Why is there no safe communication protocol (SIL 2/3) for Modbus?


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There is ProfiSAFE for Profinet/bus, Failsafe over Ethercat (FSoE), Opensafety for Powerlink, but nothing tangible in the way of Modbus, although opensafety claims this could work.

I've read somewhere on this forum that Modbus is not suitable for safety application. Any source (books, research etc) on this?

More importantly, are there any workarounds to make modbus capable of SIL 2/3?

>More importantly, are there any workarounds to make modbus
>capable of SIL 2/3?

I could be wrong, it was many years ago working with SIL levels. At the time, IIRC, if the MODBUS communication cable was in the same cabinet you could achieve X SIL level and if the cable had to route between cabinets the cable had to be in conduit, not cable tray, to achieve X SIL level.

But, it could have changed over the years and not possible in 2018.

And it might only apply to complete systems that are tested/certified not out of the box solutions.

Good luck,

The Profisafe, CIPsafe, PowerlinkSafety, etc. are an additional layer on top of existing protocols. They implement the requirements for a safety network protocol. They claim to be all underlying network independent, but of course nobody is going to replace its own protocol for that of the competitor. Theoretically you could (say) port the PowerlinkSafety on top of Modbus. The sourcecode is public. But you may not modify it, otherwise the certification is lost. So, you will have to do some changes, and then the implementation must be certified before it can be used. Don't know if Modbus is fast enough to properly support safety. After all, you don't want to wait too long if something goes wrong.

There is a book written about safety protocol requirements, but... how's your German?