One of the most common inputs for automatic signal processing in technologies. Temperature is also one of the most important quantities to affect conditions and processes in nature, generally.
Metal resistance temperature sensors – the most frequently used methods of measuring in practice. The principle of metal resistance thermometers is the dependence of clear metal upon temperature, the resistance of metal raises almost proportionally to the absolute temperature.
Sensor Material |
Measuring Range (°C) |
Temperature Coefficient of Resistance |
Pt |
–200 to +850 |
3.85 to 3.93 |
Ni |
–60 to +180 |
6.17 to 6.70 |
Cu |
–200 to +200 |
4.26 to 4.33 |
Sensors made of amorphous polycrystalline semiconductors, the so-called thermistors (thermally sensitive resistor). The dependence of electric resistance of material on temperature is used. The principle of semiconductor conductance is different, which relates to different behaviour and with different properties of these sensors. The resistance of semiconductor material weakens with growing temperature
Thermistors NTC (Negative Temperature Coefficient) have a negative temperature resistance rate, which corresponds with the mentioned description. For the use where sensor speed is important, miniature, so-called bead thermistors are interesting, as their little heat capacity shortens the time invariable of the sensor to seconds. The usual temperature scopes are -50 to 150 °C, and special ceramic thermistors for extreme temperatures (from i.e. 4 K to 1 000 °C) are also manufactured.
These are made of silicon, germanium or indium.
For temperature measurement they use thermojunctions which consist of two conductors of two different metal materials A and B, and which are conductively connected at both ends. At the temperature difference tm and ts of the second connection, thermoelectric tension and thermoelectric current generate.
Works on the basis of a physical effect, where matter owing to thermal motion of elementary parts emits energy in the form of electromagnetic radiation in the part of the spectrum, which is called infrared, but also in the visible part of the luminous spectrum.
Principle of a bolometer is that the electric resistance of the bolometer changes in dependence on its temperature which depends on the quantity of the incident infrared radiation. The change of the bolometer’s resistance therefore characterises the amount of the incident infrared radiation. Thermal insulation from the surroundings is essential. Microbolometer integrates more resistance facets on one face and in conclusion it enables a 2D thermoimage display of the radiating objects in front of the detector. Devices of many categories are nowadays available ranging from a simple one-point manual infra-thermometer up to thermocameras using the above mentioned principles with highly sophisticated digital control.
The main benefit is the contactless measuring. Other benefits are numerous, for example the possibility of measuring moving objects or possibility of 2D depiction, i.e. thermovision.