A single module for relay, limit switch or related devices for self-powering the set of contacts and sensing the state of the contacts, compatible with Opto 22 and related I/O systems interfacing microprocessors and industrial processes and the like and with further features, if desired, of a single...http://www.google.com/patents/US5083116?utm_source=gb-gplus-sharePatent US5083116 - Contact sensing module embodying loop power supply and state sensing for relays and other contacts
