就是容器内介质（液体或气体）的真实压力。 The absolute pressure is the true pressure of the medium (liquid or gas) in the container. The absolute pressure of the medium in the container may be higher than the external atmospheric pressure or equal to or lower than the external atmospheric pressure. When we measure pressure with a pressure gauge,
The pressure value measured due to the effect of the atmospheric pressure on the instrument in the atmosphere is one atmosphere lower than the absolute pressure. We call this gauge-tested pressure a gauge pressure. The pressure gauge indication value we see on the dial of the power plant is the gauge pressure value.
The absolute pressure of the medium is equal to the gauge pressure value plus the atmospheric pressure value. When the absolute pressure of the medium is greater than or equal to the atmospheric pressure, the gauge pressure is positive or zero. When the absolute pressure of the medium is less than the atmospheric pressure, the gauge pressure measured by the instrument is negative, and the gauge pressure at this time is called negative
Pressure or vacuum. In engineering, the ratio of negative pressure (vacuum) value to atmospheric pressure value is often used to indicate the negative pressure state of the medium, which is called vacuum degree. The unit is "".
In pressure measurement, the absolute pressure, gauge pressure, negative pressure or vacuum degree are usually used. The so-called absolute pressure refers to the total pressure on the unit area of the container by the measured medium, and is represented by the symbol pj. Instrument for measuring absolute pressure
。 It is an absolute pressure gauge . The average pressure generated by the air column on the ground is called atmospheric pressure, and is represented by the symbol pq. The instrument used to measure atmospheric pressure is called a barometer. The difference between absolute pressure and atmospheric pressure. Called gauge pressure, it is represented by the symbol pb. That is pb = pj-pq.
When the absolute pressure value is less than the atmospheric pressure value, the gauge pressure is a negative value (ie, negative pressure). The absolute value of this negative pressure value is called the degree of vacuum and is represented by the symbol pz. The instrument used to measure vacuum is called a vacuum gauge. Can measure both pressure and vacuum
The instrument is called a pressure vacuum gauge.
When the absolute pressure value is less than the atmospheric pressure value, the gauge pressure is negative (that is, negative pressure). The difference between this negative pressure value and the atmospheric pressure value is called the degree of vacuum degree = atmospheric pressure-absolute pressure
Additional comprehensive explanation:
"Vacuum degree" is the degree of vacuum as its name implies. It is a main parameter of vacuum pumps such as vacuum pumps, micro vacuum pumps, micro air pumps, micro air pumps, and micro air pumps.
The so-called "vacuum" refers to the state of the gas in a given space with a pressure lower than 101325 Pascal (that is, a standard atmospheric pressure of about 101KPa).
In a vacuum state, the leanness of a gas is usually expressed by the pressure value of the gas. Obviously, the smaller the pressure value is, the leaner the gas is.
There are usually two methods for identifying the degree of vacuum:
”、“绝对真空度”(即比“理论真空”高多少压力)标识；在实际情况中，真空泵的绝对压力值介于0～101.325KPa之间。 The first is to use " absolute pressure " and "absolute vacuum" (that is, how much pressure is higher than the "theoretical vacuum"); in actual conditions, the absolute pressure value of the vacuum pump is between 0 ~ 101.325KPa. Absolute pressure requires absolute pressure
Force gauge measurement. The initial value of the gauge (absolute vacuum gauge) used to measure the degree of vacuum at 20 ° C and altitude = 0 is 101.325KPa (ie, a standard atmospheric pressure).
The second is to use "relative pressure" and "relative vacuum" (that is, how much pressure is lower than "atmospheric pressure") to identify.
"Relative vacuum" refers to the difference between the pressure of the measured object and the atmospheric pressure at the measurement site. Measure with ordinary vacuum gauge. In the absence of vacuum (that is, at normal pressure), the initial value of the table is 0. When measuring vacuum, its value is between 0 and -101.325KPa
(Usually expressed as a negative number).
For example, there is a micro vacuum pump PH2506B with a measurement value of -75KPa, which means that the pump can pump a vacuum state that is 75KPa lower than the atmospheric pressure at the measurement site.
The "vacuity" commonly used in the international vacuum industry is also the most scientific one. It is labeled with absolute pressure; it refers to "limit vacuum, absolute vacuum, and absolute pressure", but "relative vacuum" (relative pressure, gauge pressure, (Negative pressure) due to measurement
The method is simple, the measuring instrument is very common, it is easy to buy, and it is cheap, so it is also widely used.