There are many radio electronic components that change some of their parameters under the influence of temperature changes. Such an element is also the thermoresistance, or as it is also called – a thermistor. From the name it is already clear that the part increases resistance when the temperature rises.
Thermal resistance is a semiconductor that is very dependent on temperature conditions; it is this parameter, as well as a high coefficient of resistance, that allows the device to be used in virtually all branches of industrial production. Thermal resistors (thermistors) are made of different materials having different resistivity. The main quality indicators of this REC are high temperature coefficient, chemical stability, melting point.
The thermistor can be different in design, but semiconductor rods covered with enamel are most common. The terminal leads outlets and contact caps, they can be used only in a dry area. A lot of similar elements function well in a certain temperature range; any overheating of them causes a negative effect and leads to the destruction of the thermistor. In order to protect them from the harmful effects of external negative factors, the design of the thermistors is placed in special sealed enclosures. Such parts can be used in any environment, even wet. If the elements were made of materials having poor conductivity, then a change in the temperature regime can lead to changes in the resistance by several tens of times. The use of a fabrication material with an ideal conductivity leads to a ratio within ten. If you comply with all the necessary standards that meet the technical specifications of a type of thermistor, you can extend their operating life to several years.
Thermistors and their types
The most popular are RECs, which use platinum, which allows withstanding a wide range of temperatures: minus 200 – plus 1200 degrees Celsius, have a high temperature coefficient, resistance to oxidation processes and manufacturability. Also, nickel, copper can be used for production of thermistors.
Copper thermo-resistors are ideal when a continuous measurement of the operating temperature is necessary, with the range ranging from minus 200 to plus 200 degrees. Advantages of copper as a material: inexpensive, free of impurities, is technologically resistant, the resistance depends linearly on temperature. The disadvantages are: the resistance is low, strong oxidation. These drawbacks lead to limitations on the use of copper thermistors.
Nickel thermistors are excellent for measuring temperatures within minus 100 – plus 300 degrees. The advantages include low thermal inertia, nominal resistance is ideal. Disadvantages: non-linear, unstable nominal static characteristics, the inability to interchange them, so there is a significant variation in the nominal resistance.