PLCs
A Programmable Logic Controller (PLC) is an industrial Microcontroller that has been ruggedized and adapted for the harsh physical and electrical conditions encountered during process control operations.
Programming
Some programmable logic controllers (PLCs) can be programmed with Ladder Logic which is essentially a way to express electrical interconnects between racks of electric relays in a written graphical format.
PLCs may use their own version of Ladder Logic, or some other proprietary language which may be graphical based, assembly based, computer language based, or even database based.
Some PLCs have a display and can be programmed from the front controls, but most also support programming over some type of serial connection as well as more modern PLCs that use Ethernet.
Programming software for PLCs is completely dependent on the Manufacturer Brand of the PLC. It can range from freely available for download online to unobtanium legacy software or very expensive proprietary software.
Reprogramming
Reprogramming PLCs that have been deployed for years is usually first dependent on the availability and price of the programming software, hardware, and documentation needed to make the proposed modifications.
The second consideration is usually the availability of the PLC’s and HMI’s currently running programming / source code. Sometimes the programming cannot be easily retrieved from the PLC or equipment manufacturer / installer.
The source programming code may be Spaghetti Code that is hard to decipher and understand. Rewriting the programming from scratch may be quicker than trying to understand, modify, and debug the existing code.
The Takeaway:
“Sometimes it might be cheaper, easier, faster, safer, and more future proof to completely replace the PLC with a new one.”
“Reinventing a wheel might last longer than patching it up.”