Vacuum gauge can be divided into absolute vacuum gauge and relative vacuum gauge according to the measurement properties. The so-called absolute vacuum gauge is a kind of vacuum gauge which determines the pressure by measuring the physical quantity itself. For example, U-type pressure gauge and compression type vacuum gauge are absolute vacuum meters. The vacuum gauge which determines the pressure by measuring the physical quantity related to pressure and comparing with absolute vacuum gauge is called relative vacuum gauge.
The ionization vacuum gauge, capacitance film vacuum gauge and heat conduction vacuum gauge we have calibrated are all relative vacuum meters. It has three electrodes: cathode f emits electrons; grid a accelerates electrons; collector C collects ions. General cathode plus zero potential, grid plus positive potential, collector plus negative potential. The main advantages of this system are that it can measure the total pressure of gas and steam; it can react quickly, can read continuously and control remotely; it has wide range, good linearity and high measurement accuracy. The disadvantage is that the filament is easy to oxidize when the pressure is higher than 10-1 Pa. once the system is exposed to the atmosphere suddenly, the gauge tube will be burned out; the outgassing of glass shell and electrode will lead to measurement error.
The following six points should be paid attention to when calibrating ionization vacuum timing
(1) Generally, when connecting the gauge and the system, first connect the unsealed gauge and measuring circuit together to check whether the gauge is normal, and then connect it to the system.
(2) In the process of calibration, if there is a fault, in the case of unknown reasons, take an unopened gauge for a test to determine whether it is a regulation problem or a circuit problem. If the unsealed regulation is normal, it indicates that there is something wrong with the original regulation; if the unsealed regulation is still abnormal, it indicates that there is something wrong with the circuit, thus reducing the scope of the fault.
(3) The gauge should be installed vertically, otherwise the grid and cathode will deform and the relative position will change during heating and degassing, which will seriously affect the measurement accuracy.
(4) Before the lamp filament is turned on, it is judged that the vacuum degree in the vacuum system to be measured is less than 10-1pa. Otherwise, the vacuum degree is too low, which will lead to the cathode oxidation of the gauge tube and burn out.
(5) Before reading, the emission current, zero point and full scale should be adjusted. The specific steps are: emission current zero fullness emission current.
(6) The ionization vacuum gauge can be calibrated only by heating it up for 10 minutes.
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