What is a "sensor"?

A sensor is an electronic device that senses the physical, chemical, or biological states or processes of the environment to be surveyed, and transforms it into electrical signals to gather information about that state or process.

Information is processed to derive qualitative or quantitative parameters of the environment, serve the needs of scientific and technical research or population and briefly referred to as measurement, serving in information transmission and processing, or in controlling other processes.

Sensors are usually housed in protective enclosures that form receivers or test probes, which can be accompanied by supporting circuits, and sometimes the whole set is always called a "sensor". However, in many literature, the term sensor is rarely used for large objects. The term is also not used for some types of parts, such as the knob of the switch that turns on the light when the refrigerator is opened, although academically this knob works as a sensor.

There are different types of sensors and can be divided into two main groups:

- Physical sensors: electromagnetic waves, light, ultraviolet, infrared, X-rays, gamma rays, radiation particles, temperature, pressure, sound, vibration, distance, motion, acceleration, magnetic field, gravity, ...

- Chemical sensors: humidity, PH, ions, specific compounds, smoke, ...

- Biosensors: blood glucose, DNA / RNA, proteins specific to diseases in the blood, bacteria, viruses ...

Sensor classification

Active sensors and passive sensors distinguish where the energy source used allows the transformation to come from.

Active sensors do not use additional power to switch to electrical signals. Typically piezoelectric sensors made of ceramic materials, which convert pressure into charge on the surface. The antennas also belong to the active sensor type.

Passive sensors use additional power to switch to electrical signals. Typically, photodiodes, when light enters, have a change in the p-n semiconductor contiguous resistance that is polarized backwards. Sensors with rheostas are also passive sensors.