A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. A thermocouple converts temperature to an output voltage which can be read by a voltmeter.For accuracy, all sensors need to be calibrated against known standards.
Sensors are used in everyday objects such as touch-sensitive elevator buttons and lamps which dim or brighten by touching the base. There are also innumerable applications for sensors of which most people are never aware. Applications include cars, machines, aerospace, medicine, manufacturing and robotics.
A sensor'ssensitivity indicates how much the sensor's output changes when the measured quantity changes. For instance, if the mercury in a thermometer moves 1 cm when the temperature changes by 1 °C, the sensitivity is 1 cm/°C. Sensors that measure very small changes must have very high sensitivities.
Technological progress allows more and more sensors to be manufactured on a microscopic scale asmicrosensors using MEMS technology. In most cases, a microsensor reaches a significantly higher speed and sensitivity compared with macroscopic approaches.
In biometrics, electrical capacitance sensors from leading manufacturers, such as AuthenTec, scan the minute radio frequency (RF) pattern beneath the live skin of a finger pad. The pattern creates a unique algorithm to identify the user. Manypopular laptops and keyboards have the RF strip sensors.
Because sensors are a type of transducer, they change one form of energy into another. For this reason, sensors can be classified according to the type of energy transfer that they detect.
Temperature sensors: thermometers, thermocouples, temperature sensitive resistors (thermistors and resistance temperature detectors),bi-metal thermometers and thermostats
Heat sensors: bolometer, calorimeter, heat flux sensor
Electrical resistance sensors: ohmmeter, multimeter
Electrical current sensors: galvanometer, ammeter
Electrical voltage sensors: leaf electroscope, voltmeter
Electrical power sensors: watt-hour meters
Magnetism sensors: magnetic compass, fluxgate compass,magnetometer, Hall effect device
Pressure sensors: altimeter, barometer, barograph, pressure gauge, air speed indicator, rate-of-climb indicator, variometer
Gas and liquid flow sensors: flow sensor, anemometer, flow meter, gas meter, water meter, mass flow sensor
Gas and liquid viscosity and density: viscometer, hydrometer, oscillating U-tube
Mechanicalsensors: acceleration sensor, position sensor, selsyn, switch, strain gauge
Humidity sensors: hygrometer
Vibration and shock sensors.
Chemical proportion sensors: oxygen sensors, ion-selective electrodes, pH glass electrodes, redox electrodes, and carbon monoxide detectors.
Odor sensors: Tin-oxide gas sensors, and Quartz crystal microbalance (QCM) sensors. Gas sensors areoften combined into an "electronic nose".
Light time-of-flight. Used in modern surveying equipment, a short pulse of light is emitted and returned by a retroreflector. The return time of the pulse is proportional to the distance and is related to atmospheric density in a predictable way
Light sensors, or photo detectors, including semiconductor devices such as photocells,photodiodes, phototransistors, CCDs, and Image sensors; vacuum tube devices like photo-electric tubes, photomultiplier tubes; and mechanical instruments such as the Nichols radiometer.
Infra-red sensor, especially used as occupancy sensor for lighting and environmental controls.
Proximity sensor- A type of distance sensor but less sophisticated. Only detects a specific proximity. May be...