Unused Profibus node in a network

Hi Everybody,

I am fairly new to profibus(siemens plc's).
In a cell I am working on, depending on the type of part being run some time a profibus node is not being used ie the field device connecting the sensors will not be there. Profibus cable to this device will be have to remain open. Could any bodu give me some info on how to go about this. What are my options. Has anybody used trunk and drop cable connecting the nodes in profibus network like devicenet.

Thanks,

kiran said:

Hi Everybody,

I am fairly new to profibus(siemens plc's).
In a cell I am working on, depending on the type of part being run some time a profibus node is not being used ie the field device connecting the sensors will not be there. Profibus cable to this device will be have to remain open. Could any bodu give me some info on how to go about this. What are my options. Has anybody used trunk and drop cable connecting the nodes in profibus network like devicenet.

Thanks,

Click to expand...

I think one of my colleages once had a profibus problem because a couple of ET200 modules were not powered, the whole network went down. May it is better not to connect the profibus connector to an unpowered profibus station.

It is only a problem if is the last station in the daisy-chain. That will probably cut the network if it is running at 1.5M, and for sure if it is running at 12M. At 187.5k you can get away with it.

If the last station can be shutdown, consider to end the daisy-chain in an active terminator, rather than a slave station.

kiran said:

Hi Everybody,

I am fairly new to profibus(siemens plc's).
In a cell I am working on, depending on the type of part being run some time a profibus node is not being used ie the field device connecting the sensors will not be there. Profibus cable to this device will be have to remain open. Could any bodu give me some info on how to go about this. What are my options. Has anybody used trunk and drop cable connecting the nodes in profibus network like devicenet.

Thanks,

Click to expand...

I like using a Siemens Repeater for this and then I put in SFC12. This system function is for activating and deactivating slaves.

In a cell I am working on, depending on the type of part being run some time a profibus node is not being used ie the field device connecting the sensors will not be there.

Click to expand...

Where is this device located in your network? At the start or end, or somewhere in between? Is it on a trunk line or in the daisy chain?

Profibus cable to this device will be have to remain open.

Click to expand...

What do you mean with "open"? Is it still attached to an connector or is the cable loose (bare copper wires).

Has anybody used trunk and drop cable connecting the nodes in profibus network like devicenet.

Click to expand...

This is not recommended by the PROFIBUS rules and it has serious restrictions in length when you use this. I believe it is a max of 6.6m total trunk length on 1.5mbits. Do not use it at speeds above 1.5 mbits. I would use repeaters or PROFIBUS hubs instead of using trunk lines.

There are lots of profibus info here:

http://www.profibus.com/nc/downloads/downloads/profibus-installation-guideline/display/

K

Jobbe said:

Where is this device located in your network? At the start or end, or somewhere in between? Is it on a trunk line or in the daisy chain?

What do you mean with "open"? Is it still attached to an connector or is the cable loose (bare copper wires).
This is not recommended by the PROFIBUS rules and it has serious restrictions in length when you use this. I believe it is a max of 6.6m total trunk length on 1.5mbits. Do not use it at speeds above 1.5 mbits. I would use repeaters or PROFIBUS hubs instead of using trunk lines.

Click to expand...

Thank you for the reply.

Quote:
Where is this device located in your network? At the start or end, or somewhere in between? Is it on a trunk line or in the daisy chain?

I plan to have this node at the end of the network.

Quote:
What do you mean with "open"? Is it still attached to an connector or is the cable loose (bare copper wires).

I mean the connector will have a terminating plug at the end. And the PLC will have one node less on the profibus network.

How do I work around this.

Is there any other way other than using a repeater. Such as handling this in PLC to ingnore this node?

Thanks,

The problem isn't necessarily that the node will not be there, it's that its the last node on the segment and it won't be there. The termination in the connector acually receives power form the node, so when you remove the connector the end of the network is not terminated properly any more.

If you can somehow make this the second to last node in the network, when you unplug it, it is not the last node, so the termination on the last node will still be present and active. The connector that you removed from the station would have two cables, one coming in and one going out, and could just be left to dangle.

You will then have a problem with the master not seeing the node but you can use OB82/OB86 to keep it from going into stop mode when that happens.

Consider using it as not last in chain, but something between the first and last. Or use active terminator. Then you can use it as last and termination will be after the node and is not changed on node removal.

Then consider using "button" either physical button connected trough some ditributed i/o or some else way, or trough hmi. Use it to disable/enable node before it is removed, after it is inserted. Siemens plc has sfc for enable/disable node.

JRW said:

I like using a Siemens Repeater for this and then I put in SFC12. This system function is for activating and deactivating slaves.

Click to expand...

I finally had a panel completed and was able to test the PNIODiag v1.7 from Siemens today. It worked great, much beyond my expectations. It internalizes the function you mentioned and I had great success with it. I could turn off (deactivate) a drive and the drive would fault with F070 for lost profibus comms but the PLC never had a red SF light. Then I'd activate it and it would go right back to working on both ends.

To the OP (original poster): I think JRW is right on the money here. Use a repeater (or some other active terminator) as the last node and then use the system function in your program to activate or deactivate the profibus node. It's a two step solution - you need the end of the bus terminated and you need the PLC to ignore the lost node.