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Sherlock Ohms

The Power of Human Touch

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Cabe Atwell
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Re: The human senslors
Cabe Atwell   5/10/2013 4:10:46 PM
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I just has a screw down terminal issue early this week. I was troubleshooting a speed sensor problem interfacing with a stepper motor control board. I was stripping wires, testing continuity, etc. Then it dawned on me... check the screw down terminal at the stepper driver. Loose.

Problem solved.

C

Charles Murray
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Re: The human senslors
Charles Murray   5/17/2013 6:53:12 PM
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Oddly enough, Rob, that sounds like the same diviide that was going on in the book (and movie), "Money Ball." The younger executives tended to trust the numbers, while the older scouts seemed to take more of a seat-of-the-pants approach. While the two areas -- engineering and baseball -- would seem on the surface to be unconnected, I do believe the phenomenon you're describing is age-related, across the board.  

William K.
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Human touch, or other temperature sensing methods.
William K.   5/18/2013 1:59:08 PM
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this is a good example indeed. I have seen a similar situation associated with motor starters used with three-phase electric motors. I was asked to investigate one which kept tripping the overload switch, which is a thermal switch designed to trip from smaller overloads. But I was not able to touch the terminals, they were live on the 480 volt circuit. But touching the wire insulation next to the termianl gave an adequate clue that it was warmer than it should be. So tightening the connections solved the problem. 

For the safety people who are freaking out that somebody would open an enclosure with the power on, understand that I had great insight into exactly which places were safe to touch, and that I was and still am able to do that kind of test safely. BUT, of course, it should not be attempted by just any person who thinks that they are qualified because they once read how to do it. That attitude is so very ISO9000!

MartyHoyodeman
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Iron
Re: Human touch, or other temperature sensing methods.
MartyHoyodeman   5/20/2013 6:58:20 PM
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A very long time ago I was working on a Tape Control Unit that had a 750 watt linear 5VDC supply (among others) and was having intemittent issues. First thing was to check the supply voltage which was just fine. I then threw a scope on the supply and saw some noise that was a bit above spec and it would come and go. I opened it up and smelled hot metal. The recitifcation was done with 2 diodes that were mounted on a couple of large aluminum plates used as heat sinks (CT xformer). The cables were bolted to the plates as the diodes were also bolted to them as connections. One of the bolts was no longer shiny and I touched it to see if it was loose.... it was..... it was also about 300 or 400 degrees. I left my finger print permanently in the now dull finish of the bolt head. I know it was warmer than the boiling point of water as I put a dab of spit on the bolt just to see how hot it was and it vaporized instantly. After cooling things down, cleaning things up and replacing the bolt/nut/washers and correctly tightening it, everything worked as expected. The point I am making here is when you are dealing with 100's of watts of power, the touch/feel test is quite useable as I found many times after that first incident, however, I tend to be much more careful and to not touch the connection points directly anymore. Infrared thermometers are cheap now and work very well as a bit of insurance. BTW - My finger prints did reappear on my finger some weeks later. LOL

Rob Spiegel
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Re: The human senslors
Rob Spiegel   6/7/2013 12:11:54 AM
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Yes, I agree, Chuck. But I would give the old timers a tad more credit. The seat-of-the-pants is actually decades worth of feel and experience. The old guys think that the numbers are less reliable than real-world experience. But, like Moneyball, you can't count the numbers out -- so to speak.

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