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PROFIBUS timeout issue

Created by: BorjaY at: 5/12/2011 7:30 AM (5 Replies)

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5/12/2011 7:30 AM	Rate (0)
BorjaY Posts: 2 Rating: (0)	Hi All, I am experiencing random PROFIBUS timeout faults in my System. The system is formed by a S7-319F PLC, 14 drives on PROFIBUS and 7 RIO ET200S on Profinet. Also another S7-300 plcconnected to the main one by MPI on a different port than thePROFIBUS network. The plc and the drives are in the same cabinet within 5m of each other and exchange 6 words of data (each). When having the PROFIBUS network speed at 1.5Mbps from time to time some drives go momentarily into fault due to a PROFIBUS timeout fault. If I reduce the speed to 500kbps it still happens but less often. If I go for the next speed down, 187kbps then it doesnt happen butthe network is too slow for my application. I guess that there is too much traffic in the network but how can I improve this? What is the relationship between OB1 execution and the cycle of the network? At the moment I am reading and writing (through SFC14 and SFC15) the values from the PROFIBUS and storing them in a DB at every cycle of OB1(3ms average). Would this mean that I am overloading the network with requests? Under bus parameters in the HW at 500kbpsit says that I can expect a tipical T tr of 16.8ms. Is this time independent of the OB1 cycle or other networks in the system?Which factors affect the system in the way that make the cycle timelonger than the Watchdog time (132ms for this settings)? Any help would be appreciated. Thanks Borja
BorjaY Posts: 2 Rating: (0)
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5/18/2011 10:29 AM	Rate (0)
Hulzhex Gold Member Joined: 8/25/2005 Last visit: 3/19/2025 Posts: 1162 Rating: (111)	Hi BorjaY, looking at your configuration, I don't think that there is too much trafic. It isn't a very large system. Think there is to much noice at your network. Reducing the speed makes it less weak. Maybe you could check the network traffic by using an analysing tool link Amprolyzer Please check you hardware, the resistance at the end of the profibus line, ... There is no relationship between OB1 execution and the cycle of the network. Looking at the information about your profibus within the hardware you will find the maximum token rotation time. Within this time every slave is poled once minimum. Normaly it is much more often. Reading data with the SFC's "only" makes a copy of the actual data to the CPU. It dosn't have any effect to the communication at the bus. So please check the topology of your bussystem, resistance, ... think there the reason will be found. Good luck Sabine

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5/20/2011 8:10 AM	Rate (0)
BorjaY Posts: 2 Rating: (0)	Thank you so much, now I can discard many things. :) I believe that at the moment the end resistor (the one on the last profibus plug) is Off, so I will put it On and try to speed the network up to see if this makes a difference. I will also try the amprolyser software. Apart from that what other checks can I do on the topology of the network? It is just a daisy chain with 15 drives. Thanks Borja
BorjaY Posts: 2 Rating: (0)
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5/20/2011 8:40 AM	Rate (0)
MavEric Bronze Member Joined: 5/28/2009 Last visit: 1/18/2025 Posts: 127 Rating: (10)	Hi. Please Find The Attachment... Attachment TopoLogy.JPG (238 Downloads)
	Regards, SKD
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5/20/2011 8:57 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 3/19/2025 Posts: 3042 Rating: (1061)	BorjaY Apart from that what other checks can I do on the topology of the network? Hello BorjaY there are a few general checks that you cna do to verify that the installation is up to scratch (the vast majority of comms problems in Profibus networks are caused by poor or incorrect installation/termination). PI (Profibus International) has a couple of really good Profibus installation (assembling) and commissioning guidelines available for free at: http://www.profibus.com/nc/downloads/downloads/profibus-installation-guideline/display/ Download them and follow their instructions to verifyyour network. While there is nothing wrong with Amprolyser (and its free too, mind you you need to have a Profibus CP), it lacks the ability to verify the physical signal quality. If you are regularily dealing with Profibus Networks and/or need to maintain a numberof them, I suggest you have a look at Procentec's Profitrace 2 for this purpose. I hope this helps
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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5/26/2011 1:50 PM	Rate (0)
aikona Posts: 487 Rating: (36)	If you are using a network card then you ca nuse the cards diagnostics to look at the profibus parameters and values and reading up on the meaning of the values you should be able see if there is a problem Eric
aikona Posts: 487 Rating: (36)
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