Abstract: This paper introduces a capacitive micro vacuum detection system. The system uses a PIC series microcontroller to measure the vacuum of a vacuum insulation panel in real time. Experimental data shows that the accuracy can reach 10⁻² Pa, which fully meets the measurement requirements. 1 Introduction With the development of science and technology, building a conservation-oriented society has become a consensus, and energy-saving materials are being used extensively. For example, one of the energy-saving measures for refrigerators is to strengthen insulation, which is often achieved by thickening the insulation layer. For insulation materials of the same thickness, the lower the thermal conductivity, the better the insulation effect. For refrigerator energy saving, increasing the thickness of the insulation layer will undoubtedly achieve energy saving, but it will increase the size of the refrigerator or reduce the usable space. Therefore, finding insulation materials with lower thermal conductivity has become the best way to achieve energy saving in refrigerator insulation. In recent years, some developed European countries have taken the lead in using vacuum insulation panels in the production of energy-saving buildings and refrigeration equipment to achieve energy saving. Vacuum insulation panels are composed of multiple layers of metal, high-barrier film and glass fiber core material, and getter. By maximizing the internal vacuum, heat conduction is isolated, achieving the purpose of heat preservation and energy saving. VIP vacuum insulation panels are an upgraded product of insulation materials, achieving a reduction in insulation material thickness by half and energy saving by half. However, measuring the vacuum degree of vacuum insulation panels is a challenge. Due to the inability to create openings in the material and the narrow vacuum cavity, ordinary measurement methods cannot be used. Miniature vacuum gauges made using microelectromechanical systems (MEMS) technology can effectively solve this problem. A miniature embedded vacuum plate vacuum measuring element, made by integrating a miniature vacuum gauge with an IC circuit, is installed in the vacuum plate and used during product inspection before shipment, thus ensuring the vacuum quality of the insulation panel product. 2 System Composition and Principle 2.1 Capacitive Miniature Vacuum Sensor Capacitive sensors mainly utilize the deformation of a silicon diaphragm under pressure, causing a change in the distance between the two plates, thereby changing the capacitance, which is used as the basis for measurement. The structure of a capacitive miniature vacuum sensor is shown in Figure 1. The sensor consists of a glass substrate, a lower electrode, an insulating layer, a silicon diaphragm (upper electrode), and an upper sealing glass layer. The lower electrode is sputtered onto the glass substrate, and an insulating layer is grown on the electrode. The silicon diaphragm is formed using double-sided photolithography, diffusion, and anisotropic etching techniques on a silicon wafer. This capacitive vacuum sensor has two cavities: the upper cavity is a vacuum chamber, and the lower cavity is bonded together and is not sealed, allowing the gas inside to communicate with the outside gas. The distance between the two plates of the capacitor can be controlled by the depth of silicon wafer etching, and the gap between the silicon diaphragm and the glass electrode is very small, which is why the silicon capacitive sensor has high sensitivity. 2.2 CVC Test System Circuit This system uses a capacitor-to-voltage converter with an incremental modulator, which can obtain adjustable signal bandwidth and detection accuracy. Its circuit is shown in Figure 2. The capacitor-to-voltage converter converts the difference in capacitance (C1-C2) into a voltage form. Then the voltage is subjected to correlated double sampling to eliminate low-frequency noise, and finally output after low-pass filtering by the incremental modulator. The output signal V′y is proportional to the capacitance difference (C1-C2). The two excitation signals (±Vs) charge capacitors C1 and C2, so the charge injected into the preamplifier is: The output of the preamplifier is: △q＝Vs(C1-C2) After testing, this circuit can effectively suppress the influence of various noises and obtain good accuracy. 2.3 Signal Amplification Circuit The overall reference voltage of the output signal is relatively small, necessitating signal amplification for convenient acquisition and transmission, and better subsequent signal processing. The output signal amplification circuit is shown in Figure 3. R4, R5, R6, and TL084CN constitute the amplifier. In the experimental testing of this system, this operational amplifier needs to amplify by approximately 150 times; therefore, R4 = 62Ω and R5 = 1kΩ are selected. 2.4 PIC16F87X System Operating Circuit This system uses the PIC16F87X operating circuit, as shown in Figure 4. Two 47kΩ resistors and the Reset button form the reset system. Capacitors C1 and C2 are both 22pF, forming the oscillation system circuit with a 32kΩ crystal oscillator. The system works as follows: 3 Measurement data and analysis (1) After the capacitive miniature vacuum sensor tests the vacuum level of the measured environment, it generates a small capacitance value corresponding to the vacuum level; (2) The capacitance value is converted into a voltage signal through the capacitance/voltage (CVC) conversion measurement circuit; (3) The voltage signal is processed and displayed by PIC16F876A. According to the measured data, the relationship curve between vacuum level and output voltage in the range of 10-2 to 10-3 Pa can be obtained, as shown in Figure 5. It can be seen that as the vacuum level increases, the output voltage increases, and the higher the vacuum level, the smaller the voltage change. This is because the higher the vacuum level, the smaller the pressure difference between the two chambers of the vacuum sensor, the smaller the change of the borosilicate film of the sensor, the smaller the capacitance value change, and consequently the smaller the voltage change. The straight line part in Figure 5 is the linear fitting curve of vacuum level and output voltage. It can be seen from the figure that the error value between the two curves is very small, which indicates that the measured voltage and vacuum level are approximately linearly related. Therefore, the capacitance value of the sensor is linearly related to the vacuum level, and its performance is good. 4. Conclusion Testing showed that the vacuum sensor can measure a vacuum level of up to 10⁻² Pa, fully meeting the requirements for vacuum measurement of vacuum insulation panels. The capacitive miniature vacuum sensor is a micro-device fabricated using MEMS technology. This device, used to measure vacuum levels, has advantages such as small size, high sensitivity, and mass production capability, making it a potential industrialization product. Since the fabrication methods and equipment for the capacitive miniature vacuum sensor are the same as those for other miniature capacitive sensors, large-scale production is easily achievable in industrialization. It can also be developed for high-precision testing in vacuum equipment and aerospace devices, as well as for general precision measurements in medical and toy applications, demonstrating significant market potential.