The PROFIsafe protocol is suitable for both PROFIBUS and PROFINET networks without impacts on these existing fieldbus standards. It is possible to transmit safety messages on the existing standard bus cables in coexistence with the standard messages. Conventional and F-instrumentation can be operated on one single bus cable including the use of standard PLCs with integrated but logically separated safety processing.
Fig. 1: The single-channel approach
The PROFIsafe protocol has not any impact on the standard bus protocols. It is as independent as possible from the base transmission channels be it copper wires, fiber optics, wireless, or backplanes. Neither the transmission rates nor the error detection mechanisms play a role. For PROFIsafe they are just "Black Channels" (Figure 2). Thus, the PROFIsafe protocol overtakes, for the users, the safety assessment of their individual backplane communication and also transmission paths beyond the PROFINET and PROFIBUS networks. It secures the whole path from the location where a safety signal originates to the location where it is processed and vice versa.
The PROFIsafe protocol can be used for safety applications up to SIL3 according to
IEC 61508 / IEC 62061, or Category 4 according to EN 954-1, or PL "e" according to
ISO 13849-1.
Fig. 2: The "Black Channel" approach
It is the task of safety communication between two partners to deliver correct data to the right destination just-in-time. Various transmission errors may occur when messages are transferred in complex network topologies, whether due to hardware failures, extraordinary electromagnetic interference, or other influences.
Out of the numerous remedies known from literature, PROFIsafe concentrates on those presented in the matrix shown in Figure 3.
Fig. 3: Transmission error types and safety remedies
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