Method for Operating a Virtual Programmable Logic Controller

A method for operating a virtual programmable logic controller with a safety program on a first computer system, and a virtual programmable logic controller with a safety program replicated from the safety program on a second computer system, a switch over to the second computer system or the virtual programmable logic controller installed thereon with the replicated safety program occurring in an event of at least one of the first computer system and the virtual programmable logic controller running thereon dropping, the method comprising:

• operating a central signature manager in which a signature and a time stamp of the safety program are entered into a management list, a correspondingly changed signature and a changed time stamp being entered into the management list in cases of a change to the safety program on the first computer system;
• operating the central signature manager to write the signature and the time stamp in a control data area of the virtual programmable logic controller;
• generating a management list image by the central signature manager of the first computer system for the second computer system and cyclically updating the management list image by the central signature manager of the first computer system upon replication of the safety program for the second computer system to ensure that, on the second computer system, which is, on an instance of the virtual programmable logic controller of the first computer system, the existing replicated safety program corresponds to the safety program on the first computer system;
• and
• operating a checking routine on the programmable logic controller on the second computer system, which compares the signature and the time stamp from the control data area with the signature and the time stamp from the management list image;
• wherein in the event the switch over to the second computer system occurs, a start process of the instance of the virtual programmable logic controller is performed to execute the replicated safety program on the second computer system only when the signatures and time stamps match.