There is always debate of which sensing technology is better to use over a broad range of applications. And for the photo sensor world, BGS or background suppression is one of these. What many users don’t realize is that a background suppression photo sensor is what I will argue as a refined offshoot of the diffuse photo sensor principle, meaning the photo emitter and receiver is in a single housing and it uses the object or target as the reflective source. I say refined because it still uses a basic diffuse methodology, but has added technology that allows for a very specific response/detection zone based on the setting of the optics.
Again, the principle starts out like a diffuse sensor type in that the emitter and receiver are built together in the same housing and it uses the object’s reflectance, but the difference is that the receiver’s lens can be adjusted so that the returning light is focused specifically on the receiver’s PSD (photo sensing detector) based on the target’s location. With this method, returning light is now “triangulated” to the PSD or is outside the PSD’s sensing area. In other words, if an object falls within the zone created from the returning triangulated light path, the PSD receives a strong signal, but if the object is outside this zone, the returning light is not received on the PSD at the needed strength and therefore creates an effective “cut off” of the returning light. (An example of a BGS sensor is shown in the illustration.)
One of the biggest advantages of this methodology is that unlike a diffuse sensor, the reflectivity or color of the background vs. the object can now be isolated. For example, regardless of the background’s high reflectivity because it is outside the triangulated response path of light (in the cut-off zone) to the PSD, the PSD does not receive strong enough light returning. This eliminates dependence on color in the detectable objects. As long as the object is inside the triangulated light response zone, it can be detected. These advantages overcome the limitations or variabilities of a standard diffuse sensor which can be affected by background reflectivity or the darker color of an object.
Background suppression sensors are typically more expensive than a standard diffuse sensor, between 20% to 35% and typically have a smaller sensing range. But the degree of reliable detection is significant, especially with reflective backgrounds in applications like conveyor systems, rotating or turret systems and part detection on assemblies.
For examples of Balluff’s background suppression photo sensors click here.
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Mark Sippel
Mark Sippel is the North American Product Marketing Manager for Object ID and Photoelectric sensors with Balluff NA.
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