How to implementing PROFIsafe
As a general rule, it is not possible to turn a standard device into a safety device (F-device) just by implementing the PROFIsafe protocol: The final SIL of the device is defined by the architecture of the safety technology of the device together with the protocol and the manner in which both are implemented.
Even though PROFIsafe is suitable for safety functions up to SIL3, it may not be necessary to design and develop the F-Device also for SIL3.
Because of the “Black-Channel” principle, the PROFIsafe layer (located above the standard protocol) has no impact on the standard bus protocols and is independent from the base transmission channels. This makes implementation of the PROFIsafe driver software in devices and hosts quite easy. The following choices exist:
- Development of the software according to the specification or
- Use of a PROFIsafe starter kit available on the market from different technology providers. The advantage of a starter kit is obvious: pre-certified PROFIsafe driver software, additional valuable information and tools, and technical support.
- For interfacing PROFIsafe technology any of the available ASICs and layer stacks are suitable; the PROFIsafe driver software must only be adapted to the specific device needs.
Versioning of PROFIsafe
The most recent Information’s of the available PROFIsafe Version can be found in the FAQ PROFIsafe Document.
According to IEC 61800-5-2 some safety features (stopping and monitoring functions) are defined for drives with integrated safety (F-drives). Parts of these functions are specified in an amendment to the PROFIdrive specification.
Field devices for process automation
F-Devices for process automation follow the sector standard IEC 61511, which also takes into account the particular aspect of "proven-in-use". The PI Working Group "PA Devices" has specified, within a separate amendment to the “PA Device” specification, how to use the PROFIsafe platform for PA devices.
F-Host implementation solutions
Depending on the strategy of system manufacturers, different kinds of architectures for F-Hosts with PROFIsafe communication are possible: stand-alone F-CPUs or integrated but logically separated safety processing within standard CPUs. Safety processing can be realized in different ways: via hardware redundancy and discrepancy checking or via "software redundancy" or via "safeguarding" or by using already existing diverse hardware platforms.
Conformity & Certification
Several products of different types from various vendors communicate within a PROFIsafe island. The products must be implemented conform to the PROFIsafe specification to ensure that this communication works correctly. Usually the conformance is documented through a certificate from the PI certification office based on the test report of one of the PI test laboratories.
The PROFIsafe tests
The PROFIsafe protocol mechanisms are based on finite state machines. Thus it was possible via a validation tool for finite state machines to mathematically prove that PROFIsafe works correctly even in cases where more than two independent errors or failures may occur. This systematically was achieved by generating all possible cases for "test-to-pass" and "test-to-fail" situations. They have been extracted as test cases for a fully automated PROFIsafe layer tester, which is used to check the PROFIsafe conformance of F-Devices and F-Hosts. It is part of a three-step-procedure within the overall safety certification process according IEC 61508 by notified bodies.
Figure 1, Test and Certification Procedures
It is important to note that the PI test laboratories perform the approved PROFIsafe layer tests on behalf of notified bodies such as
- TÜV (worldwide)
- INRS (France)
- INERIS (France)
- IFA (Germany)/(Sweden)
- SUVA (Switzerland)
- HSE (United Kingdom), UL (USA)
The mandatory safety manual of each and every F-Device (acc. IEC 61508) shall provide information about the safety characteristic values such as SIL (Safety Integrity Level) or PL (Performance Level).
PROFIsafe provides a specification for test & certification. Various international PI test laboratories are accredited for the PROFIsafe testing.
Security Aspects of PROFIsafe
Just as PROFINET is PROFIsafe well suitable to be used within secure networks without impacting the required safety level in general (acc. to IEC 62443). However availability and reliability aspects have to be considered. From a plain PROFIsafe perspective even so a clear separation in the responsibilities of the network hierarchies and structure are to be maintained.