Glossary · Automation fundamentals, platforms and components
Black channel
Also known as: Black channel principle
German: Black Channel
In functional safety communication, the black channel principle means that safety data is transmitted over a standard communication system whose reliability is not relied upon. The safety layers at both ends detect transmission errors such as corruption, loss, delay, repetition and wrong addressing.
- Automation components
- Functional safety
- Standards
In one sentence
In safety communication, a black channel is a standard network not trusted for safety; the safety layers at both ends detect all transmission errors.
Example
PROFIsafe frames travel over the same PROFINET network as standard data; the safety PLC detects a missing or delayed frame via the watchdog and brings the drive to a safe state.
How it applies
- Engineering: Safety protocols such as PROFIsafe, CIP Safety, FSoE and openSAFETY use the black channel approach. Measures include sequence numbers, CRCs, watchdog timeouts and connection identifiers, as specified in IEC 61784-3 functional safety communication profiles.
- Commissioning: Safety addresses, watchdog times and parameters must be set and verified; the watchdog time affects the reaction time of the Safety function.
- Documentation: State the safety protocol, relevant parameters and their effect on response time. Do not describe the network itself as "safe" — the safety comes from the safety layer, the devices and the overall design and validation.
Black channel vs. white channel
In a white channel approach, the communication hardware and software themselves would have to be developed and assessed to safety standards. The black channel approach avoids this by treating the standard network as untrusted, which allows ordinary switches and cables. Network availability still matters: frequent communication errors cause nuisance stops.