What are the rules for defining PLC’s obsolescence?

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Every day we live with a lot of different devices that help us to have a better life, such as cell phones, music players and car GPS.  All these devices are made to cover a specific need, but what happens when the need is already covered?  Every device at some point starts to become limited, boring and then it begins its obsolescence.

If we pay attention to our behavior with the common electronic devices, as a cell phone, we don’t care about how much we are going to use it, we know that in one year or less we have to change it for a model with a lot more features, with a better processor or anything better.  But when talking about industrial electronic controllers, how can we know when it’s time to replace these devices? A PAC (Programmable Automation Controller) it’s not a cell phone of course, it’s a device that can control thousands of variables and I/O in a critical process, so is there some rules for defining its obsolescence?

Schneider Electric, Services AutomationIt’s hard to define a rule for determining obsolescence in an automation controller, because it depends on the manufacturer and the real condition of the PAC. I’ve seen Schneider Electric PLC’s working perfectly for 20 years, in an iron ore pellet plant in which you can imagine how aggressive the environment is there.  And I’ve seen PAC’s replaced only months after commissioning, just for a firmware update that modified its behavior.  So we can’t define a specific rule for replacement without being aware of all the real conditions that affects our controllers in our particular process.

Some people think that it’s time to replace the controllers when a failure appears (I assure you that’s the worst rule for replacement).  On average, we could consider 3 to 5 years for changing the programming software, to a newer version or a complete software migration, always keeping in mind that training is mandatory for operators or maintenance teams.  However, we can also consider 8 to 10 years on average for updating the controller or the system architecture, because as cell phones, the technology involved in automation controllers evolves really fast, and we need our plants secure and updated for optimal performance.

Anyway, after all this, it doesn’t matter how much time we think,  because an important part of obsolescence is the people who are using this technology.  Engineers, maintenance teams, operators or any other users of the equipment can shorten the time in between replacements if they don’t update their knowledge and improve their skills every day.  As in a TPM methodology, every user is part of the process and should understand that their behavior and care of the process is the key for long term best results.

Do you have your own rules to determine the obsolescence of your controllers?