What's behind the target can make a tremendous difference in how well reflective sensors do their job.
Dealing with darkness
A packaging application needed a sensor able to not only detect all shades of black without error but also to work over an extended sensing range of at least 4 ft. Thus proximity sensors had to reliably detect flat black and glossy black materials. But a common problem with photoelectric sensors is that dark colors absorb more light than they reflect, which potentially shortens the sensing range.
A Pepperl+Fuchs' Series 28 photoelectric sensor with background suppression and an infrared light source handled the application. The background-suppression sensor is a diffused mode photoelectric that uses separate sensing elements to detect objects close together without detecting the background material. Its sensing range for black is just 5% less than its range for white targets, and it can operate at a variable distance. Developers installed the sensor on the yellow carriage of the top-loading machine. In operation it senses the contours of the package to let the machine automatically wrap any size package. Highly visible LEDs give operators a visual status indication from as far away as 50 ft.
Edited by Leland Teschler