Sine constant current source excitation method for eddy current displacement sensor

Abstract

The invention discloses an eddy current displacement sensor sine constant current source excitation method, and belongs to the technical field of sensor measurement and control. The method comprises the following steps: S1, generating positive and negative symmetric reference voltages through a reference voltage source circuit; s2, outputting a square wave control signal with adjustable frequency by the control chip, and driving a switching circuit to generate a square wave taking the positive and negative reference voltage as a level; s3, processing the square wave through a filter circuit to obtain a standard sine wave voltage signal; and S4, converting the sine voltage signal into sine constant current source excitation through a Howland current source circuit, and outputting the sine constant current source excitation to a sensor probe coil. According to the invention, through combination of digital control and analog conversion, the circuit structure is simplified, the cost is significantly reduced, and convenient adjustment of the output frequency and high stability and precision of the output current are realized at the same time.

Description

Technical Field

[0001] This invention relates to the field of sensor measurement and control technology, specifically to a sinusoidal constant current source excitation method for an eddy current displacement sensor. Background Technology

[0002] An eddy current displacement sensor is a non-contact measuring device based on the principle of electromagnetic induction. It typically consists of a probe coil, an extension cable, a preamplifier, and the object being measured. Its basic working principle is as follows: the oscillating current generated by the preamplifier flows into the probe coil through the extension cable, generating an alternating magnetic field H1 around the coil. When the conductor being measured approaches this magnetic field, eddy currents are induced on its surface, which in turn generate an alternating magnetic field H2 in the opposite direction to H1. The reaction of magnetic field H2 causes a change in the equivalent impedance of the probe coil, thereby altering the coil's quality factor Q and oscillation voltage. This oscillation voltage is then converted into a distance-dependent voltage signal after detection, filtering, linear compensation, and normalization, thus achieving displacement measurement.

[0003] In the aforementioned signal chain, the excitation characteristics of the probe coil are the decisive factor affecting measurement accuracy. According to Ohm's law, the voltage across the coil is U = I × R. To accurately detect minute changes in impedance R caused by distance variations, the excitation current I must be extremely stable. Therefore, providing the coil with a highly stable sinusoidal constant current source excitation is a crucial prerequisite for ensuring the accuracy of sensor measurements. An ideal constant current source excitation should possess characteristics such as fast response speed, high constant current accuracy, and good temperature stability, with its output current not fluctuating with changes in load impedance.

[0004] However, existing sinusoidal constant current source excitation methods have significant drawbacks and cannot fully meet the above requirements. Traditional solutions often employ analog oscillator circuits combined with complex feedback control structures, resulting in a complex circuit system with numerous components and high costs. More importantly, the output frequency of such solutions is usually determined by the LC or RC resonant network in the circuit, making frequency adjustment extremely inconvenient and requiring the replacement of specific components. This severely lacks flexibility and cannot adapt to the convenient adjustment requirements of the excitation frequency in different application scenarios. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides a sinusoidal constant current source excitation method for an eddy current displacement sensor that is structurally simplified, cost-reduced, and has easily controllable frequency.

[0006] A sinusoidal constant current source excitation method for an eddy current displacement sensor includes the following steps: S1: A positive reference voltage and a negative reference voltage are generated through a reference voltage source circuit, and the positive reference voltage and the negative reference voltage are symmetrical; S2: The control chip outputs a square wave control signal, which controls the switching circuit to generate a square wave signal with the frequency of the square wave control signal, using the positive reference voltage and the negative reference voltage as inputs. The high level of the square wave signal corresponds to the positive reference voltage, and the low level corresponds to the negative reference voltage. S3: The square wave signal is filtered through a filter circuit to obtain a sinusoidal voltage signal; S4: The sinusoidal voltage signal is converted into a sinusoidal constant current source excitation through the Howland current source circuit, which is used for the probe coil of the eddy current displacement sensor.

[0007] The reference voltage source circuit includes a Zener diode and a reverse circuit. The Zener diode is used to generate a reference voltage, and the reverse circuit is used to generate the negative reference voltage.

[0008] The control chip outputs the square wave control signal through an external device, and the frequency of the square wave control signal is adjustable.

[0009] The filtering circuit is a low-pass filter circuit, used to cut off the high-frequency components in the square wave signal.

[0010] The Howland current source circuit is a voltage-to-current conversion circuit suitable for grounded loads.

[0011] The current value excited by the sinusoidal constant current source is independent of the load resistance and is only related to the voltage value of the sinusoidal voltage signal.

[0012] The Zener diode is a 2DW14A type Zener diode.

[0013] The switching circuit includes two input channels, which are respectively connected to the positive reference voltage and the negative reference voltage, and the output is switched by the square wave control signal.

[0014] The positive and negative peak values ​​of the sinusoidal voltage signal are symmetrical and the level is standard.

[0015] The present invention has the following beneficial effects: The sinusoidal constant current source excitation method for eddy current displacement sensors of this invention constructs a complete signal generation and conversion chain through the cascading of four core modules: a reference voltage source circuit, a switching circuit, a filtering circuit, and a Howland current source circuit. This scheme focuses on square wave generation and waveform transformation, abandoning the complex LC oscillator or Wien bridge analog circuit structures used in traditional schemes for directly generating sine waves, thus significantly simplifying the overall circuit architecture and reducing implementation difficulty. The square wave control signal output by the control chip is the timing source of the entire method. Since the frequency of the square wave signal is directly set by the control chip, the frequency of the final generated sinusoidal constant current source excitation can be directly and linearly adjusted by changing the output frequency of the control chip, making the frequency adjustment operation extremely simple. For simplicity and flexibility, the voltage signal is converted into current excitation using a Howland current source circuit. The Howland circuit is a recognized and classic voltage-controlled current source topology. Its inherent characteristic is that, under ideal conditions, the output current is independent of the load impedance. Using this circuit as the final output stage ensures that the excitation current supplied to the sensor coil remains stable and does not fluctuate with changes in coil impedance. The symmetrical reference voltage generated by the reference voltage source circuit is used as the initial voltage reference for the entire system. The subsequent square wave level, sine wave amplitude, and final output current value are all directly or indirectly determined by this reference voltage. This gives the accuracy of the entire system a clear and single traceability point, namely the accuracy of the reference voltage source, laying the foundation for building a high-precision system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the sinusoidal constant current source excitation generated in an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the Howland current source circuit in an embodiment of the present invention. Detailed Implementation

[0018] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] like Figure 1 , Figure 2 As shown, an embodiment of the sinusoidal constant current source excitation method for an eddy current displacement sensor according to the present invention includes the following steps: S1: A positive reference voltage and a negative reference voltage are generated through a reference voltage source circuit. The positive reference voltage and the negative reference voltage are symmetrical. S2: The control chip outputs a square wave control signal, which controls the switching circuit. It takes the positive reference voltage and the negative reference voltage as inputs to generate a square wave signal with the frequency of the square wave control signal. The high level of the square wave signal corresponds to the positive reference voltage, and the low level corresponds to the negative reference voltage. S3: The square wave signal is filtered through a filter circuit to obtain a sinusoidal voltage signal; S4: Converts the sinusoidal voltage signal into a sinusoidal constant current source excitation through the Howland current source circuit, which is used for the probe coil of the eddy current displacement sensor.

[0020] The sinusoidal constant current source excitation method for eddy current displacement sensors of this invention constructs a complete signal generation and conversion chain through the cascading of four core modules: a reference voltage source circuit, a switching circuit, a filtering circuit, and a Howland current source circuit. This scheme focuses on square wave generation and waveform transformation, abandoning the complex LC oscillator or Wien bridge analog circuit structures used in traditional schemes for directly generating sine waves, thus significantly simplifying the overall circuit architecture and reducing implementation difficulty. The square wave control signal output by the control chip is the timing source of the entire method. Since the frequency of the square wave signal is directly set by the control chip, the frequency of the final generated sinusoidal constant current source excitation can be directly and linearly adjusted by changing the output frequency of the control chip, making the frequency adjustment operation extremely simple. For simplicity and flexibility, the voltage signal is converted into current excitation using a Howland current source circuit. The Howland circuit is a recognized and classic voltage-controlled current source topology. Its inherent characteristic is that, under ideal conditions, the output current is independent of the load impedance. Using this circuit as the final output stage ensures that the excitation current supplied to the sensor coil remains stable and does not fluctuate with changes in coil impedance. The symmetrical reference voltage generated by the reference voltage source circuit is used as the initial voltage reference for the entire system. The subsequent square wave level, sine wave amplitude, and final output current value are all directly or indirectly determined by this reference voltage. This gives the accuracy of the entire system a clear and single traceability point, namely the accuracy of the reference voltage source, laying the foundation for building a high-precision system.

[0021] In this embodiment, the reference voltage source circuit includes a Zener diode and a reverse circuit. The Zener diode generates a reference voltage, and the reverse circuit generates a negative reference voltage. The control chip outputs a square wave control signal via an external device, and the frequency of the square wave control signal is adjustable. The frequency of the sine wave originates from the frequency of the square wave control signal output by the control chip. By changing the frequency of this square wave signal through software or digital configuration, the frequency of the final output sinusoidal constant current source excitation can be directly and linearly adjusted. This overcomes the shortcomings of traditional LC / RC analog oscillator circuits, such as inconvenient frequency adjustment and reliance on component replacement, giving the device excellent flexibility and adaptability.

[0022] In this embodiment, the filtering circuit is a low-pass filter circuit, used to cut off high-frequency components in the square wave signal. The Howland current source circuit is a voltage-to-current conversion circuit suitable for grounded loads. The current value excited by the sinusoidal constant current source is independent of the load resistance and only related to the voltage value of the sinusoidal voltage signal. This circuit structure itself has the characteristic that the output current is independent of the load resistance; as long as the input voltage is stable, it can provide a highly stable constant current output. This ensures that the excitation current flowing into the eddy current sensor coil does not fluctuate with changes in coil impedance due to factors such as temperature and distance, laying a solid foundation for accurate measurement.

[0023] In this embodiment, the Zener diode is a 2DW14A type Zener diode. The 2DW14A Zener diode is a mature high-precision device, and its accuracy and temperature stability can be reliably guaranteed through device selection. This design makes the accuracy of the sinusoidal constant current excitation output by the system controllable and predictable, and it is easy to meet the needs of different application scenarios by selecting reference source devices with different accuracy levels.

[0024] In this embodiment, the switching circuit includes two input channels, which are respectively connected to a positive reference voltage and a negative reference voltage. The output is switched by a square wave control signal, and the positive and negative peak values ​​of the sinusoidal voltage signal are symmetrical and the level is standard. By smoothing the square wave signal through a filtering circuit, high-frequency harmonic components can be effectively filtered out, thereby obtaining a sinusoidal voltage signal with symmetrical positive and negative peak values ​​and a standard level. This provides a high-quality voltage reference for the subsequent generation of high-purity sinusoidal constant current excitation.

[0025] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sinusoidal constant current source excitation method for an eddy current displacement sensor, characterized in that, Includes the following steps: S1: A positive reference voltage and a negative reference voltage are generated through a reference voltage source circuit, and the positive reference voltage and the negative reference voltage are symmetrical; S2: The control chip outputs a square wave control signal, which controls the switching circuit to generate a square wave signal with the frequency of the square wave control signal, using the positive reference voltage and the negative reference voltage as inputs. The high level of the square wave signal corresponds to the positive reference voltage, and the low level corresponds to the negative reference voltage. S3: The square wave signal is filtered through a filter circuit to obtain a sinusoidal voltage signal; S4: The sinusoidal voltage signal is converted into a sinusoidal constant current source excitation through the Howland current source circuit, which is used for the probe coil of the eddy current displacement sensor.

2. The method as described in claim 1, characterized in that, The reference voltage source circuit includes a Zener diode and a reverse circuit. The Zener diode is used to generate a reference voltage, and the reverse circuit is used to generate the negative reference voltage.

3. The method as described in claim 1, characterized in that, The control chip outputs the square wave control signal through an external device, and the frequency of the square wave control signal is adjustable.

4. The method as described in claim 1, characterized in that, The filtering circuit is a low-pass filter circuit, used to cut off the high-frequency components in the square wave signal.

5. The method as described in claim 1, characterized in that, The Howland current source circuit is a voltage-to-current conversion circuit suitable for grounded loads.

6. The method as described in claim 1, characterized in that, The current value excited by the sinusoidal constant current source is independent of the load resistance and is only related to the voltage value of the sinusoidal voltage signal.

7. The method as described in claim 2, characterized in that, The Zener diode is a 2DW14A type Zener diode.

8. The method as described in claim 1, characterized in that, The switching circuit includes two input channels, which are respectively connected to the positive reference voltage and the negative reference voltage, and the output is switched by the square wave control signal.

9. The method as described in claim 1, characterized in that, The positive and negative peak values ​​of the sinusoidal voltage signal are symmetrical and the level is standard.

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