1、Definition of the vacuum
The vacuum system is under thin air condition which is lower than the local ATM.
The air thin degree under the vacuum state, it is represents by “the vacuum degree is high” and “the vacuum degree is low”. The vacuum degree is high to represent the good vacuum degree,the vacuum degree is low meaning the bad vacuum degree.
Usally use “Torr” as the unit，also use the Pa in the international world resently.
4、Coversion of the Torr and Pa
1Torr＝133.322Pa or 1Pa＝7.5×10-3Torr
5、Average free lift
The air granules meet each other the twice while they doing the irregular movement to fly the average distance. It is expressed by“λ”.
The air capacity passing across any random cross in the unit time is expressed by “Q”，the unit is Pa·L/s or Torr·L/s.
It expresses the vacuum pipe’s ability of passing the air through.The unit isL/s，at the steady condition,the flow conductor of the pipe is equal to flow capacity divides the difference of the two sides pressure intensity. With the sign“U”express. U＝Q/(P2- P1)
8、Pressure or pressure intensity
The force in unit area of the container wall is acted by the air molecule.It is expressed by sign “P”.
The pressure intensity is 101325dyn/cm2 indicates the atmosphere. The sign is Atm.
After the completely pumping, the container inside keeps in a definite vacuum degree steadily.This vacuum degree is limit vacuum. In general, the container must be refined for 12 hours, then pumped for 12 hours,at the final hour measure the vacuum degree once per 10 minutes.Choose the average date of the 10 times as the limit vacuum.
Under the definite pressure intensity and temperature,the pumping air capacity from the intake port in unit time is called suction capacity:Sp＝Q/（P－P0）
12、Thermocouple vacuum meter
The vacuum meter is making use of the thoery about the thermocouple force is relative with the heating components,and the components temperature also ties in the air heat conduct to measure the vacuum degree.
13、Ionization vacuum meter（also calles hot cathod ionization meter）
It is composed by the cylindraceous collection pole, web and the filament in center of web, the cylindraceous pole is out of the web.The hot cathod sends the electrons to ionizate the air molecule, the ions are collected by the collection pole. On the foundation of the ions current’s big or small to measure the air pressure, this kind of vacuum meter is ionizaion vacuum meter.
14、Multiplex vacuum meter
It is composed by the thermocouple vacuum meter and the hot cathod ionization vacuum meter.The measure scope is from ATM to 10-5Pa。
15、Cold cathod ionization vacuum meter
At the both sides of the anode canister has a pair of cathod boards, under the effect of the outside magnetic field，the inner anode canister forms Paning to discharge then comes into being the ions, according to the ions current’s big or small to measure the air pressure intensity, this kind of meter is called cold cathod inization vacuum meter.
16、Resistance vacuum meter
By way of the thoery that the resistance of the heating components is tied in the temperature,and the components temperature is also tied in the air transmission conductor and using the electrical bridge circuit to measure the vacuum degree, this kind of vacuum meter is resistance vacuum meter.
17、Mcload vacuum meter（Compressed vacuum meter）
Using the Hg (or oil)to compress the measured air into very small volume,then compare the liquid columnation of open pipe and close pipe.By way of the Boyier Law to calculate the absolute pressure of the air. This kind of vacuum meter is Mcload vacuum meter.
It is a hot cathod ionization gauge that converted by the cathod and the collected pole. The collected pole is a thread which is set in the centre at the web, and the filament is out of the web, this can reduce the influence to the X-ray, then expand the measure lowe limit. Thus can measure the ultrahigh vacuum.