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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.
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
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.
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.
More Informations:
Yes, for example, with an intelligent radio data transmission system such as DATAEAGLE, stable wireless communication between machines is possible. Schildknecht AG is a pioneer in the field of radio data links and has many years of experience with radio systems. The patented DATAEAGLE technology enables stable data transmission from PROFIBUS and also PROFIsafe.
No. The DATAEAGLE radio data transmission systems from Schildknecht do not have to be integrated into the control system via a device description file (e.g. GSDML for PROFINET or GSD for PROFIBUS). They act like a cable substitute and are transparent in communication. However, the devices can optionally be integrated into the PLC to activate the integrated diagnostics of the radio data systems. The diagnostic data provides information about radio interruptions or connection setups in the event of interruptions, allowing problems in the system such as defective cables or antennas to be detected.
Replacing cables with radio data transmission – without changes to the machine
Important for easy replacement of the solution for data transmission: If possible, nothing should have to be changed in the general setup of the machine or system. Often, the timing settings of PROFIBUS or PROFINET have proven themselves, fulfill important safety requirements, or require new approvals from TÜV and the like when they are adapted. This must be prevented. Wireless solutions often work with update times in the range of 16-32 milliseconds, while an update time of 1-2 milliseconds is common for PROFINET. Replacing it with such a solution would require intervention in the machine control system and thus possibly extensive testing and acceptance.
Wireless solutions from Schildknecht can be replaced 1:1 with existing cable or slip ring systems – without any changes to the machine. The replacement can be carried out quickly and easily by a company electrician, and extensive adjustments or re-certifications are not required.
With DATAEAGLE, no integration of data transmission into the hardware configuration is necessary. The device description files GSD (PROFIBUS) or GSDML (PROFINET) do not have to be changed and the “cable” configuration can be retained.
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