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Bad MPI connection?

Created by: thuynguyet at: 3/4/2007 4:35 AM (7 Replies)

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3/4/2007 4:35 AM	Rate (0)
thuynguyet Posts: 18 Rating: (0)	I have simple application: a SCADA with WinCC 6.0 to S7 314C-2DP through MPI connection (CP 5611 on Windows XP Pro). Problem is that sometimes (most often!?) the WinCC is disconnected (no communication error) and then reconnected after a few minutes. The distance is only about 50m. The cause would be on the MPI cable or probably on PC? or on PLC? Pls be so kind and give me some advises to find and correct the fault?
thuynguyet Posts: 18 Rating: (0)
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3/4/2007 4:55 PM	Rate (0)
Late Platinum Member Joined: 1/7/2006 Last visit: 5/11/2025 Posts: 2705 Rating: (321)	Hi, A MPI cable could be 50 meter, so you are on the edge. If there is a difference between the PLC and the PC higher then 5 Volt, nothing is garantied. Measure if the difference is lower then 5V by taking of the MPI-cable on 1 side and measure on the iron of the connector to the earth. When there is a difference please place a repeater or do something with a parrallel cable to get rid of the difference.
	I hope that the answer will help, if you have still questions, don't hesitate to ask me. All the best, Late Never say never, think in solutions, not in trouble......
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3/5/2007 1:00 PM	Rate (0)
thuynguyet Posts: 18 Rating: (0)	The distance in my case is in fact less than 50m. However I think also that my problem is probably on my MPI cable. Two tests were just done: a simple WinCC project (with a few variables only) is running quite ok (my project has about 700 vars); my project runs ok on laptop on site through MPI/USB cable! Can I be sure that it's just the cable? or it may be something else on the PC? Now, my project runs well only for about 5 minutes, then "no communication" comes shortly after this Windows message: Step7 Block Administaration ... In the case of bad cable, how could I do the best correction? Should I change into Profibus? Or simple make good grounding? Attachment image_00001.jpg (943 Downloads)
thuynguyet Posts: 18 Rating: (0)
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3/5/2007 11:08 PM	Rate (0)
Late Platinum Member Joined: 1/7/2006 Last visit: 5/11/2025 Posts: 2705 Rating: (321)	Hi, You may place the PC in the near space of the CPU and then test it. You might also try it out with Profibus, do you have the opportunity to test that? Another thing is, why is there coming a message of STEP7, that have nothing to do with the communication from WinCC...... Which Version of STEP7 is on the PC? Do you have on your laptop where you tested it also with another Version of STEP7?
	I hope that the answer will help, if you have still questions, don't hesitate to ask me. All the best, Late Never say never, think in solutions, not in trouble......
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3/6/2007 12:39 AM	Rate (0)
thuynguyet Posts: 18 Rating: (0)	I'm going to test with the PC on site today I'm also very surprised with the error on PC! On that PC there are WinCC 6.0 SP2 and Step7 5.3 SP2 and on my laptop the same WinCC version (just installed for testing) and Step7 5.3 SP3. I though about the compatibility but the error happened as well while Step7 was not installed on PC (maybe with a bit different message ) And why there is no error when the simpler WinCC project running? The PC is quite new and only has less RAM than my laptop. Maybe the communication is bad and the system is overloaded??? I think about connection the CP 5611 to Profibus DP port of CPU S7 314C-2DP ? But in that case I'd change all the variables Can I do something to make the MPI communication better? ... With the PC near to PLC, the Windows message appeared only once! Then there is mostly short disconnection (especially when operator clicked on somethings!) and automatical reconnection. Finally I've got a long disconnection, it seems that no proccess overload PC CPU but I can't go online with Step7 as well untill I stopped WinCC RT. Any way it may be better but still not ok. I think it may be both the cable and the PC(fault RAM?)???
thuynguyet Posts: 18 Rating: (0)	Last edited by: thuynguyet at: 06.03.2007 07:37 The system has poor grounding condition!?
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3/7/2007 4:31 PM	Rate (0)
Simaticus Posts: 262 Rating: (24)	Hello thuynguyet (hoping i got it right), your experience sounds like an emc problem to me. Has your cable been situated with other cables of the system like motor cables, inverters (very bad) or other devices consuming more current? In that case even a shielded cable is no solution because it is magnetically influenced. Either you build up a magnetic shield (for example a steel plate between the lines) or you move the communication lines to another place. Good luck
Simaticus Posts: 262 Rating: (24)
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3/11/2007 4:12 AM	Rate (0)
thuynguyet Posts: 18 Rating: (0)	Thanks very much for help. Unfortunately I have the PLC installed not far from the inverters. I really tried to separate my MPI cable from the others, as far as possible! Now I've got something new: the same PC runs well on site (near to PLC) with the MPI/USB cable. Could I be sure that the problem is just on my CP 5611?
thuynguyet Posts: 18 Rating: (0)
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3/16/2007 12:21 PM	Rate (0)
Simaticus Posts: 262 Rating: (24)	Hello thuynguyet, to my knowlegde the MPI/USB cable is a potentialfree connection, but not the profibus connection. Maybe there's the reason. See you ...
Simaticus Posts: 262 Rating: (24)
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