PROFIBUS bus cables. Online diagnostics via diagnostic repeater Bus cables are subjected to a lot of wear during plant operation, for example through vibration. This means that it is also important to check the PROFIBUS cables. The diagnostic repeater is available for line diagnostics during plant operation. It is integrated as RS 485 repeater in the PROFIBUS network. Diagnostics also provide the following details: Break in cable core A or B Short circuit of the signal lines on the shield Missing or excessive number of bus terminating resistors Maintenance functionality of the diagnostic repeater The diagnostic repeater identifies the topology of the bus system. When a fault occurs, the repeater, as PROFIBUS slave, automatically sends a standard diagnostic message to the master. The message contains information on the relevant bus segment the fault location (e.g. between nodes X and Y), i.e. the distance of the fault location from the repeater resp. of the nodes in meters the possible cause of the fault, e.g. short-circuit of signal line A on the shield. Even sporadic line faults, which are normally extremely difficult to find, can thus be easily detected and reported. The specified diagnostic functions also enable maintenance engineers without PROFIBUS experience to quickly and reliably localize faults in the bus cables. Thanks to the well-target and simple diagnostics, the productivity of a plant can be increased. The diagnostic repeater is visualized on the SIMATIC Maintenance Station as PROFIBUS device and represents the diagnostic status in the associated bus system. Additional detailed diagnostic information is available on the SIMATIC Maintenance Station through the engineering system, which requires that STEP 7 be installed on the Maintenance Station.