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Sherlock Ohms

Donít Like the Problem? Donít Believe It

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tekochip
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Platinum
Finding Believers
tekochip   10/1/2013 9:58:37 AM
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I had a similar issue with an instrumentation amplifier in a scale.  This was back in the days when you had to roll your own amplifier and offset drift was a major issue.  This design had a chopper amplifier which seemed to work very well, built then would suddenly become wildly unstable, possibly from solar flares, gravitational storms, or spirit orbs.  Same story; it worked great for six years, now suddenly YOU think there's something wrong with the design.
 
It turned out that the chopper frequency would sometimes drift a little with temperature and if the frequency wound up being an odd harmonic of 60Hz, the hum that is everywhere, the hum would no longer be common mode (maybe 10 ripples on the + input but only 9 on the – input).  When I found the cause, I was able to demonstrate the problem and redesign the scale with a modern, monolithic instrumentation amplifier.


Rob Spiegel
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Blogger
Re: Finding Believers
Rob Spiegel   10/1/2013 10:40:38 AM
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Thanks Tekpochip. I would guess there are a lot of stories like this -- communication problems between the engineer and others in the organization. If you have one, please send it along as a comment.

TJ McDermott
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Blogger
Do it anyway
TJ McDermott   10/1/2013 10:52:42 AM
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If quitting was in your mind, did you consider unlacing all the wire bundles to make a rat's nest before leaving?  Maybe see if you could make that former sargeant eat some crow?

bob from maine
User Rank
Platinum
Re: Do it anyway
bob from maine   10/1/2013 4:34:33 PM
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While in the Navy, I had opportunity to operate and repair a famous 1960s era VHF radio. These radios were multi frequency tube type and quite robust. The biggest downfall was the wiring, which looked exactly like a rat's nest but was very precisely set so interelement conductance was exactly balanced and made it possible for these things to work. You could move one wire to replace a resistor and if you didn't put it back exactly right, the radio would either be off frequency or have low output. Unsoldering a tube socket frequently condemned the entire set to the scrap pile. They were frequently used as 'learning tools' for bosses with more knowledge than common sense.

armorris
User Rank
Platinum
Re: Do it anyway
armorris   10/1/2013 7:52:42 PM
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TJ,

I am not a quitter. That was just the last straw. That guy was probably a former US Army drill sargent. He managed by intimidation. All the other young engineers that hired in at the same time as I did, quit. I stuck it out for a year, because I didn't have the moving money to pay back. Because I was on the night shift, I didn't have easy access to the personnel department, where I could lodge a complaint. And yes, I was intimidated by him. When I was in the Army and the drill sargents were screaming at me, I could do something about it. I could run harder, or do whatever I was being ordered to do, but, there was nothing I could do about this guy. Also, I couldn't repair the problem myself because it was a union shop. The wires weren't laced. They were just pressed into the gaps between the long wire-wrap pins. I would have had to rip the wires out and rewire them.

This employer believed that young engineers had to "pay their dues" in the shop area for a year before being alowed into the design area. That was a horrible place to work. I didn't want to work in the design area for such an employer. Exactly one year after I hired into that place, a headhunter lined me up with my next job and I got out of there. The rest of my career was good.

Ann R. Thryft
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Blogger
Re: Do it anyway
Ann R. Thryft   10/1/2013 8:43:24 PM
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There must have been a lot of former sergeants in industry back when I was in marketing in the 70s and 80s. Andrew's ex-boss sounds just like a few I had, but they managed to acquire college degrees. The 'tude was similar: if I didn't personally see it break, it can't really be broken so shut up; if it was good enough for your predecessor why are you complaining even if we could save time/money/sanity/all-of-the-above; if we could buy XYZ goods or services 10 years ago for $100, why should it cost $300 now?, etc.

TJ McDermott
User Rank
Blogger
Re: Do it anyway
TJ McDermott   10/2/2013 2:09:06 AM
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Mr. Morris, please forgive my poor choice of words.  I did not mean to imply you were a quitter.

Zippy
User Rank
Platinum
Military intelligence?
Zippy   10/2/2013 8:14:42 AM
Remember, every problem has three approaches: the right way, the wrong way, and the Army way!   :)

RogueMoon
User Rank
Platinum
using the last resort
RogueMoon   10/2/2013 9:06:42 AM
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Despite the motivation, I'm sure the decision to leave wasn't easy.  Sometimes a situation like this leaves you with few choices.  Rather than have your skills impugned by a manager clearly unqualified to judge these matters, it's perfectly reasonable to take your skills elsewhere.  I'm glad you found something better.

ratkinsonjr
User Rank
Gold
Re: Do it anyway
ratkinsonjr   10/2/2013 9:35:08 AM
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I know it can be hard working for the boss from hell, and the hardest part must have been waiting until you could afford to leave.

My question is: How come the boards were wire-wrapped?! That may be okay for a prototype, but for production hardware you always transition to a printed circuit board for improved reliability and easier maunfacturability. I can just imagine the nightmares trying to troubleshoot a board if a wire broke off or fell off of a post. The only reason I can think of for not using a PCB was if this was a low volume product. Low volume, fast-turn PCB houses are commonplace now, but were unheard of back in the 1980's when I started my career. How many sims did they actually build? 

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