An eddy current sensor system

Abstract

This invention belongs to the field of sensor technology, specifically relating to an eddy current sensor system, including a signal conditioning circuit, a coaxial cable, and a probe-end circuit. The signal conditioning circuit includes a power amplification module for superimposing a DC bias voltage with an AC excitation signal to generate a mixed signal, which is then transmitted to the probe-end circuit via the coaxial cable. The probe-end circuit includes a series capacitor, a filter circuit, and a follower. The series capacitor couples an AC excitation signal from the mixed signal to drive the probe coil. The filter circuit extracts a DC bias voltage from the mixed signal to power the follower. The follower receives the impedance change signal of the probe coil and transmits it back to the signal conditioning circuit via the coaxial cable. This invention eliminates the influence of the distributed parameters of the coaxial cable on the probe characteristics. The length of the coaxial cable can be arbitrarily extended or shortened without re-matching and calibration. It also eliminates the output drift problem caused by bending of the coaxial cable and simplifies the system wiring complexity.

Description

Technical Field

[0001] This utility model belongs to the field of sensor technology, specifically relating to an eddy current sensor system, which is mainly used for non-contact displacement measurement and condition monitoring of metal target conductors in fields such as industrial automation, precision manufacturing, aerospace, and energy power. Background Technology

[0002] An eddy current sensor consists of a probe coil, a target conductor, and a signal processing circuit. Applying a high-frequency alternating current to the probe coil induces eddy currents in the target conductor using the coil's magnetic field. These eddy current magnetic fields cancel each other out. As the distance between the coil and the target conductor changes, the strength of the eddy currents varies, thus affecting the inductance and resistance of the probe coil. The displacement of the target conductor can be obtained by measuring the impedance change of the coil. To achieve impedance measurement, a parallel resonant circuit consisting of the probe coil's inductance and capacitance is typically used. The coaxial cable connecting the probe and the signal conditioning circuit has its own equivalent distributed capacitance, which forms a parallel relationship with the probe's capacitance, leading to an increase in the total equivalent capacitance of the circuit and a decrease in the resonant frequency.

[0003] In existing technologies, the distributed parameters of the coaxial cable and the probe coil jointly determine the probe's characteristics. When the length of the coaxial cable changes, its distributed inductance and capacitance also change, leading to variations in the cable's impedance characteristics. Shifts in the resonant frequency disrupt the system's original impedance matching, resulting in decreased sensor sensitivity, poor linearity, and reduced measurement accuracy. Therefore, the length of the coaxial cable cannot be arbitrarily increased or decreased. Any change in length necessitates re-impedance matching of the signal conditioning circuit and recalibration of the system, increasing the complexity and cost of installation and maintenance.

[0004] Furthermore, in practical applications, coaxial cables inevitably experience bending or twisting. Bending alters the distributed parameters of the coaxial cable, leading to changes in impedance characteristics and directly manifesting as drift or jumps in the sensor output. This problem is particularly pronounced in confined spaces or when the probe needs frequent movement, severely impacting measurement stability and reliability. Therefore, existing eddy current sensor systems have significant shortcomings in cable routing flexibility and measurement consistency, necessitating an improved solution that eliminates the influence of coaxial cable distributed parameters. Summary of the Invention

[0005] The purpose of this invention is to provide an eddy current sensor system to solve the problems in the prior art where changes in the distributed parameters of the coaxial cable affect the probe characteristics, requiring recalibration of the circuit when the length of the coaxial cable changes, and output changes caused by bending of the coaxial cable.

[0006] To address the aforementioned problems, this utility model provides an eddy current sensor system, comprising: a signal conditioning circuit, a coaxial cable, and a probe end circuit; The signal conditioning circuit includes a power amplification module, which is used to superimpose the DC bias voltage and the AC excitation signal to generate a mixed signal, and transmit it to the probe end circuit through the coaxial cable. The probe end circuit includes: A series capacitor, whose input terminal is connected to the coaxial cable, is used to couple the AC excitation signal from the mixed signal to drive the probe coil; A filter circuit, whose input is connected to the coaxial cable, is used to extract the DC bias voltage from the mixed signal as a power supply. The follower, powered by the filter circuit, has its input connected to the probe coil to receive the impedance change signal of the probe coil, and its output transmits the impedance change signal back to the signal conditioning circuit through the coaxial cable.

[0007] Furthermore, the signal conditioning circuit further includes: A DC power supply is used to provide the DC bias voltage; An AC signal source is used to provide the AC excitation signal; The output terminals of both the DC power supply and the AC signal source are connected to the input terminal of the power amplifier module.

[0008] Furthermore, the probe end circuit also includes a measurement bridge, which is driven by the AC excitation signal output by the series capacitor. The probe coil forms one arm of the measurement bridge, and the output terminal of the measurement bridge is connected to the input terminal of the follower.

[0009] Furthermore, the filtering circuit is an LC filtering circuit.

[0010] Furthermore, the filtering circuit is an RC filtering circuit.

[0011] Furthermore, the follower is composed of an operational amplifier or discrete components.

[0012] Furthermore, the power amplification module is a power amplifier chip; or, when the operating current of the probe end circuit is less than a preset threshold, the power amplification module is an operational amplifier with an output current capability greater than the preset threshold.

[0013] Furthermore, the signal conditioning circuit also includes a conditioning circuit connection terminal for receiving the signal transmitted back by the follower through the coaxial cable and extracting the impedance change component of the probe coil from it to obtain displacement information.

[0014] Furthermore, the signal transmitted back by the follower through the coaxial cable includes a power supply current component and an impedance change component of the probe coil. The conditioning circuit connection terminal is specifically used to extract the impedance change component from the transmitted signal.

[0015] Furthermore, the coaxial cable is a single coaxial cable, used to simultaneously transmit the mixed signal from the signal conditioning circuit to the probe end circuit, and to transmit the impedance change signal back from the probe end circuit to the signal conditioning circuit.

[0016] This utility model has the following beneficial effects: (1) This utility model uses a power amplification module to superimpose the DC bias voltage and the AC excitation signal into a mixed signal, which is transmitted to the probe end circuit via a coaxial cable. Then, the AC excitation signal and the DC power supply are separated by a series capacitor and a filter circuit, realizing the multiplexing of power supply and signal transmission. This architecture makes the coaxial cable only a transmission channel, and its distributed parameters no longer form a parallel relationship with the probe coil resonant circuit, fundamentally eliminating the influence of distributed parameters on probe characteristics. The length of the coaxial cable can be arbitrarily extended or shortened without rematching and calibration.

[0017] (2) In this invention, the impedance change signal of the probe coil is transformed by the follower and then transmitted back to the connection terminal of the conditioning circuit through the coaxial cable. The high input impedance and low output impedance characteristics of the follower effectively isolate the interference of the coaxial cable impedance fluctuation on the measurement signal, so that the characteristic impedance change when the coaxial cable is bent or twisted will not be coupled into the measurement circuit, eliminating the output drift problem caused by bending, and ensuring the consistency and reliability of the measurement results.

[0018] (3) This utility model integrates the follower and power supply at the probe end through active design of the probe end circuit, requiring only a coaxial cable to complete all connections, which greatly simplifies the number of cables and wiring complexity. After the factory calibration is completed, the user can cut or lengthen the coaxial cable according to the needs without returning it to the factory for recalibration, which reduces the cost of use and maintenance and has good prospects for industrial application. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this utility model, 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 utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a circuit structure diagram of the eddy current sensor system according to an embodiment of the present invention.

[0021] Figure labeling: 10-Signal conditioning circuit; 11-Power amplifier module; 12-DC power supply; 13-AC signal source; 14-Conditioning circuit connection terminal; 20-Coaxial cable; 30-Probe end circuit; 31-Series capacitor; 33-Follower; 34-Probe coil. Detailed Implementation

[0022] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid confusion with the present invention.

[0023] To fully understand this utility model, detailed steps and structures will be presented in the following description to illustrate the technical solution of this utility model. Preferred embodiments of this utility model are described in detail below; however, in addition to these detailed descriptions, this utility model may have other embodiments.

[0024] Figure 1 This is a schematic diagram illustrating one embodiment of the eddy current sensor system of this utility model. The eddy current sensor system includes a signal conditioning circuit 10, a coaxial cable 20, and a probe end circuit 30. The coaxial cable 20 is responsible for transmitting the mixed signal from the signal conditioning circuit 10 to the probe end circuit 30 and transmitting the impedance change signal back from the probe end circuit 30 to the signal conditioning circuit 10.

[0025] The signal conditioning circuit 10 includes a DC power supply 12 and an AC signal source 13. The DC power supply 12 provides a DC bias voltage, and the AC signal source 13 provides an AC excitation signal. The outputs of both the DC power supply 12 and the AC signal source 13 are connected to the input of the power amplifier module 11. The power amplifier module 11 superimposes the DC bias voltage and the AC excitation signal to generate a mixed signal containing both DC and AC components. The output of the power amplifier module 11 is connected to one end of a coaxial cable 20, feeding the mixed signal into the coaxial cable 20 for transmission to the probe end circuit 30.

[0026] The power amplifier module 11 can be implemented using a power amplifier chip. When the overall operating current of the probe circuit 30 is small, i.e., the operating current is below a preset threshold, the power amplifier module 11 can also be an operational amplifier with an output current capability greater than the preset threshold, which can directly provide the required driving capability, thereby replacing the power amplifier chip.

[0027] In the probe-end circuit 30, the other end of the coaxial cable 20 is connected to both the input of the series capacitor 31 and the input of the filter circuit. The function of the series capacitor 31 is to couple the AC excitation signal from the mixed signal while blocking the DC bias voltage, ensuring that only the AC excitation signal can be output through the series capacitor 31. This AC excitation signal is sent to the measuring bridge to drive it. The probe coil 34 forms one arm of the measuring bridge. When the probe coil 34 approaches the target conductor, due to the eddy current effect, the equivalent impedance of the probe coil 34 changes with the distance between the probe coil 34 and the target conductor, disrupting the balance of the measuring bridge. The output of the measuring bridge generates a signal reflecting the impedance change of the probe coil 34. The output of the measuring bridge is connected to the input of the follower 33, sending the impedance change signal to the follower 33.

[0028] The input terminal of the filter circuit is connected to coaxial cable 20 to extract the DC bias voltage from the mixed signal. The filter circuit can be an LC filter circuit, consisting of an inductor and capacitor forming a low-pass filter network to filter out AC components and retain the DC bias voltage; alternatively, it can be an RC filter circuit, consisting of a resistor and capacitor forming a low-pass filter network, achieving the same purpose of extracting the DC bias voltage. The DC bias voltage extracted by the filter circuit serves as the power supply, connected to the power supply terminal of the follower 33, providing the necessary power for the follower 33 to operate.

[0029] Follower 33 is powered by the DC bias voltage output from the filter circuit. Follower 33 can be constructed using an operational amplifier or discrete components. The input terminal of follower 33 receives the impedance change signal from the output terminal of the measuring bridge, performs impedance transformation, and outputs the signal from the output terminal of follower 33. The output terminal of follower 33 is connected to coaxial cable 20, transmitting the impedance change signal back to signal conditioning circuit 10 via coaxial cable 20. Due to the high input impedance and low output impedance characteristics of follower 33, it can effectively isolate the preceding and following circuits, ensuring the stability of signal transmission.

[0030] The signal conditioning circuit 10 also includes a conditioning circuit connection terminal 14. The conditioning circuit connection terminal 14 is connected to the coaxial cable 20 and receives the signal transmitted back from the follower 33 via the coaxial cable 20. This transmitted signal contains both the power supply current component of the probe-end circuit 30 and the impedance change component of the probe coil 34, which are superimposed. The specific function of the conditioning circuit connection terminal 14 is to extract the impedance change component of the probe coil 34 from the transmitted signal and obtain the displacement information of the target conductor based on this impedance change component.

[0031] With the above structure, the supply of DC bias voltage and the transmission of AC excitation signal are multiplexed through coaxial cable 20. The AC excitation signal and DC bias voltage are separated internally by series capacitor 31 and filter circuit within probe end circuit 30. Changes in the distributed parameters of coaxial cable 20 are no longer coupled into the measurement signal path. The length of coaxial cable 20 can be extended or bent within a certain range without affecting the measurement result of the impedance change signal of probe coil 34, and there is no need to re-match and calibrate the signal conditioning circuit 10.

[0032] The preferred embodiments of this utility model have been described above. It should be understood that this utility model is not limited to the specific embodiments described above, nor is it limited to eddy current sensor systems. Devices and structures not described in detail herein should be understood as being implemented in a manner common to the art. Any person skilled in the art can make many possible variations and modifications to the technical solutions of this utility model, or modify them into equivalent embodiments, without departing from the scope of the technical solution of this utility model. This does not affect the essential content of this utility model. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this utility model, without departing from the content of the technical solution of this utility model, still fall within the protection scope of the technical solution of this utility model.

Claims

1. An eddy current sensor system, characterized in that, include: Signal conditioning circuitry, coaxial cable, and probe end circuitry; The signal conditioning circuit includes a power amplification module, which is used to superimpose the DC bias voltage and the AC excitation signal to generate a mixed signal, and transmit it to the probe end circuit through the coaxial cable. The probe end circuit includes: A series capacitor, whose input terminal is connected to the coaxial cable, is used to couple the AC excitation signal from the mixed signal to drive the probe coil; A filter circuit, whose input is connected to the coaxial cable, is used to extract the DC bias voltage from the mixed signal as a power supply. The follower, powered by the filter circuit, has its input connected to the probe coil to receive the impedance change signal of the probe coil, and its output transmits the impedance change signal back to the signal conditioning circuit through the coaxial cable.

2. The eddy current sensor system according to claim 1, characterized in that: The signal conditioning circuit further includes: A DC power supply is used to provide the DC bias voltage; An AC signal source is used to provide the AC excitation signal; The output terminals of both the DC power supply and the AC signal source are connected to the input terminal of the power amplifier module.

3. The eddy current sensor system according to claim 1, characterized in that: The probe end circuit also includes a measurement bridge, which is driven by the AC excitation signal output by the series capacitor. The probe coil forms one arm of the measurement bridge, and the output terminal of the measurement bridge is connected to the input terminal of the follower.

4. The eddy current sensor system according to claim 1, characterized in that: The filtering circuit is an LC filtering circuit.

5. The eddy current sensor system according to claim 1, characterized in that: The filtering circuit is an RC filtering circuit.

6. The eddy current sensor system according to claim 1, characterized in that: The follower is composed of an operational amplifier or discrete components.

7. The eddy current sensor system according to claim 1, characterized in that: The power amplification module is a power amplifier chip; or, when the operating current of the probe end circuit is less than a preset threshold, the power amplification module is an operational amplifier with an output current capability greater than the preset threshold.

8. The eddy current sensor system according to claim 1, characterized in that: The signal conditioning circuit also includes a conditioning circuit connection terminal, used to receive the signal transmitted back by the follower through the coaxial cable, and extract the impedance change component of the probe coil from it to obtain displacement information.

9. The eddy current sensor system according to claim 8, characterized in that: The signal transmitted back by the follower through the coaxial cable includes a power supply current component and an impedance change component of the probe coil. The conditioning circuit connection terminal is specifically used to extract the impedance change component from the transmitted signal.

10. The eddy current sensor system according to claim 1, characterized in that: The output of the power amplifier module is connected to one end of the coaxial cable, the output of the follower is connected to the coaxial cable, the mixed signal is transmitted from the signal conditioning circuit to the probe circuit, and the impedance change signal is transmitted back from the probe circuit to the signal conditioning circuit.

Images