Answer the knowledge of measuring various vacuum pump pressure parameters The gauge used to measure the pressure of rarefied gas in vacuum pump is called vacuum gauge or vacuum gauge. It can be divided into absolute vacuum gauge and relative vacuum gauge. The former calculates the pressure directly from the physical quantity measured by itself; The latter must be corrected by absolute vacuum gauge to determine the air pressure. In vacuum technology, Torr is often used as the unit of vacuum degree in addition to the pressure unit PA in the international system of units. 1) 1 Torr is equal to the pressure produced by a 1 mm high mercury column, i.e. 1 Torr = 133.3224 PA. 2) The limit pressure is the value obtained by the equipment manufacturer under the most ideal state of the pump inlet in accordance with the national standard and standard test equipment, instruments and methods before leaving the factory. 3) The final pressure is the lowest pressure that can be reached after the pump and equipment are evacuated after installation. 4) The standard pressure is lower than the atmospheric pressure of the local environment, also known as vacuum. 5) Positive pressure is the relative pressure above atmospheric pressure. 6) Absolute atmospheric pressure. The starting point of absolute zero pressure is called absolute atmospheric pressure.