Sensor is a kind of device that can transform physical or chemical quantities into electrical signals for easy use. The International Electrotechnical Committee (IEC) defines it as: "A sensor is a pre-component in a measurement system that converts input variables into measurable signals".What are the types of sensors in production and life.

1. Light sensor

The optical sensor uses the photoconductive effect or photogenerating volt effect of semiconductor. Photogenerating volt effect is detected by the voltage or current generated at the PN junction of the semiconductor as output through light irradiation. Such as photosensitive tube, photosensitive tube and so on. These effects all take advantage of the quantum properties of light. The most common example is light-controlled lighting.

2. Temperature sensor

Used to detect the physical effect of temperature, in addition to the use of Seebeck effect thermocouple, usually using Pt, W and other metal and oxygen semiconductor and non-oxide semiconductor, organic semiconductor resistance with temperature changes as a temperature sensor. In addition, there are PN junction current - voltage characteristics with temperature changes, using the Curie temperature near the magnetic properties and dielectric constant changes of the sensor, the use of dielectric constant and piezoelectric constant changes, to detect the resonance frequency changes of the temperature sensor, such as the common air conditioning temperature control.

3. Pressure sensor

Most pressure sensors use some kind of piezoresistive effect. Piezoresistive effect means that when pressure is applied to a resistance body, its resistance value will change. This phenomenon is called piezoresistive phenomenon, which is much more obvious than the change of metal resistance, mainly because of the change in the mobility of electrons or holes after compression. More common applications are electronic scales.

4. Magnetic sensor

The common effects of magnetic sensors are hall effect and reluctance effect. Using hall effect device is the hall element, it is between on both ends of a semiconductor wafer, with current if the flakes in vertical direction and a magnetic field, the carrier under the action of Laurent force and move along a direction perpendicular to the magnetic field direction, if the electrode is set in the direction, can detect the voltage to the voltage (hall). Typical application such as electric car speed regulation method.

5. Gas sensor

A gas sensor is actually a semiconductor gas sensor. Mainly gas adsorption effect. For example, the gas sensor made of semiconductor SnO2 sintering is polycrystalline. When the surface absorbs gas molecules, there will be electron exchange between the gas molecules and the sintered body. The barrier at the grain interface, which controls the movement of carriers, changes. If two electrodes are arranged on the sintered body, the resistance between them will increase and decrease with the adsorption of gas molecules. In general, the resistance value will decrease in reducing gases and increase in oxidizing gases. The most common example is smoke detectors.