Dayvieboy
Lifetime Supporting Member
Where I'm at now and the stuff we're doing? Well, we can't get a ControlLogix platform to do what we need it to do, let alone a PLC-2, PLC-3, or PLC-5.
90% of our control systems are custom boards designed in house.
So off the shelf PLC limitations are never an issue.
Off the shelf PLC's still have a pretty big place.
They are modular, can be easily rearranged & handle many fairly complex processes.
When you design a custom board it has considerably smaller footprint
but is pricey to modify, add or rearrange I/O.
You have to build & stock them yourself.
You cannot just order a new one from the local supply house.
Another big foothold PLC's have is they can be Safety rated to Sil3 (Cat4) out of the box.
No need to spend many man years to prove that your custom circuit board will safely do what it is supposed to do reliably for it to be signed off.
An EMO (E-Stop) can be sent over Ethernet/IP CIP to multiple PLC's
in both the Fab & Sub-Fab
Safety PLC's are usually requested to be used for most safety related processes in place of custom boards