Safety master

A safety master configured to communicate with a plurality of safety slaves over a safety field network or with a plurality of safety local I/O units connected by a safety back plane bus of the safety master, wherein each of the plurality of safety slaves and safety local I/O units allow connection to safety I/O devices in a plurality of cell equipment, and wherein the safety master receives a status signal indicating a “safe state” or an “unsafe state” related to cell equipment from each of the corresponding plurality of safety slaves or safety local I/O units, and controls operation/stop of cell equipment by executing an interlock operation program with the received status signal as an input to output an operation instruction signal, and transmitting the operation instruction signal to the safety slaves or safety local I/O units to realize a safety control related to each of the plurality of cell equipment and the entire series of cell equipment;

• the safety master comprising:
• an invalidation request generation unit for generating a status signal invalidation request including designation of any one of the cell equipment;
• and
• a status signal invalidation unit, arranged for each status signal of the plurality of cell equipment that becomes the input of the interlock operation program, for invalidating the status signal related to the cell equipment designated by the invalidation request when the status signal invalidation request is generated.