System and method for monitoring swing angle of fast swing mirror based on three-point capacitance displacement sensor

Abstract

The invention provides a fast oscillating mirror oscillating angle monitoring system and method based on a three-point capacitance displacement sensor. The fast oscillating mirror oscillating angle monitoring system comprises a capacitance displacement sensor, a signal conditioning circuit, a signal acquisition circuit, an FPGA angle resolving module and an upper computer. The three-point piezoelectric driving large-aperture fast oscillating mirror is a monitored component; the three capacitance displacement sensors are distributed in an equilateral triangle shape around the center of the mirror surface, the included angle between every two actuators and the center connecting line is 120 degrees, the upper polar plate is installed at the bottom of the oscillating mirror, and the lower polar plate is installed on the supporting frame and overlapped with the upper polar plate; the signal conditioning circuit converts capacitance signals into voltage signals and carries out long-distance transmission with the signal acquisition circuit through a current interface. The signal acquisition circuit is connected with the conversion FPGA angle resolving module; and the upper computer is communicated with the FPGA. According to the invention, the high displacement detection precision of the capacitive sensor and the processing characteristics of FPGA parallel calculation are fully utilized, and the high-precision and real-time swing mirror angle state monitoring of dynamic micro-swing is realized.

Description

Technical Field

[0001] The invention belongs to the field of sensors, and in particular relates to a fast-swing mirror swing angle monitoring system and method based on a three-point capacitance displacement sensor. Background Art

[0002] The large-aperture Fast Steering Mirror (FSM) is a key component of the precision image stabilization system of the space astronomical telescope. It compensates for the visual axis offset detected and fed back by the Fine Guide Sensor (FGS) to ensure high-quality imaging and long-term stability of the telescope's detector. The on-orbit working environment of the FSM is very complex. There will be errors between the closed loop and the actual swing of the actuator, and it will change due to a variety of complex factors. In order to ensure high-quality imaging and long-term stability of the telescope's detector, the capacitive displacement sensor is used as an online monitoring method. Under the condition that the fast-swing mirror's own stiffness remains unchanged, the changes in the bottom plane and substrate of the FSM are detected to monitor the execution results of the swing angle and center displacement of the actuating component.

[0003] The displacement measurement range of the capacitive displacement sensor is usually between 0.05 and 10 mm, and the accuracy can reach 0.005% of the full scale, which can meet the needs of various precision measurements. In addition, the capacitive displacement sensor also has the advantages of high sensitivity, low zero drift, wide frequency response and small nonlinearity, making it an indispensable test instrument in precision production and control. However, the displacement output capacitance change of the capacitive displacement sensor is very weak, and its capacitance change range is often only a few pF or even a few fF, which puts higher requirements on the resolution of the capacitance detection circuit.

[0004] Common angular attitude inertial gyro measurements are used, but their accuracy is not enough to detect attitude changes at the order of arc seconds. Precise swing angle measurements are usually made using laser interferometry. However, for scenarios where satellites are operating in orbit, the size, power consumption, and complexity of the laser light source and its optical path structure are large. The launch and operating environment factors can also cause the measurement equipment to become misaligned, making it unable to meet the needs of long-life operation. This is not conducive to on-orbit detection. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a fast-swing mirror swing angle monitoring system and method based on a three-point capacitive displacement sensor.

[0006] Field Programmable Gate Array (FPGA) is one of the most integrated types of Application Specific Integrated Circuit (ASIC), which is composed of a large number of basic logic units. FPGA has rich I / O resources and can be flexibly configured, which can realize true parallel computing. Currently, advanced FPGAs contain hardware cores with digital signal processing functions, which can realize the deployment of FPGAs with complex angle calculation algorithms and realize the angle calculation of the fast swing mirror of the three-point capacitive displacement sensor.

[0007] In order to achieve the above object, the present invention adopts the following technical scheme:

[0008] A fast-swing mirror angle monitoring system based on a three-point capacitive displacement sensor comprises a three-point piezoelectric driven fast-swing mirror mechanism, a capacitive displacement sensor, a signal conditioning circuit, a signal acquisition circuit, an FPGA angle calculation module and a host computer;

[0009] The host computer sends the angle control signal of the three-point piezoelectric driven fast-swing mirror mechanism to the three-point piezoelectric driven fast-swing mirror mechanism, and realizes the swing angle control by using the target displacement of the three-point piezoelectric ceramic actuator with an included angle of 120° and uniformly distributed on the concentric circles of the mirror surface; there are 6 capacitive displacement sensors in total, and every 2 are used as a group of main and backup, which are respectively located on both sides of the same cross-section of the piezoelectric actuator, and the displacement of the detection point is detected. The capacitive signal is converted into a voltage signal by the signal conditioning circuit and transmitted to the signal acquisition circuit over a long distance. After being converted into a voltage signal and amplified, it is input into the FPGA angle solution module to perform three-point displacement-swing angle calculation, and the calculation result is transmitted to the host computer to complete the real-time monitoring of the swing angle.

[0010] Furthermore, the capacitive displacement sensor is composed of an upper electrode plate and a lower electrode plate, wherein the upper electrode plate is installed below the three-point piezoelectric driven fast-swing mirror mechanism, and the lower electrode plate is installed on the base of the three-point piezoelectric driven fast-swing mirror mechanism, overlapping with the upper electrode plate. The main and backup of the six capacitive displacement sensors are grouped together, located on both sides of the piezoelectric actuator, and distributed in an equilateral triangle around the center of the mirror surface. The angle between every two actuators and the center line is 120°.

[0011] Furthermore, the signal conditioning circuit and the signal acquisition circuit are composed of three independent channels, which are used to detect three displacements respectively. The intermediate transmission realizes long-distance transmission of more than 1 meter through VI conversion and IV conversion, and the displacement of the three-point capacitor positions is detected in parallel.

[0012] Furthermore, the signal acquisition circuit includes an amplification and filtering module, a single-ended-differential conversion module and an analog-to-digital conversion module. The amplification and filtering module is used to denoise and amplify the detected weak displacement signal through a narrow-band Butterworth low-pass filter on the signal collected by the signal conditioning circuit; the single-ended-differential conversion module is used to improve the common-mode suppression capability and adapt the dynamics of the analog-to-digital conversion module; the analog-to-digital conversion module adopts a multi-channel 18-bit differential input ADC with channel selection capability, and converts the displacement analog signal into a digital signal to connect to the FPGA angle solution module.

[0013] Furthermore, the analog-to-digital conversion is performed through an 18-bit ADC, and the angle of the three-point piezoelectric driven fast-swing mirror mechanism is obtained through the FPGA angle calculation module and transmitted to the host computer to understand the control result of the piezoelectric ceramic actuator.

[0014] Furthermore, the conversion parameters of the FPGA angle solution module control the three-point piezoelectric driven fast swing mirror mechanism through closed-loop control of three piezoelectric ceramic actuators, and at the same time collect the star point information detected by the fine guide instrument, and determine the coefficient conversion relationship between the capacitance acquisition signal and the angle according to the spatial relationship between the information and the structure.

[0015] Furthermore, the closed-loop controlled piezoelectric actuator realizes the three-point piezoelectric driven fast-swing mirror mechanism to swing along the x-axis and y-axis, controls the maximum range of the swing angle, records the change in the star point position collected by the fine guide instrument in the system, and obtains the conversion parameters of the FPGA angle solution module according to the geometric relationship of the system to realize the angle detection of the fast-swing mirror.

[0016] The present invention also provides a method for monitoring the swing angle of a fast swing mirror based on a three-point capacitance displacement sensor, comprising the following steps:

[0017] Step 1, install the capacitive displacement sensor on the frame, wherein the upper electrode plate is installed below the three-point piezoelectric driven fast swing mirror mechanism, the lower electrode plate is installed on the base of the three-point piezoelectric driven fast swing mirror mechanism, and is installed overlapping with the upper electrode plate, and the three capacitive sensors are distributed in an equilateral triangle around the center of the mirror surface, and the angle between every two actuators and the center line is 120°;

[0018] Step 2, calibrate the dynamic measurement range of the capacitive displacement sensor, collect the output code values ​​of the signal acquisition circuit when the three piezoelectric ceramic actuators of the three-point piezoelectric drive fast swing mirror mechanism are at the minimum and maximum positions, and if the dynamic range exceeds the effective range of the signal conditioning circuit and the capacitive displacement sensor, modify the parameter size of the differential capacitor chip until the dynamic range of the output code value is within the effective value range;

[0019] Step 3, set the swing angle conversion parameters of the FPGA angle solution module, which requires closed-loop control of the piezoelectric actuator to realize the three-point piezoelectric driven fast swing mirror mechanism to swing along the x-axis and y-axis, control the maximum range of the swing angle, record the change in the star point position collected by the fine guide instrument, and obtain the conversion parameters of the FPGA angle solution module based on the geometric relationship of the system to realize the angle detection of the fast swing mirror.

[0020] Furthermore, in step 2, a differential capacitor chip is used to implement signal readout of the capacitive displacement sensor, and the calculation formula for the output voltage is:

[0021] ;

[0022] in, is the simulated magnification; is the conversion factor from capacitance to voltage; is the reference voltage; =CS2IN+CS2, =CS1IN+CS1, CS1IN and CS2IN are the differential inputs of the detected capacitive displacement sensor, CS1 and CS2 are the adjustable compensation capacitors inside the HJ3110 chip, which are used to adjust the bias caused by the asymmetry of the input capacitance; is the integrating capacitor of the charge integrator; the change of capacitance can be converted into the distance d between the two plates through parameter adjustment and displacement correction.

[0023] Beneficial effects:

[0024] The present invention can directly measure the actual displacement of three detection points of the fast-swing mirror by changing the distance between the bottom surface of the fast-swing mirror structure and the support frame and then converting the distance displacement into a small change in capacitance through a capacitive sensor, thereby calculating the swing angle of the mirror surface. The method has a simple structure, does not require an additional light source, has high measurement accuracy, and can meet the needs of on-track angular second-level swing angle longevity detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the fast-swing mirror swing angle monitoring system based on the three-point capacitive displacement sensor of the present invention.

[0026] Figure 2 This is the functional block diagram of the differential capacitor chip (taking the HJ3110 chip as an example).

[0027] Figure 3 Schematic diagram of the capacitive sensor installation.

[0028] Figure 4 Side view of a three-point piezoelectric-driven fast-swing mirror mechanism with a capacitive sensor.

[0029] Figure 5Block diagram of the precision image stabilization system for the space telescope.

[0030] Among them, the accompanying drawings are marked as: three-point piezoelectric driven fast-swing mirror mechanism 1, capacitive displacement sensor 2, signal conditioning circuit 3, signal acquisition circuit 4, FPGA angle calculation module 5, and host computer 6. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] like Figure 1 As shown, a fast-swing mirror angle monitoring system based on a three-point capacitive displacement sensor of the present invention includes a three-point piezoelectric driven fast-swing mirror mechanism 1, a capacitive displacement sensor 2, a signal conditioning circuit 3, a signal acquisition circuit 4, an FPGA angle solution module 5 and a host computer 6.

[0033] The host computer 6 sends the angle control signal of the three-point piezoelectric driven fast swing mirror mechanism 1 to the three-point piezoelectric driven fast swing mirror mechanism 1 through the 422 communication interface, and realizes the swing angle control by using the target displacement of the three-point piezoelectric ceramic actuator. The three-point piezoelectric ceramic actuator has an angle of 120° and is evenly distributed on the concentric circles of the mirror surface. There are 6 capacitive displacement sensors 2, each 2 as a group of main and backup, respectively located on both sides of the same cross section of the piezoelectric actuator, detecting the displacement of the point position, converting the capacitive signal into a voltage signal through the signal conditioning circuit 3 and transmitting it to the signal acquisition circuit 4 over a long distance, converting it into a voltage signal and amplifying it and inputting it into the FPGA angle solution module 5 to calculate the three-point displacement-swing angle, and the calculation result is transmitted to the host computer 6 through the 422 communication interface to complete the real-time monitoring of the swing angle.

[0034] like Figure 4 As shown, the capacitive displacement sensor 2 is composed of an upper plate and a lower plate, wherein the upper plate is installed below the FSM (three-point piezoelectric driven fast swing mirror mechanism 1), and the lower plate is installed on the base of the FSM and overlaps with the upper plate. The three capacitive displacement sensors 2 are distributed in an equilateral triangle around the center of the mirror, and the angle between every two actuators and the center line is 120°.

[0035] The signal conditioning circuit 3 and the signal acquisition circuit 4 are composed of three independent channels. The intermediate transmission realizes long-distance transmission of more than 1 meter through VI conversion and IV conversion, and the displacement of the three-point capacitor position is detected in parallel.

[0036] The signal acquisition circuit 4 includes an amplification and filtering module, a single-ended-differential conversion module and an analog-to-digital conversion module. The amplification and filtering module is used to denoise and amplify the detected weak displacement signal through a narrow-band Butterworth low-pass filter on the signal collected by the signal conditioning circuit 3; the single-ended-differential conversion module is used to improve the common-mode suppression capability and adapt the dynamics of the analog-to-digital conversion module; the analog-to-digital conversion module adopts a multi-channel 18-bit differential input ADC with channel selection capability, and converts the displacement analog signal into a digital signal to connect to the FPGA angle solution module 5.

[0037] The present invention adopts a three-point capacitive displacement sensor to detect the swing angle of the FSM, utilizes a signal conditioning circuit 3 and a signal acquisition circuit 4 to amplify the capacitor voltage signal in parallel, and performs analog-to-digital conversion through an 18-bit ADC. After passing through an FPGA angle calculation module 5, the angle of the FSM is obtained and transmitted to a host computer 6, thereby understanding the control result of the piezoelectric ceramic actuator.

[0038] Capacitance displacement sensor (CS) is a non-contact micro-displacement measuring instrument based on the principle of flat plate capacitance. It consists of an upper plate and a lower plate. The installation method is as follows: Figure 2 The working principle is shown as follows:

[0039] ;

[0040] Where C is the capacitance of the capacitive sensor, is the dielectric constant, S is the relative coverage area between the plates, d is the distance between the plates, is the relative dielectric constant, is the dielectric constant of vacuum, which is 8.85fF / m.

[0041] Differential capacitance chips can be used to realize the signal readout of capacitance displacement sensors. Taking HJ3110 chip as an example, the structure is as follows: Figure 3 The output voltage calculation formula is:

[0042] ;

[0043] in, is the simulated magnification; is the conversion factor from capacitance to voltage; is the reference voltage; =CS2IN+CS2, =CS1IN+CS1, CS1IN and CS2IN are the differential inputs of the detected capacitive displacement sensor, CS1 and CS2 are the adjustable compensation capacitors inside the HJ3110 chip, which are used to adjust the bias caused by the asymmetry of the input capacitance; is the integrating capacitor of the charge integrator; the change of capacitance can be converted into the distance d between the two plates through parameter adjustment and displacement correction.

[0044] like Figure 4 As shown in the figure, the piezoelectric ceramic actuator is a piezoelectric ceramic-based component that outputs displacement and force through an external mechanical structure. The actuator is equipped with a resistance strain gauge sensor (SGS) as a micro-displacement detection sensor for the piezoelectric actuator. Through the displacement output of the piezoelectric actuator and the measurement of SGS, closed-loop control of the piezoelectric actuator can be achieved.

[0045] By evenly distributing three piezoelectric actuators on the circumference of a FSM, closed-loop control of the FSM angle can be achieved. Combined with the measurement and processing of the star point by the guide star instrument, the calibration of the swing angle of the fast swing mirror and further closed-loop control can be achieved. The upper plate of the capacitive displacement sensor is installed below the FSM structure, and the lower plate is installed on the FSM base, overlapping with the upper plate. Figure 5 The three capacitive sensors shown are distributed in an equilateral triangle around the center of the mirror. The angle between each two piezoelectric actuators and the center line is 120°. The capacitance reflects the displacement between the bottom of the FSM structure and the FSM base. The displacement of the three points is converted into digital form by an 18-bit ADC. The FPGA angle calculation module 5 uses the displacement as a swing micro-angle detection sensor for the fast swing mechanism.

[0046] The conversion parameters of the FPGA angle calculation module 5 need to be controlled by three piezoelectric actuators through closed-loop control of the FSM, while collecting the star point information detected by the fine guide star instrument (FGS). According to the geometric relationship of the space telescope precision image stabilization system, the coefficient conversion relationship between the capacitor acquisition signal and the angle is determined. The block diagram of the space telescope precision image stabilization system is shown in Figure 5 As shown in the figure, specifically, the signal of the navigation star is focused on the main focal plane where the FGS is located through the off-axis three-mirror structure and the return of the FSM. The piezoelectric actuator is controlled by the precision image stabilization controller in a closed loop to realize the swing of the FSM along the x-axis and y-axis, so as to realize the change of the coordinate position of the navigation star on the FGS. The swing angle of the FSM is controlled to swing within the maximum range, and the change of the star point position collected by the FGS in the system is recorded (i.e. Figure 5 According to the star point information of the system, the conversion parameters of the FPGA angle calculation module 5 are obtained according to the geometric relationship of the system to realize the angle detection of the fast swing mirror. Therefore, in the subsequent use, the swing angle of the fast swing mirror can be monitored in real time according to the measurement value of the acquisition circuit.

[0047] The present invention also provides a method for monitoring the swing angle of a fast swing mirror based on a three-point capacitance displacement sensor, comprising the following steps:

[0048] Step 1, install the capacitive displacement sensor on the frame, wherein the upper electrode plate is installed below the FSM structure, the lower electrode plate is installed on the FSM base, and overlaps with the upper electrode plate. The three capacitive sensors are distributed in an equilateral triangle around the center of the mirror, and the angle between every two actuators and the center line is 120°;

[0049] Step 2, calibrate the dynamic measurement range of the capacitive displacement sensor, collect the output code values ​​of the signal acquisition circuit when the three piezoelectric actuators of the three-point piezoelectric driven fast swing mirror mechanism 1 are at the minimum and maximum positions, and if the dynamic range exceeds the effective range of the signal conditioning circuit and the capacitive displacement sensor, modify the parameter size of the differential capacitor chip until the dynamic range of the output code value is within the effective value range;

[0050] Step 3, set the swing angle conversion parameters of the FPGA angle solving module, which requires closed-loop control of the piezoelectric actuator to realize the swing of FSM along the x-axis and y-axis, control the maximum range of the swing angle, record the change in the star point position collected by FGS, and obtain the conversion parameters of the FPGA angle solving module based on the geometric relationship of the system to realize the angle detection of the fast swing mirror.

Claims

1. A fast-swing mirror angle monitoring system based on a three-point capacitive displacement sensor, characterized in that: It includes a three-point piezoelectric driven fast-swing mirror mechanism, a capacitive displacement sensor, a signal conditioning circuit, a signal acquisition circuit, an FPGA angle calculation module and a host computer; The host computer sends the angle control signal of the three-point piezoelectric driven fast swing mirror mechanism 1 to the three-point piezoelectric driven fast swing mirror mechanism, and realizes the swing angle control by using the target displacement of the three-point piezoelectric ceramic actuator with an angle of 120° and uniformly distributed on the concentric circles of the mirror surface; there are 6 capacitive displacement sensors in total, and every 2 are used as a group of main and backup, which are respectively located on both sides of the same cross section of the piezoelectric actuator, and the displacement of the detection point is detected. The capacitive signal is converted into a voltage signal by the signal conditioning circuit and transmitted to the signal acquisition circuit over a long distance. After being converted into a voltage signal and amplified, it is input into the FPGA angle solution module to perform three-point displacement-swing angle calculation, and the calculation result is transmitted to the host computer to complete the real-time monitoring of the swing angle.

2. The fast-swing mirror swing angle monitoring system based on a three-point capacitive displacement sensor according to claim 1, characterized in that: The capacitive displacement sensor 2 is composed of an upper electrode plate and a lower electrode plate, wherein the upper electrode plate is installed below the three-point piezoelectric driven fast swing mirror mechanism, and the lower electrode plate is installed on the base of the three-point piezoelectric driven fast swing mirror mechanism and overlapped with the upper electrode plate. The main and backup parts of the six capacitive displacement sensors are grouped as two, located on both sides of the piezoelectric actuator, and distributed in an equilateral triangle around the center of the mirror surface. The angle between every two actuators and the center line is 120°.

3. The fast-swing mirror angle monitoring system based on a three-point capacitive displacement sensor according to claim 1 is characterized in that: The signal conditioning circuit and the signal acquisition circuit are composed of three independent channels, which are used to detect three displacements respectively. The intermediate transmission realizes long-distance transmission of more than 1 meter through VI conversion and IV conversion, and the displacement of the three-point capacitor positions is detected in parallel.

4. The fast-swing mirror swing angle monitoring system based on a three-point capacitive displacement sensor according to claim 1 is characterized in that: The signal acquisition circuit includes an amplification and filtering module, a single-ended-differential conversion module and an analog-to-digital conversion module. The amplification and filtering module is used to denoise and amplify the detected weak displacement signal through a narrow-band Butterworth low-pass filter on the signal collected by the signal conditioning circuit; the single-ended-differential conversion module is used to improve the common-mode suppression capability and adapt to the dynamics of the analog-to-digital conversion module; the analog-to-digital conversion module adopts a multi-channel 18-bit differential input ADC with channel selection capability, and converts the displacement analog signal into a digital signal to access the FPGA angle solution module.

5. The fast-swing mirror swing angle monitoring system based on a three-point capacitive displacement sensor according to claim 1, characterized in that: The analog-to-digital conversion is performed through an 18-bit ADC, and the angle of the three-point piezoelectric driven fast-swing mirror mechanism is obtained through the FPGA angle calculation module and transmitted to the host computer to understand the control result of the piezoelectric ceramic actuator.

6. The fast-swing mirror angle monitoring system based on a three-point capacitive displacement sensor according to claim 1, characterized in that: The conversion parameters of the FPGA angle calculation module are used to control the three-point piezoelectric driven fast-swing mirror mechanism through closed-loop control of three piezoelectric ceramic actuators, while collecting the star point information detected by the fine guide instrument, and determining the coefficient conversion relationship between the capacitance acquisition signal and the angle according to the spatial relationship between the information and the structure.

7. The fast-swing mirror angle monitoring system based on a three-point capacitive displacement sensor according to claim 6, characterized in that: The closed-loop controlled piezoelectric actuator realizes the three-point piezoelectric driven fast-swing mirror mechanism to swing along the x-axis and y-axis, controls the maximum range of the swing angle, records the change in the star point position collected by the fine guide instrument in the system, and obtains the conversion parameters of the FPGA angle solution module based on the geometric relationship of the system to realize the angle detection of the fast-swing mirror.

8. A method for monitoring the swing angle of a fast swing mirror based on a three-point capacitance displacement sensor, characterized in that: The steps include: Step 1, install the capacitive displacement sensor on the frame, wherein the upper electrode plate is installed below the three-point piezoelectric driven fast swing mirror mechanism, the lower electrode plate is installed on the base of the three-point piezoelectric driven fast swing mirror mechanism, and is installed overlapping with the upper electrode plate, and the three capacitive sensors are distributed in an equilateral triangle around the center of the mirror surface, and the angle between every two actuators and the center line is 120°; Step 2, calibrate the dynamic measurement range of the capacitive displacement sensor, collect the output code values ​​of the signal acquisition circuit when the three piezoelectric ceramic actuators of the three-point piezoelectric drive fast swing mirror mechanism are at the minimum and maximum positions, and if the dynamic range exceeds the effective range of the signal conditioning circuit and the capacitive displacement sensor, modify the parameter size of the differential capacitor chip until the dynamic range of the output code value is within the effective value range; Step 3, set the swing angle conversion parameters of the FPGA angle solution module, which requires closed-loop control of the piezoelectric actuator to realize the three-point piezoelectric driven fast swing mirror mechanism to swing along the x-axis and y-axis, control the maximum range of the swing angle, record the change in the star point position collected by the fine guide instrument, and obtain the conversion parameters of the FPGA angle solution module based on the geometric relationship of the system to realize the angle detection of the fast swing mirror.

9. The method for monitoring the swing angle of a fast swing mirror based on a three-point capacitance displacement sensor according to claim 8, characterized in that: In step 2, a differential capacitor chip is used to realize the signal readout of the capacitive displacement sensor, and the calculation formula of the output voltage is: ； in, is the simulated magnification; is the conversion factor from capacitance to voltage; is the reference voltage; =CS2IN+CS2, =CS1IN+CS1, CS1IN and CS2IN are the differential inputs of the detected capacitive displacement sensor, CS1 and CS2 are the adjustable compensation capacitors inside the HJ3110 chip, which are used to adjust the bias caused by the asymmetry of the input capacitance; is the integrating capacitor of the charge integrator; the change of capacitance can be converted into the distance d between the two plates through parameter adjustment and displacement correction.

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