OPC Service Processing and Monitoring

Question

I'm writing a windows service that will be used for some data processing. The service will connect to an OPC (KepWare) service and will monitor specific items through event handlers. It will also have to write back to the OPC data item when necessary; however, the data to be written back will have to come from a windows mobile handheld device.

I'm just getting perplexed on the design aspect of this system. I'm trying to make sure that I design this in an abstract manner in order to make it scalable and easily maintainable. However, I'm just stuck on how to communicate with the service in order to tell it write this value to the OPC server. I'm thinking WCF is the way to go but I'm not exactly sure how to write it where I can obtain a reference to my connected OPC object when the client makes the call? Should I be writing a WCF library and host it inside the windows service or should I be going down a different route?

Thanks in advance

Answer 1

You should read up on the fundamentals of OPC-DA and OPC-Xi (also known as OPC .NET 3.0). The OPC Foundation has simple documentation available for free: look for the "specifications" that are available to non-members.

The KepWare server should support both (depending on the KepWare server you are using). OPC Xi is WCF-based and will be the easiest way for you to talk to it. However, that particular communication channel needs to be open and enabled for it to work.

If you don't have that, then you need to fall back to OPC-DA which is DCOM based. You can find .NET OPC client libraries that will help you with this. There are some free and some commercial ones out there from different companies.