Basic terminology for pressure gauges
1. Positive pressure and negative pressure
2. Relative pressure and absolute pressure
3. Vacuum degree
4. The expression method of pressure
There are two ways to express pressure: one is the pressure expressed based on absolute vacuum, called absolute pressure; The other type is the pressure expressed based on atmospheric pressure, known as relative pressure. Due to the fact that most pressure gauges measure relative pressure, relative pressure is also known as gauge pressure. When the absolute pressure is less than atmospheric pressure, it can be represented by a value where the absolute pressure inside the container is less than one atmospheric pressure. It is called "vacuum degree". Their relationship is as follows:
Absolute pressure=atmospheric pressure+relative pressure
Vacuum degree=atmospheric pressure - absolute pressure
The legal pressure unit in China is Pa (N/㎡), known as Pascal or Pa. Due to the small size of this unit, its 10 ^ 6 times the unit MPa (megapascals) is often used.
