Electronic temperature sensors

Components that change their resistance

NTC thermistors reduce their resistance when the temperature increases. They are based on metal oxides or semiconductors and, when used for measuring purposes, are also called thermistors.
PTC thermistors increase their resistance when the temperature rises.
Platinum measuring resistors have a nearly temperature-linear resistance curve. Depending on the design, 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 exhibit a sharp increase in resistance at a material-specific temperature. They can also be used as self-regulating heating elements or thermal fuses.

Components that directly deliver a processable electrical signal
Integrated semiconductor temperature sensors (solid-state circuits) provide a current proportional to their temperature (example: AD592, proportional to the absolute temperature 1 µA/K) and a voltage proportional to their temperature (example: LM335[2], 10 mV/K).
a digital signal dependent on its temperature (examples: AD7314, DS18B20)
The base-emitter voltage of a transistor connected as a diode decreases with increasing temperature (current-dependent; guide value at 1 mA 2.3 mV/°C).

Further procedures
Temperature sensors with a quartz crystal as the measuring element. The resonant frequency of the oscillating quartz crystal 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 in response to temperature fluctuations by altering their spontaneous polarization. They are used in pyrometers (radiation temperature measurement in the mid-infrared) and motion detectors.
Pyrometers and thermal imaging cameras work non-contact and measure thermal radiation
Mechanically operated temperature switches, e.g., bimetallic switches, which activate a switch by bending a bimetal strip. Applications in toasters and irons.
Ferromagnetic temperature sensors consist of a permanent magnet that adheres to a ferromagnetic material below the Curie temperature and detaches above this temperature, thereby holding a spring-loaded mechanism magnetically or actuating a reed switch. Depending on the distance between the magnet and the iron, the sensor either automatically switches back on after cooling or must be reset. Patented application in temperature-controlled soldering irons.
Fiber optic temperature sensors measure the temperature profile along a fiber optic cable. They rely 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.