The principle and types of pressure type thermometer

Pressure type thermometer is according to the liquid, gas or in a closed system of low boiling point liquid saturated steam heated volume expansion will cause pressure changes, and using a pressure gauge to measure the change, so you can measure the temperature. Liquid pressure type thermometer with thermal fluid in the airtight system, when the temperature increases, the inside of the bulb liquid will expand, through capillary make spring tube deformation, with the aid of the temperature of the institutions and directives, commonly used thermal liquid mercury, the thermometer measurement limit cannot under thermal fluid freezing point, ceiling can be higher than the boiling point of pressure. Due to temperature rise, thermal liquid pressure rise, make the thermal elevation of boiling point. Liquid pressure type thermometer used should be the front of the bulb into the medium under test, otherwise it will cause a big measurement error, environment temperature change is too big, also can produce certain influence to temperature. When the temperature changes, bimetallic strip produce corresponding change, it can compensate for the error because of the environment temperature change. Commonly used in the nitrogen gas pressure type thermometer closed system, there is hydrogen, the thermometer bulb volume is larger, in use for bulb all immersed in the measured medium.