The principle of a pressure type thermometer is based on the relationship between the saturated vapor pressure and temperature of the evaporated liquid in a closed temperature measurement system, and temperature measurement is carried out. When the temperature change is felt by the temperature bulb, the saturated vapor in the closed system generates corresponding pressure, causing changes in the curvature of the elastic element, causing displacement at its free end. The displacement is then converted into an indicator value by a gear amplification mechanism. This type of thermometer has the characteristics of small temperature bulb volume, fast reaction speed, high sensitivity, and intuitive reading, almost integrating all the advantages of glass rod thermometer, bimetallic thermometer, and gas pressure thermometer, It can be manufactured as shockproof and corrosion-resistant, and can achieve remote transmission of contact signals, thermal resistance signals, 0-10mA or 4-20mA signals. It is the most widely used and comprehensive mechanical temperature measuring instrument