Loss of IAC between 2 applications within the same controller during download

We have experienced possible IAC loss between 2 applications within the same controller which leads PM865 triggerd plant shutdown during downloading. We are investigating both system and application side but it will be very difficult to re-produce the issue if this is caused by the timing issue. Manual indicates there is no timeout for IAC loss if within the same controller, therfore we suspect loss caused the plant trip with SIS application.

Is it possible to loss an IAC between 2 applications in the same controller?

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asked 5 days ago



IAC runs on MMS - so under the hood, IAC is still an "MMS" message.

When you warm start an application, MMS will stop briefly. It does not matter if the applications are in the same or different controllers. This is known behaviour and is working as expected.

You need to modify your application logic to ignore momentary losses in comms and determine an appropriate period to ignore.

Rob Lyon   

answered 5 days ago


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IAC does not use MMS.

- MMS is a standardised protocol (ISO/IEC 9056-2) running on TCP port 102

- IAC is proprietary to ABB and run on UDP port 2757

Due to the nature of UDP messaging (less protocol overhead) and the binary telegram format of IAC (in contrast to asking for Access Variables identified via ASCII text strings) the latter (IAC) is more lightweight and it is estimated to be able to carry up to 5x more information, or be up to 5x more efficient than using MMS.

During warm download, changed applications will be temporarily stopped while being replaced with the new version. The larger application, the more variable content and state information needs to be copied from old to new version before the new can start executing. This time is measured as "Stop Time". It can stretch from a few millieseconds to much more and cause malfunction in time critical applications.

There are also a few known problems with IAC that could potentially lead to a shutdown. Please find more information in the release notes, e.g. 3BSE089043.

If you need more help, I suggest that you open a support case with your regional ABB support center and ask for assistance with troubleshooting the shutdown.

Stefan Stromqvist   

answered 4 days ago


By LM on 4/17/2018 | Like (0) | Report

Thanks for your response.

As per current logic SAFETY data type is passed (through IAC) from one SIL2 application to another SIL2 applications. SAFTY data types are connected to an AND_SAFETY_Type and then to as final element. In this configuration if SAFETY.Forward.Connect in SAFETY data type becomes false for a second, will trigger the Trip_Order = TRUE. How we can overcome this issue? We have multiple cases like this in our plant.

By Stefan Stromqvist on 4/17/2018 | Like (0) | Report

Sorry, I'm not dressed to give an answer here.

By Rob Lyon on 4/17/2018 | Like (0) | Report

Thankyou. I learned something new :)

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