What are the classification and working principle of thermal resistance sensors?

What are the classification and working principle of thermal resistor sensors?
Classification of thermal resistor sensors
NTC thermal resistor sensors: This type of sensor is a negative temperature coefficient sensor, that is, the sensor resistance decreases as the temperature increases; PTC thermal resistor sensors: This type of sensor is a positive temperature coefficient sensor, that is, the sensor resistance increases as the temperature increases.
Working principle of thermal resistor sensors
Thermal resistor sensors are devices that use the characteristic that the resistance of a conductor changes with temperature to detect temperature and temperature-related parameters. Thermal resistor temperature measurement is based on the characteristic that the resistance of a metal conductor increases with the increase of temperature to measure temperature. Most thermal resistors are made of pure metal materials. Currently, platinum and copper are the most widely used. In addition, materials such as nickel, manganese and rhodium are now being used to manufacture thermal resistors. They have the characteristics of large resistance temperature coefficient, good linearity, stable performance, wide operating temperature range, and easy processing. And with the development of science and technology, the temperature measurement range of thermal resistor sensors has also expanded. Low temperature has been successfully applied to temperature measurement of 1~3k, and high temperature has also seen a variety of thermal resistor sensors for 1000~1300℃.
When installing the thermal resistor, attention should be paid to ensuring accurate temperature measurement, safety, reliability, and easy maintenance, and not affecting equipment operation and production operations. To meet the above requirements, the following points should be noted when selecting the installation location and insertion depth of the thermal resistor:
1. In order to ensure sufficient heat exchange between the measuring end of the thermal resistor and the measured medium, the measuring point location should be reasonably selected, and thermal resistors should be installed near valves, elbows, and dead corners of pipelines and equipment as much as possible.
2. Thermal resistors with protective sleeves have heat transfer and heat dissipation losses. In order to reduce measurement errors, thermocouples and thermal resistors should have sufficient insertion depth:
(1) For thermal resistors that measure the temperature of the fluid in the center of the pipeline, the measuring end should generally be inserted into the center of the pipeline (vertical installation or inclined installation). If the diameter of the measured fluid pipe is 200 mm, the insertion depth of the thermal resistor should be 100 mm;
(2) For the temperature measurement of high-temperature, high-pressure and high-speed fluids (such as main steam temperature), in order to reduce the resistance of the protective sleeve to the fluid and prevent the protective sleeve from breaking under the action of the fluid, the protective tube can be shallowly inserted or a heat sleeve thermal resistor can be used. The shallow insertion thermal resistor protective sleeve should be inserted into the main steam pipe to a depth of not less than 75 mm; the standard insertion depth of the heat sleeve thermal resistor is 100 mm;
(3) When the insertion depth of the measuring element exceeds 1 m, it should be installed vertically as much as possible, or a support frame and protective sleeve should be installed.
(4) If the temperature of the flue gas in the flue needs to be measured, even if the flue diameter is 4 m, the insertion depth of the thermal resistor is 1 m.