A
proximity sensor is a
sensorA 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 glass...
able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an
electromagneticThe electromagnetic field is a physical field produced by electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. Light is the electromagnetic field in a certain frequency range...
or electrostatic field, or a beam of
electromagnetic radiationElectromagnetic radiation is a ubiquitous phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation...
(
infraredInfrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves...
, for instance), and looks for changes in the
fieldIn physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. This electric field exerts a force on other electrically charged objects...
or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors.
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A
proximity sensor is a
sensorA 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 glass...
able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an
electromagneticThe electromagnetic field is a physical field produced by electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. Light is the electromagnetic field in a certain frequency range...
or electrostatic field, or a beam of
electromagnetic radiationElectromagnetic radiation is a ubiquitous phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation...
(
infraredInfrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves...
, for instance), and looks for changes in the
fieldIn physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. This electric field exerts a force on other electrically charged objects...
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 might be suitable for a plastic target; an
inductiveInductance is the property in an electrical circuit where a change in the electric current through that circuit induces an electromotive force that opposes the change in current ....
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.
IECThe International Electrotechnical Commission is a not-for-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
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 switchA 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 touchscreen includes an array of touch switches on a display....
.
Types of sensors
- Inductive
Inductance is the property in an electrical circuit where a change in the electric current through that circuit induces an electromotive force that opposes the change in current ....
- Capacitive
- Eddy-current
- Magnetic
- Photocell (reflective)
- Laser rangefinder
- Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels. There are two kinds of sonar: active and passive. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water...
(typically active or passive)
- Radar
Radar is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for RAdio Detection And...
- Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842, 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 an observer...
(effect not a sensor)
- Passive thermal infrared
- Passive optical (such as 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...
s)
- Reflection of ionising radiation
Applications
- Car bumpers that sense distance to nearby cars for parking
- 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 U.S. FAA defines GPWS as a type of terrain awareness warning system...
for aviation safety
- Vibration | Position measurements of rotating shafts in machinery
- Sheet break sensing in paper machine.
- Anti-aircraft artillery
Anti-aircraft warfare, or air defence, is any method of engaging hostile military aircraft in defence of ground objectives, ground or naval forces or denial of passage through a specific airspace region, area or anti-aircraft combat zone...
- Mobile Phones