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Sherlock Ohms

Failing Sensors Cause Consternation

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Beth Stackpole
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Doing the digging instead of the quick fix
Beth Stackpole   5/16/2012 7:05:09 AM
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A great example of sticking to the problem and following the trail until total problem resolution is achieved. All I can say is I wish more engineers and companies practiced this kind of dogged determination to get to the truth. Kudos to you and your design team.

naperlou
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Re: Doing the digging instead of the quick fix
naperlou   5/16/2012 9:34:16 AM
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David, I agree with Beth.  It took a lot of attention to detail to find the change you mentioned.  It is interesting to note that the environment was such that even a "small" material change could cause a failure.  Good work!

Rob Spiegel
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Re: Doing the digging instead of the quick fix
Rob Spiegel   5/16/2012 11:08:49 AM
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Yes, Naperlou, this is a good example of attention to detail. Something as simple as wire insulation made difference between sensors that worked and sensors that failed. This is excellent Sherlock sleuthing.

Jon Titus
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Secondary or tertiary effects
Jon Titus   5/16/2012 12:00:02 PM
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This story provides a good example of how a secondary effect (insulation change) caused a tertiary effect (shorted contacts).  New engineers must keep these types of problems in mind when they look for the root cause of a defect. That cause isn't always obvious. Nice work.

Charles Murray
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Re: Secondary or tertiary effects
Charles Murray   5/16/2012 6:12:34 PM
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The interesting aspect of this is that the change was made, not just for cost reduction reasons, but for reliability purposes, as well. It makes me wonder if the original PTFE insulation had a problem, too. Was this a case of replacing something that wasn't working well with something that was even worse? Or was it a case of, "If it ain't broke, don't fix it?"

Ann R. Thryft
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Electrical problems are always a hassle
Ann R. Thryft   5/16/2012 6:46:16 PM
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My only comment is that troubleshooting electrical problems are much harder to diagnose--or even to recognize as such--than mechanical problems.

dboccuti
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Iron
Re: Secondary or tertiary effects
dboccuti   5/16/2012 8:42:40 PM
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Thanks for your insightful comment Charles. In this case the change was made for the right reasons (reliability; cost was a secondary benefit) by the system engineering folks, but it had an impact on a sub-system (the sensor) - an unintended consequence. Lesson learned - evaluate everything that might be affected by a change, not just how it affects "your own stuff."

Tim
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Platinum
Moisture Absorption
Tim   5/17/2012 6:52:27 AM
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The moisture absorption of polyamide is often overlooked in design.  We manufacture a polyamide product that is used on average two years before discard.  Consumers that were keeping the product over the two year mark complained of premature breakage of the product (non-safety related).  Investigation showed that the PA absorbed enough moisture to push out the plasitcizer on the product making it brittle.  As there was no other material available, we opted to put use by dates on the product to guide the consumer to when the products life was ending. 

ChasChas
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Gold
unusual
ChasChas   5/17/2012 10:27:32 AM
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To find the cause first and then the failure process is truly unusual.

William K.
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Failing sensors mystery
William K.   5/17/2012 9:15:01 PM
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It appears that on many occasions "epoxy" material is not suited for many kinds of electrical applications. I am aware of some antennas that don't work right when they are insulated with epoxy material, although one would think that they should. Moisture leaching out salts to short circuit a connector is a long way to go, though. It took good troubleshooting skills to find that problem.

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