Ebook question volume 1 Ammeter Design

Discussion in 'General Electronics Chat' started by Barry M, Feb 25, 2009.

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  1. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    Sorry, close this please ... over tired and wasnt putting in the last 9 in 4.999 ... nm in 8hrs I can sleep ... now that Ive eventually woken up.




    This could be plainly obvious but Im just having one of those 'mental blocks' but ...

    http://www.allaboutcircuits.com/vol_1/chpt_8/4.html

    It says the required resistor would be 100.02 mΩ, I keep getting 100.2 though.

    Can anyone tell me where Im going wrong please?

    If I do it the long, more challenging as the book says, way I get

    1/0.1= 10
    1/500= 0.002
    10-0.002= 9.998
    1/9.998= 0.10002000400080016003200640128026 = 100.02 mA

    If I do it V=IR way from the table I get

    0.5/4.999= 0.10020040080160320641282565130261 = 100.2mA

    I appreciate any help, making this mistake in circuits isnt something I want to do.
     
    Last edited: Feb 26, 2009
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,284
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    In the first place, 0.5/5 = .1000000000000000000000000000000 not
    0.10020040080160320641282565130261

    The numbers from the table would give:

    0.5/4.999 = 0.10002000400080016003200640128026
     
  3. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    Which goes to show how tired I am ... I'll correct that.

    And now its corrected Ive seen my error when I retyped it. I must have done the same error about 30 times as well, dunno how, dunno why.
     
    Last edited: Feb 26, 2009
  4. wr8y

    Active Member

    Sep 16, 2008
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    Because when we make a mistake - and then review our work, it is very hard to find our own mistake. It's a human thing... even tho you are proofreading, the fact is, it is YOUR mistake and it's hard for most of us to slow down and really SEE what we are looking at.

    Being tired doesn't help, but I often ask someone to look at my work when I hit a brick wall like that.
     
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    As you wish. PM one of the mods if you want it re-opened.
     
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