Proximity sensor
A proximity sensor is a sensor
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-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...

 able to detect the presence of nearby objects without any physical contact.

A proximity sensor often emits an electromagnetic
Electromagnetic field
An electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...

 or a beam of electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

, for instance), and looks for changes in the field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...

 or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive or photoelectric sensor
Photoelectric sensor
A photoelectric sensor, or photoeye, is a device used to detect the distance, absence, or presence of an object by using a light transmitter, often infrared, and a photoelectric receiver. They are used extensively in industrial manufacturing. There are three different functional types: opposed ,...

 might be suitable for a plastic target; an inductive
Inductive sensor
An inductive sensor is an electronic proximity sensor, which detects metallic objects without touching them.The sensor consists of an induction loop. Electric current generates a magnetic field, which collapses generating a current that falls asymptotically toward zero from its initial level when...

 proximity sensor requires a metal target.

The maximum distance that this sensor can detect is defined "nominal range". Some sensors have adjustments of the nominal range or means to report a graduated detection distance.

Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object.

Proximity sensors are also used in machine vibration monitoring to measure the variation in distance between a shaft and its support bearing. This is common in large steam turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

s, compressor
Compressor may refer to:* Gas compressor, a mechanical device that compresses a gas * A device used to apply video compression to a video signal* A device used to apply audio data compression to an audio signal...

s, and motors that use sleeve-type bearing
Bearing may refer to:* Bearing , a term for direction* Bearing , a component that separates moving parts and takes a load* Bearing capacity*Bearings, album by Ronnie Montrose in 2000...


International Electrotechnical Commission
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

 (IEC) 60947-5-2 defines the technical details of proximity sensors.

A proximity sensor adjusted to a very short range is often used as a touch switch
Touch switch
A touch switch is a type of switch that only has to be touched by an object to operate. It is used in many lamps and wall switches that have a metal exterior as well as on public computer terminals...


A proximity sensor is divided in two halves and if the two halves move away from each other, then a signal is activated.

A proximity sensor can be used in windows, and when the window opens an alarm is activated.

Types of sensors

  • Capacitive
    Capacitive sensing
    In electrical engineering, capacitive sensing is a technology based on capacitive coupling that is used in many different types of sensors, including those to detect and measure: proximity, position or displacement, humidity, fluid level, and acceleration...

  • Capacitive displacement sensor
    Capacitive displacement sensor
    Capacitive displacement sensors “are non-contact devices capable of high-resolution measurement of the position and/or change of position of any conductive target”. They are also able to measure the thickness or density of non-conductive materials...

  • Doppler effect
    Doppler effect
    The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...

     (sensor based on effect)
  • Eddy-current
  • Inductive
    In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...

  • Laser rangefinder
  • Magnetic, including Magnetic proximity fuse
    Magnetic proximity fuse
    A Magnetic proximity fuze was patented by P.J. Eliomarkakis, although similar devices had been in service for nearly a decade...

  • Passive optical (such as charge-coupled device
    Charge-coupled device
    A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...

  • Passive thermal infrared
    Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

  • Photocell (reflective)
  • Radar
    Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

  • Reflection of ionising radiation
  • Sonar
    Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...

     (typically active or passive)


  • Parktronic, car bumpers that sense distance to nearby cars for parking
  • Ground proximity warning system
    Ground Proximity Warning System
    A ground proximity warning system is a system designed to alert pilots if their aircraft is in immediate danger of flying into the ground or an obstacle. The United States Federal Aviation Administration defines GPWS as a type of terrain awareness warning system...

     for aviation safety
  • Vibration measurements of rotating shafts in machinery
  • Top dead centre
    Dead centre
    In a reciprocating engine, the dead centre is the position of a piston in which it is farthest from, or nearest to, the crankshaft. The former is known as top dead centre while the latter is known as bottom dead centre ....

    A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

     sensor in reciprocating engine
    Reciprocating engine
    A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

  • Sheet break sensing in paper machine.
  • Anti-aircraft warfare
    Anti-aircraft warfare
    NATO defines air defence as "all measures designed to nullify or reduce the effectiveness of hostile air action." They include ground and air based weapon systems, associated sensor systems, command and control arrangements and passive measures. It may be to protect naval, ground and air forces...

  • Mobile phones
  • Roller Coaster
    Roller coaster
    The roller coaster is a popular amusement ride developed for amusement parks and modern theme parks. LaMarcus Adna Thompson patented the first coasters on January 20, 1885...

  • Conveyor system
    Conveyor system
    A conveyor system is a common piece of mechanical handling equipment that moves materials from one location to another. Conveyors are especially useful in applications involving the transportation of heavy or bulky materials...

  • Touch screens on mobile devices that come in close proximity with the face


  • AutomationDirect
  • c3controls
    c3controls , formerly known as Control Concepts Corporation, is a U.S. manufacturer of electric controls sold worldwide. The company manufactures its products to primarily be sold directly to its customers. Its line of products includes disconnect switches, contactors, overload relays, pilot...

  • Hyde Park Electronics
  • Pepperl+Fuchs
    Pepperl+Fuchs is a worldwide company with its headquarters in Mannheim, Germany. The company manufactures products for fabrication and process automation and is specialized in sensor manufacturing, for example sensors which are used in automatic doors in elevators.Pepperl+Fuchs was founded in 1945...

  • Turck
    The Turck GmbH & Co. KG is one of the leading manufacturers in the field of industrial automation. With more than 2.800 employees working in 27 countries and representatives in further 60 states, Turck can be called a global player.With a versatile range of approximately 15.000 sensor, fieldbus,...

  • Rockwell Automation
    Rockwell Automation
    Rockwell Automation is a global provider of industrial automation, power, control and information solutions. Brands in industrial automation include Allen-Bradley and Rockwell Software....

  • ifm electronic
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