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Reflective Sensors

Reflective scanners use the same physical principles as thrubeams except that the two components - light source and photodetector - are placed together in the same housing. Light is projected into space by the source. The target object reflects some of this light, and a portion of it enters the photodetector, causing increased current flow in the photodetector circuit. Since most of the light emitted by the light source is lost, only a small percentage is collected by the photodetector.

Reflective skanners do not have the range capabilities of thrubeams, since their light/dark contrast ratio is not as great. However, they do have advantages over thrubeams in many situations. First, they need only be located on one side of the target object - this means that only once wiring is needed and that there will be no problems aligning the two separate components. Second, reflective skanners can some times detect clear, thin films such as cellophane which cannot be detected by thrubeams. Third, reflective skanners can often distinguish targets by surface characteristics such as texture and color.