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PLC Life Expectancy

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  • #16
    Originally posted by winterrossi View Post
    We have several Siemens S5 in our plant that are from mid 90s.
    I also know of a few S5's still running from the late early 90's, here in the south... lightning spikes and hot humid weather gets most in the end or just machine upgrades as technology changes

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    • #17
      In my experience (over 30 years as an engineer, doing PLC control systems integration), it is not unusual to find older PLCs still operating after 20 years or more. But I have my doubts with some of the newer PLCs, as I've seen newer base power supply's fail in less than 10 years.

      The failures I am seeing with the PLC power supplies, and I/O modules that have power filtering, have to do with electrolytic capacitors. Modern electrolytic capacitors do not have the lifetimes of the older capacitor designs; I think the capacitor designs are going to thinner insulation to make the cans smaller, and the overall unit cheaper. And cheapness seems to be driving so many engineering decisions.

      Go to Digikey (electronic parts vendor, www.digikey.com), and navigate to the aluminum electrolytic capacitors. Look at the 'lifetime at temperature' column of some of these products, while considering there are "only" 8760 hours in a year. This is why, in my control panel designs, I make every effort to keep the PLC as cool as possible.

      Note that these comments are not directed specifically toward Automation Direct products; this is a trend I am seeing in all industrial and consumer electronics.

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      • #18
        DL305 bases seem to have weaker than average power supplies. Despite not working with that many of them, I've seen several rack failures. Not that I'd use a 305 today anyway.

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        • #19
          For where I work I have changed out a few PLC power supplies a control logix processor for the battery not holding and few SLC processors for faulting out but by far the most common for us is a shorted coil takes out an output. We have some AB PLC 5s, Siemens step 5s and some series 6 PLCs that have been running for 20+ years

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          • #20
            Had a customer lose a SLC-5/05 the other day and they're buying a new one for like $8K! (L552) The equipment is about 20 years old, and I quoted them to redo the whole control system last year based on a Siemens S7-1500 but they didn't want to do it (the PLC hardware cost for the entire PLC, including remote racks, would have been less than just the 5/05 CPU and probably 200 times more capable, plus they'd have spares availability at reasonable non-obsolescence pricing for probably 15 years at least). Customers! Sheesh.

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            • #21
              Washed brain.

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              • #22
                They're not AB fanboys, they wouldn't care if the PLC was a Delta. Won't spend a dime unless it's an emergency, then panic and spend whatever when it inevitably becomes one. 10 or 12 emergencies worth of cost and downtime and they could have paid for the renovation that would give them near-perfect uptime for the next decade with WAY better performance and features, and a vastly improved horizon for spares availability. But who wants that?

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                • #23
                  Hmmm. I just read this post, and closed the browser,then I get an email telling me that ControlsGuy just posted the post that I just read.

                  sorry if it seems like i get stuck in a time loop.
                  dont know if it is forum or email service, but ...
                  i'll have to check my email to find out what i posted. Brb

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