The vacuum gauge can be divided into an absolute vacuum gauge and a relative vacuum gauge according to its measurement properties. An absolute vacuum gauge is a vacuum gauge that determines the pressure by measuring the physical quantity itself. For example, U-type pressure gauge, compression type vacuum gauge is the absolute vacuum gauge. The vacuum gauge that determines the pressure by measuring a physical quantity related to pressure and comparing it with an absolute vacuum gauge is called a relative vacuum gauge. The ionization vacuum gauge and the capacitance film vacuum gauge, the heat conduction vacuum gauge, all of which are the relative vacuum gauges.
The structure of the ionization gauge is a cylindrical triode with three electrodes: the cathode - emitting, the gate - accelerating electron, the collection of polar - collecting ions. The general cathode is plus zero potential, the grid is plus the positive potential, and the collector is plus negative potential.
Mainly advantages :
• Measure the total pressure of gas and vapor.
• Quick response, continuous readings and remote control.
• Wide measurement range, good linearity and high measurement accuracy.
• When the pressure is higher than 10-1pa, it is easy to oxidize the filament, and once the system suddenly exposes the atmosphere, the gauge will be burned.
• The error of the deflation of the glass bulb and electrode leads to the measurement error.
Calibration of ionization vacuum gauge should be pay attention to the following six points:
1. When the gauge is connected to the system, the unsealed gauge and the measuring circuits are connected together to check whether the gauge is normal and then receives the system.
2. In the process of calibration, if there is a failure and unidentified, take an unopened gauge and judge whether it is a gauge problem or a circuit problem. If it is normal to replace the unopened gauge, indicating that the original gauge is in problems; if the unopened gauge is still abnormal, indicating the problem with the circuit, thus narrowing the scope of the fault.
3. The gauge installation should be installed vertically. While heating and degassing and baking, the grid and cathode will deform, and the relative position will change, which will seriously affect the measurement accuracy.
4. Before opening the filament, it can be judged whether the vacuum in the vacuum system is less than 10-1pa, then open the filament. If the vacuum degree is too low, this will cause the cathode of gauge oxidation and burned.
5. Before reading, the emission current, zero point and full degree should be adjusted first. The specific steps are: emission current - zero point - full scale - emission current.
6. The ionizing vacuum gauge can be calibrated by only 10 minutes of preheating.