What does Black Channel mean?
The black channel principle allows the transmission of safe and non-safe process data over the same network or bus line. Regardless of the regular data transport mechanism used on this line, safety components can transmit data using an isolated safe protocol that tunnels through the underlying network channel. Since safe fieldbuses are pure application protocols without their own physical properties, the available bandwidths and cycle times depend on the data transport protocol used. Possible transmission errors are known and are listed in the relevant standards IEC 61784-3 and IEC 61508.
Black Channel explained in detail!
What does this mean for PROFIsafe?
The PROFIsafe protocol has no repercussions on the standard bus protocols. It is intended to be as independent as possible of the respective transmission channel, whether copper cable, fiber optic cable, backplane bus, or wireless. Neither the transmission rates nor the respective error detection plays a role. For PROFIsafe, the transmission channels are merely “black channels”.
Wireless PROFIsafe – Black Channel Principle
PROFIsafe – same protocol for radio and cable
Whether for a crane control system, the emergency stop transmission of a production machine, or other safety-relevant communication: PROFIsafe has been established as a standard for functionally safe communication and has been an international standard since 2007 under the designation IEC 61784-3-3. The safety-related protocol is used to transmit data between a safety controller (F-PLC or F-Host) and field devices (F-Devices). While the controller and device are usually safety-related components and must be certified accordingly, PROFIsafe, according to the system description, has no effect on the standard bus protocols used: whether with Industrial Ethernet (PROFINET IO), via RS485 (PROFIBUS-DP), via backplanes or wireless – the method used for data transmission has no influence on the safety rating. The transmission channels are merely so-called “black channels”, of which the actual PROFIsafe application is completely independent. Accordingly, the PROFIsafe system description also states: Wireless transmission is permissible as long as sufficient availability (no false alarms) and IT security are guaranteed.
Secure data transmission by radio: the black channel principle in detail
This means that the use of wireless technologies is also provided for and possible by definition, just like other radio technologies. Both the safety controller and the remote IO system – for example a safety switch – contain the safety protocol. The interface between them is merely the channel for transmitting the safety information. Accordingly, no safety certification is required for the wireless device and it is treated like other infrastructure components, such as switches or cables. This makes the recalculation or verification of the safety level (SISTEMA) for using a black channel solution obsolete.
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