A measurement system and method for verifying mass charge

Abstract

The present invention provides a system and method for measuring the charge of a test mass, which belongs to the field of precision measurement, and the method includes: placing parallel plates on both sides of the test mass, the parallel plates are parallel to the surface of the test mass and are equidistant from the test mass; applying an excitation voltage on the parallel plates so that the test mass produces a certain angular displacement; using a displacement sensor to convert the angular displacement signal into a voltage signal; inputting the voltage signal output by the displacement sensor into a controller to output the required control torque; calculating the feedback voltage corresponding to the control torque through an amplitude algorithm, and then applying the feedback voltage to the parallel plates by an electrostatic actuator, so that the test mass finally returns to the initial position through the electrostatic force generated between the parallel plates and the test mass; and calculating the charge on the test mass according to the control torque. The present invention has a precision measuring instrument for the test mass while measuring the charge of the test mass, and can continue to detect the target signal, and has a wide range of application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of precision measurement, and more specifically, relates to a measurement system and method for verifying mass charge. Background Art

[0002] In the field of precision measurement, it is usually necessary to insulate sensitive units to isolate them from external interference such as electrical and thermal noise. For example, in the LISA space gravitational wave detection program led by the European Space Agency, the sensitive probe of the inertial sensor consists of a test mass and surrounding plates. The test mass is an isolated conductor with no electrical connection to the surrounding objects. Free charges in space will attach to the test mass, resulting in charge accumulation. Although the magnitude of the accumulated charge is very small, the electrostatic force generated by the accumulated charge will interfere with the measurement results of the instrument, so the charge on the test mass needs to be controlled.

[0003] Taking the charge management solution adopted in LISA Pathfinder as an example, the charge measurement link in the process is to apply active excitation to the test mass, detect the movement of the sensitive probe through capacitive displacement sensing, and thus estimate the number of charges on the conductor; however, the noise generated by the process of the test mass being excited to move is too large to measure weak signals, so this open-loop measurement solution will inevitably terminate the precision measurement and reduce the measurement efficiency. Summary of the invention

[0004] In view of the defects of the prior art, the object of the present invention is to provide a system and method for measuring the charge of a test mass, aiming to solve the interference problem caused by the need to interrupt the target signal detection when measuring the accumulated charge of the test mass.

[0005] To achieve the above-mentioned object, on the one hand, the present invention provides a measurement system for testing mass charge, comprising: parallel plates, a displacement sensor, a control module, an electrostatic actuator and a charge measurement module;

[0006] The parallel plates are placed in parallel and in equal numbers on both sides of the inspection mass, and the parallel plates are parallel to the surface of the inspection mass and are at equal distances from the inspection mass; the output ends of each pair of parallel plates placed in parallel on both sides of the inspection mass are connected to a displacement sensor; the output end of the displacement sensor is connected to the control module; the output end of the controller is connected to the electrostatic actuator and the charge measurement module; the output end of each electrostatic actuator is connected to a parallel plate;

[0007] The parallel plates are used to receive an excitation voltage to cause the test mass to rotate; wherein the test mass is in a balanced state when it is in an initial position; the excitation voltages applied to the adjacent parallel plates on each side of the test mass are equal in magnitude and opposite in sign;

[0008] The displacement sensor is used to measure the freedom of motion of the inspection mass and convert the displacement signal into a voltage signal;

[0009] The control module is used to receive the voltage signal and calculate the control torque required to return the inspection mass to the initial position and the feedback voltage corresponding to the control torque;

[0010] The electrostatic actuator is used to apply the feedback voltage to the corresponding parallel plates, and an electrostatic force is generated between the test mass and the parallel plates, so that the test mass returns to the initial position;

[0011] The charge measurement module is used to calculate the charge on the test mass based on the control torque.

[0012] Further preferably, the number of parallel plates is 4, the first parallel plate and the third parallel plate are located on one side of the inspection mass; the second parallel plate and the fourth parallel plate are located on the other side of the inspection mass; the first parallel plate, the second parallel plate, the third parallel plate and the fourth parallel plate are at an equal distance from the inspection mass; the first parallel plate is directly parallel to the second parallel plate; the third parallel plate is directly parallel to the fourth parallel plate; a sinusoidal voltage is applied to the first parallel plate and the fourth parallel plate, and an opposite sinusoidal voltage of the same frequency is applied to the second parallel plate and the third parallel plate;

[0013] The displacement sensor includes a first displacement sensor and a second displacement sensor; the input end of the first displacement sensor is connected to the first parallel electrode plate and the second parallel electrode plate; the input end of the second displacement sensor is connected to the third parallel electrode plate and the fourth parallel electrode plate;

[0014] The electrostatic actuator includes a first electrostatic actuator, a second electrostatic actuator, a third electrostatic actuator and a fourth electrostatic actuator; the input ends of the first electrostatic actuator, the second electrostatic actuator, the third electrostatic actuator and the fourth electrostatic actuator are connected to the control module, and the output ends thereof are respectively connected to the first parallel plate, the second parallel plate, the third parallel plate and the fourth parallel plate.

[0015] Further preferably, the control module comprises: a PID (Proportion Integration Differentiation) controller and an amplitude calculator;

[0016] The output end of the PID controller is connected to the amplitude calculator and the charge measurement module; the output end of the amplitude calculator is respectively connected to the first electrostatic actuator, the second electrostatic actuator, the third electrostatic actuator and the fourth electrostatic actuator;

[0017] The PID controller is used to receive the voltage signal and output the control torque required to return the inspection mass to the initial position; the amplitude calculator is used to calculate the feedback voltage corresponding to the control torque through the amplitude algorithm.

[0018] Further preferably, the feedback voltage is:

[0019]

[0020] Among them, V 1,3 Represents the feedback voltage on the first parallel plate and the third parallel plate; V 2,4 represents the feedback voltage on the second parallel plate and the fourth parallel plate; C i is the capacitance between the ith plate and the test mass; is the angular displacement; k φ,req is the electrostatic negative stiffness demand value; To control the torque.

[0021] Further preferably, the charge on the test mass is:

[0022]

[0023] Among them, C tot is the total capacitance formed between all parallel plates and the test mass; d0 is the distance between the plates and the test mass when the test mass is in the initial position; is the control torque; ε is the electrostatic constant; S is the parallel plate area; V mod is the amplitude of the excitation voltage applied to the parallel plates.

[0024] In another aspect, the present invention provides a method for measuring mass charge, comprising the following steps:

[0025] Placing parallel plates on both sides of the test mass, wherein all the parallel plates are parallel to the surface of the test mass and are equidistant from the test mass; and the number of parallel plates on both sides of the test mass is the same;

[0026] Applying an excitation voltage to the parallel plates causes the test mass to rotate; wherein the test mass is in a balanced state when it is in an initial position; the excitation voltages applied to adjacent parallel plates on each side of the test mass are equal in magnitude and opposite in sign;

[0027] Measure the freedom of motion of the test mass and convert the displacement signal into a voltage signal;

[0028] According to the voltage signal, the control torque required to return the inspection mass to the initial position and the feedback voltage corresponding to the control torque are calculated;

[0029] Applying feedback voltage to the corresponding parallel plates generates electrostatic force between the test mass and the parallel plates, causing the test mass to return to its initial position;

[0030] The charge on the proof mass is calculated from the control torque.

[0031] Further preferably, the number of parallel plates is 4, the first parallel plate and the third parallel plate are located on one side of the inspection mass; the second parallel plate and the fourth parallel plate are located on the other side of the inspection mass; the first parallel plate, the second parallel plate, the third parallel plate and the fourth parallel plate are at an equal distance from the inspection mass; the first parallel plate is directly opposite and parallel to the second parallel plate; the third parallel plate is directly opposite and parallel to the fourth parallel plate; a sinusoidal voltage is applied to the first parallel plate and the fourth parallel plate, and an opposite sinusoidal voltage of the same frequency is applied to the second parallel plate and the third parallel plate.

[0032] Further preferably, the method for obtaining the control torque and the feedback voltage is:

[0033] The voltage signal is input to the PID controller, which outputs the control torque required to return the inspection mass to its initial position;

[0034] The feedback voltage corresponding to the control torque is calculated by an amplitude algorithm and applied to the parallel plates.

[0035] Further preferably, the feedback voltage is:

[0036]

[0037] Among them, V 1,3 Represents the feedback voltage on the first parallel plate or the third parallel plate; V 2,4 Represents the feedback voltage on the second parallel plate or the fourth parallel plate; C i is the capacitance between the ith plate and the test mass; is the angular displacement; k φ,req is the electrostatic negative stiffness demand value; To control the torque.

[0038] Further preferably, the charge on the test mass is:

[0039]

[0040] Among them, C tot is the total capacitance formed between all parallel plates and the test mass; d0 is the distance between the plates and the test mass when the test mass is in the initial position; is the control torque; ε is the electrostatic constant; S is the parallel plate area; V mod is the amplitude of the excitation voltage applied to the parallel plates.

[0041] In general, the above technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

[0042] The present invention applies an excitation voltage to parallel plates to cause the inspection mass to rotate, uses a displacement sensor and a control module to calculate the control torque required to return the inspection mass to an initial position, and simultaneously calculates a feedback voltage based on the control torque. An electrostatic actuator is used to apply the feedback voltage to the corresponding parallel plates to return the inspection mass to the initial position, thereby achieving the goal of suppressing large-scale movement of the inspection mass by means of closed-loop control, reducing noise caused by measuring charge, and avoiding interference problems caused by interrupting target signal detection when measuring the accumulated charge of the inspection mass. The precision measuring instrument having the inspection mass can continue to detect target signals while measuring the charge of the inspection mass, and has broad application prospects.

[0043] The measurement system for the test mass charge provided by the present invention has no mechanical connection with the precision measuring instrument with the test mass, and will not introduce external interference such as mechanical thermal noise into the precision measuring instrument during the process of measuring the test mass charge. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a flow chart of a closed-loop control-based test mass charge measurement method provided by an embodiment of the present invention;

[0045] Figure 2 It is a schematic diagram of the basic principle of the closed-loop control-based test mass charge measurement method provided by an embodiment of the present invention;

[0046] Marking Description:

[0047] 1: inspection mass; 2-1: first parallel plate; 2-2: second parallel plate; 2-3: third parallel plate; 2-4: fourth parallel plate; 3-1: first displacement sensor; 3-2: second displacement sensor; 4: control module; wherein, 4-1: controller; 4-2: amplitude calculator; 5-1: first electrostatic actuator; 5-2: second electrostatic actuator; 5-3: third electrostatic actuator; 5-4: fourth electrostatic actuator; 6: charge measurement unit; wherein, 6-1: unit for applying excitation voltage; 6-2: charge solution processor. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution 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.

[0049] The method for measuring the charge of a test mass provided by the present invention can be generally summarized as follows: the method for measuring the charge of a test mass provided by the present invention is a method for measuring the charge of a test mass based on closed-loop control and with AC feedback control as the basic principle. When the test mass produces a certain displacement relative to the equilibrium position due to the applied excitation voltage signal, the displacement signal is converted into a voltage signal by a displacement sensor, and a PID controller is used for closed-loop control. The voltage signal is input into the PID controller, and the control torque for controlling the test mass can be achieved through the PID algorithm of the controller. The feedback voltage related to the control torque is then calculated by the amplitude algorithm, and the feedback voltage is applied to the electrode plate to generate an electrostatic force, which finally pulls the test mass back to the equilibrium position. Using this control principle, the amount of charge on the test mass can be measured.

[0050] like Figure 1 As shown, the method for measuring the mass charge provided by the present invention comprises the following steps:

[0051] (1) Place two pairs of parallel plates on both sides of the test mass. The four parallel plates are parallel to the surface of the test mass and are equidistant from the test mass. The test mass is defined as being in an equilibrium state when it is in its initial position. Specifically:

[0052] Two pairs of parallel plates are placed on both sides of the test mass, and the four parallel plates are parallel to the conductor surface of the test mass and are equidistant from the test mass; the two plates on one side of the test mass are respectively the first parallel plate 2-1 and the third parallel plate 2-3, and the two plates on the other side are respectively the second parallel plate 2-2 and the fourth parallel plate 2-4; the center distance of the plates on both sides is denoted as b, and the center distance is the distance between the centers of the two plates on the same side; a spatial rectangular coordinate system is established with the center of mass of the test mass as the origin, and the normal direction of the plate is defined as the x direction, and the angle direction of the rotation of the test mass by the force in the x direction is φ;

[0053] (2) applying an excitation voltage to the four plates, causing the test mass to rotate and produce a small angular displacement to form a certain angular displacement;

[0054] (3) Using a displacement sensor to convert the angular displacement signal into a voltage signal;

[0055] (4) Input the voltage signal output by the displacement sensor into the PID controller to output the required control torque

[0056] (5) The feedback voltage corresponding to the control torque is calculated by an amplitude algorithm, and then the feedback voltage is applied to the parallel plates by an electrostatic actuator, so that the test mass is finally returned to its initial position through the electrostatic force generated between the parallel plates and the test mass;

[0057] (6) Calculate the charge on the test mass based on the control torque;

[0058] Among them, the control torque is the torque generated by the parallel plates on the test mass after the feedback voltage is applied; when the test mass finally returns to the initial position and stabilizes at the initial position, the control torque is equal to the torque generated by the excitation voltage applied to the plate on the test mass, and the control torque signal contains information about the charge of the test mass, and the amount of charge on the test mass is obtained;

[0059] A sinusoidal excitation voltage is applied to the four plates, wherein a sinusoidal voltage V is applied to the first parallel plate 2-1 and the fourth parallel plate 2-4. mod sin(ω m t), a reverse and same frequency sinusoidal voltage -V is applied to the second parallel plate 2-2 and the third parallel plate 2-3. mod sin(ω m t), so the voltage V on the ith parallel plate in the x direction can be i It is expressed as:

[0060] V i =α i V MOD sin(ω m t) (1)

[0061] Among them, α i = ±1, α of the first parallel plate 2-1 and the fourth parallel plate 2-4 i Take 1, the α of the second parallel plate 2-2 and the third parallel plate 2-3 i Take -1;

[0062] The sum of the AC excitation voltage amplitudes on the four parallel plates is zero, which helps to reduce the impact of the test mass on acceleration measurement due to the accumulation of charge due to electromagnetic induction;

[0063] At this time, after the excitation voltage is applied to the plate, the potential of the test mass is:

[0064]

[0065] Among them, V TM is the potential of the test mass after the excitation voltage is applied to the plate; q is the charge on the test mass; C tot is the total capacitance between the test mass and the surrounding plates; C i is the capacitance between the ith parallel plate and the test mass; the excitation voltage acts on the test mass, generating a torque in the φ direction:

[0066]

[0067] Substituting (1) and (2) into (3), the modulated frequency is 1ω m The moment at is:

[0068]

[0069] in, ε is the electrostatic constant, S is the area of ​​the parallel plates; d0 is the distance between the plates and the parallel surface of the test mass closest to them when the test mass is in the initial position;

[0070] M φ After filtering and demodulation, the torque of the test mass caused by the excitation voltage on the four plates is:

[0071]

[0072] The control torque is calculated by the PID controller Then the feedback voltage corresponding to the control torque is calculated by the amplitude algorithm. The feedback voltages of the first to fourth parallel plates used to control the rotation are recorded as V1, V2, V3, and V4 respectively.

[0073] Assuming that the test mass is angularly displaced along the positive direction of φ, in order to avoid the generation of induced charge on the test mass, the sum of the feedback voltage amplitudes should be kept zero, and we have:

[0074] V1+V2+V3+V4=0

[0075] Take the effective value of the AC control torque, the control torque and feedback voltage should satisfy:

[0076]

[0077] In the formula,

[0078] At the same time, the rotation control should not affect the translation:

[0079]

[0080] In the formula

[0081] The above three equations are not sufficient to solve the four unknowns, so the electrostatic negative stiffness requirement is supplemented during AC control. The electrostatic negative stiffness can be obtained by taking the partial derivative of the feedback force with respect to the displacement:

[0082]

[0083] Among them, k φ,req is the electrostatic negative stiffness demand value, which is a fixed value for the specified system and is a constant term in the equation;

[0084] Solving the above equations together, we get:

[0085]

[0086] Therefore, the feedback voltage required on the plate can be calculated from the control torque, and then the feedback voltage is applied to the plate by the electrostatic actuator. The electrostatic force generated between the plate and the test mass causes the test mass to move to the equilibrium position. If the test mass is not stable at the equilibrium position, the displacement is input into the displacement sensor again, and a closed-loop operation is performed again. After multiple operations, the closed-loop control will stabilize the test mass at the equilibrium position. At this time, the control torque calculated by the PID controller is balanced with the torque M generated by the excitation. The control torque and the torque (torque) of the excitation voltage on the test mass are equal in magnitude and opposite in direction, so:

[0087]

[0088] By using formulas (5) and (6), the charge q on the test mass can be obtained as:

[0089]

[0090] Therefore, the expression for the amount of charge on the test mass can be obtained according to (7);

[0091] In order to further illustrate the closed-loop control-based measurement method for the inspection mass charge provided by the embodiment of the present invention, the following is described in detail with reference to the accompanying drawings and in combination with specific examples:

[0092] like Figure 2 As shown, two pairs of parallel plates are placed on both sides of the test mass, and a sinusoidal excitation voltage is applied to the four plates, wherein a positive sinusoidal voltage V is applied to the first parallel plate 2-1 and the fourth parallel plate 2-4. mod sin(ωt), a reverse sinusoidal voltage of the same frequency -V is applied to the second parallel plate 2-2 and the third parallel plate 2-3 mod sin(ωt); This arrangement of the excitation voltage will cause the test mass to rotate under the action of the torque to produce a small angular displacement, and then the displacement difference signal is converted into a voltage signal through the displacement sensor, where the torque M is determined by formula (5); the capacitive displacement sensor outputs a combined voltage, which is input as an input signal to the controller for closed-loop control. The specific algorithm of the controller will calculate the torque control torque used to balance the torque generated by the external excitation

[0093] The magnitude of the torque exerted by the control torque and the excitation voltage on the test mass is equal, so the control torque signal contains information about the excitation signal and the charge of the test mass. From this, the charge quantity q on the test mass can be determined according to formula (7).

[0094] right Figure 2 A more specific description is as follows:

[0095] The unit 6-1 for applying excitation voltage applies excitation voltage to the first parallel plates 2-1 to the fourth parallel plates 2-4, and the inspection mass 1 generates electrostatic force with the first parallel plates 2-1 to the fourth parallel plates 2-4, and the inspection mass 1 generates displacement. The displacement is input into the first displacement sensor 3-1 and the second displacement sensor 3-2 and converted into voltage, and then input into the controller 4-1. The control torque is calculated by the PID algorithm. The amplitude calculator 4-2 then calculates the feedback voltage corresponding to each plate based on the control torque, and then the first electrostatic actuator 5-1 to the fourth electrostatic actuator 5-4 applies the feedback voltage to the corresponding first parallel plates 2-1 to the fourth parallel plates 2-4. The electrostatic force causes the inspection mass to move toward the equilibrium position. When it finally stabilizes at the equilibrium position, the displacement sensor input is 0. At this time, the controller 4-1 inputs the control torque signal into the charge calculation processor 6-2 for charge solution to finally obtain the charge quantity.

[0096] In summary, compared with the prior art, the present invention has the following advantages:

[0097] The present invention applies an excitation voltage to parallel plates to cause the inspection mass to rotate, uses a displacement sensor and a control module to calculate the control torque required to return the inspection mass to an initial position, and simultaneously calculates a feedback voltage based on the control torque. An electrostatic actuator is used to apply the feedback voltage to the corresponding parallel plates to return the inspection mass to the initial position, thereby achieving the goal of suppressing large-scale movement of the inspection mass by means of closed-loop control, reducing noise caused by measuring charge, and avoiding interference problems caused by interrupting target signal detection when measuring the accumulated charge of the inspection mass. The precision measuring instrument having the inspection mass can continue to detect target signals while measuring the charge of the inspection mass, and has broad application prospects.

[0098] The measurement system for the test mass charge provided by the present invention has no mechanical connection with the precision measuring instrument with the test mass, and will not introduce external interference such as mechanical thermal noise into the precision measuring instrument during the process of measuring the test mass charge.

[0099] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A measurement system for verifying mass charge, characterized in that: include: Parallel plates, displacement sensors, control modules, electrostatic actuators and charge measurement modules; The parallel plates are placed in parallel and in equal numbers on both sides of the inspection mass, and the parallel plates are parallel to the surface of the inspection mass and are at equal distances from the inspection mass; the output ends of each pair of parallel plates placed in parallel on both sides of the inspection mass are connected to a displacement sensor; the output end of the displacement sensor is connected to the control module; the output end of the controller is connected to the electrostatic actuator and the charge measurement module; the output end of each electrostatic actuator is connected to a parallel plate; The parallel plates are used to receive an excitation voltage to cause the test mass to rotate; wherein the test mass is in a balanced state when it is in an initial position; the excitation voltages applied to the adjacent parallel plates on each side of the test mass are equal in magnitude and opposite in sign; The displacement sensor is used to measure the freedom of motion of the inspection mass and convert the displacement signal into a voltage signal; The control module is used to receive the voltage signal and calculate the control torque required to return the inspection mass to the initial position and the feedback voltage corresponding to the control torque; The electrostatic actuator is used to apply the feedback voltage to the corresponding parallel plates, and an electrostatic force is generated between the test mass and the parallel plates, so that the test mass returns to the initial position; The charge measurement module is used to calculate the charge on the test mass based on the control torque.

2. The measuring system according to claim 1, characterized in that The number of the parallel plates is 4, the first parallel plate and the third parallel plate are located on one side of the inspection mass; the second parallel plate and the fourth parallel plate are located on the other side of the inspection mass; the first parallel plate, the second parallel plate, the third parallel plate and the fourth parallel plate are at an equal distance from the inspection mass; the first parallel plate is directly parallel to the second parallel plate; the third parallel plate is directly parallel to the fourth parallel plate; a sinusoidal voltage is applied to the first parallel plate and the fourth parallel plate, and an opposite sinusoidal voltage of the same frequency is applied to the second parallel plate and the third parallel plate; The displacement sensor includes a first displacement sensor and a second displacement sensor; the input end of the first displacement sensor is connected to the first parallel electrode plate and the second parallel electrode plate; the input end of the second displacement sensor is connected to the third parallel electrode plate and the fourth parallel electrode plate; The electrostatic actuator includes a first electrostatic actuator, a second electrostatic actuator, a third electrostatic actuator and a fourth electrostatic actuator; the input ends of the first electrostatic actuator, the second electrostatic actuator, the third electrostatic actuator and the fourth electrostatic actuator are connected to the control module, and the output ends thereof are respectively connected to the first parallel plate, the second parallel plate, the third parallel plate and the fourth parallel plate.

3. The measuring system according to claim 2, characterized in that The control module includes: a PID controller and an amplitude calculator; The output end of the PID controller is connected to the amplitude calculator and the charge measurement module; the output end of the amplitude calculator is respectively connected to the first electrostatic actuator, the second electrostatic actuator, the third electrostatic actuator and the fourth electrostatic actuator; The PID controller is used to receive the voltage signal and output the control torque required to return the inspection mass to the initial position; the amplitude calculator is used to calculate the feedback voltage corresponding to the control torque through the amplitude algorithm.

4. The measuring system according to claim 3, characterized in that The feedback voltage is: Among them, V 1,3 Represents the feedback voltage on the first parallel plate or the third parallel plate; V 2,4 Represents the feedback voltage on the second parallel plate or the fourth parallel plate; C i is the capacitance between the ith plate and the test mass; is the angular displacement; k φ,req is the electrostatic negative stiffness demand value; To control the torque.

5. The measuring system according to claim 4, characterized in that The charge on the test mass is: Among them, C tot is the total capacitance formed between all parallel plates and the test mass; d0 is the distance between the plates and the test mass when the test mass is in the initial position; is the control torque; ε is the electrostatic constant; S is the parallel plate area; V mod is the amplitude of the excitation voltage applied to the parallel plates.

6. A measurement method based on the mass charge measurement system of claim 1, characterized in that: The following steps are involved: Placing parallel plates on both sides of the test mass, wherein all the parallel plates are parallel to the surface of the test mass and are equidistant from the test mass; and the number of parallel plates on both sides of the test mass is the same; Applying an excitation voltage to the parallel plates causes the test mass to rotate; wherein the test mass is in a balanced state when it is in an initial position; the excitation voltages applied to adjacent parallel plates on each side of the test mass are equal in magnitude and opposite in sign; Measure the freedom of motion of the test mass and convert the displacement signal into a voltage signal; According to the voltage signal, the control torque required to return the inspection mass to the initial position and the feedback voltage corresponding to the control torque are calculated; Applying feedback voltage to the corresponding parallel plates generates electrostatic force between the test mass and the parallel plates, causing the test mass to return to its initial position; The charge on the test mass is calculated based on the control torque.

7. The measuring method according to claim 6, characterized in that: The number of the parallel plates is 4, the first parallel plate and the third parallel plate are located on one side of the inspection mass; the second parallel plate and the fourth parallel plate are located on the other side of the inspection mass; the first parallel plate, the second parallel plate, the third parallel plate and the fourth parallel plate are equidistant from the inspection mass; the first parallel plate is directly opposite and parallel to the second parallel plate; the third parallel plate is directly opposite and parallel to the fourth parallel plate; a sinusoidal voltage is applied to the first parallel plate and the fourth parallel plate, and an opposite sinusoidal voltage of the same frequency is applied to the second parallel plate and the third parallel plate.

8. The measuring method according to claim 7, characterized in that: The method to obtain the control torque and feedback voltage is: The voltage signal is input to the PID controller, which outputs the control torque required to return the inspection mass to its initial position; The feedback voltage corresponding to the control torque is calculated by an amplitude algorithm and applied to the parallel plates.

9. The measuring method according to claim 8, characterized in that: The feedback voltage is: Among them, V 1,3 Represents the feedback voltage on the first parallel plate or the third parallel plate; V 2,4 Represents the feedback voltage on the second parallel plate or the fourth parallel plate; C i is the capacitance between the ith plate and the test mass; is the angular displacement; k φ,req is the electrostatic negative stiffness demand value; To control the torque.

10. The measuring method according to claim 9, characterized in that: The charge on the test mass is: Among them, C tot is the total capacitance formed between all parallel plates and the test mass; d0 is the distance between the plates and the test mass when the test mass is in the initial position; is the control torque; ε is the electrostatic constant; S is the parallel plate area; V mod is the amplitude of the excitation voltage applied to the parallel plates.

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