TECHNICAL TOPIC

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TECHNICAL TOPIC

• Photoelectric Sensors
• Mike Loiselle

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Photoelectric Sensors

• Detect various materials at long ranges using
  beam of light
• Detect the presence or absence of light
• Uses object detection to change the state of the
  sensors output
• Uses visible and infrared light as light source
• Composed of an emitter and receiver

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Four Groups of Photoelectric Sensors

• Through Beam
• Retro-Reflective
• Diffuse Reflective
• Fiber Optics

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Through Beam Sensor

• Consists of emitter and receiver in separate
  housings.
• Light travels in only one direction.
• Output is switched when object interrupts beam.
• Can detect dark and mirrored objects.
• Cannot detect transparent objects.

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Through Beam Sensor

• Pros - Large detection ranges
• - Reliable detection
• Cons - Higher mounting costs
• - Cannot detect transparent objects

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Retro-reflective Sensor

• Consists of emitter and receiver in same housing.
• The emitted infrared light is reflected by a
  triple prism reflector back to the sensor.
• Output is switched when object interrupts beam.
• Blind spot created when retroreflector is
  positioned too close to the sensor.

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Retro-reflective Sensor

• Pros - Object detection independent of color or
• surface properties
• - Reliable detection
• Cons - Needs retroreflector
• - Blind spots can be created
• - Higher mounting costs

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Diffuse-reflective Sensor

• Consists of emitter and receiver in same housing
• The emitter sends out a beam of pulsed infrared
  light, which is reflected directly by the object.
• The beam of light hits the target (at any angle)
  and it is diffused in all directions and some
  light is reflected back
• The output switches when a object is detected
  within the reflective distance.

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Diffuse-reflective Sensor

• Pros - Low mounting costs
• - Large active distance
• - Uses objects own reflective
  properties.
• Cons - Trouble detecting extremely dark and
  shiny
• objects.
• - Detection range depends heavily on
  the
• reflectivity of the objects
  surface.

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Fiber Optic Sensors

• Consists of emitter and receiver in same housing
• Detection area is relocated through glass or
  plastic fibers
• Used in places inaccessible by other
  photoelectric sensors and in aggressive
  environments
• Can be used as through beam or diffuse reflective
  sensors.
• Output is switched when object interrupts beam.

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Fiber Optic Sensors

• Pros - Can be used in aggresive environments
• - Uses objects own reflective
  properties
• - Detection is independent of color,
  shape,
• and surface properties
• Cons - Higher mounting costs