Siemens S7 400 Ethernet Communication Problem

We want connect our application to a Siemens S7 400 by using an OPC server. We tried the Kepware and the Applicom Direct-Link OPS servers that are using the Siemens Industrial Ethernet protocol to read and write the values from the PLC. The problem we have is that sometimes we loses the communication. And after that all the values we read are '0', (But OPC quality is still 'Good') and we are still able to write these values. And even after that we restating the OPC server the values that we have written before are still there. So it is not that we are writting in the OPC Server cach. I also checked the values directly in the PLC and the original values are always there.
After a while we receive back the correct values from the PLC. I have measuerd the times between the interruptions of the communication and that are always around the whole minutes. So the time that the communcation is online of offline is 1, 10, 11, 12, 20, 21, 30, 31, ... with a margin of 2 seconds. Only the communication is more offline than online...
The values we are reading are contained in DB50.
Does anybody have an idee what our problem is and maybe how to fix it?

Thanks in advance,

Tim

You may be overloading the buffer on the ethernet card. Try sending the data, using OB35, which is a 100ms. send rate. Set the receive to receive every scan. I have seen where the processor runs so fast the ethernet communications can't keep up and backs up in the buffer. It will also cause the data to be "old" since there is no way to purge the buffer and has to flow out like a FIFO.

RRobbins said:

You may be overloading the buffer on the ethernet card. Try sending the data, using OB35, which is a 100ms. send rate. Set the receive to receive every scan. I have seen where the processor runs so fast the ethernet communications can't keep up and backs up in the buffer. It will also cause the data to be "old" since there is no way to purge the buffer and has to flow out like a FIFO.

Click to expand...

Thanks for answering...

Is there a way in the PLC S7 400 software that I can see that the Ethernet output has an overflow?

I have asked Siemens to allow access to the buffer, but to no avail. I would like to be able to read buffer usage, purge, reset, etc.