Photoelectric Sensors, Retroreflective Mode

Breaking a Beam

Breaking a beam has advantages over diffuse mode (proximity sensing). At times space restrictions or cost concerns make purchasing an opposed pair difficult. There is a second way to employ break-a-beam sensing without using an emitter/receiver pair. Retroreflective mode sensing offers all the same advantages of breaking a beam, but you only have to purchase a single sensor plus an inexpensive reflector. Reflectors cost very little, and they come in various sizes and shapes.

Retroreflective:

The example shown at left is easy to understand. Light from the emitter lens fans out in a familiar beam pattern, hitting the reflector. The reflector bounces the light back to the receiver lens. The target comes between the emitter and the reflector, breaking the beam. Like opposed pairs, retroreflective sensors most commonly are set up for dark operate, providing an output when the beam is broken.

Second Option to Opposed Mode

If space restrictions make it impossible to mount a receiver, those same space restrictions will likely accommodate a thin, rectangular or oval reflector. While you don't get the big excess gain of opposed pairs, retroreflective mode nevertheless offers good sensing ranges and beam-break sensing technology.