Detecting Dark Objects

Excess gain is an important metric for any application, but it is especially important when detecting dark objects. Excess gain is a measure of the minumum light energy needed for reliable sensor operation. A high excess gain helps the sensor overcome a weaker signal reflected by a dark object.  

The amount of excess gain you need, over and above what you might need for a "typical" target, will depend on how dark your target is as well as the environment of your application.  Pristine environments with little dust will require less excess gain than a dirty environment with debris that can cloud the sensor lens and further reduce signal strength. 

Fortunately, determining the amount of gain you need doesn't have to be a manual process. Smart sensors can recognize if very little light is returning to the receiver and automatically adjust exposure settings for additional gain and a stronger signal.

Some targets are designed specifically to absorb red light. For example, solar wafers are designed to absorb as much sunlight as possible and are covered in anti-reflective coating. This makes solar wafers very difficult for traditional photoelectric sensors to detect. 

In these applications, a photoelectric sensor with a blue LED light can be a cost-effective solution. Blue light is not absorbed by dark objects to the same extent as red light. Since more light is remitted back to the sensor, a sensor with blue light will be able to detect extremely dark objects with greater reliability.