“Safety automata” — A new specification language for the development of PLC safety applications

This contribution defines for the first time “safety automata”, a specification language for safety control functions. This fills an important gap in the method tool box of the automation engineer. The definition has a profound potential to broaden the use of automata and their well-known advantages in industrial applications. The advantages and application of safety automata are explained by example via the function block SF_Equivalent of the PLCopen specification. Stepwise, the authors illustrate the specification of this function block by means of safety automata, the transformation rules to implement the automata in fully functional PLC code, and finally the generation of test cases that allow checking both the automata and the PLC code.