Precise capacitance micrometer system and micrometer method

Abstract

The precision capacitance micrometer system comprises a modulation signal source, a sensitive probe, a differential transformer bridge circuit, a signal amplification link, a multiplier and a low-pass filter circuit which are electrically connected in sequence, a double-limit comparator is arranged between the signal amplification link and the multiplier; the input end of the double-limit comparator is connected with the output end of the signal amplification link, the output end of the double-limit comparator is connected to one input end of the multiplier, and the double-limit comparator is used for shaping the amplified modulation signal and taking the shaped signal as the demodulation input signal. The invention also provides a precise capacitance micrometer method. The precise capacitance micrometer system provided by the embodiment of the invention ensures that the system output is insensitive to phase difference fluctuation within a certain demodulation phase difference range, and finally realizes high-precision measurement of micro displacement. All the modules complete full-link conversion from physical quantity to measurable voltage signals through step-by-step signal transmission and function complementation.

Description

Technical Field

[0001] This application relates to the field of precision measurement technology, and more specifically, to a precision capacitance micrometer system and micrometer measurement method. Background Technology

[0002] Capacitive micrometry, a high-precision non-contact measurement method, works by detecting the change in capacitance caused by the minute displacement of the object under test to invert the displacement. Due to its high sensitivity, good stability, fast dynamic response, and relatively simple structure, this technology is widely used in scenarios with extremely high measurement accuracy requirements, such as core sensing instruments like gravimeters, seismographs, gyroscopes, and accelerometers. In these applications, the measurement system often needs to maintain stable and reliable performance under complex conditions such as large temperature variations and electromagnetic interference. Therefore, improving the anti-interference capability and long-term stability of capacitive micrometry systems has always been a key research direction for those skilled in the art.

[0003] Currently, the differential transformer bridge structure based on sinusoidal carrier modulation and demodulation has become the main technical solution for achieving high-precision capacitance micrometry. This solution modulates a low-frequency displacement signal onto a high-frequency carrier, providing favorable conditions for subsequent signal amplification and noise suppression. In the existing technical solutions mentioned above, the demodulation stage typically requires a reference signal (such as a square wave) with the same frequency as the carrier to be multiplied by the modulated input signal. However, a phase difference inevitably exists between the demodulated reference signal and the input signal. θ Both theoretical analysis and practical application show that the final output of the system is related to cos... θ Proportional, meaning that any phase difference caused by ambient temperature drift, component parameter variations, or differences in signal transmission paths is proportional. θ Even minute fluctuations in phase difference can directly translate into measurement errors in the system output, severely limiting further improvements in measurement accuracy. To overcome this deficiency, existing technologies have proposed using orthogonal demodulation to suppress the impact of phase difference fluctuations. However, this method is structurally complex, introducing not only orthogonal errors but also a high degree of dependence on the gain and phase symmetry of the orthogonal and in-phase channels in the demodulation circuit. This makes it difficult to achieve and maintain ideal performance in practical engineering applications, increasing system complexity and cost, and making it difficult to effectively guarantee its actual anti-interference effect. Therefore, finding a demodulation scheme with a relatively simple structure, insensitive to phase difference fluctuations, and stable performance has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] In view of at least one defect or improvement need in the prior art, this application provides a precision capacitance micrometer system and micrometer method, which can solve at least one of the problems existing in the above-mentioned background art.

[0005] To achieve the above objectives, according to the first aspect of this application, a precision capacitance micrometer system is provided, comprising a modulation signal source, a sensitive probe, a differential transformer bridge, a signal amplification link, a multiplier, and a low-pass filter circuit, which are connected in sequence. The modulation signal source is used to generate a sinusoidal carrier signal. The sensitive probe includes a test mass and upper and lower plates forming a differential capacitance with the test mass, used to convert micro-displacement into a differential capacitance signal. The differential transformer bridge is connected to the differential capacitor through a primary coil to form a balanced bridge, used to modulate the differential capacitance signal onto the sinusoidal carrier and output a modulation voltage signal. The signal amplification link is connected to the differential transformer bridge, used to amplify and suppress noise in the modulation voltage signal. The multiplier is used to receive the demodulation input signal and the demodulation reference signal, perform multiplication demodulation operations, and output a demodulated signal. The low-pass filter circuit is connected to the output of the multiplier and is used to filter out high-frequency components in the demodulated signal generated by the multiplication demodulation operation and extract a DC voltage signal proportional to the micro-displacement as the system output. The feature is that it further includes a dual-limit comparator disposed between the signal amplification link and the multiplier, wherein the input terminal of the dual-limit comparator is connected to the output terminal of the signal amplification link, and the output terminal is connected to one input terminal of the multiplier, for shaping the amplified modulation signal and using the shaped signal as the demodulation input signal.

[0006] Furthermore, in the aforementioned precision capacitance micrometer system, the dual-limit comparator includes a threshold comparison unit and a 2-to-1 analog switch; The threshold comparison unit is used to determine whether the amplitude of the input signal exceeds the range defined by the upper threshold voltage and the lower threshold voltage; The 2-to-1 analog switch is controlled by the output of the threshold comparison unit. When the amplitude of the input signal is outside the range defined by the upper threshold voltage and the lower threshold voltage, the output is a signal consistent with the input signal. When the amplitude of the input signal is within the range defined by the upper threshold voltage and the lower threshold voltage, the output is a zero-level signal.

[0007] Furthermore, in the aforementioned precision capacitance micrometer system, the threshold comparison unit includes a dual-channel differential comparator, which is connected to the upper threshold voltage and the lower threshold voltage respectively. The output of the dual-channel differential comparator is compared with the upper threshold voltage and the lower threshold voltage through a combination of diodes or logic gate circuits to generate a control signal that is transmitted to the control terminal of the 2-to-1 analog switch.

[0008] Furthermore, in the aforementioned precision capacitance micrometer system, the threshold comparison unit includes an analog-to-digital converter and a programmable gate array or microprocessor. The analog-to-digital converter is used to acquire the analog signal output from the signal amplification link, and the programmable logic device or microprocessor is used to compare the digitized signal amplitude with the upper threshold voltage and the lower threshold voltage to generate a corresponding control signal, which is then transmitted to the control terminal of the 2-to-1 analog switch.

[0009] Furthermore, in the aforementioned precision capacitance micrometer system, the signal amplification link is a three-stage cascaded amplifier circuit, comprising a front-end amplifier circuit, a differential amplifier circuit, and an AC amplifier circuit connected in sequence: The front-end amplifier circuit is used to amplify the modulated voltage signal output by the differential transformer bridge and suppress input stage noise. The differential amplifier circuit is used to amplify the displacement-related differential signal and suppress common-mode noise; The AC amplifier circuit is used to amplify signals near the carrier frequency and suppress outside-bandwidth noise.

[0010] Furthermore, in the aforementioned precision capacitance micrometer system, the multiplier is a switching multiplier, and the demodulation reference signal is a waveform that is at the same frequency as the sinusoidal carrier and is symmetrical in both directions.

[0011] Furthermore, in the aforementioned precision capacitance micrometer system, the absolute values ​​of the upper threshold voltage and the lower threshold voltage are equal, and their amplitudes are lower than the amplitude of the output signal of the AC amplifier circuit.

[0012] Furthermore, in the aforementioned precision capacitance micrometer system, the dual-channel differential comparator is either integrated or constructed from discrete components.

[0013] According to a second aspect of this application, a method for precision capacitance micrometry is also provided, comprising: S100 uses a modulation signal source to generate a sinusoidal carrier signal; S200 detects the micro-displacement of the capacitor through a sensitive probe and converts the micro-displacement into a differential capacitance signal; S300 modulates the differential capacitor signal onto the sinusoidal carrier and outputs the modulated voltage signal; S400 amplifies and suppresses noise in the modulated voltage signal, inputs it to a multiplier for multiplication and demodulation, and outputs a demodulated signal. The S500 uses a low-pass filter circuit to filter out high-frequency components in the demodulated signal generated by the multiplication demodulation operation and extracts a DC voltage signal proportional to the micro-displacement as the system output. After amplifying and noise-suppressing the modulated voltage signal, and before inputting it to the multiplier, a dual-limit comparator is set to shape the amplified and noise-suppressed modulated signal, and the shaped signal is used as the demodulation input signal and input to the multiplier.

[0014] Furthermore, in the aforementioned precision capacitance micrometry method, the step of setting a dual-limit comparator to shape the modulated signal after amplification and noise suppression specifically includes: The instantaneous amplitude of the amplified modulation signal is compared with the preset upper threshold voltage and lower threshold voltage in real time. When the instantaneous amplitude of the amplified modulation signal is greater than the upper threshold voltage or less than the lower threshold voltage, the control signal is set to the first state. When the instantaneous amplitude of the amplified modulation signal is neither greater than the upper threshold voltage nor less than the lower threshold voltage, the control signal is set to the second state. Based on the state of the control signal, the output signal is selected by an analog switch. When the control signal is in the first state, the waveform output by the analog switch that is consistent with the amplified modulation signal is used as the demodulation input signal. When the control signal is in the second state, the signal output by the analog switch is set to a zero-level signal as the demodulation input signal.

[0015] Overall, compared with the prior art, the above-described technical solutions conceived in this application can achieve the following beneficial effects: This application uses a dual-limit comparator to shape the demodulated input signal, ensuring that the system output remains constant within a continuously varying phase difference range. The system output is completely insensitive to phase difference fluctuations, effectively overcoming the long-standing performance bottleneck that has limited high-precision capacitive micrometry. The shaping process of the dual-limit comparator not only affects the signal itself but also effectively suppresses noise in the low signal-to-noise ratio region near the zero-crossing point. By embedding zeros in the input signal within the range where the amplitude is below a preset threshold, mixed noise interference within this range is filtered out, improving the signal-to-noise ratio of the signal entering the demodulation stage. Simultaneously, since the system performance no longer depends on a phase relationship that is difficult to maintain absolutely stable over long periods, its tolerance to factors such as ambient temperature changes and component parameter drift is significantly enhanced, thus ensuring measurement stability and reliability in complex industrial environments or long-term monitoring tasks.

[0016] This application improves upon the differential transformer bridge structure by adding a dual-limit comparator module, which can be implemented using either an analog or a hybrid digital-analog approach. This eliminates the need for complex channel matching and calibration, avoids quadrature errors, and reduces the stringent requirements for component consistency. The pure analog solution offers fast response and low latency, making it suitable for high-dynamic measurement scenarios. The digital-analog solution allows for flexible adjustment of threshold parameters via software, easily achieving adaptive functionality and integration with subsequent digital processing. This design flexibility enables the application to optimize performance, cost, and flexibility for different application scenarios, broadening its application scope.

[0017] The precision capacitance micrometer system provided in this application organically combines the precision of capacitance micrometer measurement with the anti-interference capability of signal conditioning through the design of a core module: a dual-limit comparator. The dual-limit comparator ensures, through threshold judgment and signal shaping, that the system output is insensitive to phase difference fluctuations within a certain demodulation phase difference range, ultimately achieving high-precision measurement of micro-displacements. Each module completes the end-to-end conversion from physical quantities to measurable voltage signals through step-by-step signal transmission and functional complementarity. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments 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 This is a schematic diagram of the structure of a precision capacitance micrometer system provided in an embodiment of this application; Figure 2 This is a schematic diagram of a typical dual-limit comparator structure provided in an embodiment of this application; Figure 3 This is a schematic diagram of the low-pass filter circuit provided in an embodiment of this application; Figure 4 A schematic diagram of an integrated dual-channel differential comparator and a single-channel 2-to-1 analog switch structure provided in an embodiment of this application; Figure 5 A schematic diagram of a discrete dual-channel differential comparator and a single-channel 2-to-1 analog switch provided in an embodiment of this application; Figure 6 A schematic diagram of a digital comparator and a single-channel 2-to-1 analog switch provided in an embodiment of this application; Figure 7 This is a schematic diagram of the front-end amplifier circuit structure provided in an embodiment of this application; Figure 8 This is a schematic diagram of the differential amplifier circuit structure provided in an embodiment of this application; Figure 9 This is a schematic diagram of the AC amplifier circuit structure provided in an embodiment of this application; Figure 10 The coefficient expressions provided for the embodiments of this application and θ A diagram illustrating the changing relationships.

[0020] Figure reference numerals: 1: Modulation signal source; 2: Sensitive probe; 21: Test mass sensitive to micro-displacement; 22: Capacitance formed by the test mass and the upper plate. C 1; 23: Test mass and capacitance formed by the lower plate C 2; 22 and 23 form a differential capacitor pair, i.e., Δ C = C 1- C 2; 3: Differential transformer bridge circuit; 31 and 32: Two inductors of the primary coil of the transformer. L 1 and L 2, with C 1 and C 2 forms a bridge structure; 4: front-end amplifier circuit; 5: differential amplifier circuit; 6: AC amplifier circuit; 4, 5, and 6 form a signal amplification link; 7: dual-limit comparator; 8: multiplier; 9: demodulation reference signal; 10: low-pass filter circuit. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Furthermore, the technical features involved in the various embodiments described below can be combined with each other as long as they do not conflict with each other.

[0022] The terms "first," "second," "third," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0023] Figure 1 This is a schematic diagram of the structure of a precision capacitance micrometer system provided in an embodiment of this application, as shown below. Figure 1As shown in the figure, an embodiment of this application provides a precision capacitance micrometer system, comprising a modulation signal source, a sensitive probe, a differential transformer bridge, a signal amplification link, a multiplier, and a low-pass filter circuit, which are connected in sequence. The modulation signal source is used to generate a sinusoidal carrier signal. The sensitive probe includes a test mass and upper and lower plates forming a differential capacitance with the test mass, used to convert micro-displacement into a differential capacitance signal. The differential transformer bridge is connected to the differential capacitor through a primary coil to form a balanced bridge, used to modulate the differential capacitance signal onto the sinusoidal carrier and output a modulation voltage signal. The signal amplification link is connected to the differential transformer bridge, used to amplify and suppress noise in the modulation voltage signal. The multiplier is used to receive the demodulation input signal and the demodulation reference signal, perform multiplication demodulation operations, and output a demodulated signal. The low-pass filter circuit is connected to the output of the multiplier and is used to filter out high-frequency components in the demodulated signal generated by the multiplication demodulation operation and extract a DC voltage signal proportional to the micro-displacement as the system output. The feature is that it further includes a dual-limit comparator disposed between the signal amplification link and the multiplier, wherein the input terminal of the dual-limit comparator is connected to the output terminal of the signal amplification link, and the output terminal is connected to one input terminal of the multiplier, for shaping the amplified modulation signal and using the shaped signal as the demodulation input signal.

[0024] Specifically, such as Figure 1 As shown, the precision capacitance micrometer system provided in this application includes a modulation signal source, a sensitive probe, a differential transformer bridge, a signal amplification link, a multiplier, and a low-pass filter circuit connected in sequence. Each module in the system is described below: The modulation signal source can be directly implemented using mature DDS integrated chips, such as AD9850 and AD9959; alternatively, it can be implemented using discrete components / circuits, including digital-to-analog converters (DACs), reference voltage sources, crystal oscillators, and bandpass filters. In the field of electronics, for the generation of sinusoidal carrier waves, the more mature technologies currently used include direct analog frequency synthesis, phase-locked loop synthesis, and direct digital frequency synthesis (DDS). Among these, DDS technology stands out due to its advantages of low cost, low power consumption, high resolution, and fast conversion time, meeting the requirements of high-precision micrometry. The sinusoidal carrier signal needs to be loaded onto the test quality. Existing loading methods include direct connection via gold wire and loading via capacitive coupling. To meet the requirements of high-precision micrometry, the gold wire connection method is gradually being replaced by capacitive coupling due to the introduction of significant thermal noise. This technology can "load" weak low-frequency displacement signals to form a modulated signal with a high-frequency carrier envelope, realizing the conversion of displacement physical quantities into high-frequency electrical signals. This not only provides a spectral basis for subsequent noise suppression but also improves the stability of signal transmission and processing. The core of the sensitive probe consists of the test mass and the upper and lower parallel plates, primarily made of metallic materials or other conductive materials. The upper and lower plates are arranged parallel to the test mass, forming two differential capacitor structures. C 1: Upper electrode plate - Test quality; C 2: The lower plate (test mass) forms a low-frequency differential capacitor. The test mass is initially located in the middle of the upper and lower plates. A sinusoidal carrier wave is applied to the differential capacitor circuit, modulating the capacitance change onto the carrier wave. Simultaneously, the output is connected to the subsequent circuit to achieve capacitance-to-voltage conversion. The sensitive probe module mainly converts the micro-displacement of the test mass into a capacitance signal, realizing the conversion of non-electrical quantity to electrical quantity.

[0025] The core component of a differential transformer bridge circuit is a precision transformer containing two primary coils and one secondary coil. To ensure bridge balance, matching resistors, capacitors, and other basic components are required. The differential capacitors, acting as the two variable arms of the bridge, together with the two primary coils of the transformer and the matching components, form a balanced bridge. The secondary coil outputs the signal, connecting to subsequent amplification circuits. Its main function is signal conversion: when there is no minute displacement in the test quality... C 1= C 2. When the bridge circuit is in a balanced state, the voltage at the output terminal of the secondary coil is 0; when the test mass undergoes a slight displacement, C 1≠ C 2. Bridge circuit imbalance, the secondary coil output modulated voltage is proportional to the capacitance change. The amplifier circuit module is a three-stage amplification link, consisting of a front-end amplifier circuit, a differential amplifier circuit, and an AC amplifier circuit, cascaded together according to the signal flow. The core component is an operational amplifier, which can be an instrumentation operational amplifier or a general-purpose operational amplifier, supplemented by precision resistors and capacitors used to set the amplifier circuit gain and stabilize the circuit phase. The modulation voltage output from the secondary coil passes through the input terminals of the front-end amplifier circuit, the differential amplifier circuit, and the AC amplifier circuit. The amplification factor of each amplifier circuit is set by changing parameters such as the resistance value of the precision resistor and the capacitance value.

[0026] The dual-limit comparator is the core unit of this technical solution, used to reshape the amplified AC sinusoidal modulated signal to match the input requirements of the multiplier. A typical dual-limit comparator structure consists of two operational amplifiers, two reference voltage sources, and a diode / logic gate output stage, such as... Figure 2 As shown. Its working principle is as follows: two reference voltage sources output upper threshold voltage U respectively. A and lower threshold voltage U B When the input voltage u I >U A When A1 outputs a high level and A2 outputs a low level, diode D1 is turned on and D2 is turned off, resulting in an output voltage u. O It is high level; when the input voltage u I B When A1 outputs a low level and A2 outputs a high level, diode D1 is cut off and D2 is turned on, resulting in an output voltage u. O Still high level; when U B I A At this time, both A1 and A2 output a low level, and the output voltage u O The signal is at a low level. However, a typical dual-limit comparator cannot meet the requirements of this technical solution because the shaped signal after shaping using a typical dual-limit comparator only retains the frequency and phase information of the original modulating signal, while the amplitude information of the original modulating signal is lost. The low-frequency differential capacitor is precisely located within the amplitude information of the original modulating signal. Therefore, this technical solution will connect a 2-to-1 analog switch to the output of the typical dual-limit comparator, so that when u... O When it is high, the analog switch output is related to u. I Consistent, when u O ​​​When the level is low, the analog switch output is 0. The dual-limit comparator provided in this application can be implemented using a purely analog method (a typical analog dual-limit comparator + a 2-to-1 analog switch) or a combination of digital and analog methods (a typical digital dual-limit comparator + a 2-to-1 analog switch). The core function of the dual-limit comparator is to perform three-interval threshold detection and signal preprocessing on the amplified AC sinusoidal modulated signal, providing a standardized and highly stable input signal for the multiplier, and adapting to the system's precision measurement requirements that are insensitive to demodulation phase difference fluctuations. It is the core module of this technical solution. The core components of the multiplier and demodulation reference signal are multiplier chips. Analog multipliers, such as the AD633, can be used. In this case, the demodulation reference signal needs to be a square wave signal with the same frequency as the sinusoidal carrier. The generation of this square wave is similar to that of the sinusoidal carrier, requiring DDS technology, and both must be based on the same frequency reference. Alternatively, a switching multiplier, such as the AD630, can be used. In this case, the demodulation reference signal can utilize any waveform with the same frequency and symmetrical top and bottom, such as a sine wave or a triangular wave. This is because within the switching multiplier, the demodulation reference signal first passes through a comparator (1 for greater than 0, -1 for less than 0), and the resulting square wave with the same frequency is then multiplied by the demodulation input signal. Compared to analog multipliers, switching multipliers have stronger anti-interference capabilities and are less sensitive to device parameter drift, making them more suitable for high-precision micrometry requirements. Of the two input terminals, one is connected to the shaping signal output from the dual-limit comparator, and the other is connected to the demodulation reference signal; the output terminal is connected to a subsequent low-pass filter circuit. It can perform the core demodulation operation to separate the low-frequency displacement signal, preparing it for subsequent filtering and extraction.

[0027] like Figure 3 As shown, the core component of the low-pass filter circuit is an operational amplifier, supplemented by precision resistors and capacitors to set the gain and bandwidth of the low-pass filter circuit, thus forming an active low-pass filter circuit. Its input is connected to the output of the multiplier, and the output is the final output port of this technical solution. By designing a reasonable bandwidth, the high-frequency components generated by the multiplication operation are filtered out, extracting the low-frequency displacement-related signal. The amplitude of this signal is proportional to the micro-displacement of the measured mass. Simultaneously, filtering reduces signal ripple, improving the stability of the output signal and ensuring the precision of the micro-displacement measurement.

[0028] The precision capacitance micrometer system provided in this application organically combines the precision of capacitance micrometer measurement with the anti-interference capability of signal conditioning through the design of a core module: a dual-limit comparator. The dual-limit comparator ensures, through threshold judgment and signal shaping, that the system output is insensitive to phase difference fluctuations within a certain demodulation phase difference range, ultimately achieving high-precision measurement of micro-displacements. Each module completes the end-to-end conversion from physical quantities to measurable voltage signals through step-by-step signal transmission and functional complementarity.

[0029] Optionally, in the precision capacitance micrometer system provided in this application embodiment, the dual-limit comparator includes a threshold comparison unit and a 2-to-1 analog switch; The threshold comparison unit is used to determine whether the amplitude of the input signal exceeds the range defined by the upper threshold voltage and the lower threshold voltage. The 2-to-1 analog switch is controlled by the output of the threshold comparison unit. When the amplitude of the input signal is outside the range defined by the upper threshold voltage and the lower threshold voltage, the output is a signal consistent with the input signal. When the amplitude of the input signal is within the range defined by the upper threshold voltage and the lower threshold voltage, the output is a zero-level signal.

[0030] Optionally, in the precision capacitance micrometer system provided in this application embodiment, the threshold comparison unit includes a dual-channel differential comparator, which is connected to the upper threshold voltage and the lower threshold voltage respectively. The output of the dual-channel differential comparator is compared with the upper threshold voltage and the lower threshold voltage through a combination of diodes or logic gate circuits to generate a control signal that is transmitted to the control terminal of the 2-to-1 analog switch.

[0031] Specifically, a typical analog dual-limit comparator can be implemented using integrated comparator chips, such as dual-channel differential comparator chips LM393 and LM2903, requiring only an external reference voltage source and matching resistor; alternatively, discrete components including general-purpose operational amplifiers and diodes can be used to build the above structure, with general-purpose operational amplifier chips such as OPA2227 selected.

[0032] The 2-to-1 analog switch is implemented directly using a single-channel integrated analog switch chip, such as the JTM3157. The specific implementation method of this technical solution using a pure analog approach to implement the dual-limit comparator is as follows... Figure 4 and Figure 5 As shown. When u O When the signal is high, the control terminal is 1, and the output is B1 (i.e., the output is the same as u). I (Keep in line); when u O When the level is low, the control terminal is 0, and the output is B0 (i.e., the output is 0).

[0033] Optionally, in the precision capacitance micrometer system provided in this application embodiment, the threshold comparison unit includes an analog-to-digital converter and a programmable gate array or microprocessor. The analog-to-digital converter is used to acquire the analog signal output by the signal amplification link, and the programmable logic device or microprocessor is used to compare the amplitude of the digitized signal with the upper threshold voltage and the lower threshold voltage to generate a corresponding control signal to be transmitted to the control terminal of the 2-to-1 analog switch.

[0034] Specifically, the digital comparator uses an analog-to-digital converter (ADC) to acquire the amplified analog signal from the AC circuit. The signal amplitude is compared with the threshold voltage by the digital logic of a programmable gate array (FPGA) or microprocessor (MCU), and the output digital signal is input to the control terminal of a 2-to-1 analog switch.

[0035] The 2-to-1 analog switch works the same as the pure analog method. This technical solution uses a combination of digital and analog methods to achieve the specific implementation of step 7, as shown below. Figure 6 As shown. In this technical solution, digital judgment logic is used to implement the comparator function, and AND gate logic is used to replace the diode's on / off state. Only when U... B I A When the AND gate output (control terminal) is 1, the output is B1 (i.e., the output is 0); otherwise, when the AND gate output (control terminal) is 0, the output is B0 (i.e., the output is ANDed with u). I (To maintain consistency). This is also why the analog switch connection differs between the combined digital / analog scheme and the purely analog scheme, i.e., u I Should we connect to B0 or ​​B1?

[0036] Compared to a purely analog scheme, the threshold voltage of a combined digital and analog scheme can be flexibly adjusted by software and is easily integrated with subsequent demodulation.

[0037] Optionally, the signal amplification link is a three-stage cascaded amplifier circuit, including a front-end amplifier circuit, a differential amplifier circuit, and an AC amplifier circuit connected in sequence. The front-end amplifier circuit is used to amplify the modulated voltage signal output by the differential transformer bridge and suppress input stage noise. The differential amplifier circuit is used to amplify the displacement-related differential signal and suppress common-mode noise; The AC amplifier circuit is used to amplify signals near the carrier frequency and suppress outside-bandwidth noise.

[0038] Specifically, the front-end amplifier circuit, differential amplifier circuit, and AC amplifier circuit provided in the embodiments of this application are respectively as follows: Figure 7 , Figure 8 , Figure 9 As shown.

[0039] The front-end amplifier circuit mainly amplifies the weak modulation voltage output by the differential transformer bridge circuit while suppressing input stage noise. The differential amplifier circuit mainly suppresses common-mode noise and amplifies the displacement-related differential signal to improve the signal-to-noise ratio. The AC amplifier circuit mainly amplifies the AC signal near the carrier frequency and can also greatly suppress low-frequency noise and high-frequency interference outside the bandwidth, further purifying the modulation signal.

[0040] ​​Optionally, in the precision capacitance micrometer system provided in this application embodiment, the multiplier is a switching multiplier, and the demodulation reference signal is a waveform with the same frequency as the sinusoidal carrier and symmetrical vertically.

[0041] Specifically, the multiplier provided in this application embodiment is a switching multiplier, such as the AD630. In this case, the demodulation reference signal can be any waveform with the same frequency and symmetrical top and bottom, such as a sine wave or a triangular wave. This is because inside the switching multiplier, the demodulation reference signal first passes through a comparator (1 for greater than 0, -1 for less than 0), and the square wave with the same frequency generated therefrom is then multiplied with the demodulated input signal. Compared with analog multipliers, switching multipliers have stronger anti-interference capabilities and are less sensitive to device parameter drift, making them more suitable for high-precision micrometry requirements.

[0042] Optionally, in the precision capacitance micrometer system provided in this application embodiment, the absolute values ​​of the upper threshold voltage and the lower threshold voltage are equal, and their amplitudes are lower than the amplitude of the output signal of the AC amplifier circuit.

[0043] Optionally, in the precision capacitance micrometer system provided in this application embodiment, the dual-channel differential comparator is either integrated or constructed from discrete components.

[0044] This application also provides a method for precision capacitance micrometry, including: S100 uses a modulation signal source to generate a sinusoidal carrier signal; S200 detects the micro-displacement of the capacitor through a sensitive probe and converts the micro-displacement into a differential capacitance signal; S300 modulates the differential capacitor signal onto the sinusoidal carrier and outputs the modulated voltage signal; S400 amplifies and suppresses noise in the modulated voltage signal, inputs it to a multiplier for multiplication and demodulation, and outputs a demodulated signal. The S500 uses a low-pass filter circuit to filter out high-frequency components in the demodulated signal generated by the multiplication demodulation operation and extracts a DC voltage signal proportional to the micro-displacement as the system output. After amplifying and noise-suppressing the modulated voltage signal, and before inputting it to the multiplier, a dual-limit comparator is set to shape the amplified and noise-suppressed modulated signal, and the shaped signal is used as the demodulation input signal and input to the multiplier.

[0045] Specifically, the signal flow and functional implementation of the precision capacitance micrometer method provided in this application follow the logic of "displacement - electrical signal - modulation - amplification - shaping - demodulation - extraction", and the specific process is as follows: Displacement-capacitance conversion and modulation specifically include: when the test mass undergoes a slight displacement, the differential capacitance with the upper and lower plates changes in the opposite direction; a sinusoidal carrier signal is coupled to the differential capacitor through a differential transformer bridge, modulating the low-frequency capacitance change signal onto the high-frequency carrier, and outputting a modulated voltage signal.

[0046] Signal amplification and noise suppression specifically include the following steps: the modulated voltage is sequentially amplified by the front end (to increase the amplitude of weak signals), differential amplified (to suppress common-mode noise), and AC amplified (frequency-selective amplification to filter out noise outside the bandwidth) to obtain an amplified modulated signal with a high signal-to-noise ratio.

[0047] Signal shaping specifically includes inputting the amplified sinusoidal modulated signal into a dual-limit comparator, determining the threshold value to shape it into a demodulated input signal that is insensitive to phase fluctuations, and preserving the signal's frequency, phase, and amplitude information.

[0048] The demodulation operation specifically includes inputting the shaped signal and the demodulation reference signal into a multiplier for multiplication to demodulate the modulated signal and output a mixed signal containing low-frequency displacement signal and high-frequency components.

[0049] Signal extraction and measurement specifically include: after the mixed signal is filtered out by a low-pass filter circuit, a low-frequency voltage signal proportional to the micro-displacement of the test mass is output; by measuring this output signal, the micro-displacement information of the test mass can be accurately extracted.

[0050] Optionally, the precision capacitance micrometer method provided in this application, wherein setting a dual-limit comparator to shape the modulated signal after amplification and noise suppression processing specifically includes: The instantaneous amplitude of the amplified modulation signal is compared with the preset upper threshold voltage and lower threshold voltage in real time. When the instantaneous amplitude of the amplified modulation signal is greater than the upper threshold voltage or less than the lower threshold voltage, the control signal is set to the first state. When the instantaneous amplitude of the amplified modulation signal is neither greater than the upper threshold voltage nor less than the lower threshold voltage, the control signal is set to the second state. Based on the state of the control signal, the output signal is selected by an analog switch. When the control signal is in the first state, the waveform output by the analog switch that is consistent with the amplified modulation signal is used as the demodulation input signal. When the control signal is in the second state, the signal output by the analog switch is set to a zero-level signal as the demodulation input signal.

[0051] The following detailed explanation, using specific implementation diagrams and Fourier spectrum analysis, illustrates how this application achieves insensitivity to demodulation phase fluctuations. To simplify the analysis, the demodulation input signal phase is set to 0, and the phase difference is... θThe phase of the demodulation reference signal is represented, therefore the phase difference fluctuations between demodulated signals all originate from the demodulation reference signal.

[0052] Let the time-domain expression of 1 be: V sin ( t )= V p ·cos( ω 0 t Then the low-frequency differential capacitor Δ C ( t The modulated output after being modulated to 1 is V p ·Δ C ( t )·cos( ω 0 t If the gains of 3, 4, 5, and 6 are respectively H 3. H 4. H 5. H 6. If no phase change is introduced, then the output of 6 is

[0053] Let the time-domain expression of 9 be: V sq ( t )=sign[cos( ω 0 t+θ )], where sign[] represents the sign function. Through Fourier series extension, the time-domain expression of 9 is transformed into its frequency-domain form, i.e.:

[0054] in S 2p-1,cos and S 2p-1,sin They represent V sq ( t The amplitudes of the cosine and sine components can be expressed as:

[0055] If 7 is not introduced V o6 ( t The cosine in ) will be with V sq ( t The fundamental frequency cosine component acts as the input, and then the high-frequency components are filtered out by a 10-bit filter, thus outputting the DC component. Therefore, the output is...

[0056] If we introduce 7,V o6 ( t The cosine in ) will be shaped. Because Δ C ( t The frequency is much smaller than ω 0, therefore in a ω 0 cycles T Within 0, Δ C ( t Let Δ be approximately a constant, and without loss of generality, let this constant be Δ. C Set the threshold voltage U to 7. A =-U B And the amplitude is half the amplitude of the output signal of the AC amplifier circuit (i.e., 0.5). H 3 H 4 H 5 H 6 V p Δ C ),but V o6 ( t The output after shaping V o7 ( t )for

[0057] Similarly, for V o7 ( t Perform Fourier series expansion to convert the time domain to the frequency domain, i.e.

[0058] in A 2p-1,cos express V o7 ( t The cosine component can be expressed as

[0059] at this time, V o7 ( t The fundamental frequency cosine component in ) and V sq ( t The effect of the fundamental frequency cosine component in ) and V o7 ( t (2) p -1) The cosine component of the harmonic and V sq ( t (2) p-1) The frequency is doubled by a cosine component, and then the high-frequency components are filtered out by a 10-fold filter, thus the DC component is output. Therefore, the output is...

[0060] Comparing the final outputs in the two cases, excluding H 3 H 4 H 5 H 6 V p· Δ C ( t This common part, the remaining coefficient expressions are analyzed graphically, such as Figure 10 As shown. It can be observed that when the phase difference θ When variations occur within the dashed area, this technical solution achieves insensitivity to phase difference fluctuations, i.e. V out_B ( t )right θ partial derivatives δV out_B ( t ) / δθ =0. Essentially, it is precisely because the original demodulated input signal was shaped in the time domain that the shaped signal... V o7 ( t The amplitude of the demodulated reference square wave signal is 0 for two time periods. When the amplitude of the demodulated reference square wave signal changes from -1 to 1 within these two time periods, the waveform of the signal after multiplying the demodulated input signal and the demodulated reference signal remains unchanged. Therefore, the final output of the system is also constant, which is manifested as the phase difference... θ When changes occur within the dashed area V out_B ( t It remains constant.

[0061] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0062] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0063] In the several embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some service interface; the indirect coupling or communication connection between devices or units may be electrical or other forms.

[0064] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0065] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0066] The foregoing description is merely an exemplary embodiment of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Those skilled in the art will readily conceive of embodiments of this disclosure upon considering the specification and practicing the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of this disclosure are defined by the claims.

[0067] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A precision capacitance micrometer system, comprising a modulation signal source, a sensitive probe, a differential transformer bridge, a signal amplification link, a multiplier, and a low-pass filter circuit connected in sequence, wherein, The modulation signal source is used to generate a sinusoidal carrier signal. The sensitive probe includes a test mass and upper and lower plates forming a differential capacitance with the test mass, used to convert micro-displacement into a differential capacitance signal. The differential transformer bridge is connected to the differential capacitor through a primary coil to form a balanced bridge, used to modulate the differential capacitance signal onto the sinusoidal carrier and output a modulation voltage signal. The signal amplification link is connected to the differential transformer bridge, used to amplify and suppress noise in the modulation voltage signal. The multiplier is used to receive the demodulation input signal and the demodulation reference signal, perform multiplication demodulation operations, and output a demodulated signal. The low-pass filter circuit is connected to the output of the multiplier and is used to filter out high-frequency components in the demodulated signal generated by the multiplication demodulation operation and extract a DC voltage signal proportional to the micro-displacement as the system output. The feature is that it further includes a dual-limit comparator disposed between the signal amplification link and the multiplier, wherein the input terminal of the dual-limit comparator is connected to the output terminal of the signal amplification link, and the output terminal is connected to one input terminal of the multiplier, for shaping the amplified modulation signal and using the shaped signal as the demodulation input signal.

2. The precision capacitance micrometer system as described in claim 1, characterized in that, The dual-limit comparator includes a threshold comparison unit and a 2-to-1 analog switch; The threshold comparison unit is used to determine whether the amplitude of the input signal exceeds the range defined by the upper threshold voltage and the lower threshold voltage; The 2-to-1 analog switch is controlled by the output of the threshold comparison unit. When the amplitude of the input signal is outside the range defined by the upper threshold voltage and the lower threshold voltage, the output is a signal consistent with the input signal. When the amplitude of the input signal is within the range defined by the upper threshold voltage and the lower threshold voltage, the output is a zero-level signal.

3. The precision capacitance micrometer system as described in claim 2, characterized in that, The threshold comparison unit includes a dual-channel differential comparator, which is connected to the upper threshold voltage and the lower threshold voltage respectively. The output of the dual-channel differential comparator is compared with the upper threshold voltage and the lower threshold voltage through a combination of diodes or logic gate circuits to generate a control signal that is transmitted to the control terminal of the 2-to-1 analog switch.

4. The precision capacitance micrometer system as described in claim 2, characterized in that, The threshold comparison unit includes an analog-to-digital converter and a programmable gate array or microprocessor. The analog-to-digital converter is used to acquire the analog signal output from the signal amplification link. The programmable logic device or microprocessor is used to compare the amplitude of the digitized signal with the upper threshold voltage and the lower threshold voltage to generate a corresponding control signal, which is transmitted to the control terminal of the 2-to-1 analog switch.

5. The precision capacitance micrometer system as described in claim 1, characterized in that, The signal amplification link is a three-stage cascaded amplifier circuit, including a front-end amplifier circuit, a differential amplifier circuit, and an AC amplifier circuit connected in sequence: The front-end amplifier circuit is used to amplify the modulated voltage signal output by the differential transformer bridge and suppress input stage noise. The differential amplifier circuit is used to amplify the displacement-related differential signal and suppress common-mode noise; The AC amplifier circuit is used to amplify signals near the carrier frequency and suppress outside-bandwidth noise.

6. The precision capacitance micrometer system as described in claim 1, characterized in that, The multiplier is a switching multiplier, and the demodulation reference signal is a waveform that is at the same frequency as the sinusoidal carrier and is symmetrical vertically.

7. The precision capacitance micrometer system as described in any one of claims 1 to 6, characterized in that, The absolute values ​​of the upper threshold voltage and the lower threshold voltage are equal, and their amplitudes are lower than the amplitude of the output signal of the AC amplifier circuit.

8. The precision capacitance micrometer system as described in claim 3, characterized in that, The dual-channel differential comparator can be integrated or built from discrete components.

9. A precision capacitance micrometer method, comprising: S100 uses a modulation signal source to generate a sinusoidal carrier signal; S200 detects the micro-displacement of the capacitor through a sensitive probe and converts the micro-displacement into a differential capacitance signal; S300 modulates the differential capacitor signal onto the sinusoidal carrier and outputs the modulated voltage signal; S400 amplifies and suppresses noise in the modulated voltage signal, inputs it to a multiplier for multiplication and demodulation, and outputs a demodulated signal. The S500 uses a low-pass filter circuit to filter out high-frequency components in the demodulated signal generated by the multiplication demodulation operation and extracts a DC voltage signal proportional to the micro-displacement as the system output. The feature is that, after amplifying and noise-suppressing the modulated voltage signal and before inputting it to the multiplier, a dual-limit comparator is set to shape the modulated signal after amplification and noise suppression, and the shaped signal is used as the demodulation input signal and input to the multiplier.

10. The precision capacitance micrometer method as described in claim 9, characterized in that, The setting of the dual-limit comparator to shape the modulated signal after amplification and noise suppression specifically includes: The instantaneous amplitude of the amplified modulation signal is compared with the preset upper threshold voltage and lower threshold voltage in real time. When the instantaneous amplitude of the amplified modulation signal is greater than the upper threshold voltage or less than the lower threshold voltage, the control signal is set to the first state. When the instantaneous amplitude of the amplified modulation signal is neither greater than the upper threshold voltage nor less than the lower threshold voltage, the control signal is set to the second state. Based on the state of the control signal, the output signal is selected by an analog switch. When the control signal is in the first state, the waveform output by the analog switch that is consistent with the amplified modulation signal is used as the demodulation input signal. When the control signal is in the second state, the signal output by the analog switch is set to a zero-level signal as the demodulation input signal.

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