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Guest jonnie75

Opc

4 posts in this topic

I was wondering if anyone that has worked much with OPC can explain a few things to me. I have never actually dealt with a real OPC application. I have read some information and played with a demo version from automated soultions. Does it go something like this? 1. The server is set up on a pc that has the capability to get PLC values (I/O, timer values etc.), this particular pc would need some sort of network card. I am guessing a 1784KT, 1784KTx or something of this nature. What other ways would someone gather data from a PLC or a PLC network? 2. The server will be configured for a specific piece of hardware (card), nodes are selected, tags are made for specific a specific piece of data ( I/O, timer values etc.), these tags can be arranged in groups. 3. A client is configured on a remote computer (off in the distance) to have access to the data that was configured on the pc where the server is located. I have seen that alot of places offer Ethernet OPC servers. How is the Ethernet different from the Internet with regards to an OPC server and client? Can a person setup a Server at work and a Client at home (cable modem) and still view the data? 4. A person can now view only data values using the client on a remote computer. How would one go about creating animated or graphical displays based on the tag data from the server not just a simple data view of the tag, Visual Basic? 5. I have read that this data can be utilized in the Visual Basic programming language, does anyone know if this can be done with Visual C++, will an ActiveX control be needed? So to make a long story even longer, I am wondering how a person can gather data from PLC's to a PC then across the internet to a home computer and then create graphical displays with the ability to read/write data back to the PLC?

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jonnie, That's quite a lengthy message.  I'll attempt to answer your questions.  First some background.  I have written multiple applications as OPC clients using VB, C++, and other tools like RSView32.  So, I'll attempt to address each issue. 1.  These statements are correct.  You basically set up the OPC Server PC to "point" toward (communicate with) the PLC/PLC Network or device through various means including the KT Card.  Another communication method is through ethernet if you have an ethernet supported PLC or device. 2.  Although OPC servers generally allow for "predefined" tags at the OPC server level, you don't normally have to do this.  The tags that the OPC clients use can normally be defined at the OPC client and can even be defined dynamically at runtime.  Tag read groups are important.  They define where the data is coming from within the OPC server and how they are to be updated. 3.  OPC clients are either local (on the same computer as the OPC server) or remote (a different computer from the OPC server).  Because of the technology used to develope OPC servers and clients, they can support remote access.  However some servers may have licensing issues with remote clients (i.e. RSLinx/RSLinx Gateway).  Because the client and server do not have to run on the same computer, it is possible to run accross the internet. However, it is not recommended.  There are a few issues such as bandwidth, slower update rates, and of course security.  So to answer your question about getting access from home over a cable modem, yes it can be done.  However, I would not recommend opening up your control system to the internet. 4.  As far as animation, you can use developement tools like RSView32, Iconics Genisis32, Intellution, and others.  You can also write custom code in VB, VC++, and other developement platforms.  This is all done using the OPC client interface. 5.  As mentioned earlier.  Quite simply, the answer is yes.  There are some ActiveX OPC client controls out there, or you can use the OPC API to the COM/DCOM interface directly.  I have used both VB and VC++. I hope this answers your questions.

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I am just now starting to learn Visual C++. So I guess I will need to learn about using Com/Dcom if I am wanting to connect with the OPC? Thanks for reply.

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Yes.  I would not start out by learning VC++ and COM/DCOM with OPC at the same time.  That's would be a big, frustrating learning curve.  If you want to learn VC++, start there and get comfortable with it first.

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