A pilot light on a relay or other industrial control module provides human readable information with low frequency modulation and machine readable information at high frequency modulation unintelligible to the human eye. The use of the pilot light eliminates the need for a separate and space consuming...http://www.google.fr/patents/US5308965?utm_source=gb-gplus-shareBrevet US5308965 - Pilot light interface for small industrial controls
Pilot light interface for small industrial controls
