Skip to Content

Register Login

Industry Online Support

Technical Forum

Navigation

Profibus fault tolerance

Created by: GeekFSL at: 2/24/2009 9:56 PM (3 Replies)

Rating (0)

Thanks 1

4 Entries

2/24/2009 9:56 PM	Rate (0)
GeekFSL Posts: 3 Rating: (0)	Thanks for reading this... I amfairly new to siemens PLCs and have a question regarding the fault tolerance of Profibus connections. My application is a fairly simple comms processing system where I use two 317-2DP processors to bridgetwo separateIElinks between my two 317processors and a different network segment from another control system (interfacing via UDP to two319s). On the other side, we havea redundant pair of PC servers running our proprietary Server and HMI software on Simatic PCs. The network is interfaced using a pair of CP 343-Lean modules in each 317 rack. this system is working fine using AG_SEND / AG_RECEIVE functions and the usual application layer error-checking required when using UDP. Where we have a concern is that on each of the two 317 PLCs we have two remote IO drops to ET200M (IM153-1) over Profibus (four ET200Ms in total - two on each of two separate Profibus segments). The core processing functionality of the PLC (i.e. the UDP comms) is mission-critical and we do not want this to be stopped in the event of an error on either of the remote IO units. We have therefore included the OB86 block to process any failures on the remote IO without stopping the main PLC. This works fine, witht the PLC continuing to work even if one of the remote ET200s is disconnected. When this is done, the other (connected) ET200 still responds to the main PLC despite the errors being generated by the 'missing' IO rack. It is a different story however if one of the remote IO racks is powered-down. In this case, the absence of power to the ET200 causes it to 'pull down' the Profibus segment, preventing comms between the CPU and theoperational remote IO drop. This effectively renders all remote IO faulty for something as simple as a power-down of one of the remote units. Here's the questions: 1. Can I split the Profibus into twoseparate physical networks by using both 9-pin connectors on the 317-2DB front panel (of course sacrificing the MPI connection) - and would this provide better fault tolerance? If so - how is the Profibus on X1 connector 'enabled'? 2. If this can't be done, am I doing something stupid with the Profibus wiring? I have a double connector at the PLC heading off to the two remote units? Any comments / suggestions gratefully received! thanks, GeekFSL
GeekFSL Posts: 3 Rating: (0)
Suggestion To thank Quote Answer

2/25/2009 1:25 PM	Rate (0)
Mario Braganca Posts: 124 Rating: (17)	Hello GeekFSL First you could analyse the CPU Diagnostic Buffer to see if another Error OB was called. Maybe this OB was not found and then the CPU stops. It would be good to know if there are anything uncommon in your Profibus Network like if it is very long, adequate baude rate, grounding problems, noise, etc. You could verify this also. There are other three possibilities to solve this problem: 1. Repeater Enables you to isolate the Network in two segments and reforces the signal (for long distances). https://mall.automation.siemens.com/WW/guest/index.asp?aktprim=0&nodeID=10008350&lang=en&foldersopen=-11376-1-4223-4224-4511-4518-4522-4532-4533-&jumpto=4533 2. Diagnostic Repeater The same, but shows you where is the problem (Reflexion, Termination, Broken Wire, etc) https://mall.automation.siemens.com/WW/guest/index.asp?aktprim=0&nodeID=10008351&lang=en&foldersopen=-11376-1-4223-4224-4511-4518-4522-4532-4533-4534-&jumpto=4534 3. Terminator Profibus is an active network, so it needs to be alive. This enables you to turns the ET200 off without turning off the network. https://mall.automation.siemens.com/WW/guest/index.asp?aktprim=0&nodeID=10008830&lang=en&foldersopen=-11376-1-4223-4224-4511-4518-4522-4532-&jumpto=4532 Good Luck Regards Mario Braganca
Mario Braganca Posts: 124 Rating: (17)
Suggestion To thank Quote Answer
This contribution was helpful to 1 thankful Users GeekFSL

2/25/2009 2:18 PM	Rate (0)
GeekFSL Posts: 3 Rating: (0)	Thanks for your information Mario, There is nothing unusual about the Profibus - just two ET200s and the 317. We are currently performing testing on a simulated system - and the Profibus segments are very short (less than 1m as the test kit is just on the bench). The installed application will have 2 x 30m branches to tht ET200s (approximately). Since posting the original request I have tried a couple of different cabling options, and with the PLC in the centre of the two remote units the system is better (i.e. doesn't always crash the Profibus when one of the ET200s is powered down). This may improve with the longer bus lengths - so we will simulate the installed cable lengths next. Thanks for your three suggestions - I will evaluate these also. Best, Geek
GeekFSL Posts: 3 Rating: (0)
Suggestion To thank Quote Answer

2/25/2009 3:25 PM	Rate (0)
Mario Braganca Posts: 124 Rating: (17)	Hello Even with the CPU in the centre, the problem will probably repeat because you should not turn off the extreme point of the Profibus Network. Profibus needs an active Termination.Soif you need to turn off the ET200you should use the Active Terminator and it must be always on. Regards Mario P.S.: Profibus is very reliable. Your network is small.But be carefull to use Profibuscables and connectors.I have seen many customers with problems caused by low quality or self-made products.
Mario Braganca Posts: 124 Rating: (17)
Suggestion To thank Quote Answer

|

Share this page:

Share this page on...

Follow us on