and constructing a voltage divider detection node using the first and second capacitors. Specifically, when changes in ambient temperature cause impedance drift in the probe coil, the reverse impedance change generated by the temperature drift suppression circuit cancels it out at the node, suppressing the influence of temperature on the detection signal; and when changes in target distance cause impedance changes, this change is converted into a phase shift of the excitation signal, which is extracted by the detection circuit. This design directly eliminates the main temperature error at the signal acquisition front end, reducing reliance on complex compensation algorithms at the back end and ensuring the measurement stability of the eddy current sensor over a wide temperature range. Furthermore, the detection circuit consists only of the first and second capacitors, both standard passive components. This allows for flexible parameter adjustment and easy matching with different probes, significantly improving product consistency and reliability while simplifying the circuit structure and reducing implementation complexity.

[0017] Secondly, this application provides a detection device, which includes the eddy current sensor in any of the above embodiments. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of an eddy current effect provided in an embodiment of this application; Figure 2 A schematic diagram of an impedance network provided in an embodiment of this application; Figure 3 This is a schematic diagram of the structure of an eddy current sensor provided in an embodiment of this application; Figure 4 A schematic diagram of an equivalent circuit of a probe coil provided in an embodiment of this application; Figure 5 This is a circuit diagram of a detection circuit provided in an embodiment of this application; Figure 6 A circuit diagram of a general impedance converter provided in this application embodiment; Figure 7 A circuit diagram of another general-purpose impedance converter provided in the embodiments of this application; Figure 8 A circuit diagram of another general-purpose impedance converter provided in the embodiments of this application; Figure 9 A schematic diagram showing the relationship between interference intensity and the resistance value of a low-temperature drift resistor provided in the embodiments of this application; Figure 10 This is a schematic diagram of a testing device provided in an embodiment of this application.

[0020] Explanation of reference numerals in the attached figures: 1-Detection Circuit 10-Eddy Current Sensor 100-impedance network; 1001 - Probe coil; 1002 - Temperature drift suppression circuit; 1003 - Universal impedance transformer 10021 - First amplifier; 10022 - Second amplifier; 10023 - First impedance element; 10024 - Second impedance element; 10025 - Third impedance element; 10026 - Fourth impedance element; 10027 - Fifth impedance element; R0 - Resistor; L0 - Inductor; R1 - First resistor; R2 - Second resistor; R3 - Third resistor; R4 - Fourth resistor; R5 - Fifth resistor; R6 - Sixth resistor; R7 - Seventh resistor; R8 - Eighth resistor; 200-Driver Circuit; 2001 - Reference circuit; 2002 - Signal generator; 2003 - Excitation follower circuit; 300 - Detection circuit; C1 - First capacitor; C2 - Second capacitor; C3 - Third capacitor; C4 - Fourth capacitor; 400-Demodulation circuit; 4001 - Signal follower circuit; 4002 - First comparator; 4003 - Second comparator; 4004 - XOR gate; 4005 - Filter circuit; η - Interference intensity; R T - The resistance value of the low-temperature drift resistor. Detailed Implementation

[0021] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0022] The terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," or "third," etc., may explicitly or implicitly include one or more of that feature. Furthermore, in the embodiments of this application, the words "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design solutions. Specifically, the use of "exemplary" or "for example," etc., is intended to present the relevant concepts in a concrete manner for ease of understanding.

[0023] Eddy current sensors are non-contact sensors based on the principle of electromagnetic induction. They are commonly used for position detection, distance measurement, displacement measurement, vibration detection, and thickness measurement of metal targets. Because eddy current sensors do not require direct contact with the target during operation, they offer advantages such as fast response, high reliability, resistance to oil and dust, and suitability for complex working environments, making them widely used in industrial measurement and control.

[0024] Generally, an eddy current sensor consists of a probe coil and a drive circuit. The probe coil is typically made of copper, silver, or other metals. In the circuit, the probe coil is not an ideal inductor but can be considered equivalent to an impedance element with both inductive and resistive components. The drive circuit is coupled to the probe coil and provides a high-frequency AC excitation signal, such as a sinusoidal AC signal with a frequency of approximately 1 MHz.

[0025] like Figure 1 As shown, when a high-frequency AC excitation signal is applied to the probe coil, an alternating magnetic field is formed around the probe coil. When the target being measured approaches the probe coil, this alternating magnetic field induces eddy currents in the target. The induced magnetic field generated by the eddy currents reacts on the probe coil, causing a change in the equivalent impedance of the probe coil. Typically, as the target approaches the probe coil, the electromagnetic coupling between the probe coil and the target increases, and the equivalent inductance of the probe coil decreases; simultaneously, the eddy currents generated within the target consume some electromagnetic energy, increasing the energy loss of the detection circuit, and consequently causing problems in the detection circuit. Figure 1The amplitude, phase, or resonance characteristics of the target (not shown) change. Since these changes are related to the distance between the target and the probe coil, the eddy current sensor can determine whether there is a conductor near the probe coil by detecting changes in parameters such as the inductance, impedance, phase, amplitude, or resonance characteristics of the probe coil, and further obtain information about the distance between the target and the probe coil.

[0026] In existing eddy current sensors, there are many circuit schemes for measuring changes in the inductance of the probe coil, such as phase detection, amplitude detection, resonant frequency detection, bridge detection, or demodulation detection. Although these detection methods differ in their specific implementations, they all require obtaining the position information of the target based on changes in the electrical parameters of the probe coil. Therefore, the detection result is affected not only by changes in the position of the target but also by changes in the parameters of the probe coil itself. When changes in ambient temperature cause a drift in the resistance, inductance, or equivalent impedance of the probe coil, the detection circuit ( Figure 1 The output detection signal (not shown) will also change accordingly, thus generating measurement error.

[0027] In practical applications, probe coils are typically made of metal wires such as copper or silver. The resistance of these metal wires changes with temperature. For example, the temperature coefficient of resistance of copper wire is typically about 3900 ppm / ℃ (ppm represents parts per million), meaning that for every 1℃ change in temperature, the resistance of copper wire changes by 3900 ppm. When the ambient temperature changes, even if the actual distance between the target and the probe coil remains constant, the impedance of the probe coil will still drift with temperature changes. Since the resistive and inductive components of the probe coil jointly affect the output characteristics of the detection circuit, the temperature drift of the impedance corresponding to the probe coil will cause changes in the calculated amplitude, phase, or equivalent inductance value of the detection circuit output. This can lead the eddy current sensor to mistakenly believe that the position of the target has changed, ultimately resulting in ranging or position measurement errors.

[0028] To reduce the impact of temperature changes on measurement results, methods such as material compensation, structural compensation, or temperature detection compensation can be employed. For example, a low-temperature drift material, such as palladium-silver alloy, can be used to fabricate the probe coil, reducing the drift in the probe coil's resistance caused by temperature variations. Low-temperature drift materials are those with a low temperature coefficient of resistance, for example, less than 25 ppm / ℃ and greater than 0. Another example is adding a differential compensation coil to the sensor, where the differential output between the induction coil and the compensation coil partially offsets the temperature drift. Yet another example is placing an additional thermistor, temperature sensor, or other temperature-sensing device near the probe coil, measuring the ambient temperature or probe temperature near the coil, and correcting the detection results according to a pre-calibrated temperature compensation curve. Finally, a detection circuit or additional circuit can be used to measure the resistance of the probe coil, calculate its temperature, and then compensate for the ranging results based on the calculated temperature.

[0029] In the aforementioned compensation methods, using low-temperature drift materials such as palladium-silver alloys to fabricate the probe coil increases the material cost of the probe coil because these materials typically include precious metals. When using a differential compensation coil, to reduce the impact of the compensation coil on the original detection characteristics of the induction coil, the compensation coil usually needs to maintain a certain distance from the induction coil, thus increasing the structural size of the sensor probe. When using an additional temperature sensing device for compensation, the temperature sensing device detects the temperature at its own location, which may differ from the actual temperature of the probe coil; when there is a temperature gradient or localized heating within the probe, these differences will affect the compensation accuracy. When estimating the temperature by measuring the resistance of the probe coil, the measurement result may be affected by factors such as lead resistance, contact resistance, and coil impedance coupling, resulting in a deviation between the estimated temperature and the actual temperature of the probe coil.

[0030] Therefore, in eddy current sensors, how to compensate for the impedance drift of the probe coil caused by temperature changes and reduce the impact of this impedance drift on the detection results has become a technical problem that urgently needs to be solved in the design of eddy current sensors.

[0031] Based on this, this application proposes an eddy current sensor 10. For example... Figure 2As shown, the eddy current sensor 10 includes a probe coil 1001 and a temperature drift suppression circuit 1002 coupled to the probe coil 1001. The impedance of the probe coil 1001 changes with temperature at a first rate of change, and the impedance of the temperature drift suppression circuit 1002 changes with temperature at a second rate of change, the absolute value of the second rate of change being less than the absolute value of the first rate of change. Specifically, the direction of impedance change of the temperature drift suppression circuit 1002 with temperature can be opposite to the direction of impedance change of the probe coil 1001 with temperature, or the direction of impedance change of the temperature drift suppression circuit 1002 with temperature can be the same as the direction of impedance change of the probe coil 1001 with temperature, but the absolute value of the second rate of change is less than the absolute value of the first rate of change. By setting up the temperature drift suppression circuit 1002, the absolute value of the rate of change of the impedance of the impedance network 100 formed by the probe coil 1001 and the temperature drift suppression circuit 1002 with temperature is made to be between the absolute values ​​of the second rate of change and the first rate of change, that is, less than the absolute value of the rate of change of the impedance of the probe coil 1001 with temperature. Therefore, when the distance between the target and the probe coil 1001 remains constant while the ambient temperature changes, the drift of the detection signal caused by temperature changes can be reduced, the ranging error caused by temperature changes can be decreased, thereby improving the measurement stability and accuracy of the eddy current sensor.

[0032] In some possible implementations, such as Figure 3 As shown, the eddy current sensor 10 includes a drive circuit 200, a detection circuit 300, a demodulation circuit 400, and an impedance network 100. It should be noted that... Figure 3 Only a portion of the structure related to the embodiments of this application is shown schematically. The eddy current sensor 10 may also include other circuit structures for realizing detection, power supply, control or signal processing functions.

[0033] The drive circuit 200, coupled to the probe coil 1001, is configured to generate a sinusoidal signal, adjust the signal parameters of the sinusoidal signal to generate an excitation signal, and provide an excitation signal to the probe coil 1001.

[0034] In some implementations, such as Figure 3 As shown, the driving circuit 200 includes a reference circuit 2001, a signal generator 2002, and an excitation follower circuit 2003.

[0035] Reference circuit 2001 is configured to generate a voltage reference signal. This voltage reference signal can be used to provide a DC reference for other signals to determine the DC reference level or DC bias voltage of the other signals. Thus, other signals can form a stable DC operating point based on this voltage reference signal. This application does not limit the specific structure of reference circuit 2001. Reference circuit 2001 can be implemented using any voltage reference generation circuit in related technologies, as long as it can output a voltage reference signal used to determine the DC reference level of other signals. For example, reference circuit 2001 can be a bandgap reference circuit. A bandgap reference circuit can output a voltage reference signal that is substantially unaffected by power supply voltage fluctuations and ambient temperature changes.

[0036] The signal generator 2002 is configured to generate a sinusoidal signal with a preset frequency. Exemplarily, the preset frequency can be 1 MHz. In other embodiments, the preset frequency can also be set to other values ​​based on the parameters of the probe coil 1001, the detection distance range, or the required detection sensitivity. The signal generator 2002 can employ an RC oscillator, an LC oscillator, a crystal oscillator, etc. This application does not limit the specific implementation of the signal generator 2002.

[0037] The excitation follower circuit 2003 is coupled to both the signal generator 2002 and the reference circuit 2001. The excitation follower circuit 2003 is configured to receive a sinusoidal signal and a voltage reference signal, and adjust the DC reference level of the sinusoidal signal according to the voltage reference signal. In other words, the excitation follower circuit 2003 can use the voltage reference signal as a DC reference to perform bias superposition or level shifting processing on the sinusoidal signal. The excitation follower circuit 2003 is also configured to buffer and / or amplify the adjusted sinusoidal signal to generate an excitation signal with a preset driving capability. This excitation signal has a preset driving capability and can drive the probe coil 1001 to generate an alternating magnetic field for eddy current detection. The excitation follower circuit 2003 can employ a voltage follower, a power amplifier circuit, etc. This application does not limit the specific implementation of the excitation follower circuit 2003.

[0038] Based on the above implementation, the driving circuit 200 can generate an excitation signal with stable frequency and amplitude and a preset DC reference level, enabling the probe coil to stably generate an alternating magnetic field for detection. Since the excitation conditions of the probe coil remain stable, the influence of excitation signal fluctuations on the amplitude and phase of the detection signal can be reduced. This provides a reliable foundation for the subsequent detection circuit to obtain a stable detection signal and for the demodulation circuit to accurately extract phase changes, thereby improving the detection stability and measurement accuracy of the eddy current sensor.

[0039] The detection circuit 300 is coupled to the impedance network 100. The impedance network 100 is composed of a probe coil 1001 and a temperature drift suppression circuit 1002 connected in series. The detection circuit 300 is configured to: receive an excitation signal, change the phase of the excitation signal according to the total impedance change of the probe coil and the temperature drift suppression circuit connected in series, and generate a detection signal; wherein the detection signal has a phase change relative to the excitation signal corresponding to the total impedance change of the probe coil and the temperature drift suppression circuit.

[0040] In some implementations, such as Figure 5 As shown, the detection circuit 300 includes a first capacitor C1 and a second capacitor C2. The first capacitor C1 is coupled between the drive circuit 200 and the probe coil 1001. Specifically, the first terminal of the first capacitor C1 is configured to receive the excitation signal, and the second terminal of the first capacitor C1 is coupled to the first terminal of the probe coil 1001. The first terminal of the second capacitor C2 is coupled to the second terminal of the first capacitor C1 (i.e., at node N between the first capacitor C1 and the probe coil 1001), and the second terminal of the second capacitor C2 is grounded. Thus, the first capacitor C1, the second capacitor C2, the probe coil 1001, and the temperature drift suppression circuit 1002 can together form an AC detection network. When the distance between the target and the probe coil 1001 changes, the electromagnetic coupling state between the probe coil 1001 and the target changes, causing a change in the impedance of the probe coil 1001, which in turn causes a corresponding phase change in the detection signal output from node N relative to the excitation signal. The subsequent demodulation circuit 400 can generate a demodulated signal based on this phase change to characterize the change in distance between the target and the probe coil 1001. When the distance between the target and the probe coil 1001 remains unchanged but the ambient temperature changes, the temperature drift suppression circuit 1002 can reduce or offset the influence of impedance changes caused by temperature drift of the probe coil 1001 on the detection signal.

[0041] The demodulation circuit 400 is coupled to the detection circuit 300 and the probe coil 1001 respectively, and is configured to receive the excitation signal and the detection signal, and output the demodulation signal corresponding to the phase change of the detection signal relative to the excitation signal.

[0042] In some implementations, such as Figure 3 As shown, the demodulation circuit 400 includes a signal follower circuit 4001, a first comparator 4002, a second comparator 4003, an XOR gate 4004, and a filter circuit 4005.

[0043] The signal follower circuit 4001 is coupled to the detection circuit 300. The signal follower circuit 4001 is configured to receive the detection signal and adjust the DC reference level of the detection signal according to the voltage reference signal to obtain the adjusted detection signal.

[0044] The first comparator 4002 is coupled to the signal follower circuit 4001. The first comparator 4002 is configured to use a voltage reference signal as a comparison reference to convert the adjusted detection signal into a first square wave signal.

[0045] The second comparator 4003 is coupled to the excitation follower circuit 2003. The second comparator 4003 is configured to convert the excitation signal into a second square wave signal using a voltage reference signal as a comparison reference.

[0046] XOR gate 4004 is coupled to the first comparator 4002 and the second comparator 4003. XOR gate 4004 is configured to perform an XOR operation on the first square wave signal and the second square wave signal to output a pulse signal. The larger the phase difference between the first and second square wave signals, the larger the duty cycle of the pulse signal output by XOR gate 4004; the smaller the phase difference between the first and second square wave signals, the smaller the duty cycle of the pulse signal output by XOR gate 4004.

[0047] The filter circuit 4005 is coupled to the XOR gate 4004. The filter circuit 4005 is configured to filter the pulse signal to output a demodulated signal corresponding to the duty cycle of the pulse signal. Since the duty cycle of the pulse signal is related to the phase difference between the detection signal and the excitation signal, the demodulated signal output by the filter circuit 4005 can characterize the phase change of the detection signal relative to the excitation signal.

[0048] Based on the above implementation, the signal follower circuit 4001 can adjust the DC reference level of the detection signal, making the detection signal and the excitation signal have a consistent comparison reference, thus improving the stability of the subsequent comparison process. The first comparator 4002 and the second comparator 4003 respectively convert the excitation signal and the adjusted detection signal into corresponding square wave signals, facilitating the comparison of the phase difference between the two signals. The XOR gate 4004 performs an XOR operation on the two square wave signals, converting the phase difference into a pulse signal with a duty cycle corresponding to the phase difference; the filter circuit 4005 further filters the pulse signal, converting the duty cycle into a corresponding demodulated signal. Thus, the phase change of the detection signal relative to the excitation signal can be converted into a voltage signal, enabling the demodulated signal to accurately reflect the impedance changes of the impedance network, providing a basis for subsequently determining the position changes of the target under test.

[0049] The following is combined with Figure 4 The principle of temperature drift suppression circuit 1002 in reducing temperature drift error is explained. Figure 4 This is a schematic diagram of the equivalent circuit of a probe coil 1001 provided in an embodiment of this application.

[0050] Since the probe coil 1001 is typically wound with copper wire, it is not an ideal inductive element, but rather possesses both resistive and inductive components. Specifically, as... Figure 4 As shown, the probe coil 1001 can be equivalent to a resistor R0 and an inductor L0 connected in series. The resistance of R0 is mainly generated by the coil wires and varies with ambient temperature; the inductance of L0 is mainly determined by the coil structure and the electromagnetic coupling between the probe coil 1001 and the target being measured. Therefore, the impedance of the probe coil 1001 can be expressed as: (1).

[0051] in, This indicates the impedance corresponding to probe coil 1001; Indicates the reference temperature; This indicates the actual temperature of the environment in which the probe coil 1001 is located; This indicates that probe coil 1001 is at the reference temperature. The resistance value below; α0 represents the temperature coefficient of resistance of probe coil 1001; Indicates the imaginary part unit; This represents the angular frequency of the excitation signal. This indicates the inductance value of probe coil 1001; This indicates the resistance value of resistor R0 at temperature T.

[0052] From equation (1), it can be seen that at the current temperature, the impedance of probe coil 1001 includes and Among them, resistance It is mainly used to reflect changes in the distance between the probe coil 1001 and the target being measured. When the target being measured moves closer to or further away from the probe coil 1001, the electromagnetic coupling state between the probe coil 1001 and the target changes, causing the inductance value of the probe coil 1001 to change. The inductance changes, which in turn causes a change in the impedance of the probe coil 1001. However, the impedance change of the probe coil 1001 does not originate solely from the inductance value. The resistance of probe coil 1001 (which can be equivalent to the resistance of resistor R0) changes with the ambient temperature. Even if the position of the target being measured does not change, the resistance of probe coil 1001 will change with the temperature, which will cause the impedance of probe coil 1001 to change.

[0053] For eddy current sensors employing impedance or phase detection methods, the detection circuit 300 typically determines the distance between the target and the probe coil 1001 based on the impedance change of the probe coil 1001. Therefore, when the impedance change of the probe coil 1001 originates from a temperature change rather than a distance change, the detection circuit 300 may still misinterpret this impedance change as a change in the target's position, resulting in temperature drift error and reducing the measurement accuracy and stability of the eddy current sensor.

[0054] To reduce the aforementioned temperature drift error, this application connects a temperature drift suppression circuit 1002 in series with the probe coil 1001, so that the probe coil 1001 and the temperature drift suppression circuit 1002 are connected in series to jointly form an impedance network 100. The impedance corresponding to the impedance network 100 can then be expressed as: (2).

[0055] in, This represents the impedance corresponding to impedance network 100. This indicates the impedance corresponding to the temperature drift suppression circuit 1002.

[0056] In some implementations, the impedance corresponding to the temperature drift suppression circuit 1002 It changes with temperature, and this impedance The trend, magnitude, and / or rate of change with temperature can be pre-designed to suppress or compensate for impedance drift in the probe coil 1001 caused by temperature variations. Specifically, the resistance of the probe coil 1001 easily changes with temperature, causing impedance drift. By incorporating a temperature drift suppression circuit 1002, the impact of temperature drift in the resistance of the probe coil 1001 on its impedance can be reduced.

[0057] In some embodiments, the direction of impedance change with temperature corresponding to the temperature drift suppression circuit 1002 is opposite to the direction of resistance change with temperature corresponding to the probe coil 1001. The absolute value of the second rate of change of the impedance corresponding to the temperature drift suppression circuit 1002 with temperature is less than the absolute value of the first rate of change of the resistance of the probe coil 1001 with temperature. That is, when the resistance of the probe coil 1001 increases with increasing temperature, the impedance corresponding to the temperature drift suppression circuit 1002... The impedance can decrease as the temperature increases. Therefore, the impedance change of the temperature drift suppression circuit 1002 can offset the resistance change of the probe coil 1001, thereby reducing the amount of impedance change of the impedance network 100 with temperature, and even keeping the impedance of the impedance network 100 basically stable within a preset temperature range.

[0058] In other embodiments, the impedance of the temperature drift suppression circuit 1002 changes in the same direction as the resistance of the probe coil 1001 changes with temperature, but the rate of change of the impedance of the temperature drift suppression circuit 1002 with temperature is less than the rate of change of the resistance of the probe coil 1001 with temperature. That is, when the resistance of the probe coil 1001 increases with increasing temperature, the impedance of the temperature drift suppression circuit 1002... The impedance can also increase with rising temperature, but the increase in impedance is less than the increase in resistance of probe coil 1001. By properly setting the impedance value, temperature coefficient, and connection relationship between temperature drift suppression circuit 1002 and probe coil 1001, the rate of change of impedance of impedance network 100 with temperature can be reduced, thereby weakening the impact of temperature drift of probe coil 1001 on the detection results.

[0059] Therefore, when the distance between the target and the probe coil 1001 remains constant, the temperature drift suppression circuit 1002 can compensate for the temperature drift of the probe coil 1001 when the ambient temperature changes, making the impedance drift of the impedance network 100 less than the impedance drift of the probe coil 1001 itself. Since the impedance drift of the impedance network 100 decreases with temperature changes, the phase drift or amplitude drift of the detection signal output by the detection circuit 300 also decreases accordingly, thereby reducing the temperature drift error in the detection signal and improving the measurement stability and detection accuracy of the eddy current sensor.

[0060] Furthermore, the impedance change corresponding to the impedance network 100 will affect the phase of the detection signal relative to the excitation signal. Specifically, as... Figure 5 As shown, the impedance network 100 and the capacitive element in the detection circuit 300 together form a phase detection network, the phase response of which is corresponding to the impedance of the impedance network 100. When the position of the target changes, the electromagnetic coupling state between the probe coil 1001 and the target changes, causing a change in the impedance of the impedance network 100, which in turn causes a corresponding phase change in the detection signal relative to the excitation signal. Conversely, when the position of the target remains unchanged but the ambient temperature changes, the temperature drift suppression circuit 1002 can reduce the drift of the impedance of the impedance network 100 caused by the temperature change, thereby reducing the phase drift in the detection signal caused by the temperature change.

[0061] In some implementations, such as Figure 5 As shown, the impedance network 100 is connected in parallel with the second capacitor C2 in the detection circuit 300 to form a parallel network. The impedance corresponding to the second capacitor C2 is... It can be represented as: (3).

[0062] in, This indicates the capacitance value of the second capacitor, C2. ω represents the angular frequency of the excitation signal, and j represents the imaginary unit.

[0063] The impedance corresponding to this parallel network It can be represented as: (4).

[0064] in, This represents the impedance corresponding to impedance network 100.

[0065] The first capacitor C1 is connected in series with the parallel network to form an AC detection network. The impedance corresponding to the first capacitor C1 is... It can be represented as: (5).

[0066] in, This indicates the capacitance value of the first capacitor C1.

[0067] The frequency of the excitation signal is generally selected from the resonant frequency. Then the angular frequency: .

[0068] The transfer function of the detection circuit 300 can be expressed as: (6).

[0069] Furthermore, the phase shift of the detection signal output by the detection circuit 300 relative to the excitation signal... It can be represented as: (7).

[0070] Where Im(H) represents the imaginary part of the transfer function H, and Re(H) represents the real part of the transfer function H.

[0071] From equations (2) to (7), it can be seen that the phase of the detected signal is determined by the transfer function of the detection circuit 300. The decision, and the transfer function Impedance corresponding to parallel network Related, and The impedance corresponding to impedance network 100 Therefore, the phase θ of the detection signal is related not only to the inductance L of the probe coil 1001, but also to the resistance of the probe coil 1001 and the impedance of the temperature drift suppression circuit 1002.

[0072] Therefore, when the distance between the target and the probe coil 1001 remains constant, if the ambient temperature changes, the resistance of the probe coil 1001 may drift with the temperature change. By setting the temperature drift suppression circuit 1002, the impedance drift of the probe coil 1001 caused by temperature changes can be suppressed or compensated, so that the impedance of the impedance network 100 is maintained. The amount of change with temperature decreases. Therefore, the phase drift of the detection signal caused by temperature changes can be reduced, and even the phase drift can be made close to zero within a preset temperature range.

[0073] Based on the above analysis, it can be seen that the temperature drift suppression circuit 1002 can reduce the phase drift of the detection signal by reducing the amount of impedance change of the impedance network 100 with temperature. To achieve this, the temperature drift suppression circuit 1002 can adopt an impedance structure with high temperature stability and a small impedance change amplitude with temperature. In some possible embodiments, the second rate of change is greater than or equal to zero and less than a preset value. The preset value is less than the absolute value of the first rate of change. That is, the impedance of the temperature drift suppression circuit 1002 can increase with the increase of temperature, but the increase in impedance is less than the increase in resistance of the probe coil 1001. With this setting, the impedance of the impedance network 100 can be increased after the temperature drift suppression circuit 1002 is connected in series with the probe coil 1001. Since the rate of change of impedance of the temperature drift suppression circuit 1002 with temperature is less than the rate of change of impedance of the probe coil 1001 with temperature, the amount of impedance change of the probe coil 1001 due to temperature change is less than the impedance change of the probe coil 1001. The relative proportion in the impedance network is reduced. Therefore, the impedance corresponding to impedance network 100 can be reduced. The decrease in the relative rate of change with temperature reduces the phase drift of the detection signal caused by temperature changes, thereby improving the measurement stability of the eddy current sensor.

[0074] In some embodiments, the temperature drift suppression circuit 1002 may include a low-temperature drift resistor. A low-temperature drift resistor is a resistor with a low temperature coefficient of resistance. The temperature coefficient of resistance characterizes the proportion of change in resistance relative to the initial resistance value when the temperature changes by 1°C, and its unit can be ppm / °C. For example, the temperature coefficient of resistance of the low-temperature drift resistor may be less than or equal to 25ppm / °C. In this case, the resistance of the temperature drift suppression circuit 1002 itself changes less with temperature, thereby helping to reduce its influence on the temperature drift of the detection signal output by the detection circuit 300. Of course, this application is not limited to this; the temperature coefficient of resistance of the low-temperature drift resistor can also be set to other values ​​according to the temperature drift characteristics of the probe coil 1001, the detection accuracy requirements, or the operating temperature range. It should be noted that impedance can include different forms such as resistance, inductive reactance, and capacitive reactance. When the temperature drift suppression circuit 1002 is implemented using a resistor, its impedance mainly exhibits resistive characteristics; therefore, the impedance of the temperature drift suppression circuit 1002 can be expressed by the resistance value of the resistor.

[0075] Because the temperature coefficient of resistance of the low-temperature drift resistor is much smaller than that of the probe coil 1001, its resistance changes little or almost constantly with temperature variations. Connecting the low-temperature drift resistor in series with the probe coil 1001 increases the impedance of the impedance network 100. Thus, when the probe coil 1001 experiences impedance drift due to temperature changes, the ratio of the resistance drift of the probe coil 1001 to the corresponding impedance of the impedance network 100 decreases, thereby reducing the rate of change of the impedance of the impedance network 100 with temperature. This reduces the phase or amplitude drift of the detection signal caused by changes in ambient temperature, thus lowering the temperature drift error in the detection signal.

[0076] In some embodiments, assuming the initial resistance of probe coil 1001 at a reference temperature is 10Ω and the temperature coefficient of resistance of probe coil 1001 is 3900ppm / ℃, when the temperature increases by 10℃, the change in resistance of probe coil 1001 is approximately: 10Ω × 3900ppm / ℃ × 10℃ = 0.39Ω. If probe coil 1001 is not connected in series with a low-temperature drift resistor, the 0.39Ω resistance change accounts for approximately 3.9% of the initial resistance of 10Ω, which can easily cause phase or amplitude drift of the detection signal. If a 100Ω low-temperature drift resistor is connected in series with probe coil 1001, and the temperature coefficient of resistance of the low-temperature drift resistor is 25ppm / ℃, then when the temperature increases by 10℃, the change in resistance of the low-temperature drift resistor is approximately: 100Ω × 25ppm / ℃ × 10℃ = 0.025Ω.

[0077] At this point, the initial resistance of impedance network 100 at the reference temperature increases from 10Ω to 110Ω; when the temperature rises by 10℃, the total resistance change of impedance network 100 is approximately 0.39Ω + 0.025Ω = 0.415Ω. It can be seen that the resistance change still mainly originates from probe coil 1001. Although the resistance change of probe coil 1001 itself remains approximately 0.39Ω, its proportion relative to the total resistance of impedance network 100 decreases from 0.39Ω / 10Ω to approximately 0.415Ω / 110Ω, that is, from approximately 3.9% to approximately 0.38%. Therefore, by connecting a low-temperature-drift resistor in series, the relative impact of the temperature drift of probe coil 1001's resistance on the overall impedance of impedance network 100 can be significantly reduced, thereby improving the detection stability of the eddy current sensor under temperature variation environments.

[0078] Based on the foregoing analysis, it can also be seen that the temperature drift suppression circuit 1002 can reduce the phase drift of the detection signal by decreasing the amount of impedance change of the impedance network 100 with temperature. To achieve this, the temperature drift suppression circuit 1002 can also employ an impedance structure with a negative impedance temperature coefficient. In some possible implementations, the second rate of change is less than zero. That is, the temperature drift suppression circuit 1002 has a negative temperature drift characteristic, meaning that the impedance of the temperature drift suppression circuit 1002 decreases as the ambient temperature increases. Since the impedance of the probe coil 1001 typically increases with temperature, the temperature drift suppression circuit 1002 with negative temperature drift characteristics can generate an impedance change in the opposite direction to the impedance change of the probe coil 1001 when the temperature rises.

[0079] Specifically, when the ambient temperature rises, the impedance of the probe coil 1001 may increase due to its increased resistance, while the impedance of the temperature drift suppression circuit 1002 decreases with increasing temperature. As the temperature rises, the decrease in impedance of the temperature drift suppression circuit 1002 can partially or completely offset the increase in impedance of the probe coil 1001, thereby reducing the rate of change of impedance of the impedance network 100 formed by the probe coil 1001 and the temperature drift suppression circuit 1002 with temperature. Therefore, when the distance between the target and the probe coil 1001 remains constant while the ambient temperature changes, the impedance change of the impedance network 100 caused by the temperature drift of the probe coil 1001 itself can be reduced, decreasing the phase or amplitude drift of the detection signal caused by temperature changes, thereby reducing measurement errors and improving the measurement accuracy and stability of the eddy current sensor.

[0080] In some implementations, such as Figure 6As shown, the temperature drift suppression circuit 1002 is a universal impedance transformer 1003. The universal impedance transformer 1003 includes multiple impedance elements, and the rate of change of the impedance of each impedance element with temperature is greater than zero. The rate of change of the equivalent impedance of the universal impedance transformer 1003 with temperature is the second rate of change mentioned above. In some embodiments, the universal impedance transformer 1003 includes a first amplifier 10021, a second amplifier 10022, and multiple impedance elements. The multiple impedance elements include a first impedance element 10023, a second impedance element 10024, a third impedance element 10025, a fourth impedance element 10026, and a fifth impedance element 10027 connected in series. The first end of the first impedance element 10023 is coupled to the probe coil 1001. The non-inverting input of the first amplifier 10021 is coupled to the end of the first impedance element 10023 that is not coupled to the second impedance element 10024. The inverting input of the first amplifier 10021 is coupled to node B between the second impedance element 10024 and the third impedance element 10025. The output of the first amplifier 10021 is coupled to node C between the third impedance element 10025 and the fourth impedance element 10026. The non-inverting input of the second amplifier 10022 is coupled to node D between the fourth impedance element 10026 and the fifth impedance element 10027. The inverting input of the second amplifier 10022 is coupled to node B between the second impedance element 10024 and the third impedance element 10025. The output of the second amplifier 10022 is coupled to node A between the first impedance element 10023 and the second impedance element 10024. In other embodiments, the universal impedance transformer can also... Figure 6 Adding resistors or capacitors to the basic components can achieve impedance transformation, and these will not be listed one by one.

[0081] Through the aforementioned connections, the first amplifier 10021, the second amplifier 10022, and the first impedance element 10023 to the fifth impedance element 10027 together constitute an impedance transformation circuit. This impedance transformation circuit can perform an equivalent transformation on the impedance of each impedance element, so that the temperature drift suppression circuit 1002 appears as an equivalent impedance on the probe coil 1001 side. That is to say, although the temperature drift suppression circuit 1002 internally includes an amplifier and multiple impedance elements, when viewed from the probe coil 1001 side, the temperature drift suppression circuit 1002 can be equivalently represented as an impedance element connected between the probe coil 1001 and the ground terminal.

[0082] Furthermore, by appropriately setting the impedance values ​​and temperature characteristics of the first impedance element 10023 to the fifth impedance element 10027, the impedance and its temperature change characteristics presented by the temperature drift suppression circuit 1002 from the probe coil 1001 side can be adjusted. For example, this impedance can be made to have a negative temperature drift characteristic. In this way, when the ambient temperature rises, the impedance corresponding to the temperature drift suppression circuit 1002 can decrease with the increase in temperature, thereby offsetting the increasing impedance trend of the probe coil 1001 caused by the increase in temperature. As a result, the amount of impedance change of the impedance network 100 with temperature can be reduced, thus reducing the impact of temperature changes on the detection signal.

[0083] Specifically, any one of the first impedance element 10023, the second impedance element 10024, the third impedance element 10025, the fourth impedance element 10026, and the fifth impedance element 10027 includes at least one of a resistor, a capacitor, or an inductor. That is, all five impedance elements can be resistors, or they can include two or three combinations of resistors, capacitors, and inductors; this application does not limit this. By configuring the element types of the first to fifth impedance elements, a temperature drift suppression circuit 1002 with different impedance characteristics can be constructed, providing a basis for subsequent adjustment of the impedance value and temperature characteristics of the temperature drift suppression circuit 1002.

[0084] In some embodiments, the rate of change of impedance corresponding to the first impedance element 10023, the second impedance element 10024, the third impedance element 10025, the fourth impedance element 10026, and the fifth impedance element 10027 with temperature is greater than zero, and the second rate of change is less than zero. That is, all five impedance elements can be impedance elements with a positive temperature coefficient. For example, all five impedance elements can be resistors with a positive temperature coefficient of resistance. Although the impedance of each impedance element increases with increasing temperature, the direction and degree of its influence on the equivalent impedance of the temperature drift suppression circuit 1002 differs due to the different positions of each impedance element in the impedance transformation circuit. Therefore, by configuring the temperature coefficient of each impedance element, the equivalent impedance of the temperature drift suppression circuit 1002 can be made to decrease with increasing temperature, thereby causing the temperature drift suppression circuit 1002 to exhibit a negative temperature coefficient impedance characteristic overall.

[0085] In some embodiments, such as Figure 7As shown, the first impedance element 10023 is the first resistor R1, the second impedance element 10024 is the second resistor R2, the third impedance element 10025 is the third resistor R3, the fourth impedance element 10026 is the fourth resistor R4, and the fifth impedance element 10027 is the fifth resistor R5. All impedance elements 10023 to 10027 are implemented using resistors. Therefore, the temperature drift suppression circuit 1002 can form an impedance transformation structure composed of multiple resistors, facilitating the adjustment of the impedance of the temperature drift suppression circuit 1002 and its temperature-dependent variation trend by configuring the resistance value and temperature coefficient of each resistor. Furthermore, using resistors to implement the above impedance elements results in a relatively simple circuit structure, and the components are easy to select and integrate, which improves the ease of implementation and stability of the temperature drift suppression circuit 1002.

[0086] At this time, the impedance of the temperature drift suppression circuit 1002 is: Z T =R1×R3×R5 / (R2×R4) (8).

[0087] Among them, Z T The impedances corresponding to the temperature drift suppression circuit 1002 are represented by R1, R2, R3, R4 and R5, which respectively represent the resistance values ​​of the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4 and the fifth resistor R5.

[0088] In other embodiments, such as Figure 8 As shown, the first impedance element 10023 is the third capacitor C3, the second impedance element 10024 is the sixth resistor R6, the third impedance element 10025 is the seventh resistor R7, the fourth impedance element 10026 is the eighth resistor R8, and the fifth impedance element 10027 is the fourth capacitor C4. In other embodiments, the first to fifth impedance elements can also be other combinations of capacitors, inductors, and resistors.

[0089] The following will provide a detailed introduction. Figure 7 The working principle of the temperature drift suppression circuit 1002 shown is illustrated below. Equation (8) is derived below based on the operating states of the first amplifier 10021 and the second amplifier 10022. Both the first amplifier 10021 and the second amplifier 10022 can be operational amplifiers, and both operate in the linear amplification region. The non-inverting input terminal of the first amplifier 10021 is connected to a voltage V. IN The inverting input of the first amplifier 10021 is coupled to node B, and the voltage at node B is voltage V. B The non-inverting input of the second amplifier 10022 is coupled to node D, and the voltage at node D is voltage V. DThe inverting input of the second amplifier 10022 is coupled to node B, and the voltage at node B is voltage V. B The voltage at node A is V. A The voltage at node C is V. C .

[0090] Since both the first amplifier 10021 and the second amplifier 10022 operate in the linear amplification region, according to the virtual short characteristic of operational amplifiers, we have: V IN =V B V D =V B Thus, V is obtained. IN =V D (9).

[0091] Meanwhile, based on the virtual open characteristic of the operational amplifier input, the input currents of the first amplifier 10021 and the second amplifier 10022 are approximately zero. Therefore, the current flowing through the second resistor R2 is equal to the current flowing through the third resistor R3, that is: (10).

[0092] And because of V IN =V B Equation (10) can be transformed into: (11).

[0093] Furthermore, the current flowing through the fifth resistor R5 is equal to the current flowing through the fourth resistor R4, that is: (12).

[0094] And because of V IN =V D Then equation (12) can be transformed into: (13).

[0095] Input current of temperature drift suppression circuit 1002 This can be expressed as the current flowing through the first resistor R1, that is: (14).

[0096] From equation (11), we can obtain: (15).

[0097] Substituting equation (13) into equation (15), we get: (16).

[0098] Substituting equation (14) into equation (16), we get: (17).

[0099] Therefore, the impedance of the temperature drift suppression circuit 1002 is expressed as: (18).

[0100] As can be seen from the above derivation, the impedance of the temperature drift suppression circuit 1002 is not determined by the resistance value of a single resistor, but by the combined resistance of R1, R2, R3, R4, and R5. Specifically, R1, R3, and R5 are located in the numerator of the impedance expression (18). When their resistance values ​​increase, the impedance Z of the temperature drift suppression circuit 1002 increases. T As the resistance increases, the impedance Z of the temperature drift suppression circuit 1002 also increases; R2 and R4 are in the denominator of the impedance expression (18), and as their resistance increases, the impedance Z of the temperature drift suppression circuit 1002 also increases. T Instead, it decreases. Therefore, by configuring the resistance values ​​of each resistor and their temperature coefficients, the impedance of the temperature drift suppression circuit 1002 and the trend of its change with temperature can be adjusted.

[0101] Based on the aforementioned impedance transformation relationship, even if some or all of the resistors used in the temperature drift suppression circuit 1002 have a positive temperature coefficient of resistance, the temperature drift suppression circuit 1002 can exhibit low or negative temperature drift characteristics by placing resistors with larger temperature coefficients in the denominator and / or placing resistors with smaller temperature coefficients in the numerator. Thus, the temperature drift suppression circuit 1002 can be used to suppress or compensate for impedance drift in the probe coil 1001 caused by temperature changes.

[0102] In some embodiments, the ratio of the rate of change of resistance of the first resistor R1, the third resistor R3, and the fifth resistor R5 with temperature to the rate of change of resistance of the corresponding second resistor R2 with temperature is less than 0.1, and the ratio of the rate of change of resistance of the first resistor R1, the third resistor R3, and the fifth resistor R5 with temperature to the rate of change of resistance of the corresponding fourth resistor R4 with temperature is less than 0.1. That is, the first resistor R1, the third resistor R3, and the fifth resistor R5 can be low-temperature drift resistors with a positive temperature coefficient of resistance, and the second resistor R2 and the fourth resistor R4 can be high-temperature drift resistors with a positive temperature coefficient of resistance. A low-temperature drift resistor refers to a resistor whose resistance changes little with temperature, for example, a temperature coefficient of resistance greater than zero and less than or equal to 25 ppm / ℃; a high-temperature drift resistor refers to a resistor whose resistance changes significantly with temperature, for example, a temperature coefficient of resistance greater than 2000 ppm / ℃. The ratio of the temperature coefficient of resistance of the first resistor R1, the third resistor R3, and the fifth resistor R5 to the temperature coefficient of resistance of the second resistor R2 is less than 0.1, and the ratio of the rate of change of resistance of the first resistor R1, the third resistor R3, and the fifth resistor R5 with temperature to the rate of change of resistance of the corresponding fourth resistor R4 with temperature is less than 0.1. In some embodiments, this ratio may be further less than 0.08, 0.05, or 0.01. For example, the first resistor R1, the third resistor R3, and the fifth resistor R5 may be resistors with a temperature coefficient of resistance of 25 ppm / ℃, and the second resistor R2 and the fourth resistor R4 may be resistors with a temperature coefficient of resistance of 2850 ppm / ℃, and their ratio 25 / 2850 = 0.009 < 0.1.

[0103] With the above configuration, when the ambient temperature rises, the resistance changes of the second resistor R2 and the fourth resistor R4 are much greater than those of the first resistor R1, the third resistor R3, and the fifth resistor R5. Since R2 and R4 are in the denominator of the impedance expression, increasing R2 and R4 will reduce the impedance of the temperature drift suppression circuit 1002. Therefore, even if the first resistor R1 to the fifth resistor R5 are all positive temperature drift resistors, the impedance transformation relationship can make the temperature drift suppression circuit 1002 present a negative temperature drift impedance overall.

[0104] To more effectively compensate for the positive temperature drift impedance of the probe coil 1001, the temperature coefficients of resistance of the second resistor R2 and the fourth resistor R4 can be further matched with the temperature coefficient of resistance of the probe coil 1001. A detailed analysis will be provided below. Further, in some embodiments, the temperature coefficients of resistance of the second resistor R2 and / or the fourth resistor R4 can be equal to or close to the temperature coefficient of resistance of the probe coil 1001. For example, when the probe coil 1001 is wound with copper wire, the second resistor R2 and / or the fourth resistor R4 can be resistors with temperature coefficients close to those of copper wire. Exemplarily, the temperature coefficient of resistance of the probe coil 1001 is 2900 ppm / ℃, and the temperature coefficients of resistance of the second resistor R2 and / or the fourth resistor R4 can be 2850 ppm / ℃ or 2900 ppm / ℃, or other values ​​close to the temperature coefficient of resistance of the probe coil 1001. In some embodiments, the second resistor R2 and / or the fourth resistor R4 are metal film resistors. For example, a metal film resistor can be a platinum film resistor.

[0105] By setting it up in this way, the negative temperature drift characteristic of the temperature drift suppression circuit 1002 can be matched with the positive temperature drift characteristic of the probe coil 1001. When the temperature rises, the resistance of the probe coil 1001 increases with the temperature, while the impedance of the temperature drift suppression circuit 1002 decreases with the temperature. The two change in opposite directions, thus reducing the impedance change of the impedance network 100.

[0106] To enable the impedance of the temperature drift suppression circuit 1002 to more effectively compensate for the positive temperature drift impedance of the probe coil 1001, the impedance of the temperature drift suppression circuit 1002 at the reference temperature can be further adjusted. The relationship between the impedance of the temperature drift suppression circuit 1002 and temperature is further explained below.

[0107] The temperature coefficient of resistance of the second resistor R2 is α2, and the temperature coefficient of resistance of the fourth resistor is α4, where α2>0 and α4>0. The first resistor R1, the third resistor R3, and the fifth resistor R5 are all low-temperature drift resistors, whose resistance changes little with temperature and can be approximated as not changing with temperature.

[0108] At the reference temperature T0, the resistance of the first resistor R1 is R1, the resistance of the second resistor R2 is R2, the resistance of the third resistor R3 is R3, the resistance of the fourth resistor R4 is R4, and the resistance of the fifth resistor R5 is R5. At this time, the initial impedance Z(T0) of the temperature drift suppression circuit 1002 at the reference temperature T0 can be expressed as: (19).

[0109] When the temperature rises from T0 to T, the temperature change is ΔT, where ΔT = T - T0. At this time, the resistance of the second resistor R2 can be approximated as R2 × (1 + α²ΔT), and the resistance of the fourth resistor R4 can be approximated as R4 × (1 + α⁴ΔT). Since the first resistor R1, the third resistor R3, and the fifth resistor R5 are low-temperature drift resistors, their resistance changes can be approximated as negligible. At temperature T, the impedance Z(T) of the temperature drift suppression circuit 1002 can be expressed as: (20).

[0110] As can be seen from equation (20), since the second resistor R2 and the fourth resistor R4 are located in the denominator of the resistance expression, when the resistance values ​​of the second resistor R2 and the fourth resistor R4 increase with increasing temperature, the impedance Z(T) of the temperature drift suppression circuit 1002 decreases with increasing temperature. Therefore, even though the second resistor R2 and the fourth resistor R4 are both positive temperature drift resistors, the temperature drift suppression circuit 1002 can be made to exhibit negative temperature drift characteristics as a whole through impedance transformation.

[0111] Furthermore, when both α2ΔT and α4ΔT are small, equation (20) can be approximated as: (twenty one).

[0112] According to equation (21), the equivalent temperature coefficient of the temperature drift suppression circuit 1002 is approximately (α2+α4). That is to say, the second resistor R2 and the fourth resistor R4 each contribute negative temperature drift regulation to the temperature drift suppression circuit 1002. After the two work together, the equivalent resistance of the temperature drift suppression circuit 1002 decreases as the temperature increases.

[0113] The initial resistance of probe coil 1001 at the reference temperature T0 is R0, and the temperature coefficient of resistance of probe coil 1001 is α0. When the temperature increases from T0 to T, the resistance of probe coil 1001 can be approximately expressed as: R0×(1+α0ΔT).

[0114] Therefore, the resistive component in the impedance network 100 formed by the probe coil 1001 and the temperature drift suppression circuit 1002 connected in series can be approximately expressed as: R0×(1+α0ΔT)+ (twenty two).

[0115] If the decrease in resistance of the temperature drift suppression circuit 1002 is to offset the increase in resistance of the probe coil 1001, then the following must be satisfied: R0×α0ΔT .

[0116] After sorting, we can obtain: (twenty three).

[0117] As shown in equation (23), the impedance Z(T0) of the temperature drift suppression circuit 1002 at the reference temperature T0 can be set according to the resistance R0 of the probe coil 1001, the temperature coefficient of resistance α0 of the probe coil 1001, the temperature coefficient of resistance α2 of the second resistor, and the temperature coefficient of resistance α4 of the fourth resistor. In this way, the decrease in resistance of the temperature drift suppression circuit 1002 can be matched with the increase in resistance of the probe coil 1001, thereby reducing the temperature drift of the impedance network 100 formed by the probe coil 1001 and the temperature drift suppression circuit 1002.

[0118] Implementation method 1: The second resistor R2 and the fourth resistor R4 are both used as temperature drift adjustment resistors.

[0119] In this embodiment, when the rates of change of the resistance values ​​of the second resistor R2 and the fourth resistor R4 with temperature are between 95% and 105% of the first rate of change, it can be considered that the rates of change of the resistance values ​​of the second resistor R2 and the fourth resistor R4 with temperature are approximately equal to the first rate of change. Specifically, when the temperature coefficients of resistance α2 of the second resistor R2 and α4 of the fourth resistor R4 are between 95% × α0 and 105% × α0, it can be considered that α2 ≈ α4 ≈ α0. Further, when α2 and α4 are between 97% × α0 and 103% × α0, it can be considered that α2 ≈ α4 ≈ α0. In some embodiments, the second resistor R2 and the fourth resistor R4 are metal film resistors. Exemplarily, the metal film resistor can be a platinum film resistor. For ease of explanation, the following description uses α2 = α4 = α0 = α as an example.

[0120] When α2=α4=α, equation (20) can be transformed into: (twenty four).

[0121] when When the value is small, equation (24) can be approximated as: (25).

[0122] According to equation (25), as the temperature increases, the impedance Z(T) of the temperature drift suppression circuit 1002 decreases, and its equivalent temperature coefficient is approximately 2α. That is to say, both the second resistor R2 and the fourth resistor R4 participate in temperature drift regulation, and both are located in the denominator of the resistance expression, therefore each contributes approximately... The equivalent temperature coefficient of α, after the combined effect of the two, the equivalent temperature coefficient of the temperature drift suppression circuit 1002 is approximately 2α.

[0123] At this point, according to equation (23), we can obtain: (26).

[0124] When both the second resistor R2 and the fourth resistor R4 are used as temperature drift adjustment resistors, and the temperature coefficients α2 and α4 of the second resistor R2 and the fourth resistor R4 are both set between 95%×α0 and 105%×α0, and the initial impedance of the temperature drift suppression circuit 1002 is set to 45%~55% of the initial resistance of the probe coil 1001, i.e., Z(T0)≈R0 / 2, then when the temperature increases by ΔT, the increase in resistance of the probe coil 1001 is approximately: R0×α×ΔT; the decrease in resistance of the temperature drift suppression circuit 1002 is approximately: (R0 / 2)×2α×ΔT, which is approximately: R0×α×ΔT; that is, the increase in resistance of the probe coil 1001 is basically equal to the decrease in resistance of the temperature drift suppression circuit 1002. It should be noted that since the actual resistance value of the resistor deviates from the ideal resistance value, i.e., parameter error, the initial impedance of the temperature drift suppression circuit 1002 can actually be 45% to 55% of the initial resistance value of the probe coil 1001, and the above effect can be achieved.

[0125] In summary, to ensure that the impedance reduction of the temperature drift suppression circuit 1002 can completely offset the resistance increase of the probe coil 1001, the initial impedance of the temperature drift suppression circuit 1002 needs to be set to 45%~55% of the initial resistance of the probe coil 1001, and the rate of change of the resistance of the second resistor R2 and the resistance of the fourth resistor R4 with temperature should be between 95% and 105% of the first rate of change. In other words, by setting the temperature coefficient of resistance α2 of the second resistor R2 and the temperature coefficient of resistance α4 of the fourth resistor R4 to be approximately equal to the temperature coefficient of resistance α0 of the probe coil 1001 (e.g., α2=α4=α0=α), and setting the initial impedance of the temperature drift suppression circuit 1002 to 45%~55% of the initial resistance of the probe coil 1001 (e.g., Z(T0)≈R0 / 2), the initial impedance and the rate of change of impedance with temperature of the temperature drift suppression circuit 1002 can be configured simultaneously so that the absolute value of the impedance change is approximately equal to the absolute value of the resistance change of the probe coil 1001. Therefore, when the ambient temperature changes, the temperature drift suppression circuit 1002 generates an impedance change in the opposite direction to the resistance change of the probe coil 1001, and partially or completely cancels the impedance drift of the probe coil 1001. This reduces or keeps the overall impedance of the impedance network 100 formed by the probe coil 1001 and the temperature drift suppression circuit 1002 from changing with temperature, thereby reducing the temperature drift of the detection signal and improving the measurement stability and accuracy of the eddy current sensor.

[0126] Implementation method 2: The second resistor R2 serves as the main temperature drift adjustment resistor.

[0127] In this embodiment, the ratio of the rate of change of resistance of the first resistor R1, the third resistor R3, the fourth resistor R4, and the fifth resistor R5 with temperature to the rate of change of resistance of the second resistor R2 with temperature is less than 0.1. In some embodiments, this ratio may be further less than 0.08, 0.05, or 0.01. Specifically, the first resistor R1, the third resistor R3, the fourth resistor R4, and the fifth resistor R5 are all low-temperature drift resistors, whose resistance changes little with temperature and can be approximated as not changing with temperature. The second resistor, as the main temperature drift adjustment resistor, is a high-temperature drift resistor with a resistance temperature coefficient of α2.

[0128] When the temperature rises from T0 to T, the resistance of the second resistor R2 can be approximately expressed as R2×(1+α2ΔT).

[0129] Since the resistance changes of the first resistor R1, the third resistor R3, the fourth resistor R4, and the fifth resistor R5 can be approximated as negligible, the impedance Z(T) of the temperature drift suppression circuit 1002 can be expressed as: (27).

[0130] When α2 When T is small, equation (27) can be approximated as: (28).

[0131] According to equation (28), as the temperature increases, the impedance Z(T) of the temperature drift suppression circuit 1002 decreases, and its equivalent temperature coefficient is approximately α2.

[0132] At this point, if it is desired that the decrease in impedance of the temperature drift suppression circuit 1002 can basically offset the increase in resistance of the probe coil 1001, then the following needs to be met: .

[0133] After sorting, we can obtain: (29).

[0134] When the temperature coefficient of resistance α2 of the second resistor R2 is between 95%×α0 and 105%×α0, it can be considered that α2≈α0. Further, when α2 is between 97%×α0 and 103%×α0, it can be considered that α2≈α0. Equation (29) can be further simplified to: Z(T0)≈R0. At this time, the second resistor R2 can be a metal film resistor. For example, the second resistor R2 can be a platinum film resistor. In summary, in order to ensure that the impedance reduction of the temperature drift suppression circuit 1002 can basically offset the resistance increase of the probe coil 1001, the initial impedance corresponding to the temperature drift suppression circuit 1002 is set to between 95% and 105% of the initial resistance corresponding to the probe coil 1001, and the rate of change of the resistance of the second resistor R2 with temperature is between 95% and 105% of the first rate of change. It should be noted that since the actual resistance value of the resistor deviates from the ideal resistance value, i.e., parameter error, the initial impedance of the temperature drift suppression circuit 1002 can actually be 95% to 105% of the initial resistance value of the probe coil 1001, and the above effect can be achieved.

[0135] In other words, the second resistor R2 serves as the primary temperature drift adjustment resistor. Its temperature coefficient of resistance α2 is set to be equal to or close to the temperature coefficient of resistance α0 of the probe coil 1001. The initial impedance of the temperature drift suppression circuit 1002 is set to be similar to the initial resistance of the probe coil 1001, i.e., Z(T0)≈R0. This allows for the simultaneous configuration of the initial impedance and the rate of change of impedance with temperature of the temperature drift suppression circuit 1002, ensuring that the absolute value of its impedance change is approximately equal to the absolute value of the resistance change of the probe coil. Consequently, when the ambient temperature changes, the temperature drift suppression circuit 1002 generates an impedance change in the opposite direction to the resistance change of the probe coil 1001, partially or completely offsetting the impedance drift of the probe coil 1001. This reduces or essentially maintains the overall impedance of the impedance network 100 formed by the probe coil 1001 and the temperature drift suppression circuit 1002 as a function of temperature, thereby reducing the temperature drift of the detection signal and improving the measurement stability and accuracy of the eddy current sensor.

[0136] Implementation method 3: The fourth resistor R4 serves as the main temperature drift adjustment resistor.

[0137] In this embodiment, the ratio of the rate of change of resistance of the first resistor R1, the second resistor R2, the third resistor R3, and the fifth resistor R5 with temperature to the rate of change of resistance of the fourth resistor R4 with temperature is less than 0.1. In some embodiments, this ratio may be further less than 0.08, 0.05, or 0.01. Specifically, the first resistor R1, the second resistor R2, the third resistor R3, and the fifth resistor R5 are all low-temperature drift resistors, whose resistance changes little with temperature and can be approximated as not changing with temperature. The fourth resistor R4, as the main temperature drift adjusting resistor, is a high-temperature drift resistor with a resistance temperature coefficient of α4.

[0138] When the temperature rises from T0 to T, the resistance of the fourth resistor R4 can be approximately expressed as R4×(1+α4ΔT).

[0139] Since the resistance changes of the first resistor R1, the second resistor R2, the third resistor R3, and the fifth resistor R5 can be approximated as negligible, the impedance Z(T) of the temperature drift suppression circuit 1002 can be expressed as: (30).

[0140] When α4 When T is small, equation (30) can be approximated as: (31).

[0141] According to equation (31), as the temperature increases, the impedance Z(T) of the temperature drift suppression circuit 1002 decreases, and its equivalent temperature coefficient is approximately α4.

[0142] At this point, if it is desired that the decrease in impedance of the temperature drift suppression circuit 1002 can substantially offset the increase in coil resistance of the probe coil 1001, then the following conditions must be met: .

[0143] After sorting, we can obtain: (32).

[0144] When the temperature coefficient of resistance α4 of the fourth resistor R4 is between 95%×α0 and 105%×α0, it can be considered that α4≈α0. Further, when α2 is between 97%×α0 and 103%×α0, it can be considered that α2≈α0. Equation (32) can be further simplified to: Z(T0)≈R0. At this time, the fourth resistor R4 can be a metal film resistor. For example, the fourth resistor R4 can be a platinum film resistor. In summary, in order to ensure that the impedance reduction of the temperature drift suppression circuit 1002 can basically offset the resistance increase of the probe coil 1001, the initial impedance corresponding to the temperature drift suppression circuit 1002 is set to 95%~105% of the initial resistance corresponding to the probe coil 1001, and the rate of change of the resistance of the fourth resistor R4 with temperature is between the first rate of change of 95% and 105%. It should be noted that since the actual resistance value of the resistor deviates from the ideal resistance value, i.e., parameter error, the initial impedance of the temperature drift suppression circuit 1002 can actually be 95% to 105% of the initial resistance value of the probe coil 1001, and the above effect can be achieved.

[0145] In other words, the fourth resistor R4 serves as the primary temperature drift adjustment resistor. The temperature coefficient of resistance α4 of the fourth resistor R4 is set to be equal to or close to the temperature coefficient of resistance α0 of the probe coil 1001. The initial impedance of the temperature drift suppression circuit 1002 is set to the initial resistance value of the probe coil 1001, i.e., Z(T0)≈R0. This allows for the simultaneous configuration of the initial impedance and the rate of change of impedance with temperature of the temperature drift suppression circuit 1002, ensuring that the absolute value of its impedance change is approximately equal to the absolute value of the resistance change of the probe coil 1001. When the ambient temperature changes, the temperature drift suppression circuit 1002 generates an impedance change in the opposite direction to the resistance change of the probe coil 1001, partially or completely offsetting the impedance drift of the probe coil 1001. This reduces or essentially maintains the overall impedance of the impedance network 100 formed by the probe coil 1001 and the temperature drift suppression circuit 1002 as a function of temperature, thereby reducing the temperature drift of the detection signal and improving the measurement stability and accuracy of the eddy current sensor.

[0146] As can be seen from the above three embodiments, when both the second resistor R2 and the fourth resistor R4 participate in temperature drift adjustment, their combined effect makes the equivalent temperature coefficient of the temperature drift suppression circuit 1002 approximately [value missing]. (α2+α4). If both α2 and α4 are close to the temperature coefficient of resistance α0 of the probe coil 1001, then the impedance of the temperature drift suppression circuit 1002 at the reference temperature can be set to 45%~55% of the corresponding resistance value of the probe coil 1001. When the second resistor R2 or the fourth resistor R4 participates in temperature drift adjustment, the equivalent temperature coefficient of the temperature drift suppression circuit 1002 is approximately α2 or α4. If the temperature coefficient of resistance of the temperature drift adjustment resistor is close to the temperature coefficient of resistance α0 of the probe coil 1001, then the impedance of the temperature drift suppression circuit 1002 at the reference temperature can be set to the resistance value corresponding to the probe coil 1001.

[0147] With the above settings, the impedance of the temperature drift suppression circuit 1002 can be flexibly set according to the number of resistors involved in temperature drift adjustment and their resistance temperature coefficients. This allows the negative temperature drift change of the temperature drift suppression circuit 1002 to match the positive temperature drift change of the probe coil 1001, thereby reducing the impedance drift of the impedance network 100 formed by the probe coil 1001 and the temperature drift suppression circuit 1002, and improving the measurement stability and accuracy of the eddy current sensor.

[0148] Furthermore, to further illustrate the impact of introducing the temperature drift suppression circuit 1002 on the detection signal, the following analysis uses an example where the temperature drift suppression circuit 1002 includes a low temperature drift resistor. This example is only used to illustrate the compensation effect of the temperature drift suppression circuit 1002 and does not constitute a limitation on the specific structure of the temperature drift suppression circuit 1002.

[0149] Assuming the inductance of probe coil 1001 is L when it is at the center of the measurement range, the inductance change of probe coil 1001 across the entire measurement range is approximately ±10%. When the target moves from the center of the measurement range to the edge, the inductance of probe coil 1001 changes. Taking the case where the inductance of probe coil 1001 decreases from L to 0.9L as an example, under this operating condition, the effects of temperature changes and target displacement changes on the phase of the detection signal are analyzed.

[0150] The first scenario involves phase changes caused by temperature variations. When the target is held at the edge of the measurement range, the inductance of the probe coil 1001 remains at 0.9L. Only changes in ambient temperature cause a change in the resistance of the probe coil 1001. For example, assuming the resistance of the probe coil 1001 increases by 1% due to temperature rise, the phase change output by the detection circuit 300 is denoted as θ. t Because of θ t This is caused by temperature changes when the position of the target being measured remains unchanged, therefore θ t This is a temperature drift interference signal.

[0151] The second scenario involves a phase change caused by displacement. In this case, the ambient temperature remains constant, therefore the resistance of the probe coil 1001 remains constant; only when the target being measured moves a displacement near the edge of the measurement range does the inductance of the probe coil 1001, 0.9L, change. For example, assuming the inductance changes by 1% after the target moves a displacement near the edge of the measurement range, the phase change output by the detection circuit 300 is denoted as θ. LBecause of θ L It reflects the positional change of the target being measured, therefore θ L This is a valid detection signal.

[0152] By comparing the temperature drift interference signal θ t and effective detection signal θ L This can be used to evaluate the degree of influence of temperature changes on the detection results. Specifically, the interference intensity η can be used to represent the temperature drift interference signal θ. t Relative to the effective detection signal θ L The proportion between: (33).

[0153] Where, the smaller η is, the greater the temperature drift interference signal θ t Relative to the effective detection signal θ L The smaller the proportion of η, the lower the impact of temperature changes on the detection results; the larger η is, the more it indicates temperature drift interference signal θ. t The easier it is to effectively detect the signal θ L It causes interference.

[0154] Combining equations (2) to (7), further analysis reveals that as the resistance of the low-temperature drift resistor gradually increases, the temperature drift interference signal θ... t and effective detection signal θ L Both will decrease. This is because, when the cryogenic drift resistor is connected in series with the probe coil 1001, it increases the impedance of the impedance network 100, thus reducing the sensitivity of the impedance network 100 to changes in the impedance and inductance of the probe coil 1001. Therefore, both the phase change caused by temperature changes and the phase change caused by changes in the position of the target being measured will decrease as the resistance of the cryogenic drift resistor increases.

[0155] However, compared to the effective detection signal θ L Temperature drift interference signal θ t The phase drop is more pronounced. In other words, the low-temperature drift resistor significantly affects the temperature drift interference signal θ. t The suppression effect is stronger than that on the effective detection signal θ L The weakening effect. Therefore, as the resistance of the low temperature drift resistor increases, the temperature drift interference signal θ... t Relative to the effective detection signal θ L The proportion of interference gradually decreases, meaning the interference intensity η gradually decreases. Simulation analysis under typical operating conditions of R0=10Ω, L=10μH, C1=0.2nF, C2=0.8nF, and f=1.59MHz reveals that η varies with the resistance R of the low-temperature drift resistor. T The changing relationship curve. For example... Figure 9 As shown, simulation results indicate that as the resistance R of the low-temperature drift resistor increases...T The gradual increase and continuous decrease of η indicate that after connecting the low-temperature drift resistor in series, the temperature drift interference signal θ caused by temperature changes is reduced. t The proportion of this signal in the detection signal is reduced, thus effectively reducing measurement errors caused by changes in ambient temperature.

[0156] Therefore, although connecting a low-temperature drift resistor in series will reduce the detection sensitivity of the impedance network 100 to the displacement change of the target to some extent, it can more significantly reduce the phase drift caused by temperature changes, thereby reducing the temperature drift interference signal θ. t The proportion of the detected signal. Therefore, by connecting a low-temperature drift resistor in series, the effective detected signal can be guaranteed to have sufficient amplitude while improving the temperature stability and measurement reliability of the eddy current sensor.

[0157] It should be noted that the aforementioned low temperature drift resistor is only one example of the temperature drift suppression circuit 1002. In other embodiments, the temperature drift suppression circuit 1002 may also employ a negative temperature drift resistor, an active negative temperature drift resistor, or other impedance compensation circuits capable of reducing the temperature coefficient of the impedance network. As long as the temperature drift suppression circuit 1002 can ensure that the rate of change of impedance of the impedance network 100 formed by the probe coil 1001 and the temperature drift suppression circuit 1002 with temperature is less than the rate of change of impedance of the probe coil 1001 itself with temperature, the detection error caused by the temperature drift of the probe coil 1001 can be reduced.

[0158] like Figure 10 As shown, this application also provides a detection device 1. The detection device 1 includes the eddy current sensor 10 in any of the above embodiments.

[0159] This inspection equipment is applicable to core semiconductor manufacturing processes such as plasma etching, physical / chemical vapor deposition, atomic layer deposition, chemical mechanical polishing, wafer inspection, and handling. It primarily addresses high-precision measurement challenges related to online wafer thickness monitoring, nanometer-level displacement positioning, vibration control, surface flatness detection, and process endpoint determination. Given that the process chambers of these devices often experience high temperatures and drastic temperature fluctuations during continuous operation, traditional eddy current sensor probe coil resistance can easily drift, affecting the equipment's position control accuracy, process repeatability, and wafer processing yield. This solution utilizes eddy current sensors with temperature drift suppression capabilities in the inspection equipment, effectively offsetting measurement errors caused by ambient temperature changes at the hardware front end. This significantly improves the equipment's measurement stability, process consistency, and long-term operational reliability under complex conditions, possessing significant engineering application value for ensuring the stability and yield of semiconductor manufacturing processes.

[0160] The above-described preferred embodiments have further illustrated the purpose, technical solutions, and advantages of this application. It should be understood that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An eddy current sensor, characterized in that, include: The probe coil, wherein the impedance of the probe coil changes with temperature at a first rate of change; as well as, A temperature drift suppression circuit is coupled to the probe coil. The impedance of the temperature drift suppression circuit changes with temperature at a second rate of change, and the absolute value of the second rate of change is less than the absolute value of the first rate of change.

2. The eddy current sensor according to claim 1, characterized in that, The second rate of change is greater than or equal to zero and less than a preset value; wherein the preset value is less than the absolute value of the first rate of change.

3. The eddy current sensor according to claim 1, characterized in that, The second rate of change is less than zero.

4. The eddy current sensor according to claim 3, characterized in that, The temperature drift suppression circuit is a universal impedance transformer, which includes multiple impedance elements. The rate of change of the impedance of the multiple impedance elements with temperature is greater than zero, and the rate of change of the equivalent impedance of the universal impedance transformer with temperature is the second rate of change.

5. The eddy current sensor according to claim 4, characterized in that, The universal impedance transformer includes: The plurality of impedance elements includes a first impedance element, a second impedance element, a third impedance element, a fourth impedance element and a fifth impedance element connected in series, wherein the first end of the first impedance element is coupled to the probe coil; A first amplifier has its non-inverting input coupled to the end of the first impedance element not coupled to the second impedance element, its inverting input coupled to the node between the second and third impedance elements, and its output coupled to the node between the third and fourth impedance elements; and... The second amplifier has its non-inverting input coupled to the node between the fourth and fifth impedance elements, its inverting input coupled to the node between the second and third impedance elements, and its output coupled to the node between the first and second impedance elements. The first impedance element, the second impedance element, the third impedance element, the fourth impedance element, and the fifth impedance element all include at least one of a resistor, a capacitor, or an inductor.

6. The eddy current sensor according to claim 5, characterized in that, The first impedance element is a first resistor, the second impedance element is a second resistor, the third impedance element is a third resistor, the fourth impedance element is a fourth resistor, and the fifth impedance element is a fifth resistor.

7. The eddy current sensor according to claim 6, characterized in that, The ratio of the rate of change of resistance of the first resistor, the third resistor, and the fifth resistor with temperature to the rate of change of resistance of the second resistor with temperature is less than 0.1, and the ratio of the rate of change of resistance of the first resistor, the third resistor, and the fifth resistor with temperature to the rate of change of resistance of the fourth resistor with temperature is less than 0.

1.

8. The eddy current sensor according to claim 7, characterized in that, The initial impedance corresponding to the temperature drift suppression circuit is 45% to 55% of the initial resistance corresponding to the probe coil, and the rate of change of the resistance of the second resistor and the resistance of the fourth resistor with temperature is between 95% and 105% of the first rate of change.

9. The eddy current sensor according to claim 6, characterized in that, The ratio of the rate of change of resistance of the first resistor, the second resistor, the third resistor, and the fifth resistor with temperature to the rate of change of resistance of the fourth resistor with temperature is less than 0.

1.

10. The eddy current sensor according to claim 9, characterized in that, The initial impedance corresponding to the temperature drift suppression circuit is set to 95% to 105% of the initial resistance value corresponding to the probe coil, and the rate of change of the resistance value of the fourth resistor with temperature is between 95% and 105% of the first rate of change.

11. The eddy current sensor according to claim 6, characterized in that, The ratio of the rate of change of resistance of the first resistor, the third resistor, the fourth resistor, and the fifth resistor with temperature to the rate of change of resistance of the second resistor with temperature is less than 0.

1.

12. The eddy current sensor according to claim 11, characterized in that, The initial impedance corresponding to the temperature drift suppression circuit is set to 95% to 105% of the initial resistance value corresponding to the probe coil, and the rate of change of the resistance value of the second resistor with temperature is between 95% and 105% of the first rate of change.

13. The eddy current sensor according to any one of claims 1-12, characterized in that, The eddy current sensor includes a detection circuit; The detection circuit is configured to: receive an excitation signal, change the phase of the excitation signal according to the total impedance change of the probe coil and the temperature drift suppression circuit connected in series, and generate a detection signal; wherein the detection signal has a phase change relative to the excitation signal corresponding to the total impedance change of the probe coil and the temperature drift suppression circuit; The detection circuit includes a first capacitor and a second capacitor; a first terminal of the first capacitor is configured to receive the excitation signal, a second terminal of the first capacitor is coupled to the probe coil, a first terminal of the second capacitor is coupled to the second terminal of the first capacitor, and a second terminal of the second capacitor is grounded.

14. A testing device, characterized in that, Including the eddy current sensor as described in any one of claims 1-13.

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