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Rob Spiegel
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Blogger
The overlooked obvious
Rob Spiegel   7/10/2012 3:01:30 PM
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Another great example of a Sherlock Ohms story where the engineer had to figure out something very obvious that is easy to overlook -- that is, that most wooden furniture has metal nails. Good sleuthing.

warren@fourward.com
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Platinum
Re: The overlooked obvious
warren@fourward.com   7/10/2012 7:47:22 PM
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Every time a parameter is changed, you have to reanalyze the test.  Something as simple as a table might seem innocent, but I will be checking out my tables and other fixtures when I don't get desired results with no explanation.  Good job!

streetrodder
User Rank
Gold
Re: The overlooked obvious
streetrodder   7/11/2012 9:33:22 AM
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I always enjoy these articles.  I particularly like trying to solve the problem along the way.  I got lucky this time and 'nailed' it as well.  Excellent job.

Battar
User Rank
Platinum
No metal
Battar   7/11/2012 9:35:41 AM
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Some years ago we were involved in certification of an ISM band product at an FCC approved lab. One of the resident engineers gave me a tour of the facility and showed me a large test room on the roof of the building built mainly of wood. He proudly explained how the structure had been assembled with no metal fasteners anywhere.  I would expect the test lab to have a sense of professionalism.

Car-Nut
User Rank
Iron
Re: The overlooked obvious
Car-Nut   7/11/2012 11:20:08 AM
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Reminds me of an occurance years ago when I was an automated sewing eqipment technician. This was back in the day old fashion "electric eye" sensors were still crude. An operator reported a problem that the machine seemed to have a mind of its own and would activate for no apparent good reason. After severl attemps at adjusting the sensitivity of the "eye" and various other adjustments the problem would appear to be resolved only to re-occur the next day. This went on for several days and I finally recruited the assistance from one of our engineers. We both went through every conceivable theory and process as to what could be causing the problem when out of the blue he asked me to walk away from the machine. "Miraculously" the problem stopped only to start again as I got closer. The engineer then asked me to change my shirt, without giving any reasonable explanation. Being in a sewing plant this was not hard to do. I simply walked to the end of the line and chose a nice black sweatshirt that had just been completed. Problem fixed. it seemed there was just enough sunlight from a nearby window that would reflect from my previous white shirt just enough to cause the sensor to activate. No problem on a cloudy day but if clouds were moving across the area the reflection problem seemed to just be random. This was another example of a much simpler overlooked but not so obvious baffling situation. Final solution---put a piece of cardboard over the window. There, that fixed it.

 

Rob Spiegel
User Rank
Blogger
Re: The overlooked obvious
Rob Spiegel   7/11/2012 5:20:36 PM
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Yes, it was a good job, Warren. The trick is to think of the hidden metal in a wooden table. I remember in the late 1970s, Sandia Labs was testing aerospace equipment and needed a mammoth wooden structure -- about 100 yards long, 50 yards wide. It was built entirely with wood. No nails because metal would interfere with the testing.

Rob Spiegel
User Rank
Blogger
Re: The overlooked obvious
Rob Spiegel   7/11/2012 5:27:22 PM
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This is a good story, Car-Nut. How about submitting it to Sherlock Ohms. It would need to be at least 350 words, and we would need a short bio (about two or three sentences).

Please send it along to rob.spiegel@ubm.com

Jon Titus
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Blogger
Re: The overlooked obvious
Jon Titus   7/11/2012 7:22:22 PM
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On the southwest corner of the campus at Worcester Polytechnic Institute (Worcester, MA) stands a stone building used some time ago as a magnetics and electricity lab. It contains no magnetic materials. Read a short history and see a photo here: http://www.wpi.edu/about/tour/skull.html.  The street-car line no longer exists.  I cannot vouch for the veracity of stories about the Skull society and any "secret" ceremonies.

 

I heard a story about engineering students who created a wireless robot that would crawl through metal pipes. The robot would into the pipe, but at exactly the same point it would stop communicating.  Turned out the pipe formed a nice waveguide and acted like a dead short for the RF, so communications ended abruptly.  My memory is a bit hazy, so maybe some other waveguide effect caused loss of comms--I'm not a microwave guy.

Rob Spiegel
User Rank
Blogger
Re: The overlooked obvious
Rob Spiegel   7/11/2012 8:50:17 PM
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Hey, Jon, were they able to retrieve the robot once they lost communications with it?  I would think they would lose control of it when communication stopped.

Jon Titus
User Rank
Blogger
Re: The overlooked obvious
Jon Titus   7/12/2012 10:26:06 AM
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As best I can recall, the students ran tests in a section of pipe for their project, so they could pull out the robot in case of problems.  Maybe they used a low-tech retrieval system--string.

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