This post could have been called "Isn't DCOM Dead Yet?" Distributed Component Object Model (DCOM) has been deprecated for years now but it still rears its ugly head, particularly when dealing with OPC servers on remote machines.This led to the rise of OPC tunnelers as a solution, whereby the travails of dealing with DCOM and its associated security vulnerabilities were addressed. But now, two Ignition gateways can do the the same thing, but better, by leveraging OPC-UA. The cost is next to nothing.
The Ignition platform is, for all intents and purposes, an OPC-UA client that includes a free OPC-UA server module. The module comes with many of the more common drivers, including A-B drivers.
For moment disregard the fact that we could use Ignition's free A-B driver and assume instead we want to talk to an RSLinx OPC server, as the diagram shows. RSLinx uses the older OPC-DA technology relying on Windows COM technology. Since Ignition is written in Java and can run on any OS, the Ignition OPC COM Module is required – which costs $350 but is the only cost to this OPC-UA "tunneler" solution.
In the past, this solution wouldn't work because one piece was missing, but now it can be downloaded here and it is free. This is the "tunneler module" which would be installed in the remote Ignition gateway and will allow you to browse and access your remote PLC address space locally. Setting up and configuring the two Ignition gateways takes just minutes (less than ten) and is a piece of cake.
Of course, with OPC-UA coming of age, most of this is just for picking up those already-configured legacy OPC servers or those supporting oddball protocols. In the example above you would most likely use the free Ignition drivers or for unsupported protocols use the latest KEPServerEX which now supports OPC-UA (installed at the remote location).
I thought you might like the data on this little problem-solver.
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