Working on a new project with a single PLC on site (two sites total) controlling a small process system. We were planning on using Edge (with Panel for local visualization/control) to talk to the PLC and then have it sync its data with a central (cloud) Gateway (one Edge/PLC combo per site). Essentially this architecture (without EAM):
If the client wants to add a second Edge device (for an additional operator station), what are the considerations with having two Edge devices talking to a single PLC? In my head, we have additional comms load on the PLC, potential duplication of tag events, potential duplication of tag history in the central Gateway, and maintenance of two separate Edge projects.
Obviously we can get rid of Edge and put up a feature limited Gateway in its place with a limited client license pool (to reduce cost). This can then also be connected to the central Gateway similarly to the Edge client(s). My issues with this approach is that it will be more expensive (at least until the number of individual Edge clients gets high enough) and have more hardware to install and maintain on site.
The client prefers cloud servers that they aren't responsible for so that also makes me hesitant to add more hardware on site. I also don't like the idea of a remote Gateway (via internet connection) being required for local control.
What are the thoughts here?
If they lose connectivity to the cloud server, then they use the one Edge panel.
I'm not a fan of this attitude. If the servers are important to production (OT), then they belong on the plant floor, on the plant floor network, secured as a unit.
To be clear, when you say "don't", you are referring to only having a single Edge device for local control? Don't add multiple ones talking to the same PLC?
In case I wasn't clear in my above description, my thought is that the central Gateway wouldn't even be involved locally (site A and site B are in different states, and they intended audience for the central Gateway is in a third state). The central Gateway would be for remotely monitoring live values, trending, and reporting. The actual operator(s) wouldn't even have to know it exists.
I agree with you on having the servers required for local control located locally.
You'd have to confirm for sure with Edge, but I know a single client license with full Ignition gives you one client on gateway plus one remote client (with caveat that local gateway client can't be browser, if using Perspective). If this is true of Edge, you could have two devices with gateway and client on one and just the client on the other device.
Another option if typically only one touch screen will be used at once is to connect two touch screens to the one Edge device.
I would avoid connecting two servers to the same PLC, if possible, although it certainly could work as long as you're not asking for more coms than the PLC can handle.