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Former Member


We are testing xMII v11.5 with OPC UDS and KEPWare v4 on a standalone ethernet network. We have a ControLogix PLC, and a KEPWare .opf file with around 450 tags. Tagnames are quite long by the time you consider that the fully qualified tagname =

We have a requirement to poll blocks of 8 specific PLC tags (4 string, 3 int, 1 bool). Current round trip for an 8-tag block from xMII to PLC and back via KEPWare / OPC UDS is 3-4 secs, which seems rather slow to me.

I have been tweaking various parameter settings and combinations of settings but cannot get a faster response (eg: block size, read mode, read descriptions, load metadata etc).

The KEPWare OPC client seems to indicate that it's talking to the PLC quite fast.

The "taglist" mode in an xMII query returns quite fast from KEPWare.

But join the dots in an end-to-end data query and we get quite some overhead, and I just can't seem to track down where it is!

What experience does anybody have with the xMII OPC UDS and KEPWare, and are there any "tricks" to optimise performance? In KEPWare? In the UDS?

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1 Answer

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    Former Member
    Aug 09, 2007 at 01:18 PM


    Unfortunately there are several "things" (not really issues, but not really non-issues either) that you are hitting.

    First I would recommend creating an alias file (I know this seams really lame and it is, but it should increase performance) because there is some overhead in looking up the item id.

    The other 'thing' with this version of the xMII OPC UDS is that it actually reads the 8 tags individually, and if you know OPC then you know this is also inefficient.

    Right now there is a internal product line (the mysterious 4.0 UDSs) that should improve performance, but there are people in SAP that are still (yes almost a year after development finished) dragging their feet on making a decision in "IF" to release the next generation UDSs. I recommend to anyone wanting them to be released to put a little pressure on their contacts.

    ... Now how much of a backlash am I going to get for that last statement :P ... Let the pain begin.


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