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Optical Sensor

Optical Sensors
 Light

propagates linearly and in all directions in
space.
 With aids of mirrors and lenses, light can be
deflected or concentrated in a beam.

Optical Sensors
 The
1)
2)
3)

are three main optical sensors:

Through Beam Sensor
Retro-Reflective Sensor
Diffuse Sensor

1) Through Beam Type

Through Beam Sensor
 This

through beam sensor usually use in
industry sector.
 The sensor light is aimed directly at a
separately mounted sensor/control unit.
 Objects between the two units break the light
beam.
 The light beam is focused, narrow, and not
deliberately bounced off an object or a
reflector
 The distance depend on strength of beam.

Advantages
 Able

to “see” at great distances
 Can “see” through most dirt and
moisture
 Can sense through some objects
 Most reliable form of counting

Disadvantages
 Sometimes

too powerful-senses through

a object.
 Cost more to purchase and install
 Difficult to set up (align) at great
distance.
 Cannot detect the close object.

2) Retro-Reflective Type

Retro-reflective Sensors
 Emitter
 Transmit

infrared

light
 Reflector
 Reflect

transmitted
infrared light

 Receiver
 Receive

transmitted
infrared light

Advantages
 More

cost effective then transmitted
beam sensing
 Very easy to align the system
 Reflector

is forgiving when mounted on
vibrating surfaces

 Great

for sensing large objects on
conveyors

DISADVANTAGES OF RETROREFLECTIVE
 Does

not have the strength of the transmitted
beam mode
 Can’t sense “shiny” object reliably or proxing
 Work

poorly in moisture and dirty
environments

 Damaged

or cheaper reflector weakens
system performance

3) Diffuse Type

Advantages and Disadvantages
Optical Sensor

Advantages

Disadvantages

Thru-Beam

-see great distances (10m)
-see thru most dirt and
moisture
-most reliable for counting

-costly
-diff to install or align
compare to others

Retro-Reflective

-easy to align the sensor
-cheaper than thru-beam
-reflector is suitable at to
mount at vibrating surfaces
-great for sensing large
object

-does not have the
strength compare to thrubeam
-work poorly in dirt and
moisture environment
-object cannot be shining

Diffuse

-can detect shiny object
-poor sensing range
-best when background not -sensing range varies upon
present
object’s surface and colour

Modes of Operation
Direct Detection
Sensors

Trans./Receiv.
Object

Through-Beam
Sensors

Transm.

Receiver

Object

Retro-Reflective
Sensors

Trans....
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