Differences and application selection methods between thermocouples and thermistors

Temperature measuring instruments are often used in daily work. Thermistors and thermocouples are both temperature measuring instruments. Should thermal resistance or thermocouple be chosen for the same temperature measurement location?
Construction of Thermocouples
There are three types of external shapes for the thermocouple front joint. Depending on the type, wire diameter, and operating temperature of the thermocouple, gas welding, butt welding, resistance welding, arc welding, and silver welding can be used for welding. In industrial applications, in order to facilitate installation and extend the service life of thermocouples, the method of adding sleeves is usually adopted
The casing is generally divided into maintenance tube type and armor type.
A thermocouple with a maintenance tube is a thermocouple used to insert the core wire and insulation tube of the thermocouple into the maintenance tube. The maintenance tube can maintain the mechanical strength of the thermocouple while avoiding oxidation and corrosion of the core wire.
Armored thermocouple
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 ℃, 8.0mm ф At 1050 ℃.
Thermal resistance structure
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.
distinguish
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