Design standards and their application to the digital retrofit ofexisting analog safety-critical systems

摘要

The functional requirements for an analog safety-critical systemare typically similar to those found in its replacement digital system.However, the overall system specifications, especially those regardingmaintenance and testability, must drastically change to accommodate thenew digital technology. Attempting to re-create a digital version of thecurrent analog safety system without making significant modifications isnot a reasonable goal. Such a reverse engineering process only serves toincrease the number of system failure modes by adding digital failuremodes to the existing system. In addition, a reverse engineering processfails to take advantage of the true capabilities of digital technology.A safe and effective digital retrofit can be accomplished by ensuringthe modification design process includes complete execution of alldesign steps beginning with the requirements phase