In the field of vacuum technology, "absolute vacuum" and "relative vacuum" are two core concepts that not only have significant differences in theory, but also have their own characteristics in practical engineering applications. This article will systematically analyze the definitions, measurement methods, and conversion relationships of these two.

　　1、 Basic Concept Analysis

　　Absolute vacuum (also known as absolute pressure or ultimate vacuum) is a measurement method that uses theoretical vacuum as the zero point reference to indicate how much pressure is higher than theoretical vacuum. Its values are all positive, and the smaller the value, the closer it is to the theoretical vacuum state. The international vacuum industry generally adopts this scientific labeling method, usually with "abs." as the suffix.

　　Relative vacuum (also known as relative pressure or gauge pressure) is based on the atmospheric pressure at the measurement location, representing the difference between the pressure of the object being measured and the atmospheric pressure. Its value is represented by a negative number (often omitting the negative sign), and the larger the absolute value, the higher the vacuum degree, usually with "g" as the suffix.

　　2、 Measurement method and unit

　　Absolute vacuum needs to be measured using an absolute pressure gauge. Under standard conditions (20 ° C, 0 meters above sea level), the initial value of the gauge is 101.325KPa (1 standard atmosphere). The relative vacuum is measured using a regular vacuum gauge, with an initial value of 0 at atmospheric pressure and a measurement range of 0 to -101.325KPa.

　　The commonly used units of vacuum degree include:

　　International units: Pa (pascal) hPa、KPa、MPa

　　Other units: Torr, mmHg, mbar, bar, etc

　　3、 Actual application differences

　　In industrial practice:

　　Absolute vacuum is mainly used in high-precision fields, such as:

　　The liquid ring pump is marked with a vacuum degree of 3300Pa

　　Double stage rotary vane pump with vacuum degree marked as 0.06Pa

　　Relative vacuum is widely used in China due to its simple measurement and widespread use of instruments (such as ordinary vacuum gauges, which are inexpensive). For example, if the measured value of a vacuum pump is -75KPa, it means that it can pump to a state that is 75KPa lower than atmospheric pressure.

　　4、 Conversion Relationship and Examples

　　The two can be converted to each other through formulas:

　　```

　　Absolute vacuum degree=atmospheric pressure+relative vacuum degree

　　Relative vacuum degree=Absolute vacuum degree - Air pressure at the measurement location

　　```

　　Typical application cases:

　　When the experiment requires 0.08MPa (gauge pressure), which means a relative vacuum degree of -800mbar, the corresponding absolute vacuum degree is 213mbar (assuming atmospheric pressure is 1013mbar)

　　A certain micro vacuum pump VM8001 has an absolute pressure of 80KPa, and at standard atmospheric pressure (100KPa), the relative vacuum degree displayed is -20KPa (-0.02MPa)

　　5、 Vacuum area division

　　According to the pressure range, it can be divided into:

　　Low vacuum: 760~10 Torr (101325~1333 Pa)

　　Medium vacuum: 10~10 ⁻³ Torr (1333-1.33 × 10 ⁻¹ Pa)

　　High vacuum: 10 ⁻³~10 ⁻⁸ Torr (1.33 × 10 ⁻¹~10 ⁻⁶ Pa)

　　Ultra high vacuum: 10 ⁻⁸~10 ⁻¹² Torr (10 ⁻⁶~10 ⁻¹⁰ Pa)

　　Extremely high vacuum:<10 ⁻¹² Torr (<10 ⁻¹⁰ Pa)

　　Theoretical absolute vacuum (completely devoid of matter) is difficult to achieve in reality, even in high vacuum environments where trace gas molecules and quantum fluctuations still exist. Therefore, in engineering applications, more attention is paid to the achievable "relative vacuum" state.

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