A backup method for a multiple source optical scanner which alerts an operator when one of the sources has failed. A controller monitors the operation of each source and flags the failed sources. In the case of a scanner having dual full-time channels, the controller removes power from the failed source...http://www.google.co.uk/patents/US5404002?utm_source=gb-gplus-sharePatent US5404002 - Backup method for multiple source optical scanner
