Through-beam sensors are a true time proven solution to many photoelectric applications. These sensors can detect anything regardless of color, texture or reflectivity, all that needs to happen is the light beam needs to be blocked. Add an optional aperture and you can detect even the smallest of parts. With the various light sources available and you can detect small parts (with a laser light) or blast through the harshest of environments with an infrared light source. These sensors come in several housings or styles for instance tubular (as small as 8mm), block, fiber optic and the fork style sensor.
Through-beam sensors are used in applications that require sensing ranges from 2 millimeters to 100 meters and in some cases longer. Since these sensors require a light emitter and a receiver that are in separate housings, you have to mount and wire each component separately. Once mounted you have the task of aligning the receiver to the emitter, which could be a tedious task. Just imagine trying to line up the devices that use an infrared light source with a working range of 50 meters or even 150 millimeters.
Fork sensors, also referred to, as c slot or u slot, are the ideal through-beam sensor. First, they are self-contained in one housing so there is no need to align the emitter and receiver. This is important because in the harsh environments if the sensor is bumped or jarred the receiver and emitter stays aligned. Secondly, the housings are typically metal offering an extremely robust sensor. Third, since the sensor is integrated into one housing installation is much easier, one part to mount and only one wiring connection. These sensors are available from 5mm to 220 mm wide openings.