Capacitive thin film vacuum gauge
In recent years, great progress has been made in capacitive thin film vacuum gauge. With the advent of a new type of double capacitance thin film vacuum gauge, the accuracy of this kind of vacuum gauge has been improved, and the measuring range has been expanded, so that the lower limit of measurement can reach 10-3pa. In this paper, the development of two kinds of double capacitance thin film vacuum gauge is introduced.
The first is a differential double capacitance film vacuum gauge
The new double capacitance film vacuum gauge is a differential structure. Fixed electrodes are symmetrically arranged on both sides of the elastic diaphragm to form static capacitances C01 and C02 respectively. The pressure measurement system and the vacuum diaphragm are connected into a reference tube respectively. The capacitors C01 and C02 are used as two arms of the bridge circuit. When the pressure difference in the regulation is zero, the bridge is in equilibrium. When the pressure difference P1 Pb > 0, the bridge will lose balance due to the reverse change of capacitance C01 and C02, and the corresponding electrical signal will be output.
The advantages of the differential double capacitance film vacuum gauge are: the change of measured pressure causes the capacitance C01 and C02 to change, and the direction is opposite, which increases the unbalance degree of the bridge, thus improving the measurement sensitivity; in addition, due to the symmetrical setting of the fixed bridge on both sides of the elastic diaphragm, the change effect of capacitance C01 and C02 caused by environmental temperature and other factors is eliminated, thus reducing the measurement error The measurement accuracy is improved.
The differential double capacitance film vacuum gauge is a total pressure gauge, which has the characteristics of high measurement accuracy (generally 0.1% - 2%), fast reaction speed (2-100ms), small temperature influence and wide measurement range. The lower limit of measurement can reach 10-3 ~ 10-2 PA.
The second is a single side double capacitance film vacuum gauge
The difference between it and the differential double capacitor structure is that the fixed electrode in the measuring chamber is moved into the reference chamber and is located in the off-axis position beside the fixed electrode. It is considered that the maximum displacement of the elastic diaphragm is reflected by the central electrode and the small displacement of the elastic diaphragm is reflected by the off-axis electrode. The curvature change signal of the elastic diaphragm - "curvature indication" is output by the two electrodes together, and the difference value is used as the indication of the measured difference.
The single side double capacitance thin film vacuum gauge has the advantages of high sensitivity, constant dielectric constant of gas, no influence of gas composition on pressure reading and fast reaction speed. The absolute pressure of 10-3pa and above can be measured if degassing agent is added in the regulatory reference room and pumped to 10-5pa.