PHOTOELECTRONIC SENSORSDiffuse Sensors (proximity mode)

Transmitted beam (through beam)

Retro-reflective

DIFFUSE SENSOR

Rely on sensing light reflected off a target object Standard, Sharp Cutoff, Background Suppression, Fixed

Focus, and Wide Angle

TRANSMITTER-RECEIVER (THROUGH)

Comprised of a light source and a sensor to detect its beam. Both parts require a power source, can come from different supplies. When a part passes between the transmitter and receiver, the beam is broken and the sensor sends a signal to the automation controller

IR, laser, LED

Dark and Light Applications

http://www.baumerelectric.com/be130.html?L=1&country=US

RETROREFLECTIVE The transmitter and receiver are incorporated into

a single housing. A reflector is mounted opposite to the sensor and returns transmitted light back to the receiver.

The effective beam describes the area that must be completely interrupted in order to reliably sense a target and it increases as the distance between the sensor and reflector increases. When the target is directly in front of the reflector, it must be at least as large as the reflector. Smaller objects can be detected if they are located closer to the sensor and they are at least as large as the optics.

Dark and Light Applications

SUMMARY

Transmitter-Receiver is not valid because of mounting limitations.

Diffuse requires background suppression – expensive

Retro-reflective is picky and hard to mount, but might prove to be most reliable. Sensitivity is issue. http://sensor.baumerelectric.com http://www.ab.com/catalogs/sensors/index_prodtype.ht

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All require an A/D converterDifferent power suppliesReliability has been questioned (due to errors in

mounting)

WEBSITES

http://machinedesign.com/article/a-background-check-for-photoelectric-sensors-0519

http://everything2.com/title/Photoelectric%2520sensor

http://www.ab.com/sensors/sensorstoday/nov01/techtalk/index.html

http://ugpro143.blogspot.com/2008/06/basics-of-ir-transmitter-and-receiver.html

http://www.solarbotics.net/library/circuits/sensors_prox.html

http://www.ifmefector.com/ifmus/web/pinfo1_40_10_40_20.htm

COMPARISON

Sensor Type Difference Advantages Disadvantages

Diffuse (general)Sensative to reflective, shape, etc. Access to other side of obj is not required

Reliability, tough to precisely control the sensing range, triggers on shiny objectsDifferent sensing distances and sensitivity settings are required for different objects (colors)

Sharpsends light to a smaller, fixed area

objects close to reflective background

Background Suppression Ignores the background Can detect object and background More complex, expensive

Wide Anglesends light to a wide area

ignore imperfections in target, not sensitive to angle of view, metal reflects well, does not need a background

http://www.acroname.com/robotics/parts/R146-GP2D120.html

THROUGH COMPARISON

Advantages Disadvantage

only receiver needs to be connected to smart device Crosstalk (alter sides to fix)

 Commercially available in a wide range of distances 2x components of diffuse

 Can be reasonably priced 2 power supplies (or lines)

  Sense both sides of device

 The transmitter must be aligned directly at the receiver and will fail if either part is bumped or moved out of position.

  dirty environments, where dust and particles in the air might impede light

RETROREFLECTIVE COMPARISON

Advantages Disadvantages

Large sensing range must compelely break beam to count

Matte finished objects are recognized independent of their surface properties. target cannot be highly reflective

Can fixed to a moving target