TECHNICAL TOPIC Photoelectric Sensors Mike Loiselle

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 sensor’s output  Uses visible and infrared light as light source  Composed of an emitter and receiver

Four Groups of Photoelectric Sensors  Through Beam  Retro-Reflective  Diffuse Reflective  Fiber Optics

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.

Through Beam Sensor Pros - Large detection ranges - Reliable detection Cons - Higher mounting costs - Cannot detect transparent objects

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.

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

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.

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.

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.

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