The meaning of vacuum refers to the state of gas below one atmospheric pressure in a given space, which is a
A physical phenomenon. In vacuum technology, the vacuum system refers to the atmosphere and generally refers to a specific space
Part of the substance inside is discharged, so that the pressure is less than a standard atmospheric pressure, we generally call it
This space is in a vacuum or vacuum state. Vacuum commonly used Pascal (Pascal) Tor (Torr)
Millibar (mbar), etc. as a unit of pressure
Vacuum gauge (Vacuum Gauge), also known as vacuum gauge, vacuum gauge, is to measure vacuum
Degree or low pressure instrument. Generally, the change of a certain physical effect of the gas under different pressures is used.
The measurement of air pressure is carried out. It is widely used in scientific research and industrial production. Measure according to vacuum gauge
The different physical mechanisms used in the principle can divide the main vacuum gauges into three categories

They are vacuum using mechanical properties, using gas dynamics and using charged particle effects.
count.
When electrons fly in an electric field, they obtain energy from the electric field. If they collide with gas molecules, the gas molecules will be ionized with a certain probability to produce positive ions and secondary electrons. The ionization probability is related to the electron energy. The number of positive ions generated by electrons during the flight is proportional to the gas density n, and at a certain temperature, it is proportional to the gas pressure p. Therefore, the degree of vacuum can be indicated according to the magnitude of the ion current. This is how the ionization vacuum gauge works.
The ionization vacuum gauge that is heated by the filament to provide the electron source is called the hot cathode ionization vacuum gauge. There are many types, each with different characteristics and different pressure measurement ranges.
By changing the electrode structure of the gauge and the electrical parameters of each electrode, and using anti-oxidation materials to make the cathode (such as iridium wire coated with yttrium oxide), the upper limit of linear measurement can be increased. The high pressure ionization vacuum gauge is made, and the upper limit of pressure measurement pmax can reach more than 100Pa. Figure 9 shows the DL-5-gauge electrode structure; Figure lO shows the DL- 8-gauge electrode structure.
The grid-shaped anode is bombarded by electrons to generate X-rays, and the ion collector receives this ray to generate photoelectron emission, forming a photoelectric background current Ix that is independent of pressure. Reducing Ix can reduce the lower limit of linear pressure measurement pmin, and the following four measures can be taken:
(1) Reduce the area of ​​the ion collector irradiated by the soft X-ray from the geometric structure of the electric plate. This is the design idea of ​​the B-A ionization gauge;
(2) Place an electrode (suppressor) with a negative potential relative to the ion collector near the ion collector. The photoelectrons emitted from the surface of the ion collector can be folded back by the electric field to eliminate the background current. This method is called photoelectron Suppression methods, such as suppression of ionization gauges;
(3) This is a method of subtracting the background photocurrent from the ion collector current, called the ion current modulation method, such as modulating the B-A ionization gauge;
(4) The background pressure indication px corresponding to the background photocurrent Ix is inversely proportional to the gauge coefficient K, so increasing the gauge coefficient K can reduce the lower limit of measurement pressure pmin such as ballistic gauges and hot cathode magnetron ionization gauges.
In various vacuum and pressure measurement systems, it is necessary to clearly understand the meaning of different pressure indicators.
The unit of measurement usually used for vacuum measurement is Torr, which is equal to 1mmHg. It represents the atmospheric pressure required to increase the height of the mercury sinking column by 1.0mm. A standard atmospheric pressure is equal to 760 Torr. In the vacuum measurement of some vacuum systems, the derivative unit of Torr or 1/1000 Torr is used. The vacuum degree greater than 1.0 mTorr is usually expressed in scientific notation (for example, 5.0E-06 Torr). Vacuum and meteorological measurement in vacuum systems commonly used in Europe and Asia usually divide the bar graph into 1/1000 to generate milli Bar (mbar).
The commonly used pressure metric in the United States is psi or “pounds per square inch”. Using this metric, the measured value of atmospheric pressure at sea level is 14.69 psi. For comparison, pressure measurements in Europe and Asia define atmospheric pressure as 1.0 bar. Another indicator is “water height in inches”, which is usually used to report the air pressure in the US weather forecast. The unit refers to the height of the underwater water column supported by atmospheric pressure. Using this metric, the atmospheric pressure is 406.8 inches of water column (at 4°C), and sometimes this unit of measurement is used for vacuum measurement in industrial processes.
The international unit measurement of pressure is Pascal (abbreviated as Pa), named after the French mathematician and physicist Blaise Pascal. It is defined as a measure of force per unit area, equal to one newton per square meter. The atmospheric pressure in SI units is 1.01325E+05 Pa. Some air pressure measurements are usually reported in kilopascals (kPa).

 

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