| CPC G05B 19/406 (2013.01) [H04L 41/046 (2013.01); G05B 2219/50193 (2013.01)] | 18 Claims |

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1. A guard apparatus for monitoring operability of an input module and an output module of a control device having a modular structure, the guard apparatus comprising:
a bus module part configured to receive state information from at least one of the input module and the output module;
a logic module part configured to evaluate the state information from the input module and the output module; and
an output module part configured to confirm an output signal of the output module based on the evaluation,
wherein:
the input module and the output module form a first potential group within the modular structure, and
at least the logic module part of the guard apparatus forms a second potential group independent of the first potential group within the modular structure.
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