REPORT ON TYPES OF PROXIMITY SENSORS

1. PROXIMITY SENSORS sensing instrumentation practise
PROXIMITY SENSORS
K.BHOLANATH - EDM18B030
RAVIRAJKUMAR.P - EDM18B043
S.Y.P NARASIMHA - EDM18B045
I. INTRODUCTION
Basically Sensor is a device or system which purpose is to
detects events or changes in the environment and to send that
information to the electronic devices connected to it mostly
the computer processor.
II. TYPES OF SENSORS
There are different types of sensors available. Some of them
are:
• Vision and imaging sensors
• Temperature sensors
• Radiation sensors
• Proximity sensors
• Pressure sensors
• Position sensors
A. Proximity sensor
A proximity sensor is a sensor able to detect the presence
of nearby objects without physical contact.
It often emits an electromagnetic field and looks for the
change in the field or for the incoming signal.
The proximity sensors have high reliability and long func-
tional life because there is no physical contact between the
sensor and the objects.
These are applied in many areas like Mobile devices, con-
veyor systems,parking systems, Anti aircraft missile systems.
1) Common types of Proximity sensors::
• Inductive Proximity sensor
• Capacitive proximity sensor
• Optical proximity sensors
• Ultra sonic Proximity sensor
III. INDUCTIVE PROXIMITY SENSOR
An Inductive proximity sensor is an electronic proximity
sensor , which detects metallic objects without touching them
Inductive sensors operate on the basis of Faraday’s Law. One
way to state Faraday’s Law is that a change in magnetic flux
in a coil of wire will induce a voltage in a nearby coil. This
is applied in inductive proximity sensors
Gambar 1. INDUCTIVE PROXIMITY SENSOR
Gambar 2. INDUCTIVE PROXIMITY SENSOR
A. WORKING PRINCIPLE
The Main Components Of The Inductive Proximity Sensor
Are. Coil, Oscillator, Detector And The Output Circuit
The operation of a typical inductive proximity sensor is
shown
The sensor itself contains an oscillator circuit and a coil
from which an electromagnetic field radiates out and induces
eddy currents in any nearby metallic objects. So when we keep
any metallic object near the sensor The eddy currents have
the effect of attenuating the oscillations from the amplifier.
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2. PROXIMITY SENSORS sensing instrumentation practise
This reduction in oscillations is registered as the presence of
a metallic object.
B. WHY ONLY METALLIC OBJECTS?
Because only metallic objects have inductive properties,
inductive sensors can’t be used to detect plastic or cardboard
or other non-metallic objects. However, different metals have
different inductive properties and the type of metal being
sensed will influence the sensing distance
C. ADVANTAGES
• They are very accurate compared to other technologies.
• They have a high switching rate.
• They are capable of working in harsh environmental
conditions.
• It has longer life
D. DISADVANTAGES
• The sensing range of an inductive sensor dependents on
the type of metal being detected, its shape, its size and
also coil size used in the design. Due to above reason,
inductive sensor has distance limitations for sensing
• It can detect metallic targets only.
E. APPLICATIONS
The use of inductive proximity sensors is increasing glob-
ally, on the back of industrial applications such as: the search
coil magnetometer that is used in electromagnetic waves
measurement; metal detectors; traffic lights; car washes; and
a host of other automated industrial processes.
IV. CAPACITIVE PROXIMITY SENSOR
Gambar 3. CAPACITIVE PROXIMITY SENSOR
Capacitive proximity sensors are similar in function to
inductive sensors but have certain unique design specifications
and operating parameters. Capacitive proximity sensors sense
”target” objects due to the target’s ability to be electrically
charged. Since even non-conductors can hold charges, this
means that just about any object can be detected with this
type of sensor.
A. COMPONENTS
The Main Components Of The Capacitive Proximity Sensor
Are Plate, Oscillator, Threshold Detector And The Output
Circuit.
Gambar 4. CAPACITIVE PROXIMITY SENSOR
B. WORKING PRINCIPLE
Inside the sensor , 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 tries to charge a capacitor. we
also know 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.
C. ADVANTAGES
• It can be used to detect non-metallic targets.
• It can detect through containers of certain types also.
• It is simple in construction and adjustable.
• It can detect dense targets and liquids.
• It is lower in cost.
• It has higher sensitivity and can be operational with small
magnitude of force.
• It can be used for the measurement of force, pressure and
humidity etc.
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3. PROXIMITY SENSORS sensing instrumentation practise
• It has very good resolution (as low as 0.003 mm) and
frequency response.
D. DISADVANTAGES
• It is very much sensitive to changes in environmental
conditions such as temperature, humidity etc. This will
affect the performance.
• The measurement of capacitance is hard compare to
measurement of resistance.
• Capacitive proximity sensor are not so accurate compare
to inductive sensor type.
E. RANGE
Capacitive proximity sensors usually have a larger sensing
range than their inductive counterparts, and it typically falls
between 5 and 40 millimeters. The detection distance depends
on plate diameter
F. APPLICATIONS
Capacitive sensors are used in the measurement of brake
disc deformation. Due to the high temperature development,
very few sensors are suitable for operating close to the
measurement object. Capacitive transducers detect changes in
the nanometer range and measure the wear on the brake disc
V. PHOTOELECTRIC PROXIMITY SENSOR
Gambar 5. PHOTOELECTRIC PROXIMITY SENSOR
A sensor which detects the presence of object by the action
of light. The main components of this sensor are emitter,
detector and associated electronics. Emitter (Light Emitting
Diode, laser diode) sends a beam of light. The detector (photo
diode or phototransistor) detects emitted light.An associated
electronics required to amplify the detected signal. The emitter
sometimes called the sender transmits a beam of either visible
or infrared light to the detecting receiver. All photoelectric
sensors operate under similar principles. Dark-on and light-
on classifications refer to light reception and sensor output
activity. With no reception of light, the output produces then
the sensor is dark-on. If output from light received then it is
light-on.
A. TYPES OF PHOTOELECTRIC PROXIMITY SENSOR
There are three main sensing methods of the photoelectric
proximity sensor and they are,
• Through beam method
• Retro-reflective method
• Diffuse or Reflective method
B. WORKING PRINCIPLE
1) Through beam method: In this type of method, an
emitter sends out a beam of light directly in the line-of-sight of
the emitter to a receiver. When an object breaks this beam of
light, it detects as a presence. This type of setup requires two
components they are an emitter and a separate detector, which
makes it a bit more complex to install and wire. However, the
advantage is that it’s the most accurate of the sensing methods
with the longest sensing range.
Gambar 6. Through beam
New laser diode emitter models can transmit a well-
collimated beam 60 m for increased accuracy and detection. At
these distances, some through-beam laser sensors are capable
of detecting an object the size of a fly, at close range,
that becomes 0.01 mm. One ability unique to throughbeam
photoelectric sensors is effective sensing in the presence of
thick airborne contaminants.
2) Retro-reflective method: In this method, detection occurs
when the light path breaks or disturbs. Both the light emitting
and light receiving elements are in same housing. The light
from the emitting element hits the reflector and returns to the
light receiving element. When a target is present, the light gets
interrupt. One reason for using a retro-reflective sensor over
a through-beam sensor is for the convenience of one wiring
location, the opposing side only requires reflector mounting.
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4. PROXIMITY SENSORS sensing instrumentation practise
3) Diffuse or Reflective method: As in retro-reflective sen-
sors, emitters and receivers located in the same housing. In
this Diffuse method, Both the light emitting and light receiving
elements contain in a single housing. The sensor receives the
light reflected from the target.
Diffuse photoelectric sensors are similar in some respects
to reflective sensors. This is because like reflective sensors
they emit a light beam in the direction of the object to be
detected. However, instead of a reflector used to bounce the
light back to a detector, the object to be sensed functions as the
reflector, bouncing some of the light back to be detected and
register an object’s presence. Mostly, the diffuse sensors use in
public washroom sinks, where they control automatic faucets.
Hands placed under the spray head act as reflector, triggering
(in this case) the opening of a water valve. diffuse sensors
are somewhat color dependent, certain versions are suitable
for distinguishing dark and light targets in applications that
require sorting or quality control by contrast.
C. ADVANTAGES
• The sensor senses all kinds of materials.
• It has longer life, long sensing range and very reliability.
• Very fast response time and less costly.
• Diffuse photoelectric sensor detects small objects includ-
ing color mark and label detection.
• mostly retro-reflective type sensor can detect transparent
objects.
• Through beam type can detect long range and it is tolerant
of dirty environment.
D. DISADVANTAGES
• Over coarse of time lens get contaminated.
• Generally, the sensing range is affected due to color and
reflectivity of the target.
• Through beam type requires transmitter (Tx) and receiver
(Rx) at two separate locations
• Retro reflective type requires reflector in addition to
Tx/Rx. This makes system installation complex
E. APPLICATIONS
• Checking objects on production lines or conveyors
• Counting of small objects
• Detection of colours
• Monitoring bigger areas for objects with light grids
• Measuring distance
• Logistics and materials handling
VI. ULTRASONIC PROXIMITY SENSOR
• An ultrasonic sensor is an instrument that measures the
distance to an object using ultrasonic sound waves.
• An ultrasonic sensor uses a transducer to send and receive
ultrasonic pulses that relay back information about an
object’s proximity.
• High-frequency sound waves reflect from boundaries to
produce distinct echo patterns.
Gambar 7. ULTRASONIC PROXIMITY SENSOR
A. WORKING PRINCIPLE
Ultrasonic proximity sensors emit and receive sound waves.
The carrier signal is a high frequency, inaudible sound wave.
They detect the presence of the target object in one of two
configurations.
1) TYPES OF ULTRASONIC PROXIMITY SENSOR:
• Diffuse or Reflective
• Opposed or Thru-Beam
Gambar 8. ULTRASONIC PROXIMITY SENSOR
2) Diffuse or Reflective: Diffuse or Reflective sensors have
the transmitter and receiver packaged in the same housing.
When a target enters the sensing range of the device, the
ultrasonic waves are reflected back to the sensor.
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5. PROXIMITY SENSORS sensing instrumentation practise
3) Opposed or Thru-Beam: Opposed or Thru-Beam sensors
have the transmitter and receiver packaged separately. The
receiver is mounted facing the transmitter and when an object
enters the sensing range of an opposed sensor, it blocks the
transmitted signal. Rather than activating the trigger when the
frequency is received, the trigger is activated when the signal
is broken.
B. ADVANTAGES
• Not affected by color or transparency of objects
• Can be used in dark environments
• Advantages and Limitations of Ultrasonic Sensors
• Low-cost option
• Not highly affected by dust, dirt, or high-moisture envi-
ronments
C. DISADVANTAGES
• limited testing distance
• inaccurate readings
• inflexible scanning methods
D. APPLICATIONS
used in many manufacturing and automation applications.
Mainly for object detection and distance measurement, they’re
commonly used in food and beverage processing and various
packaging
VII. 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 in-
siderailway coaches. The building and automotive sector are
further industries using high volumes of proximity sensors.
VIII. REFERENCES
http://www.fargocontrols.com/sensors.html
http://www.ia.omron.com/support/guide/41/overview.html
http://www.engineershandbook.com/Components/proximitysensors.
html
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