PLC Modernization vs. Retrofit — What's Best?

Navigating PLC upgrades.
Brandon Dilley
Feb 20, 2024

As PLCs age, maintenance becomes tedious, because finding replacement parts or reprogramming resources becomes more and more difficult. At some point some, or all, of your hardware and software will become obsolete. So, when should you upgrade a PLC, and when should you retrofit?

The first thing to consider is that PLC modernizations are not possible if the PLC program is missing, or the original backup programs are not provided. When the PLC TAGS and descriptors are absent it is very labor intensive to recreate them.

Why do you need the original backup programs?

Without those, it is impossible to tell if the programs loaded into the PLC are the intended version. Therefore, It is possible that after a PLC modernization, the system will not function as intended. In this case, we would need to revert to the old hardware and software. If Dillengr has previously worked on your PLCs, you don’t need to worry about this, because we would have created a backup for disaster recovery for your system.

Now, what’s different about the two anyway?

For a PLC modernization, you are changing the PLC setup configuration for the new hardware, but the PLC programming (logic) remains unchanged.

On the other hand, when you retrofit, you change the PLC setup configuration of the hardware, but you are also changing the PLC logic to match today’s standards.

What this all boils down to:

There is logic dependent on the actual hardware. The PLC logic and the hardware have to be able to talk to each other. If you can’t make the two match up, it would be more cost-effective to do a retrofit.