The measurement principle of armored thermocouples is the same as that of thermocouples with maintenance tubes. It replaces insulating tubes (ceramics) with slender metal tubes (called sleeves) and uses magnesium oxide (MgO) powder as insulation material. Due to its thin outer diameter and tendency to bend, it is more suitable for measuring the temperature of objects on the opposite side and narrow gaps. In addition, compared to thermocouples with maintenance tubes, their response speed is more flexible. The outer diameter range of armored thermocouples is very wide, which can be stretched to 8.0 millimeters ф To 0.5 millimeters ф Various sizes of. The thinner the core wire is stretched, the lower the upper limit of the common temperature. For example, a K-type thermocouple with a sleeve outer diameter of 0.5mm ф The commonly seen upper temperature limit is 600 degree , 8.0mm ф At 1050 degree .

There are three types of components for thermal resistors, with ceramic packaging being the main type currently used. Ceramic encapsulation type is used for thermal resistors with maintenance tubes and armored thermal resistors. The bare wire diameter of ceramic and glass encapsulated platinum wire is about tens of micrometers, while the bare wire diameter of mica plate type is about 0.05 millimeters.

Although they are all contact thermometers, their temperature measurement ranges are different. Thermocouples are used in high-temperature environments because the output thermoelectric potential in the medium to low temperature region is very small (can be checked by looking up the table). When the potential is low, the requirements for opposing interference measures and secondary meters are high, otherwise the measurement will be inaccurate. Moreover, in the low-temperature region, the relative error caused by changes in cold end temperature and ambient temperature is very prominent, making it difficult to obtain sufficient compensation. At this time, at medium and low temperatures, the temperature measurement range of the thermal resistance is generally between 200 and 500, or even lower