Siemens S7-200 ethernet problem

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Thread Starter

Jeff Couperus

I am using a Kepware OPC server to interface an Intellution SCADA system to 2 Siemens S7-200 PLCs through their CP243-1 modules. The Siemens PLCs were supplied by someone else and I'm not to familiar with them but the ethernet setup looks pretty straight forward. The problem I am having is they will communicate for a day to a week and then one of the processors loses communications to the Kepware driver. It's not always the same processor and it's very intermittent so I can't nail down what is going on.

When communications is lost the Kepware driver appears to be polling and getting failed reads. Its error is "Device Not Responding". It's as though the ethernet module just stops replying to the polls. I changed my poll times down to about 1 poll every 10 seconds to make sure I'm not overwhelming the modules but it didn't have any affect. Cycling power to the failed Siemens PLC usually immediately reestablishes communications. Both PLCs are set up the same with one configured connection. There is only one computer on the ethernet network. Both PLCs have the same TSAP addresses but different IP addresses. Could the same TSAP addresses be causing an intemittent problem?

There are Allen Bradley devices in the same system connected through the same ethernet switch and network hardware so I don't think its a network problem. The PLCs appear to be running a lot of logic. They are also communicating RS485 and profibus to other devices. Could they be overload or are there settings in the PLC which need adjusting? If anyone has had any experience with these PLCs help would be greatly appreciated.
 
Hi, in this PLC, you can configure a percent of time for comunications they have 10% for standar, you can increase even 50%, how amount of time do you have now? you can check an change this settings in the system block in microwin.
 
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marc sinclair

Did you find out what was going on? I would be interested to hear your experience.

marc sinclair
 
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Mark Hensley (Kepware)

Dear Jeff,

One thing that I noticed when we first developed the driver for the CP243 module was that there appeared to be some subtle difference in the TCP/IP stack operation depending on whether you were operating the Cp-243 in 10Mbit mode or 100Mbit mode. If you are allowing the module to auto negotiate or you are running it at 10Mbit but your wiring and system can handle 100Mbit I would force the Module into 100Mbit mode. I spoke with Siemens about this way back when and at that time I was in touch with the developers. They could not get the problem to reproduce on their end. I was able to send them some IP Sniffer captures that showed that the TCP/IP Stack on the mdoule was actually getting out of sync and it would start sending old sequence numbers in TCP/IP packets.

I can't say this is the issue in your case but I found that at 100Mbit this sequencing issue did not seem to occur. If you can try it it might be worth it since its only a configuration change on the Cp-243.

If this does not help please contact us here at Kepware. We may be able to offer some other suggestions and possible even walk you through getting a new Ethernet sniffer capture so we can see if the same thing is happening in your application.

Keep us posted.
 
Hello Mark Hensley

I am a great admirer of your company's product and therefore understand that if you were making enquiries such as this they would have been rather technical in nature. I would like to know if you found someone at Siemens who could assist you with your problem as I have some similar problems with TCP connection to S7300/400 and I only seem to get NAKs from the hotline when I ask for help.

If you could find us a contact perhaps it would be more discrete to email it to me on donaldp(at)iasicc.co.za

Much obliged
DonaldP
 
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