The first is to use "absolute pressure", "absolute vacuum" (ie how much higher than the "theoretical vacuum");
In the actual case, the absolute pressure of the vacuum pump is between 0 and 101.325 KPa. The absolute pressure value needs to be measured with an absolute pressure meter. At 20 ° C and altitude = 0, the initial value of the instrument for measuring the vacuum (absolute vacuum gauge) is 101.325 KPa (ie, a standard atmospheric pressure).
The second is to use "relative pressure", "relative vacuum" (ie, how much pressure is lower than "atmospheric pressure").
The "relative vacuum degree" refers to the difference between the pressure of the object to be measured and the atmospheric pressure of the measurement site. Measured with a conventional vacuum gauge. In the absence of a vacuum (ie, at atmospheric pressure), the initial value of the table is zero. When measuring vacuum, its value is between 0 and -101.325 KPa (generally expressed as a negative number).
For example, if a micro vacuum pump measures -75KPa, it means that the pump can draw a vacuum of 75KPa lower than the atmospheric pressure at the measurement site.
The “vacuum degree†commonly used in the international vacuum industry is also the most scientifically marked with absolute pressure; it refers to “extreme vacuum, absolute vacuum, absolute pressureâ€, but “relative vacuum†(relative pressure, vacuum gauge pressure, Negative pressure) Because of the simple measurement method, the measurement instrument is very common, easy to buy and inexpensive, it is also widely used. In theory, the two can be converted to each other. The conversion methods are as follows:
Relative vacuum = absolute vacuum (absolute pressure) - pressure at the measurement site
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