Make your PLC Last Just a Bit Longer

Industrial Management Consulting
Industrial Management Consulting

Don’t get me wrong, I understand the many benefits of upgrading a legacy control system, and in fact, that is a major part of my upcoming projects. However, most facilities do not have unlimited cash flow and it seems to be all too common for upper management to de-prioritize the project as it is not generating revenue on the face. In reality, we have to do the best with what we are given and for most control engineers or engineering managers, that isn’t very much.

This article shares a few ways to extend the life of your legacy control system and also permanently convince your manager that you will never have to spend money again.



Of course, you knew that this would be first on the list. Control engineers can’t move without hearing about virtualization and with good cause. With budgets rock bottom, the rip and replace method is a few years out and, generally, you can virtualize some aspects of the system out of the general maintenance budget.

So what can you do? Ask your controls integrator!

Generally, a simple PC box under $1000 with VMWare is about all you need for many applications and a few days worth of engineering time to obtain an image and configure the PC relative to communication protocols/ports will provide you with valid backup. Yes, there are more complex cases, but even in those, we are talking under $10,000 instead of the $100,000 and higher a full upgrade can cost.

As HMI applications tend to be popular, if you are interested in those, Cross Company’s Jim Bowser wrote a blog on the topic, which was re-published by Control Engineering magazine.


Routine Maintenance

If I had a nickel for every time I’ve seen a control engineer grab a bundle of network cables or I/O wires and shake or pull to find something, I would have like 10 nickels…but the point remains true: keeping the terminals on your system tight and clean is necessary, especially if you have engineers constantly looking for wires and lost neutrals.

Of course, maintenance hardly matters if your system hasn’t seen the yellow glow of the high bays in a generation or two, but if you have a system that is just a few years old, then it is time to start maintaining that system now. Just because you cannot put a grease fitting on the “Analog Out” card doesn’t mean that your legacy control system should be ignored until someone lets the smoke out.

Do your research by reading the manuals and looking up common cause failures. Perhaps you can catch something well before and get a few more years out of your legacy control system.


Change Control Process

This is my own personal opinion. Pharmaceutical, complex chemical, and regulated food and beverage all have a good process in place, “change control.” These industries use change control to “guarantee” that the system has not changed and the previous certifications and/or validations are still accurate.

Why not do something similar to make your legacy control system last longer? Here is my idea. Instead of letting any maintenance guy with a hot stick get into your control system, create a process for maintenance that only allows qualified engineers to touch the components. This one change alone will gain you so much favor with EHS that your future hot work permits will be signed in hours, not days.

Always have at least two engineers working together and use your 3rd party controls integrator if you are unsure of what to do. Most controls integrators have support plans that guarantee fast “call-backs” just to talk you through different scenarios without having to come to the site. If you document, the money will come. Make that your mantra.

Perhaps it makes sense to sit down with that same controls integrator and ask for support in developing a maintenance plan around the control system that will be the most gentle and start to develop professional best practices through those that you trust. I already know what you are thinking, of course, I can sell you a support package. Thanks for asking!


Air Conditioning

This should probably be in the maintenance section but I had to point it out. I also almost named this section “Environment” but I really do feel that people assume the intense heat on their systems is a minor issue. Depending on your plant environment, components in the panel, and the amount of air flow, systems can vary drastically in lifespan.

So you saved $30 on a power supply only to find out that it puts off heat 25 degrees higher than the more expensive version. Who cares? Well, you should because that change can cost you years relative to your controller life. It is similar to moving the belt and pulley on your motor shaft another half inch toward the bearing (in case mechanical engineers are reading).

Use a temperature rise calculator (most manufacturers have a free version) and figure out if your system is sitting nice, reclined back, watching football and drinking sweet tea, or sweating it out on the gazelle listening to motivational tapes. Do yourself a favor and make your legacy system comfortable.


The goal of this temporary measure is for your legacy control system to make it to budget approval time. Take an active role in your control systems health. Just letting it run and hoping for the best is not a great policy, but it tends to happen due to the unending amount of “to-do” list items. If you are in the situation where management struggles to understand just how important this issue is, then try partnering with a veteran controls engineer at your trusted integrator. Believe me, they have those conversations all the time and sometimes have a unique ability to get through to the boss.

Of course, if you really just want to upgrade everything and be done…then let it fail. That will get management’s attention.

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