CODEWITHSUNDEEP
opc
gembird
gembird

Reputation: 14053

How groups on OPC Server work?

I am using Matricon OPC Simulation. I created two groups e.g. 'g1' and 'g2' and assigned one variable e.g. 'Bucket Brigade.Int1' to both groups.

How the group works?

I see that when I update value of variable 'Bucket Brigade.Int1' in group 'g1' then value of variable 'Bucket Brigade.Int1' in group 'g2' changes as well.

Is it possible to create somehow isolated groups? Or the variables remain everytime the same regardless in what group thay are used?

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Upvotes: 2

Views: 4699

Answers (1)

ZbynekZ
ZbynekZ

Reputation: 1608

Each "variable" in your post (also called "tag", the actual proper OPC term would be "OPC item") represents a value in the underlying device or system. As such, the same variable, if used at multiple places, is generally expected to have the same value - that's the whole purpose of it.

OPC groups are the way the OPC client tells the OPC server which OPC items it is interested in. They exist mainly for performance reasons: All OPC items in the same OPC group share some common characteristics, such as update rate, whether they are actively updated, and so on. This way, once the group is created and items added to it, the client does not have to address each item individually and repeat the data if it wants to "do something" to the whole group (such as change the update rate, or unsubscribe all the items).

OPC clients have full freedom in how they create the OPC groups, and which items they put into them. Not only you can have the same item in multiple groups; in fact you can even have the same item multiple times in the same group (though I doubt it is useful for anything). Therefore the answer to your questions is negative, at least as far the OPC server is concerned: You cannot "isolate" the groups; if you put an item into one group, the server must (to be compliant) allow you to put it into other groups as well (remember that there may be are also other clients that create their groups, too - and they should not be influenced either).

If you were writing an OPC client, then, of course, you could impose any limitations you like to what it allows the user to do or not.

Upvotes: 10

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