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What are proximity sensors?
A proximity sensor is a sensor able to detect the
presence of nearby objects without any physical
Most likely a plate of glass or plastic separates the
two. Although you are likely to touch the separating
element, there is no physical contact with the sensor.
Proximity sensing technology enables adaptive
controls, alleviates isolation issues, improves overall
application robustness, generates almost unlimited
design flexibility and fosters new functionalities.
TYPES OF PROXIMITY SENSORS
Capacitive displacement sensor
Doppler effect (sensor based on effect)
Laser range finder
Magnetic, including Magnetic proximity fuse
Passive optical (such as charge-coupled devices)
Passive thermal infrared
Reflection of ionising radiation
Sonar (typically active or passive)
Ultrasonic sensor(sonar which runs in air)
LASER RANGE FINDER
A laser rangefinder is a rangefinder which uses
a laser beam to determine the distance to an object.The
most common form of laser rangefinder operates on
the time of flight principle by sending a laser pulse in a
narrow beam towards the object and measuring the time
taken by the pulse to be reflected off the target and
returned to the sender.
A proximity sensor often emits an electromagnetic field
or a beam of electromagnetic radiation (infrared, for
instance), and looks for changes in the field 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 inductive proximity sensor always
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.
Common Sensing Technologies
Technology Detection Mode Advantages Disadvantages
Operates in harsh
Ultrasonic Virtually all objects Sound wave echo
No idea of
Photoelectric Solid objects
absorption of light
Parking sensors, systems mounted on car bumpers that sense distance to
nearby cars for parking
Ground proximity warning system for aviation safety
Vibration measurements of rotating shafts in machinery
Top dead centre (TDC)/camshaft sensor in reciprocating engines
Sheet break sensing in paper machine.
Beverage and food can making lines
Touch screens that come in close proximity to the face
Attenuating radio power in close proximity to the body, in order to
reduce radiation exposure
Proximity Sensors in smartphones
The proximity sensor is common on most smart-
phones, the ones that have a touch screen. This is
because the primary function of a proximity sensor is to
disable accidental touch events. The most common
scenario being- The ear coming in contact with the
screen and generating touch events, while on a call.
If a proximity sensor close to the speaker,
then it will detect any object in the vicinity of
the speaker. If any object is present (ex.
user's ear), then the touch events can be
assumed to be accidental & ignored.
Parking sensors are proximity sensors for road vehicles designed to
alert the driver to obstacles while parking.
These systems feature ultrasonic proximity detectors to measure
the distances to nearby objects via sensors located in the front
and/or rear bumper fascias or visually minimized within adjacent
grills or recesses.
The sensors emit acoustic pulses, with a control unit measuring the
return interval of each reflected signal and calculating object
distances.The system in turns warns the driver with acoustic tones,
the frequency indicating object distance, with faster tones
indicating closer proximity and a continuous tone indicating a
minimal pre-defined distance. Systems may also include visual aids,
such as LED or LCD readouts to indicate object distance. A vehicle
may include a vehicle pictogram on the car's infotainment screen,
with a representation of the nearby objects as coloured blocks.
Automatic Door Openers
One of the most common applications for presence detection is the automatic
door.Typically, as you approach a door you are detected by an optical sensor, or
your weight closes a contact in the floor.
The electric field sensor can be integrated into the floor and can detect the
presence of a person through different substances (wood, tile, carpet, etc.).There
are no moving parts and the sensor is impervious to rust and virtually
indestructible, making it a suitable replacement technology for the mechanical
pressure sensor.The physical nature of the electrode ensures a well defined and
limited sensing area, unlike that of an optical solution where you need to define a
volume and sensitivity threshold.
Alternatively, proximity sensors can be embedded in the wall or other object to be
activated only by voluntary movement.This also allows the door to be opened
without any physical contact.
Optimizing access control can also lead to benefits in energy consumption.
Minimizing the time a doorway remains open ensures the shortest possible
exchange between hot or cold outside air with the conditioned air in the building.