hey folks

I am fresh out of college. At work i encounter profibus problems. The thing that is hard for me is that the i am not sure which node gives the problem. We have hmi and it displays all the nodes as faulty. I understand why it shows all nodes since all are in series but how do i identify which particular node causing problem.please help

 

Dear Unsigned,

If ALL nodes are in fault then I would tend to think that something common to all the nodes is at fault. This could be the master or the cable joining the nodes together. It could be the end terminator, the plug at the master, or the master config.

A profibus network can operate if some nodes are missing. You will get partial comms with some nodes working and others not.

If nothing is working then you have nothing to lose by simplifying the system down to the minimum. Get that working and then expand out until you get to the fault.

I would start by isolating the network at the first node, so that only the master and the first node are connected. Normally the proibus plugs has an isolation switch which will disconnect the outgoing leg and terminate the network there.

(When I say 'first node' I mean follow the cable routing, not the node numbers)

If the first node is communicating, then the cable fault is further downstream. Put the first node plug back to normal and isolate at the second node. repeat until the node you have isolated at does not appear.

If the first node does not communicate, then the cabling and plugs between the master and the first node is at fault.

As you go down the cable from the master to each node, keep an eye for common faults

1. accummulated cable length too long

2. the installation of the cable (earthing, bend radius, minimum node distance, etc)

3. ensure that the cores do not get crossed over between nodes

4. duplicate node addresses

5. double termination (some devices have internal termination resistors which are unneeded unless at the cable end.)

6. water ingress at junction boxes.

I have seen all these faults crop up from time to time.

Other questions to ask: Has it ever worked? If so, what has changed. If not, then is the master configured correctly with the correct GSD files and modules selected.

Have fun, this is often a head scratcher.