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.
There are a wide variety of fork sensors including four different light sources to solve the most difficult applications. Red light is the general most economical version that can detect parts as small as 0.4mm. Pinpoint red light has a more concentrated beam (higher precision) that eliminates possible cross talk and can detect parts as small as 0.3mm. Laser is the smallest diameter light beam, which allows for small part detection, down to 0.08mm. The infrared light source is perfect for the dirty, smoky, or misty environments however; the smallest detected part is 1mm.
In addition to the fork sensor shown above there is an angle sensor that is based on the same technology. This housing style is perfect for gripper applications where you need to ensure the object is in position however, you only have access to two sides. The leg lengths on these sensors vary from 40mm to 110mm.
The next time your application calls for a through-beam sensor, instead of using a fiber optic or two tubular housings try one of the fork or angle sensors, I think you will be impressed by their features and ease of use.