Strategies for upgrading PLC hardware

As technology advances, hardware needs to be updated for optimal efficiency.

By Evan Novakowski, Avanceon July 5, 2018

The programmable logic controller (PLC) first came out in the late 1960s. It’s important to know when to update old hardware and controllers with new technology updates and to ensure replacement parts are available in the event of an emergency. Buying replacement parts on the internet isn’t a reliable best practice.

Key reasons why an upgrade might be necessary include:

  • With controllers that use a tag-based system rather than data tables, users can match the tags in the PLC to the tag used on the process and instrumentation diagrams. For instance, when troubleshooting an issue with a temperature transmitter as displayed on the human-machine interface (HMI), a search can be conducted in the program for that tag name.
  • Upgrading may mean easing the onboarding process for new personnel who aren’t familiar with the current PLCs being used. For example, the updated hardware tags may be in English instead of data table addresses, which would be easier to understand and remember.
  • Updated controller programs allow users to take advantage of user-defined datatypes (UDTs), which facilitate standardization of similar systems across processors or within a program. This helps keep a program organized.
  • Updated controller programs are task-based rather than continuous scan-based. If a certain function needs to be executed at certain time intervals, certain hardware is available to implement that. This setting would be difficult or not possible with an existing PLC.

Controller hardware upgrades

Some PLCs have a simple conversion kit as it’s very low risk and requires little downtime. It’s not necessary to do any rewiring, and existing swing arms will fit directly onto the conversion modules. The conversion kit can also be prepped and pre-assembled before going into the field. You typically will not have to do the input/output (I/O) checks or error checking that needs to be done with a complete rewiring.

Although if you can afford the downtime, a complete rewiring may seriously need to be considered. While it’s a more painstaking approach than using a conversion kit, rewiring allows for a clean and complete break from old PLC hardware. The benefit of this approach is it affords greater flexibility for the future that is not possible with a conversion kit.

Evan Novakowski is a project engineer at Avanceon, a CFE Media content partner. Edited by Emily Guenther, associate content manager, Control Engineering, CFE Media,


KEYWORD: programmable logic controller (PLC)

  • Upgrading PLC hardware
  • The benefits of upgrading old hardware
  • When to consider upgrading hardware.

Consider this:

Would it benefit your facility to invest in upgrading older PLC hardware?