Dear All,

Am facing issue communication issue in a small profibus network. Maximum 16 nodes- all are 3rd party devices. 1.5Mb/S is the network speed. Maximum length of the network is 30-40m. Application is paint booth. 

System was working for last 6 years. Last 1 month facing communication issue.

Installation seems to be ok. cables are routed not with power cable. Shield is connected to connectors properly. Terminations are kept on for last nodes. After this communication issues, replaced cable and connectors. The 1 meter rule is violated for 12 nodes. But all are inside the panel, no drives are in network.

The problem coming for nodes 41 to 78.

Checked the network with Profitrace, found differential stable voltage for CPU, NODE6 are below threshold. But voltage on either side of CPU is @ higher level. Is it really possible ?

How can i troubleshoot the problem.. Attaching the profitrace report, any suggestions are welcome ..

Hello vipz

I would also say the Voltage level at nodes 6-10 are to low. there could also be up and downs in the Levels (peaks) so that the PROFIBUS cannot work stable.

-> I would use a Profibus repeater to stabilise your Levels

What if you unplug the Nodes 6-10 and do the Test again. how are the Levels now? Usually every node decreases the Level a little bit.

Bye Murof 

Dear Murof,

 thank you for the reply.

Yes, adding repeater we can try, But as you seen this is very small network with less speed. So without repeater also it should work. 

One of my colleague suggested to concentrate between node 42&41. there is a voltage drop more than 1v and it is very nearby node.

Any other suggestions?

Hi,

Customer had implemented seperate earth for the devices and problem not repeated for last 2 days..

Hello vipz

Thank you for your reply.

We also had a project in the future and we had problems with other high Voltage Cables nearby the PROFIBUS cables. Here we had also a small network but a repeater helped.

Bye Murof

I had also faced same issue at our plant where random failure was occured . It was as any time any day random node was failing. Following steps were taken ,

1.At 'Bus Parameter' ,Increasing of retry limit to max and calculate by selecting Network setting to 'User Defined' and then Download it.

2. Decrease the Transmission rate to one step further or below as per you process requirement. 

In our case we had decreased from 1.5Mbps to 500Kbps ,as our process wouldn't require fast action process ..

It helped a lot.