A proximity sensor detects nearby objects without physical contact by emitting electromagnetic fields or beams. There are several types of proximity sensors including inductive, capacitive, ultrasonic, and optical sensors. Inductive sensors detect metal objects using magnetic fields while capacitive sensors can detect both metals and non-metals by measuring capacitance changes. Ultrasonic sensors use sound waves while optical sensors use light beams. Each sensor type has advantages and applications depending on the target object and environmental factors.

1. DEFINITION:
A proximity sensor is a sensor able to detect the presence of nearby
objects without any physical contact. 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.
Types of Proximity Sensors:
There are various types of proximity sensors. Among them four types of
sensors havewiderangeof applications. They are:
1. InductiveProximity Sensors
2. Capacitive Proximity Sensors
3. Ultrasonic Proximity Sensors
4. Optical Proximity Sensors
Among these Ultrasonic Proximity Sensors are of two types: Active &
Passive. OpticalProximity Sensors areof basically of two types:

2. Thru beam and Reflective, in which Reflective Proximity Sensors are
divided in three types:
a) Direct Reflection
b) Reflection with reflector
c) Polarized reflection with reflector
INDUCTIVE PROXIMITY SENSORS:
Inductive proximity sensors are used for non-contact detection of
metallic objects. Their operating principle is based on a coil and
oscillator that creates an electromagnetic field in the close surroundings
of the sensing surface. The presence of a metallic object in the operating
area causes a dampening of the oscillation amplitude. The rise or fall of
such oscillation is identified by a threshold circuit that changes the
output of the sensor. The operating distance of the sensor depends on
the actuator's shape and size and is strictly linked to the nature of the
material.
COMPONENTS AND WORKING PRINCIPLE:
The main components of Inductive Proximity Sensors are coil, oscillator,

3. detector and the output circuit. The operating distance of the sensor
depends on object’s shape and size and strictly linked to the nature of
the material.
WORKING:
The coil generates high frequency magnetic field in front of the face.
When the metallic target comes in this magnetic field it absorbs some of
the energy. When a piece of conductive metal enters the zone defined
by the boundaries of the electromagnetic field, some of the energy of
oscillation is transferred into the metal of the target. This transferred
energy appears as tiny circulating electrical currents called eddy
currents. This is why inductive proximity sensors are sometimes called
eddy current sensors. This creates a small amount of power loss in the
form of heat (just like a little electric heater) so the amplitude (the level
or intensity) of the sensor’s oscillation decreases. Eventually, the
oscillation diminishes to the point that another internal circuit called a
Schmitt Trigger detects that the level has fallen below a pre-determined
threshold. This threshold is the level where the presence of a metal
target is definitely confirmed. Upon detection of the target by the
Schmitt Trigger, the sensor’s outputis switched on.

4. ADVANTAGES OF INDUCTIVE PROXIMITY SENSORS:
Inductive Proximity Sensors are very accurate compared to other
technologies. They have high switching rate, and they can be used in
harsh environmentalconditions.
DISADVANTAGES OF INDUCTIVE PROXIMITY SENSORS:
The only disadvantage of Inductive Proximity Sensors is that it can only
detect metallic objects. Thus its industry level applications are limited.
COMMON APPLICATIONS:
Inductive Proximity Sensors are used in metal detectors, car washes etc.
Because these sensors does not require physical contact these are useful

5. where access presents challenge and dirt is prevalent. Sensing range is
rarely greater than 6 cm but it has no directionality.
CAPACITIVE PROXIMITY SENSORS:
Capacitive Proximity Sensors are used for detection of metallic objects as
well as non-metallic objects (liquid, plastic, wooden material etc). These
sensors use variation of capacitance between the sensors and the
object. Variation in distance down to 1 micro inch can be measured
accurately. All targets having dielectric constant more than air can be
detected.
COMPOMENTS AND WORKING PRINCIPLE:
The main components of the Capacitive Proximity sensor Are Plate,
Oscillator, ThresholdDetector and theOutput Circuit.
WORKING:
Inside the sensor is a circuit that uses the supplied DC power to
generate AC, to measure the current in the internal AC circuit, and to
switch the output circuit when the amount of AC current changes. Unlike
the inductive sensor, however, the AC does not drive a coil, but instead

6. tries to charge a capacitor. Remember that capacitors can hold a charge
because, when one plate is charged positively, negative charges are
attracted into the other plate, thus allowing even more positive charges
to be introduced into the first plate. Unless both plates are present and
close to each other, it is very difficult to cause either plate to take on
very much charge. Only one of the required two capacitor plates is
actually built into the capacitive sensor! The AC can move current into
and out of this plate only if there is another plate nearby that can hold
the opposite charge. The target being sensed acts as the other plate. If
this object is near enough to the face of the capacitive sensor to be
affected by the charge in the sensor's internal capacitor plate, it will
respond by becoming oppositely charged near the sensor, and the
sensor will then be able to move significant current into and out of its
internal plate.

7. ADVANTAGES OF CAPACITIVE PROXIMITY SENSORS:
The main advantage of Capacitive Proximity Sensors is that it can detect
metallic as well as non metallic objects such as wood, liquid, plastics etc.
Also detection speed is very high and it has good stability. It uses low
power and it is less costly.
DISADVANTAGES OF CAPACITIVE PROXIMITY SENSORS:
The main disadvantages of these sensors are, they are affected by
temperate and humidity. Also these sensors are less accurate than
InductiveProximity Sensors. Thesesensors aredifficultto design.
COMMON APPLICATIONS:
Capacitive touch sensors are used in laptop track pads, digital displays,
mobile phones, mobile displays and many more. More and more design
engineers are selecting Capacitive Sensors for their versatility, reliability,
robustness and costeffectiveness over mechanical switches.
ULTRASONIC PROXIMITY SENSOSORS:
Ultrasonic sensors are based on measuring the properties of sound
waves with frequency above the human audible range. Systems typically
use a transducer which generates sound waves in the ultrasonic range,

8. above 18 kHz, generally in the range of 40 kHz, by turning electrical
energy into sound, then upon receiving the echo turn the sound waves
into electrical energy which can be measured. The Ultrasonic Sensor can
measure distances in centimeters and inches. It provides good readings
in sensing large-sized objects with hard surfaces.
COMPONENTS AND WORKING PRINCIPLE:
Active ultrasound sensors emit sound waves from quartz-crystal
transducers. The waves strike objects within the field of detection and as
long as there are no movement the waves are not disrupted. However,
when movement occurs the sound wave is disrupted and is reflected
back to the system’s receiver.

9. ADVANTAGES OF ULTRASONIC PROXIMITY
SENSORS:
Ultrasonic proximity sensors are not affected by atmospheric dust,
snow, rain etc. These sensors can work in adverse conditions where
application of other sensors is not easy. Sensing distance of these
sensors is morecompared to inductive or capacitive proximity sensors.
DISADVANTAGES OF ULTRASONIC PROXIMITY
SENSORS:
These sensors find difficulties in sensing reflections from small, curved,
thin and soft objects.
GENERAL APPLICATIONS OF ULTRASONIC
PROXIMITY SENSORS:
Ultrasonic Thru beam sensors are used for bottle counting in drink filling
machines. The bottles pass the sensor too quickly and the gaps between
the bottles are often too small. For this reason, ultrasonic thru-beam
sensors are particularly suitable for bottle counting. Even in areas
with strong steam generation, reliable detection of bottles is guaranteed
with ultrasonic thru-beam sensors. These sensors also find application in
vehicle detection in automatic barrier systems, where proximity sensor
is used to detect any vehicle under the barrier, if a vehicle is detected

10. under the barrier, it automatically opens the barrier.
OPTICAL PROXIMITY SENSORS:
An optical proximity sensor offers non-contact sensing of almost any
object up to a range of 10 meters. It includes a light source, (usually an
LED in either infrared or visible light spectrum) and a detector
(photodiode). The light source generates light of a frequency that the
light sensor is best able to detect, and that is not likely to be generated
by other nearby sources. Infra-red light is used in most optical sensors.
To make the light sensing system more foolproof, most optical proximity
sensor light sources pulse the infra-red light on and off at a fixed
frequency.
COMPONENTS AND WORKING PRINCIPLE:
Optical sensors are basically of two types: Thru Beam Optical Sensors
and Reflective type Optical Sensors. Reflective type Optical sensors can
be again classified in three types: Direct reflection, Reflection with
reflector and Polarizedrefectionwithreflector.

11. THRU BEAM OPTICAL SENSOR:
In Thru Beam Optical Sensors the emitter and the receiver are housed
separately. Optical signal, which is pulsated by the pulse generator is
sent by emitter and is received by the receiver. Whenever there is an
object between emitter and the receiver light beam cannot pass
through, thus disrupting the optical signal, which is detected by the
sensor and it gives proper output. These sensors allow the longest range
of detection.

12. REFLECTIVE METHOD:
Unlike Thru Beam Sensors, in Reflective type sensors emitter and
receiver are housed together. In this case reflection occurs either from
the target or a reflector, which reflects the beam emitted by emitter,
and this reflected signal is received by receiver.
These sensors aredivided in three types:
DIRECT REFLECTION:
In Direct Reflection method the light beam emitted is reflected of the
object, which is sensed by the sensor. The sensing range depends upon
the surfacetypeand colour of the object.

13. REFLECTION WITH REFLECTOR:
Here the emitter and receiver is housed together at one point, but a
separate reflector is needed in another point of the system, which
reflects the light beam emitted, this reflected light beam is received by
receiver. An object is detected when it interrupts the light beam
between the sensor and reflector. These photocells allow longer sensing
distances, as the rays emitted are almost totally reflected towards the
receiver.

14. POLARIZED REFLECTION WITH REFLECTOR:
Often shiny objects reflect the light beam emitted by emitter in
reflection with reflector methods. Thus shiny objects are not properly
sensed. This problem is handled by using polarized reflective sensors.
Polarized reflective sensors contain polarizing filters in front of the
emitter and receiver that orient light into a single plane. These filters are
perpendicular or 90° out of phase with each other. The light beam is
polarized as it passes through the filter. When polarized light is reflected
off an object, the reflected light remains polarized. When polarized light
is reflected off a depolarizing reflector, the reflected light is depolarized.
The receiver can only detect reflected light that has been depolarized.
Therefore, the receiver cannot see (receive) light from reflective objects

15. that did not depolarize the light. The sensor can “see” a reflection from a
reflector, and it cannot“see” a reflection frommostshiny objects.
All standard reflectors depolarize light and are suitable for polarized
reflective sensing.
ADVANTAGES OF OPTICAL PROXIMITY SENSORS:
These sensors are effective in Dusty or noisy environments, uses
focused beam, higher sensing distance compared to Inductive and
capacitive type sensors and they are immune to visible light
interference.

16. DISADVANTAGES OF OPTICAL PROXIMITY
SENSORS:
The main disadvantageof Opticalsensors is they are costly.
APPLICATIONS OF OPTICAL PROXIMITY SENSORS:
Optical proximity sensors finds applications in lift door mechanisms,
components positioning sensing in electronic industry, security and
safety applications, counting of bottles/containers in factories etc.
CONCLUSION:
The global market for these proximity sensors is expected to grow at a
steady rate. Major industries using proximity sensors are machine
tools, woodworking machines, packaging machines and other types
of machinery.
Further applications of proximity sensors are automatic door units
such as garage doors or doors inside buildings, elevator doors or
doors insiderailway coaches.
The building and automotive sector are further industries using high
volumes of proximity sensors.

17. REFERENCES:
http://literature.rockwellautomation.com/idc/groups/literature/docu
ments/ca/c116-ca502_-en-p.pdf
http://en.wikipedia.org/wiki/Proximity_sensor
http://www.fargocontrols.com/sensors.html
http://www.autonics.co.in/products/products_2.php?big=01&mid=0
1/01
http://www.ia.omron.com/support/guide/41/overview.html
http://www.sensorcentral.com/photoelectric/proximity01.php
http://www.engineershandbook.com/Components/proximitysensors.
htm
http://www.ab.com/en/epub/catalogs/12772/6543185/12041221/12
041223/Retroreflective-and-Polarized-Retroreflective.html