For the continuous recording of processes in system operation as well as of events, a non-volatile memory is provided (cyclic buffer). The “operationally relevant” signals, each fully tagged with date and time at signal start and signal end, are entered in chronological order. The signals relevant for operation include control actions such as function disabling and enabling and triggers for testing and resetting. The start and end of system events that represent a deviation from normal operation such as overloads, ground faults or short-circuits are also recorded. The operating data memory can be cleared/reset.

The signals stored in the operating data memory are counted.