Different kinds of pressure type thermometer, you picked the right?

Pressure type thermometer is according to the liquid, gas, or in a closed system of low boiling point liquid saturated steam heated volume expansion pressure changes caused by this principle, and pressure gauge to measure the change, and the measured temperature. According to the different of heat medium, pressure type thermometer can be divided into three categories. ( A) Working principle of the liquid pressure type thermometer liquid pressure type thermometer is in the sealed bag full of thermal fluid in the warm, when the temperature rises, the temperature inside the package liquid expansion, the capillary make spring tube deformation, according to the commonly used thermal liquid mercury, pointer - temperature measurement range Upper limit of 30 ℃ ~ + 500 ℃, up to 650 ℃. If if you measure the temperature of the material under 150 ℃ and 400 ℃ respectively using methanol and dimethyl benzene as thermal fluid. But remember, this thermometer measurement threshold cannot under thermal liquid freezing point, but it can be higher than the boiling point of pressure limit. This is due to the temperature rise, thermal liquid pressure rising, the thermal liquid boiling point. ( 2) Gas pressure type thermometer gas pressure type thermometer is in the closed system pressure filling gas, because of the gas expansion coefficient is much bigger than solid, so constant volume can be regarded as closed system, the pressure is proportional to the temperature inside. Is when the temperature rise of temperature, package, pressure is put inside airtight system, indicates the corresponding temperature. Often filled with nitrogen gas pressure type thermometer closed system, the general measuring range is - 50℃~500℃。 If the filling is hydrogen, is the lowest temperature can be measured 120℃。 ( 3) Steam pressure type thermometer pressure type thermometer is based on the low boiling point liquid saturation yan gas pressure with temperature change of the nature of the work. Metal temperature package for low boiling point liquid, two-thirds of the volume of the rest of the closed system space filled with the fluid saturated steam. The use of steam pressure type thermometer temperature limit is generally not more than 200 ℃, the commonly used low boiling point liquid with harmonic chloride methane, ethane, ether, acetone, etc. But must pay attention to the steam pressure type thermometer is not suitable for measuring temperature and environmental temperature close to the medium, as the steam in the capillary tube and spring prone to condensation or vaporize completely unstable situation. Through the above introduction, I believe you know more about pressure type thermometer, in use is also more know how to choose.