A safety application requiring SIL 3 can use the same Ethernet network as ordinary control traffic when the complete safety system is correctly designed and validated. PROFIsafe checks communication using a running sequence number, a CRC checksum and an F-address, together with an F-monitoring time. The simulation exposes these checks so you can introduce a communication fault and observe the F-device substitute its safe state.
This example sends safety data from the F-CPU to an F-device and illustrates the associated communication checks. The receiver checks whether the data is valid and timely. Use the controls to corrupt the CRC, delay it past the watchdog, or replay an old sequence number, then watch the receiver reject the invalid exchange and apply safe values. The diagram illustrates the checks rather than the byte layout of a real telegram.
A good exchange lets the simulation continue using the process data. A detected communication fault, such as an invalid checksum, stale sequence or monitoring timeout, makes it use safe values instead. This example holds that state until acknowledgement. Actual reintegration depends on the configured F-device and safety application.
These mechanisms address communication errors such as corruption, loss, repetition, resequencing, delay and masquerade. With the black-channel approach, PROFIsafe supplies safety communication over a standard network. Applications up to SIL 3 / PL e still require suitable safety devices, configuration and validation; the ordinary network alone does not establish that capability.
The CRC checks data integrity. Why does PROFIsafe also track the progression of consecutive safety messages?