NUT and RPI

Was losing communications of random I/O modules in a specific rack I came upon a slew of Alignment errors and FCS errors which the helpful guys on this forum pointed me in the direction of Ethernet cables or fiber. I replaced all these things and could not get the comm issue to go away.



I started working taking a look at the RPI settings which were all 100ms. I dropped those on every card down to 20ms just to see if this had an effect and It did completely eliminate the comm losses, however I have tried to get an understanding of what NUT is, how do I find out what we are running and then how do you go about determining the recommended RPI for modules. Can someone explain this or point me to some literature. I am concerned that I may have this too low which could cause other issues.

The Network Update Time (NUT) is specific to the scheduling algorithm of ControlNet. It has no role in how EtherNet/IP systems work.

In my opinion, the improvement of your I/O reliability is a coincidence. A happy coincidence, but a coincidence nonetheless.

Decreasing the RPI values just data on the network more frequently. It does not change the timeout multiplier and in general puts more load on the network modules and the network switches.

An excellent publication that discusses RPIs and network module loading is the EtherNet/IP Network Design Considerations reference manual, RA Publication number ENET-RM002.

There's also a good document on the RA Knowledgebase called the "EtherNet/IP Book of Knowledge".

Thanks Ken, I will see what I can figure out on this.