SiggyTheViking

Yes!

In an ideal world, it would be possible (and cost nothing) to connect every PLC and Netduino etc. directly to the Internet, and a SCADA system that fetches measurements from all these devices over the Internet (well, if the data is not time- or safety-critical). Then the PLCs and Netduinos and SCADA systems would have to support some common standard, let's say OPC UA.

In reality, it makes more sense to have a PC or the like as aggregator for several devices, as you said. If this aggregator is powerful enough, it could translate between the OPC UA standard protocols and the PLC's/Netduino's proprietary formats. (Especially if these formats were designed to facilitate the translation.) Such a gateway scenario is the original OPC standard's primary use case. Because of COM, it required a Windows PC. With OPC UA, this restriction doesn't exist anymore. But as Randy pointed out, a Netduino is not necessarily a good choice for such a gateway.

Best regards

Cuno

So let me see here. We could have a machine that talks to various devices using a protocol they understand, and then presents it in a normalized protocol to a machine that records and aggregates all this I/O. Maybe we could call them an I/O server and a Historian. That would be some wonderful software. We could call it, um, Wonderware. Ja, that's it. AHHHHHHHHHHHHH!!! It hurts!!! It's too late for me. Turn back while you still can!

Yes, indeed, we have a common task to achieve, and an industry with a handful of players, all solving the problem with the same broad strokes, but subtly different details. It is time for me to look back into OPC UA again (it's been a couple of years for me, too), since I tire of working in a Babble of Wonderware, Modicon, and Allen-Bradley (with a few others too weird to mention.)

Oh, and to be vaguely on topic, I am meandering toward using my N+ as the PLC for my ranch (open the gate, monitor starts and stops of the well, etc.) I have this new wheel I'm working on, I think I'll call it Supervisory Control and Data Acquisition, or maybe something like that ;-)

Cheers,

Siggy