Siemens S7-300 CPU318-2 Newbie Questions

[parky]

If there is a limit it would be in the PLC I would suggest, Kepware have applications out there with over a million tags on one system (pretty slow I would think). I also believe it is some sort of configuration of the data types.

 

[JesperMP]

An S7-300 has a socalled PDU size of 240 Bytes, and S7-400 has 480 Byte PDU.
An S7-318 is actually an S7-400 in S7-300 clothing.
The PDU is the maximum no of bytes the CPU can transfer by a single read request.
If more than 240 or 480 bytes are requested, it will cause the transfer to be split into several transfers. It will still work, only it will take longer. This is usually not a problem for the various OPC servers that support Siemens S7.

Another bottleneck is that in this particular case, the connection is via a CP (CP343-1 ?) in the S7-300 rack, not directly by an interface port on the CPU.
The CP communicates with the CPU by the slow backplane of the S7-300 rack. This can become overwhelmed if too many data has to pass via the CP.
This could potentially have something to do with the new problem. After the update, does the Kepserver request more data than before ? Or does it request the data at a faster rate than before ?

 

[cardosocea]

Ok - The good news is the PLC didn't have a password so I was able to successfully use the trial software to upload the blocks and hardware from the PLC onto my PC for safe keeping

Slight warning, Siemens has different password levels on the 300 series. It may be configured to let you read from the PLC but not write to it (i.e. change the program).

 

[parky]

I would think rather than no data on a particular type of tag that the errors would be com timeout so intermittent data, I have seen 400's with 4000 I/O reading over hundreds of DB's of various sizes probably cumulating in 10 or 15 thousand tags via a CP on the rack using Simatic net not kepware. Although Jesper has a point, however, I think this is unlikely be the cause. I look forward to hearing the updates.
Also how fragmented are the tags, Kepware tries to optimise the tags where possible so very often they are grouped. Also the update time of the tags but I have upgraded a similar system and opening the tag database did not alter anything on the tags as far as I'm aware.