WinCC 6, OPC and .NET

Hi.

I have made a couple of windows forms applications in c# (.net) that communicate with WinCC's OPC-DA server. I also first tried out the old VB6 method (using the DAAutomation 2.0dynamic link library file). This also caused errors for me and I never got it to work. It does not apparently work in the .net environment because it (at least partly) uses 1 as a numeric base and not 0 as .net always does. This is when I abondoned trying to use this dll file in a c# application.

Manually making the OPC connection from scratch is not an option for me. I realized that after some reading at the official OPC foundation web site. Not nearly all the offcial OPC standard documents are available there because you would have to be member of the OPC foundation in order to gain access to them. Anyway - the time and trouble is not worth it.

I then found the site opcconnect.com which salma also had a link to. This site has a list of available options for doing OPC communication in .net. I then evaluated many of the commercially available opc components (or more specifically the OPC-DA components) and then eventually bought a copy of Advosol's OPC-DA component. Some other components were a little easier to use but Advosol's let me do all the things I needed with the OPC-DA connection.

I encountered a little problem with the applications though which I haven't had time to diagnose more carefully. I had about 300 tags that I needed to read periodicallyfrom WinCC using OPC-DA. I first set all the OPC items to active state - meaning that any change in the tags are sent to the c# applicationbyWinCC's OPC-DA serverwithout the need for polling. This worked but with the side-effect that the WinCC screens took many seconds to refresh when changes occured to tags. I then made only five OPC items active and then manually read the otherOPC items' values when one of the five tags tells me to. This was acceptable and the refresh lag in the WinCC screens is now hardly noticeable.

I now also remember reading somewhere that WinCC 6.0's OPC-DA server is to blame for this, but as I said, I haven't had the time to diagnose the problem more fully. Anyway - I'm bringing this up because it might be a better option to use the Simatic NET's OPC server to communicate with the PLC instead of using WinCC's OPC-DA server. I didn't think of this option back when I made these applications that I'm talking about but I will try it out in future projects where OPC-DA communicationis involved.