Life span of a PLC?

Pete.S. · Jun 12, 2016

This is a hypothetical question.

If you bought a new production line with all new PLCs, what would you consider to be the life span of the control system? How many years before you should plan to replace it all?

We are assuming a 24/7/365 production environment where productions stops are costly and you have knowledgeable people at the location and a small collection of spare parts at hand.

Let's also assume you have safety components in this system such as safety relays, safety PLCs, interlocked guards, light curtains, VFDs and servo drives with STO etc.

keithkyll · Jun 12, 2016

Infinite.
Relays, Capacitors and LED's have a limited lifespan. Power supplies, HMI's, and VFD's will be the issue. As long as replacements are available, you can run forever.

jstolaruk · Jun 12, 2016

Based on systems I've updated from older architectures, 20 years is not unusual. This is in the auto industry, I wouldn't doubt its longer in other industries.

DeKemp · Jun 12, 2016

Siemens S5 was released in 1979 that is 37 years ago. There are still plenty of installations running with that. Spare/refurbished parts also are still available from specialized company's.

JordanCClark · Jun 12, 2016

Whenever I see questions like this, I try to point them them to this article.

bob1371 · Jun 12, 2016

We've got 15 or so Cutler Hammer D100's still running 2 shifts a day without much trouble. They were installed early 80's.

However I am slowly replacing them with AD Productivity 2000's.

Most of our projects I have used the Compact Logix controllers and expect they will be around for some time also.

T Gibbs · Jun 12, 2016

We have a machine running on an Idec FA-1Jr.

geniusintraining · Jun 13, 2016

DeKemp said:
Siemens S5 was released in 1979 that is 37 years ago. There are still plenty of installations running with that. Spare/refurbished parts also are still available from specialized company's.

I still know of a few running and the environment is not favorable to electronics, they were very good PLC's

JohnCalderwood · Jun 13, 2016

When we used to plan new production buildings, we worked on the premise that the PLCs would be written off over 15 years, but the PC-based part of the control was just 5-10 years, as technology was moving on.

One of the first I was involved in, the PLCs lasted 25 years, the operator control panels, 20 years (only because we had a service contract with Rockwell) and the PC-based SCADA and Recipe System was changed at least 3 times over that period.
Mind you, we bought a state-of-the-art 386 Hewlett Packard Vectra for the early years of that project and it cost us £6000........

Pete.S. · Jun 13, 2016

I'm thinking a little along JohnCalderwood's line on this and the link JordanCClark pointed to.

Just because we could make a PLC run for a very long time doesn't mean that it is the logical way or that it makes economic sense.

Many people would for example buy a new car now and then when it is actually possible to have it running for at least 50-60 years.

BTW, how long does PLC manufacturers promise to keep spare parts around?

Dravik · Jun 13, 2016

We plan for 7-10 years for depreciation. Viable lifespan is often 2-3x that.

jraef · Jun 13, 2016

I think this is a critical line from that article too.

"Ask yourself: Do I really want to rely on spare parts from eBay to keep my plant in production?"

I see that so much that it saddens me for our industry. I was at one facility recently where we had talked about upgrading their PLC-2 system from 1979 (which I had originally installed!) and the user pointed to his shelf full of eBay and PLC Center purchased spare cards and CPUs. Some of the boxes were disintegrating into dust or had water damage on them and he even admitted that sometimes, he has to try 2 or 3 different cards before he finds one that works. So did he agree to upgrade? No... "It costs too much". He just accepts down time cost as a "normal" cost of doing business.

bob1371 · Jun 13, 2016

jraef said:
"Ask yourself: Do I really want to rely on spare parts from eBay to keep my plant in production?"

For the price of the last couple D100's we got from Ebay I am able to purchase complete AD Productivity 2000 system and a 6" C-more HMI.

RET · Jun 13, 2016

It just depends on how long you're able to find support (i.e. parts) for the system you install.

But 20 years what we assume as a life expectancy.

FLAengineer · Jun 13, 2016

I think 20 years is a good middle ground estimate. Here, we still have some SQ-D SyMax running equipment (30 years old, will replace next year). Also some Allen Bradley PLC-5s (12-16 years old), and SLC 500s. The PLC-5 are the only ones still running with the original processors. ** Also what I think may drive replacements in the future is two things no one has mentioned yet: 1. SECURITY - enhanced security on a newer model may force you to replace a PLC that is not very old. and 2. COMMunication options - for example, moving the rest of the plant to Ethernet would force you to upgrade non-Ethernet PLCs. This would include protocols such as Modbus, Profibus, Fieldbus, etc. The industry seems pretty stable in that area right now, but who can say if something newer/better will be out in 8 or 10 years.

Life span of a PLC?

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