Abstract: A safety controller with redundant controllers, each executing safety tasks and comparing their results, provides an improved interface in which a user interacts with a single processor and the second processor is invisible. The interacting processor provides for the transmission of programs and variables to both processors when they are safety tasks and coordinates synchronization of the two programs and comparison of their operation all without additional user input.

Abstract: Re-certification of a control program loaded in a safety controller is avoided through the use of a digital snapshot and digital signature, the snapshot providing a rapidly loadable memory image file and the signature providing a confirmation that the file loaded matches a previously certified copy so as to avoid the need for time consuming re-certification.

Abstract: A safety controller provides for reliable mixed execution of standard and safety control programs held in a common memory by providing a hardware lock that is locked at times when the safety program is not executing to minimize potential corruption of the safety program by the standard program.