A three-electrode vacuum measurement sensor

Abstract

The present invention relates to the technical field of vacuum gauges, and provides a three-electrode vacuum measurement sensor, which includes: a housing; an electrode plate, which is arranged inside the housing and divides the housing into a reference cavity and a process cavity; an elastic film, which is arranged in the process cavity and is connected to the electrode plate to form a closed cavity; a first electrode, the first end of the first electrode penetrates through the closed cavity and is connected to the elastic film, and the second end of the first electrode passes through the reference cavity and extends out of the housing; a second electrode and a third electrode, the first ends of the second electrode and the third electrode are connected to the electrode plate, and the second ends of the second electrode and the third electrode pass through the reference cavity and extend out of the housing. By separately leading out the electrodes of the elastic film in the present invention, three separate electrode plates, namely an inner ring electrode, an outer ring electrode, and a common electrode, are formed, so that an inner ring capacitor and an outer ring capacitor are formed, improving the ability of the sensor itself to resist stray capacitance, weakening the crosstalk caused by the housing, and enhancing the stability.

Description

Technical Field

[0001] The present invention relates to the technical field of vacuum gauges, and particularly to a three-electrode vacuum degree measurement sensor. Background Art

[0002] A vacuum degree measurement sensor is a commonly used sensor for measuring vacuum degree or air pressure in industrial practice, and is widely used in various industrial automatic control environments, involving many industries such as oil pipelines, water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, military industry, petrochemical industry, oil wells, electric power, ships, machine tools, ventilation ducts, etc. Vacuum degree measurement sensors can be classified into thin film gauges, Pirani gauges, and ionization gauges according to different physical mechanisms they utilize. Among them, thin film gauges have been widely used due to their high accuracy, good linearity, and insensitivity to the types of process gases. The essence of a thin film gauge is a variable pole pitch capacitive sensor, and its working principle is that the pressure of the medium inside the process chamber directly acts on the elastic film of the sensor, causing the elastic film to generate a micro-displacement proportional to the medium pressure. The change in the displacement of the elastic film leads to a change in the capacitance value of the sensor, and then the circuit is used to detect this capacitance change and convert it into a standard signal corresponding to this pressure.

[0003] The capacitance change range of a capacitive thin film type vacuum degree measurement sensor is very small, generally in the pF order of magnitude, and it is easily affected by stray capacitance and parasitic capacitance. The current commonly used measurement method is mainly based on analog circuits, and the elastic film of the capacitor is led to the housing, and the housing is then connected to the ground through the equipment. This method can obtain better test results when the user's equipment is well grounded, but in actual use, the user's equipment cannot guarantee good grounding. In the case of no good grounding, the sensor circuit is easily interfered by the outside world, affecting the measurement result, and in severe working conditions, the sensor will be damaged. Summary of the Invention

[0004] The present invention provides a three-electrode vacuum degree measurement sensor to solve the defect in the prior art that the sensor circuit is interfered due to the housing not being able to be well grounded, affecting the measurement result and even damaging the instrument.

[0005] The present invention provides a three-electrode vacuum degree measurement sensor, including:

[0006] A housing;

[0007] An electrode plate, which is arranged inside the housing and divides the housing into a reference chamber and a process chamber;

[0008] An elastic film, which is arranged in the process chamber and is connected to the electrode plate to form a closed chamber;

[0009] A first electrode, the first end of the first electrode penetrates through the closed cavity and is connected to the elastic film, and the second end of the first electrode passes through the reference cavity and extends out of the housing;

[0010] A second electrode, the first end of the second electrode is connected to the electrode plate, and the second end of the second electrode passes through the reference cavity and extends out of the housing;

[0011] A third electrode, the first end of the third electrode is connected to the electrode plate, and the second end of the third electrode passes through the reference cavity and extends out of the housing.

[0012] A three - electrode vacuum degree measurement sensor provided by the present invention further includes: an isothermal body, the isothermal body is a hollow structure, and the housing is arranged inside the isothermal body.

[0013] A three - electrode vacuum degree measurement sensor provided by the present invention further includes: a temperature control device, and the temperature control device is arranged on the isothermal body.

[0014] For a three - electrode vacuum degree measurement sensor provided by the present invention, the temperature control device includes: a heating wire or a heating film, and the heating wire or the heating film covers the outer side surface of the isothermal body.

[0015] A three - electrode vacuum degree measurement sensor provided by the present invention further includes: a micro - controller, and the micro - controller is electrically connected to the heating wire for controlling the heating effect of the heating wire.

[0016] A three - electrode vacuum degree measurement sensor provided by the present invention further includes: a temperature sensor, and the temperature sensor is arranged inside the isothermal body and is communicatively connected to the micro - controller; the temperature sensor is used to monitor the temperature change inside the isothermal body and feedback it to the micro - controller, and the micro - controller adjusts the heating power of the heating wire according to the temperature change data monitored by the temperature sensor.

[0017] A three - electrode vacuum degree measurement sensor provided by the present invention further includes: a capacitance detection circuit, and the capacitance detection circuit is arranged inside the isothermal body. The capacitance detection circuit is respectively connected to the second end of the first electrode, the second end of the second electrode, and the second end of the third electrode, and is used to receive the difference change between the second electrode and the first electrode, the difference change between the third electrode and the first electrode, and calculate the air pressure value.

[0018] For a three - electrode vacuum degree measurement sensor provided by the present invention, the capacitance detection circuit includes a digital circuit module.

[0019] A three - electrode vacuum degree measurement sensor provided by the present invention forms three separate electrode plates, namely an inner - ring electrode, an outer - ring electrode, and a common electrode, by separately leading out the electrodes of the elastic film. The inner - ring electrode and the common electrode form an inner - ring capacitor, and the outer - ring electrode and the common electrode form an outer - ring capacitor, which improves the sensor's own ability to resist stray capacitance, weakens the crosstalk caused by the housing, and enhances the stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following - described drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 is the external view of the three - electrode vacuum degree measurement sensor provided by the present invention;

[0022] Figure 2 is the perspective view of the three - electrode vacuum degree measurement sensor provided by the present invention;

[0023] Figure 3 is the schematic diagram of the external structure of the capacitive thin - film vacuum gauge provided by the present invention;

[0024] Figure 4 is the schematic diagram of the internal structure of the capacitive thin - film vacuum gauge provided by the present invention;

[0025] Figure 5 is the schematic diagram of the principle of the capacitance detection circuit provided by the present invention;

[0026] Figure 6 is the temperature - control logic diagram of the micro - controller provided by the present invention.

[0027] Reference numerals:

[0028] 100: capacitive thin - film vacuum gauge; 200: isothermal body; 300: capacitance detection circuit;

[0029] 1: housing; 2: electrode plate; 3: elastic film; 4: first electrode; 5: second electrode; 6: third electrode; 7: reference cavity; 8: process cavity. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To make the objectives, technical solutions, and advantages of the present invention more clear, the following will, in conjunction with the accompanying drawings of the present invention, clearly and completely describe the technical solutions in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts fall within the scope of protection of the present invention.

[0031] The following will, in conjunction with Figures 1 to 6 Describe a three - electrode vacuum degree measurement sensor of the present invention. The three - electrode vacuum degree measurement sensor includes three major parts: a capacitive thin - film vacuum gauge 100, an isothermal body 200, and a capacitance detection circuit 300. Among them, the capacitive thin - film vacuum gauge 100 includes: a housing 1, an electrode plate 2, an elastic film 3, a first electrode 4, a second electrode 5, and a third electrode 6.

[0032] The electrode plate 2 is disposed inside the housing 1 and divides the housing 1 into a reference cavity 7 and a process cavity 8; the elastic film 3 is disposed in the process cavity 8 and is connected to the electrode plate 2 to form a closed cavity; the first end of the first electrode 4 penetrates through the closed cavity and is connected to the elastic film 3, and the second end of the first electrode 4 passes through the reference cavity 7 and extends out of the housing 1; the first end of the second electrode 5 is connected to the electrode plate 2, and the second end of the second electrode 5 passes through the reference cavity 7 and extends out of the housing 1; the first end of the third electrode 6 is connected to the electrode plate 2, and the second end of the third electrode 6 passes through the reference cavity 7 and extends out of the housing 1.

[0033] Specifically, except for the inlet used to connect to the gas source, the housing 1 is welded into a sealed part by welding technology. The electrode plate 2 is horizontally fixed inside the housing 1. The reference cavity 7 is located above the electrode plate 2, and its interior is in a high-vacuum environment; the process cavity 8 is located below the electrode plate 2, and its interior is connected to the gas source to be measured through the inlet. One end of the first electrode 4 passes through the closed cavity and is connected to the elastic film 3, and the other end passes through the housing 1 and is connected to the capacitance detection circuit 300; one ends of the second electrode 5 and the third electrode 6 are connected to the electrode plate 2, and the other ends pass through the housing 1 and are connected to the capacitance detection circuit 300. In the present invention, the above-mentioned first electrode 4, second electrode 5, and third electrode 6 are separately led out and connected to the capacitance detection circuit 300, so it is called a three-electrode circuit. The three-electrode vacuum degree measurement sensor of the present invention is essentially a differential variable pole pitch type sensor. When calculating the air pressure value, the second electrode 5 and the first electrode 4 form an inner ring capacitor, and the third electrode 6 and the first electrode 4 form an outer ring capacitor. The change in the air pressure in the process cavity 8 will cause the change in the distance between the elastic film 3 and the inner ring capacitor and the outer ring capacitor, thereby causing the change in the difference between the inner and outer ring capacitors. By calculating the difference between the second electrode 5 and the first electrode 4 and the difference between the third electrode 6 and the first electrode 4, and performing digital demodulation and filtering processing on the difference between the inner and outer rings, an analog output signal corresponding to the air pressure value can be obtained.

[0034] Furthermore, the three-electrode vacuum degree measurement sensor of the present invention is an absolute pressure type sensor, and a vacuum area is sealed inside as the reference cavity 7, and the lower gauge tube part is connected to the process cavity 8. When the air pressure inside the process cavity 8 changes, the elastic film 3 will deform due to the pressure. Taking the outer ring capacitor alone, assuming its change amount is △d and the differential capacitance change amount is △C, then there is the following relationship:

[0035] (△C / C) = (△d / d)(1 + △d / d)

[0036] It can be seen from the above formula that to improve the sensitivity of the variable pole pitch type sensor, the initial distance d must be reduced, but the non-linear error will increase as d decreases. To solve the above contradiction, a differential structure is adopted to reduce the non-linear error. When the outer ring capacitor changes, the inner ring capacitor also changes accordingly. Due to the difference in their installation positions, the change amount of the outer ring capacitor will be greater than that of the inner ring. The difference between the two capacitors is proportional to the pressure value in the process cavity 8. The differential method greatly weakens the influence brought by the common mode noise, so that the anti-interference ability of the sensor is enhanced.

[0037] A three - electrode vacuum degree measurement sensor provided by the present invention forms three separate plates, namely an inner - ring electrode (i.e., the second electrode 5), an outer - ring electrode (i.e., the third electrode 6), and a common electrode (i.e., the first electrode 4) by separately leading out the electrodes of the elastic film 3. The inner - ring electrode and the common electrode form an inner - ring capacitor, and the outer - ring electrode and the common electrode form an outer - ring capacitor, improving the sensor's own ability to resist stray capacitance, weakening the crosstalk caused by the housing 1, and enhancing stability.

[0038] In one embodiment of the present invention, the three - electrode vacuum degree measurement sensor further includes: an isothermal body 200. The isothermal body 200 has a hollow structure, and the housing 1 is disposed inside the isothermal body 200. Specifically, the isothermal body 200 has the function of keeping the temperature inside it constant. Since the housing 1 is generally made of metal material, it is extremely vulnerable to the thermal stress caused by temperature changes. By keeping the temperature inside the isothermal body 200 constant, the offset of the pressure measurement value caused by the influence of the external temperature is reduced or even eliminated.

[0039] In one embodiment of the present invention, the three - electrode vacuum degree measurement sensor further includes: a temperature - control device disposed on the isothermal body 200. Specifically, the temperature - control device includes: a heating wire or a heating film, and the heating wire or the heating film covers the outer side surface of the isothermal body 200. In this embodiment, by winding the heating wire or covering the heating film around the outer periphery of the isothermal body 200, the isothermal body 200 is heated to ensure that the three - electrode vacuum degree measurement sensor is always in a state of constant temperature. Specifically, the isothermal body 200 is an aluminum shell wrapped with a heating wire in structure, and its main function is to ensure that the sensor is in a constant - temperature environment and reduce the drift caused by temperature.

[0040] In one embodiment of the present invention, the three - electrode vacuum degree measurement sensor further includes: a micro - controller electrically connected to the heating wire and used to control the heating effect of the heating wire. In this embodiment, the micro - controller controls the heating power of the heating wire to control its heating effect.

[0041] In one embodiment of the present invention, the three - electrode vacuum degree measurement sensor further includes: a temperature sensor disposed inside the isothermal body 200 and communicatively connected to the micro - controller; the temperature sensor is used to monitor the temperature change inside the isothermal body 200 and feedback it to the micro - controller, and the micro - controller adjusts the heating power of the heating wire according to the temperature change data monitored by the temperature sensor. In this embodiment, by monitoring the temperature change inside the isothermal body 200 with the temperature sensor and sending the temperature change data to the micro - controller, when the micro - controller determines that the temperature inside the isothermal body 200 is lower than the set value, it controls to increase the heating power of the heating wire to ensure that the temperature inside the isothermal body 200 is constant. In this embodiment, the temperature sensor uses a thermistor, such as Figure 6As shown in the figure, first, the MCU reads the temperature of the thermistor inside the isothermal body 200. When the temperature fails to reach the set temperature, the MCU calculates through PID and then controls the high-level time of PWM to indirectly control the heating power. The thermistor real-time feedbacks the temperature of the isothermal body 200, thus realizing the closed-loop control of the temperature of the entire isothermal body 200, ensuring that the sensor is in a constant temperature environment and reducing the drift of the capacitance value of the sensor caused by temperature.

[0042] In one embodiment of the present invention, the three-electrode vacuum degree measurement sensor further includes: a capacitance detection circuit 300, which is arranged inside the isothermal body 200. The capacitance detection circuit 300 is respectively connected to the second ends of the first electrode 4, the second electrode 5, and the third electrode 6, and is used to receive the difference changes between the second electrode 5 and the first electrode 4, and between the third electrode 6 and the first electrode 4, and calculate the air pressure value. Further, the capacitance detection circuit 300 in this embodiment includes a digital circuit module. Specifically, the capacitance detection circuit 300 is a digital circuit module. Using digital circuits can overcome the defects of high cost, complex testing, and inaccurate testing brought by analog circuits, save costs, and at the same time obtain more accurate testing parameters. The principle of the capacitance detection circuit 300 is an operational amplifier circuit. The amplification factor A of the operational amplifier is very large, and the input impedance Z i is very high. As Figure 5 shown, where C x is the sensor capacitance, C is a fixed capacitance, U is the input AC carrier, U o is the output voltage, ∑ is the virtual ground point, ε is the permittivity, S is the plate surface area, d is the plate spacing, and jw corresponds to the Laplace transform complex frequency domain.

[0043] It can be deduced from the figure that:

[0044] For the inner ring or outer ring capacitors,

[0045] Therefore, finally, it can be obtained that:

[0046] As can be seen from the above formula, for a single capacitor (inner or outer ring), its output voltage has a linear relationship with the plate spacing, and the negative sign indicates that the output is out of phase with the power supply voltage. In addition, this circuit uses a digital circuit to generate an AC carrier U, which is a sinusoidal AC signal with adjustable phase and amplitude. This AC carrier signal is applied to the capacitance of the vacuum gauge. The carrier is introduced from the elastic film 3 of the vacuum gauge, and then the output signal is led out from the outer ring plate and the inner ring plate to the operational amplifier. After differential amplification, the signal is converted into a digital signal through an ADC chip again. After filtering and demodulation processing of the digital signal, a digital quantity proportional to the capacitance change is obtained. Then, scale conversion is performed on this digital quantity signal to obtain the voltage output Uo corresponding to the vacuum degree.

[0047] Based on the above several embodiments, a three-electrode vacuum degree measurement sensor provided by the present invention has the following beneficial effects:

[0048] In the first aspect, the elastic film 3 is separately led out through electrodes to form three separate plates, namely the first electrode 4, the second electrode 5, and the third electrode 6 (as Figure 3 shown). This solution of completely leading out all three electrodes has strong anti-stray capacitance interference ability and good stability;

[0049] In the second aspect, the isothermal body 200 provided by the present invention is an aluminum shell wrapped with heating wires on the outside, and a thermistor is fixed inside the shell. The wires of the heating wires and the thermistor are led out to the microcontroller through terminals; its principle block diagram is as Figure 6 shown. The temperature is PID-regulated by adjusting the form of the PWM pulse width, ensuring that the sensor is in a constant temperature environment and reducing the drift caused by temperature.

[0050] In the third aspect, the change amount of the film capacitor is as low as the pF level, and it is difficult to accurately measure the small capacitance. Currently, among many different capacitance measurement circuits, only the charge and discharge circuit and the AC capacitance measurement circuit can suppress the influence of stray capacitance. Considering drift and signal-to-noise ratio, the AC measurement circuit is superior to the charge and discharge circuit because the AC capacitance measurement circuit works in the AC mode, while the charge and discharge circuit works in the DC mode; the present invention adopts an AC measurement circuit, generates an AC carrier using a digital circuit, and calculates the change of the equivalent capacitance value by using the method of digital demodulation. The measurement system designed by this method has good stability, linearity, and resolution.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A three-electrode vacuum measurement sensor, characterized in that Comprising: A housing; Electrode plates, which are arranged inside the housing and divide the housing into a reference chamber and a process chamber; An elastic film, which is arranged inside the process chamber and forms a closed chamber in connection with the electrode plates; A first electrode, the first end of which penetrates through the closed chamber and is connected to the elastic film, and the second end of which passes through the reference chamber and extends out of the housing; A second electrode, the first end of which is connected to the electrode plates, and the second end of which passes through the reference chamber and extends out of the housing; A third electrode, the first end of which is connected to the electrode plates, and the second end of which passes through the reference chamber and extends out of the housing; When calculating the air pressure value, the second electrode and the first electrode form an inner-ring capacitor, and the third electrode and the first electrode form an outer-ring capacitor. The change in the air pressure in the process chamber will cause the change in the distance between the elastic film and the inner-ring capacitor and the outer-ring capacitor, thereby causing the change in the difference between the inner and outer-ring capacitors. By calculating the difference between the second electrode and the first electrode and the difference between the third electrode and the first electrode, and performing digital demodulation and filtering processing on the difference between the inner and outer rings, an analog output signal corresponding to the air pressure value can be obtained; Further comprising: an isothermal body, which is of a hollow structure, and the housing is arranged inside the isothermal body.

2. The tri - electrode vacuum measurement sensor according to claim 1, wherein, Further comprising: A temperature control device, which is arranged on the isothermal body.

3. The three-electrode vacuum measurement sensor according to claim 2, characterized in that, The temperature control device includes: a heating wire or a heating film, and the heating wire or the heating film covers the outer side surface of the isothermal body.

4. A three - electrode vacuum degree measurement sensor according to claim 3, characterized in that, Further comprising: A microcontroller, which is electrically connected to the heating wire and is used to control the heating effect of the heating wire.

5. A three - electrode vacuum degree measurement sensor according to claim 4, characterized in that, Further comprising: A temperature sensor, which is arranged inside the isothermal body and communicates with the microcontroller; the temperature sensor is used to monitor the temperature change inside the isothermal body and feedback it to the microcontroller, and the microcontroller adjusts the heating power of the heating wire according to the temperature change data monitored by the temperature sensor.

6. A three - electrode vacuum degree measurement sensor according to any one of claims 1 to 5, characterized in that, Further comprising: A capacitance detection circuit, which is arranged inside the isothermal body, and the capacitance detection circuit is respectively connected to the second end of the first electrode, the second end of the second electrode and the second end of the third electrode, and is used to receive the change in the difference between the second electrode and the first electrode and the change in the difference between the third electrode and the first electrode, and calculate the air pressure value.

7. The three-electrode vacuum measurement sensor according to claim 6, characterized in that, The capacitance detection circuit includes a digital circuit module.

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