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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Predictive failures
Date: Wed, 17 Apr 2024 04:05:37 -0700
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On 4/17/2024 12:56 AM, Liz Tuddenham wrote:
> Don Y <blockedofcourse@foo.invalid> wrote:
> 
>> ...When I was designing for pharma, my philosophy was
>> to make it easy/quick to replace the entire control system.  Let someone
>> troubleshoot it on a bench instead of on the factory floor (which is
>> semi-sterile).
> 
> That's fine if the failure is clearly in the equipment itself, but what
> if it is in the way it interacts with something outside it, some
> unpredictable or unrecognised input codition?  It works perfectly on the
> bench, only to fail when put into service   ...again and again.

Then the *replacement* -- now installed in the system -- would have
the same faulty behavior as the "pulled" unit.  Lending credibility
to the pulled unit NOT being at fault.

When the control system is a 7 ft tall, 24 inch rack, bolted to
the floor, your only option is to troubleshoot the system there,
taking the system out of production while doing so.