ion-based failure diagnosis for discrete event systems Klaus Schmidt∗ Chair of Automatic Control, University of Erlangen-Nuremberg, Cauerstrasse 7, 91058 Erlangen, Germany a r t i c l e i n f o Article history: Received 11 May 2009 Received in revised form 8 September 2009 Accepted 7 November 2009 Available online 22 November 2009