What is Sensor?
[[File:CCD Image sensor.jpg|300px|thumb|A CCD (charge-coupled device) has a [[grid]] of sensors that [[wikt:react|react]] to light.]] [[File:Cathode ray diffraction.png|300px|thumb|A television tube or other CRT (cathode ray tube) detects electrons on its screen.]] [[File:Rumfords Photometer.jpg|thumb|This photometer measured brightness by comparing shadows]] A '''sensor''' is a [[device]] that measures a [[physical quantity]] and converts it into a '[[Signal processing|signal]]' which can be read by an observer or by an instrument. For example, a mercury [[thermometer]] converts the measured temperature into the expansion and contraction of a [[liquid]] which can be read on a calibrated glass tube. [[Video camera]]s and a [[digital camera]]s have an [[image sensor]]. There are many different types of sensors. Some are used in everyday objects, and some are separate. == Thermal sensors == A sensor that detects [[temperature]]. Thermal sensors are in many [[Laptop|laptops]] and computers in order to sound an alarm when a certain temperature has been exceeded. * temperature sensors: [[thermometers]], [[thermostat]]s * heat sensors: [[Bolometric magnitude|bolometer]], [[calorimeter]] == Electromagnetic sensors == An electronic device used to measure a physical quantity such as pressure or loudness and convert it into an electronic signal of some kind (e.g. a [[voltage]]). * [[electrical resistance]] sensors: ohmmeter * electrical [[voltage]] sensors: [[voltmeter]] * [[electrical power]] sensors: watt-hour meter * [[magnetism]] sensors: magnetic compass * [[metal detector]]s * [[Radar]] An electromagnetic sensor is anything that can detect things like [[photon]]s, [[electron]]s, [[magnetic field]]<nowiki/>s etc. It can be as simple as a white wall, a sheet of white paper, etc., or as new as a [[charge-coupled device]]. When a [[laser]] is aimed at a detection screen, a bright spot can be seen on the screen, or when an electron hits the [[phosphor]]s on another kind of screen, it makes that screen glow. == Mech