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Uncertainty with a log function

  1. Mar 21, 2010 #1
    1. The problem statement, all variables and given/known data
    Im trying to find the uncertainty for a log function. I have that

    f = 20log(V_in/V_out)

    and i want to know (delta)f

    2. Relevant equations

    f = 20log(V_in/V_out)

    3. The attempt at a solution

    I was going to do it the calculus way:

    f = 20log(V_in) -20log(V_out)

    df = 20*f*[(dV_in/V_in) - (dV_out/V_out)]

    but this doesn't seem right to me. I've never seen subtraction in an error calculation before. And im not sure if this is a relative error or a percent error. I want a relative error (with units), the only problem is that my function has no units, soI'm not sure what I should do in that case (if that makes sense).

    Is there another simple formula for log function errors?
  2. jcsd
  3. Mar 24, 2010 #2


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    Last edited by a moderator: Apr 24, 2017
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