Availability, Reliability or Redundancy ... Relieving the Confusion

Abstract Reliability and redundancy are two terms vised frequently in discussions concerning the ability of an industrial process control system to withstand module or system failure. The interchangeable nature with which these terms are used often clouds the real issue of availability and creates an environment where expensive decisions are made, in error, based on technical data of questionable validity. This article will differentiate availability from reliability and redundancy, emphasize the importance of the failure definition, and outline a methodology for industrial process control system failure evaluation.