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Gage RR and measurement uncertainty

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  • #23706

    Peter Γ–rtlund
    Participant

    Hello
    In Gage R&R you can calculate repeatability and reproducibility were repeatability is considered be variation due to gage.
    I am not a super expert in the area measurement uncertainty, but shouldnΒ’t it be the same as repeatability?
    My question is can I calculate measurement uncertainty by using gage R&R repeatability?
    I would like to state: My measurement system is accurate +/- #units (or percent) in this given application/measurement casewith 95%confidence.
    Thanks in advance

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    #56986

    Mertens
    Participant

    Peter,
    I struggled with the same problem.
    When you look from the viewpoint of metrology the theory will be this (according to me):

    Y = y Β± U
    Y = true measurement
    y = obeserved measurement
    U = expanded uncertainty
    U = k u(y)
    k = coverage factor (k = 2 for a normal distribution and a probabality of 95%)
    u(y) = standard deviation of the total uncertainty of the measurment system
    Repeatability and reproducibility are only a part of u(y).
    If you have the AIAG MSA Manual 3rd Edition, please have a look at page 61.

    More information about uncertainty you can find in EA-4/02 which can be downloaded from the internet, But be aware this paperΒ isΒ very thoeretical.
    When you have done a GR&R you can do the following. First you have to make the assumption/statement that the reperatability and reproducibility are the biggest contributors to the total uncertainty. In that case you can use the standard deviation of the repeatability and reproducibility together as u(y). In the MSA Manual 3rd Edition you can use the GRR as mentioned on page 114. This is not true for the 2nd Edition (there the total spread is calculated in stead of the standard deviation).
    Β 
    JeroenM.

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    #57086

    Sivaprasad
    Member

    Mr. Peter,
    Please mail the download link of MSA manual of third addition, mentioned by you to clarify the doubt. It will be helpful to me.

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    #57783

    Karimkonda
    Participant

    I am well aware about the measurement uncertainty principles and the result of the uncertainty budgets, but i had also started doing Gauge R and R studies in my factory with regard to my customer requirement and six sigma drive.
    I am under the confusion that which method is more appropriate, can i really go with one single method and validate all my measurements??
    Β 

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    #57784

    Karimkonda
    Participant

    From my knowledge, we cannot estimate uncertainty just by knowing the Gauge R and R Results, there are many more factors which we need to condider in uncertainty budgeting
    ISO – GUM gives a very clear estimation methods for various situations.
    Β 
    Thanks
    Ashwin

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