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Calculate uncertainty in pressure, temperature and time?

  1. Feb 12, 2017 #1
    1. The problem statement, all variables and given/known data

    After doing a lab on air compressors, we were asked to calculate Error in Pressure, Temperature and time measurements taken (all at 30 second intervals). We took pressure and temperature values at time = 0,30,60,90,120,150 and 180 seconds. We repeated the experiment 5 times. Before each repetition, we took atmospheric pressure and temperature. The values of n I calculated using equation 2 were:
    We were asked
    1) What type of compression is occuring (Isothermal, Isentropic or Polytropic)?
    2) Are the Values on n equal from each set of data?
    3) Do they increase or decrease when placed in chronological order?
    4) Explain the cause of any differences?
    5)What is the uncertainty in pressure, temperature and time measurements?

    2. Relevant equations
    (P1)(V1)^n = (P2)(V2)^n (1)

    n = (ln(Pf/P0))/(ln(Pf/P0)-ln(Tf/T0)) (2)

    3. The attempt at a solution
    My attempt at a solution is partly explained under the 'problem statement' section. However, I have found that we also probably need to use the Root Mean Square to calculate the uncertainty in each of our values, by manipulating Equation 1 possibly? I also included questions 1-4 as maybe they are needed to answer question 5. I will be on this forum constantly to clarify anything. Thank you
  2. jcsd
  3. Feb 12, 2017 #2


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    2017 Award

    Staff: Mentor

    For the uncertainties in the measured values you'll have to check the measurement apparatus and the way you got your values. I would avoid using the 5 different data points for an estimate as they will probably overestimate your measurement error (can you guarantee that the compression was done in exactly the same way every time?).

    Equation (2) will help to propagate the uncertainties to an uncertainty of n.
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