What exactly is the hardware inside of an HMI?

[BobB]

HMI stands for Human Machine Interface - in my view this can also include devices such as switches, indicating lights and the like.

 

[RocketTester]

It is not difficult to write a simple HMI from scratch. I do so w/ Visual Basic.net in Windows to interact with a Beckhoff PLC. I use standard VB objects like command buttons and sliders (display a tank level or setpoint). For fancier 3-D images w/ shading, look at the free AdvancedHMI by Archie (he posted above), including source code. The VB (or C#) program sends requests to the PLC over ethernet. It can start/stop the PLC, control flow, get data arrays, etc, all from dll calls in TwinCAT. AdvancedHMI works the same, and I expect Indusoft and WonderWare interact similarly. You can run the compiled VB (*.exe) HMI right on a Beckhoff CX CPU, or from a desktop PC, it doesn't care. You can run the same VB program from two PC's at the same time. They don't slow the PLC since simply polling it. You can also manage HMI from within Beckhoff PLC code on a CX, using their "Visualization" tools.

I expect the interaction is similar w/ an A-B or Siemens PLC (AdvancedHMI supports them). More people probably use A-B's RSView since it comes in the package and they have experience. Beckhoff now tightly integrates the VB and PLC code within Visual Studio in TwinCAT 3, so HMI and PLC source code is managed in the same place. It seems they expect many users will use VB or C# for HMI.

The trend is for simpler HMI screens without all the colors and graphics clutter, so that emergency conditions are more obvious. Plus, photo-realism is not as impressive today. For my apps, I find I can make the screens I need simpler and faster in VB. I add a few photo images to the screen to impress big-wigs who pop in, but the images don't help the daily users.

 

[sparkie]

Thanks guys, I'm still paying attention to this thread and looking for more useful information!

 

[arlenjacobs]

Sparkie, can you describe a bit more what you wanted to find out?
The hardware? components? How it compares to a computer? Why are they good for harsh environments? etc...

If you can give more detail why you are asking, or what you are hoping to do with the info it could get some more specific responses.