DeviceNet Fault - Safety IO

Hey Guys,

I am in the middle of commissioning a safety installation and I am having some rudimentary problems with the safety IO modules and network stability.

We are using a 1756-L62S. The devicenet network consists of 8 nodes (mix of 1791DS-IB12 and 1791DS-IB4XOW4), 5 in one enclosure, three in the other. The enclosures are about 60 meters apart. The problem that I am having is that I can have 7 nodes on the network, but as soon as I plug in the 8th, the network faults.

I can have ANY 7 of the modules alive and happy on the network, but the network will fall over as soon as the last one comes online and attempts to communicate.

Tomorrow morning I am going to go through the basics - check network wiring, grounding, powersupply, termination resistors, that sort of thing to see if I can see anything obvious.

I was wondering if anyone else has seen anything like this and to make sure I am on the right path.

Thanks in advance!!

And then it occurred to me that I must also check my RPI and baud rate settings.. if they are set to default, the network will time out and fault.

What is the baud rate of your DNet?
I had a similar thing a few years ago and I had to increase the baud rate to 500.
I could only connect to about 5 or 6 devices at 125, about 11 devices at 250 and all 14 at 500.
I also found out later that I could reduce the data (some status data that we were not using) from each node and that would have allowed me to see more nodes at the low network speeds.

Alan

Couldn't sleep, so I ended up coming in overnight when the line was down so that I could crash the network as much as I wanted to.

I was not satisfied with the cabling of the network. They had multiple earths on the drain, the power supply DC common was not earthed, the shield was not earthed, but all of that was not the problem.

I did read some literature that pointed towards RPI and baudrate, and after your message that is where I started.

The baud rate was originally 125. I ended up changing it to 250 and the network stayed healthy. 250kbps will be just on the maximum length of the network when it is all finished, so I will see how I go.

Thanks for your reply and many cheers.

Also, check the length of time in the Devicenet configuration that is allocated to the safety scan. When I experienced the same problem as you, I found that the default was much too short.