Temperature sensor

Temperature sensors are mostly electrical or electronic components that deliver an electrical signal as a measure of the temperature .

Examples

Components that change their resistance

• NTC thermistors reduce their resistance when the temperature rises, they are based on metal oxides or semiconductors and are also called thermistors when they are used for measuring purposes .
• PTC thermistors increase their resistance when the temperature rises.
  • Platinum measuring resistors have an almost temperature -linear resistance curve. Depending on the version, they can be used between −200 ° C and +850 ° C.
  • Silicon measuring resistors are used in the temperature range from −50 ° C to +150 ° C.
  • Ceramic PTC thermistors show a strong increase in resistance at a material-specific temperature. They can also be used as a self-regulating heating element or as a thermal fuse .

Components that directly supply a processable electrical signal

• Deliver integrated semiconductor temperature sensors ( solid state circuits )
  • a current proportional to its temperature (example: AD592, proportional to the absolute temperature 1 µA / K)
  • a voltage proportional to its temperature (example: LM335, 10 mV / K)
  • a digital signal depending on its temperature (examples: AD7314, DS18B20)
• The base-emitter voltage of a transistor connected as a diode decreases with increasing temperature (depending on the current; guide value at 1 mA 2.3 mV / ° C).

Further procedures

• Temperature sensor with quartz oscillator as the measuring element. The resonance frequency of the oscillating quartz changes depending on the temperature and can be measured very precisely.
• Thermocouples convert a temperature difference into an electrical voltage using the Seebeck effect .
• Pyroelectric materials change the charge carrier density on their surface with temperature fluctuations by changing the spontaneous polarization . Use in pyrometers (radiation temperature measurement in the middle infrared ) and motion detectors .
• Pyrometers and thermal imaging cameras work without contact and measure thermal radiation
• Mechanically operating temperature switches , e.g. B. Bimetal switches that operate a switch by curvature of a bimetal . Applications in toasters and irons.
• Ferromagnetic temperature sensors consist of a permanent magnet that adheres to ferromagnetic material below the Curie temperature and drops above this temperature, magnetically holding a spring-loaded mechanism or actuating reed switches . Depending on the distance between the magnet and the iron, the sensor switches itself on again after cooling or has to be reset. Patented application in temperature-controlled soldering irons .
• Fiber optic temperature sensors measure the temperature profile along a glass fiber . They are based on the Raman effect or the temperature-dependent change in the refractive index in fiber Bragg grating sensors (FBGS).

Other terms for temperature sensors are: heat sensor, temperature sensor, heat sensor.

Integrated temperature sensors

Temperature sensors are built into many integrated circuits in order to achieve temperature-dependent regulation or protection against overheating. Temperature measuring devices or temperature threshold switches can be found, for example:

• in microprocessors as overtemperature protection: when a temperature threshold is reached, for example, the clock frequency is reduced in order to avoid a further increase in temperature.
• in DRAM memories to control the refresh frequency, which is highly temperature-dependent (it has roughly an exponential behavior)
• in power semiconductors and power supply IC as overheating protection (e.g. sometimes also in power MOSFET )

See also

• Heat meter
• Heat cost allocator
• Thermography
• Energy harvesting
• Data logger with integrated temperature sensors for temperature measurement

Web links

Wiktionary: Temperatursensor  - explanations of meanings, word origins, synonyms, translations

Individual evidence

1. ↑ Data sheet AD592
2. ↑ data sheet LM335
3. ↑ Data sheet AD7314
4. ↑ Description of the DS18B20
5. ↑ Data sheet DS18B20
6. ↑ Miklos Herpy, Analog Integrated Circuits , 1976, Franzis, p. 58