OPC servers


Thread Starter


I'm going to define an application with Visual Basic with the OPC server technology. Does someone know when it's better use only one OPC server or more?

Thanks a lot.
It depends on your requierements. If you want to read data simultaneoualy from more than 1 opc servers, you will need to reference all of them in your vb application. Again they can be running on the same machine as your vb client app or on another machine and u can access through DCOM technology.

In our opc client product we have provided a redundancy with 6 OPC Servers, meaning if 1 opc server fails the client will switch to the next and so on.

Robert McDonald

I'm not sure of the original posters reasons, but I can suggest at least these scenario where you may require more than one OPC server.

1. You require data collected from two different brands of PLC.
2. You require data collected from various existing SCADA packages to store in a central SQL data store. i.e. 3 Citect collecting data from PLC networks.

In both of these cases you would need to connect to and get data from more than one OPC server.

We developed our own in-house web/xml/OPC Scada solution to bypass the licensing, maintenance fees and limitations the traditional packages placed on our clients needs. It was quickly evident that multiple OPC servers would need to be interfaced to so as to provide a corporate wide
"web" view of the data.

Hope that helps.

Robert McDonald
Tristar Electrical
Thanks a lot for your answer. My require is reading simultaneoualy data from more PLC. Do you think use more OPCServer (one for each PLC) declared in the same VB application could be a good solution?

Best regards
Thanks a lot for your help. My will is to declare more than one OPCserver (of the same brand and declared in the same Visual Basic application) to collect data from PLCs on a network.

Each OPCserver will be "linked" to a PLC CPU.
What do you think of this my idea insted of using on OPCsever for all the CPUs.

Best regards and thank you very much.
If the PLCs use the same communication protocol just use a single OPC server to communicate with all of them. Use many OPC servers only if the PLCs use different protocols.

I don't think you can run more than one instance of one particular OPC server in the same computer. I think there will be registry issues. Usually multiple OPC servers are possible if they are made for different protocols, because then they have different names and CLSID etc.

I don't see you gaining any advantage of running multiple OPC servers for devices sitting on the same network. Usually an OPC server polls the network to the limit permitted by the network bandwidth, so you are always going full throttle anyway. Or am I missing something?

If you want to have more than one OPC server for the same network I think they must run in different computers. We often do this when systems require redundancy. The network now has two masters so the protocol or OPC servers need to support multiple masters or arbitrate the redundancy...

Jonas Berge SMAR
[email protected]
Mr Jonas Berge thanks a lot for your hint. My intention was to gain resorces to fire group events.

What do you think?

Best regards