The Black Channel Principle
Safety Field Networks
Safety-oriented field buses simplify placement of components within a plant or machine. In most cases, two cables, one for power and one for communication, are all that is required. Sensors can be attached
directly to the safety network. They do not require separate cables for the return of diagnostic signals. This results in a reduction of required hardware components.
Using the Black Channel Principle, safety-relevant data as well as diagnostic information is exchanged via the existing network connections. This enables faster responses. Sensors receive their parameter setting and configuration via the network. This allows the
download of optimized parameter settings to the sensors in case of changes to the mode of operation and also eliminates the need to adjust parameters at the device itself in case of component replacement after failure. All this adds to a maximized productivity and reduced down time.
Safety Data Transport via Standard Bus or Network Lines
The Black Channel Principle allows transmission of failsafe and standard data via the same network or bus line. Independent of the regular data transport mechanism used on that line, safety components can transmit data using an isolated safe protocol tunneling the underlying network channel. As safe fieldbuses are pure application protocols without physical characteristics of their own, available bandwidth and cycle times depend on the data transport protocol used. Possible transmission errors are known and listed in the relevant standards IEC 61784-3 and IEC 61508. Their prevention needs to be implemented as a crucial part of the safety data transmission protocols. The required quality of transmission error detection depends on the safety level that needs to be achieved.