What is a Programable Logic Controller?

[tobybirch007]

I have to do a group presentation next week over PLC's and I'm not even sure what they are. Specifically, we have to do the presentation over EMBEDDED PLC's. So, we know they are used for manufacturing automation, but we're not sure about much else. Any insight would be very helpful.

Thanks

[Al_The_Man]

PLC's are a software mode of replacement for machine logic control that was originally done with relays.
They take the system inputs and after processing the internal logic, the result placed on physical outputs.
The Boolean type logic is often programmed using either Ladder or Mnemonic format.
If you do a Google of PLC, Boolean or Ladder program, you should find more information.
Al.

[beone]

In other words a PLC is a special purpose computer for machine or process control. They are typically modular with configurable inputs and outputs. They have the advantage over a pc type controller in that they continue to process no matter what. It takes a lot to get one to fault or stop.
Dave

[tobybirch007]

Thanks for the info. Does anyone know of a few good examples of a plc in use? what are the differences between plc's and the standard microcontroller that's in just about everything? So far, the only difference i can find is that PLC's are able to operate in more extreme environments. Is there any other differences?

[Al_The_Man]

If you mean application examples, there as many as there are industrial machines, typical is automation assembly lines, conveyor systems, a local International Bus manufacturer even uses them for on board automation of the bus controls.
PLC's and embedded Micro's are similar, except PLC's are designed for flexible programming and trouble shooting/diagnostics of the machine status in the field.
Micro's are aimed at dedicated processes, and are more word oriented rather than bit oriented.
Al.

[keebler303]

PLC's also have more rugged inputs and outputs than most microcontrollers. A PLC is really a microcontroller with a lot of addons. It includes all the circuitry for interfacing with high voltage circuits, an easy way to change the program (usb) and a lot of other cool features.

Matt