The problem comes when in 9 years something blows and then you have troubles finding the particular replacement card.
If you have really benign conditions room temp, no inductive loads, clean power, short connections, low cycle times, and clean environment then a PLC could last for 20 years.
Ask the mfg, any reputable one will have some failure data to share (however biased it may be).
Generally, something in the system gets upgraded and the PLC requires updating before its reached the end of its life (hardware wise), which very well could be 20 years or more.
Many PLCs die the "incompetence death" long before the hardware is used up. Even if you have the same people that were around when the thing was commissioned, you will find that they have forgotten all about it. They cannot find the documentation either. And spare parts have probably been pulled out and put on the shelves a lot more times than you like to admit. Without finding out if they were really faulty.
I would say: Plan to change the whole thing every tenth year. That will keep your systems serviceable and also user friendly. And try to stick to one set of hardware during that period. It makes everything much easier.
In December of 2004, I had the pleasure of reprogramming a Giddings & Lewis PIC 409. I believe that the unit was originally comissioned around 1984.The client wanted the ability to run with OR without automation on any or all of the 3 stations controlled by the plc.
I know that this particular machine is STILL in production today. Just remember to keep a DOS capable (not psuedo DOS like XP) laptop around so you can run the application software. Oh, and get ready for the lightning quick file transfers at 4800 baud. (And we thought dial-up was slow!)
There is some proof for the 20+ year pudding.
Hope this helps,
Scott
In a hundred years, it isn't going to matter anyway.
One of my client is still using one of the first Modicon Quantum line of PLCs. It is about 12 years old.
We are not adding additional IOs to it. We can still get IO modules that work with it (the new ones are backwards compatible), just not necessarily the original models (but then, the old model is probably not so good anymore).
I guess we are hoping it will go another 12 years ... so the life span is about 20 - 25 years?
I quit working for Square-D's PLC division in 1988. Some old customers who still know where to find me call with issues they need help on because their Sy/Max PLCs are still in use and working, but only a handful of people at Schneider US know anything about them. As I recall, we used to quote an MTBF of 26 years. I suppose the jury is still out, but it's looking good.
Unfortunately for those users, I killed off those brain cells long ago... I usually just recommend they bite the bullet and upgrade for performance issues anyway.
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Yes Jeff. That is what I call "competence death". And it comes earlier than you may think. Given the high job change rate I think that even ten years is on the high side. My recommendation stays: Upgrade to new systems every ten years. It helps a lot.
I have the same situation when it comes to old analogue control systems. I am the only survivor from the seventies that still is mobile enough to actually help people with these dinosaurs (like Modulpac, Transidyn, Combiflex and so on). It gives me a lot of interesting travel to all five continents. But on the whole, I think that it would have been a lot more cost effective to replace them with modern ones.
I will actually help them change an old Modulpac to new microprocessor controlled gear. So they can keep the machine running for another ten (or, as it may turn out, thirty) years.
Thank you all for your help. With the longevity of PLC's, where do you all think PLC technology will go in the next 5-10 years? I'm just curious. Do you foresee any major technological changes to the form, fit, or function of the PLC?
Over the past few years, as processor power has increased and robust high-speed communications have become commonplace, the performance gap and system architecture differences between classic DCS architecture and PLC-based systems has become much less distinct. For example, top-of-the-line PLCs are now in service in processor-heavy applications like turbine control which has historically been DCS territory. The major difference tends to be the auxiliaries like historian functions and data processing which currently still sits better with DCS. Over time this line will blur too.
Given the current trend, PLC control capabilities will come standard in your PECPAD (Personal Entertainment, Communication and Processing Auxilliary Device), the successor to your cell phone/IPod/PDA.
And it will only cost you $49.99 with a 10 year service contract.
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I'm seconding what everyone has said so far - if there wasn't a design flaw in the PLC hardware, and it was installed properly it'll be running well beyond the point where support software is readily available.
I have five A-B PLC-2 racks installed circa 1985, and think we've had one legit hardware failure (a bad input module) maybe a year or so after installation. Just remember to change out the memory backup batteries on a reasonable schedule.
It may be that the overall limiting factor is how long it takes for the electrolytic capacitors to start drying out, and failing.
I know of a Sq D Sy/MAX in service (on a draw bridge) since 1983.
I/O is usually the hardware that dies,,,, I'm trying to think if I ever ran into a CPU failing without having had major damage as the cause!
The problem is kinda like backing-up your hard drive; when it crashes you find out how good your backups were. Sure, it's possibly cheaper to replace a PLC than keep repairing it after some point, but if your prog and doc's are 20 yrs old, you MAY have a huge project on your hands. ....and I LOVE those kind of projects!
A PLC is very well capable of outlasting it's "manufacturer", like Sy/MAX, T.I., GE, Allen Bradley.... Oh yeah, AB still supports all those oldies,,,, just like Schneider and Siemens and Fanuc do.
My bet is that 10 yrs from now AB will still be making and selling some SLCs, and along with the rest of the major players they'll be doing systems with a CPU unit and all I/O will be remote or "smart". PLCs direct, and a Chinese company will be making cheap "old style" PLCs, and you'll get one with 64 discrete I/O (10-300V AC/DC) and a bunch of high-speed timer counters, for $100.
Of course there will also be a Linux based "open architecture" standard by then......
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