hmi with soft plc

I have heard of these units that integrate an hmi with a soft plc. Was wondering what they are like and why they call them a soft plc

A soft plc is a PC program used like a PLC. An HMI is Human Machine Interface, it can be its own unit or it can be a program used on a PC. It is possible to obtain soft plc software, components, etc and use on the same PC that has HMI software used to be an interface.

You call it soft PLC as opposed to hard PLC because it's strictly software. So basically you can rely on soft PLC as much as you can rely on the machine running it (and any other software running in the machine that might crash it, aswell as any pheriphials that might crash the machine).

Sometime it can be very economical to run soft PLC. I know of one company in Sweden that sells Touchscreens with a built in HMI/Scada application and a soft PLC program that you can connect to Vision cameras and I/Os over Ehternet. Running Windows CE. These units had a very nice price, but I personally wouldn't trust them with any machine that could damage itself or any person (or valuable goods / material). But perhaps I'm being old fashioned (at the age of 26).

Siemens has the WinAC product that I've used along with PRoTool/Pro (HMI s/w). It worked pretty good.