1. P HOTOELECTRONIC S ENSORS Diffuse Sensors (proximity mode) ‏ Transmitted beam (through beam) ‏ Retro-reflective

2. D IFFUSE S ENSOR Rely on sensing light reflected off a target object Standard, Sharp Cutoff, Background Suppression, Fixed Focus, and Wide Angle

3. T RANSMITTER -R ECEIVER (T HROUGH ) ‏ 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

4. R ETRO R EFLECTIVE 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

5. S UMMARY 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.html All require an A/D converter Different power supplies Reliability has been questioned (due to errors in mounting)

6. W EBSITES 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

7. C OMPARISON Sensor TypeDifferenceAdvantagesDisadvantages 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 objects Different sensing distances and sensitivity settings are required for different objects (colors) Sharp sends light to a smaller, fixed area objects close to reflective background Background SuppressionIgnores the backgroundCan detect object and backgroundMore complex, expensive Wide Angle sends 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

8. T HROUGH C OMPARISON AdvantagesDisadvantage only receiver needs to be connected to smart deviceCrosstalk (alter sides to fix) Commercially available in a wide range of distances2x components of diffuse Can be reasonably priced2 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

9. R ETRO R EFLECTIVE C OMPARISON AdvantagesDisadvantages Large sensing rangemust 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