Photoelectric sensing advances

摘要

In the last couple of decades the technological aspects of photoelectric sensors have advanced dramatically. While the fundamentals remain the same - light is transmitted, then either received directly by a receiver or returned by a reflector if not blocked by an object; alternatively the object reflects the transmitted light back to the device - the developments within the sensors to make these principles more reliable go unseen. Only the results are important. It didn't take long, for example, for users of retroreflective types to discover that a shiny object could mimic the reflector and fool the sensor into thinking it wasn't there. Polarising the light cured this, but you do not see the difference.