220K=130k????

Discussion in 'General Electronics Chat' started by magnet18, May 18, 2011.

  1. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Hey, I was building a signal generator, and happened to measure the resistance of the resistor I was using... good thing too, because it's supposed to be 220kΩ, but instead it measured 130kΩ... and it's not just one of them, all of them. I even replaced my meters battery, and it still showed this.

    I know it's radioshack, but I thought even they had standards better than this, that's like 30% error or something :mad:
    Can I sue?

    also, out of curiosity, what would happen in the following circuit if R1 was 130kΩ?
    Might explain why I couldn't get a signal generator to work....
    [​IMG]
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Have you tried any other resistors using that meter? Does the meter have a low battery indicator? Were your fingers touching the resistor leads while you measured them?

    I've run into bad parts, but first eliminate the obvious. 220KΩ is a fairly high resistance, make sure your body isn't being measured along with them or the meter hasn't gone south.
     
  3. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    *sigh...

    Maybe I'm not meant to do electronics...

    Yea, my fingers were touching, it's interesting, they usually touch and it has never had any effect before :\
     
  4. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Is it possible to be color band dyslexic?
    because I think I am...
    And why must blue and green look EXACTLY the same? :(
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Maybe you're partially color blind .....

    I think a substantial percentage of males are color blind - although I think the problem is often more in the Red-Green department. One of my many deficiencies unfortunately.
     
  6. KJ6EAD

    Senior Member

    Apr 30, 2011
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  7. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    I think I'm a tiny bit colorblind with blue and green, but it's not enough to bother me or prevent me from passing every colorblindness test with flying colors ;)

    I'll probably never know for sure, I can tell blue from green just fine... unless it's a resistor.


    WANT!
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    220k in parallel with 318k skin resistance will give you 130k. 318k is well within the range of dry skin. Your actual skin resistance will vary, depending on a lot of factors.
    You can generally check low-value resistors while holding them, but, as you discovered, not the high-value ones.

    http://www.allaboutcircuits.com/vol_1/chpt_3/4.html
     
  9. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Apparently my skin measures about 550K :p
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    No, it was about 318k.
     
  11. nbw

    Member

    May 8, 2011
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    I don't know if this helps, but when I was first starting out in electronics, I measured what I thought was a 4K7 resistor. It came up about 2K7. I thought I was going crazy.

    I desoldered it off the board - 4K7.
    Put it back in, measured the resistance across it - 2K7.

    Going nuts?!

    Nope, just didn't realise (then) that other resistances and components around that resistor changed the resistance I was measuring.

    I can laugh about it now, but at the time I was so mad!!
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    One of the things I've done as lead tech is to create a troubleshoot print, where I document the resistance we expect to measure in the circuit, not the resistor. It can be very handy. For the most part ignore the semiconductors (treat them as opens), and calculate all the other resistors as if they were parallel to the resistor under test through the power supply buss.
     
  13. retched

    AAC Fanatic!

    Dec 5, 2009
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    :D

    Only in America!
     
  14. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    The resistance I posted was right before posting, I think my fingers were a bit sweaty earlier, which explains the difference.
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    If the resistors are cheap Chinese junk (sold by RadioShack) then they use exactly the same paint color for blue and green bands. They also use the same paint colour for red, orange and brown bands.
     
  16. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    not EXACTLY...
    I think it's the same base color, then they add half a drop of the color to each vat ;)