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What should be the Order of Activties in a MSA Study?

Discussion in 'Gage R&R and MSA - Measurement Systems Analysis' started by Juggler_IN, Oct 20, 2015.

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  1. Juggler_IN

    Juggler_IN New Member

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    For a variable Gage R&R study we study the following:

    Gage Precision:
    - Repeatability
    - Reproducibility

    Gage Accuracy:
    Bias
    Linearity
    Stability
    Calibration

    Gage Resolution:
    Distinct Categories

    Now, as per my understanding, as far as the sequence is concerned, the process flow for Gage R&R studies is:

    Resolution
    Bias
    Linearity
    Calibration
    Repeatability
    Reproducibility
    Stability

    Let me know if the order is any different.
     
  2. Bev D

    Bev D Moderator Staff Member

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    By resolution do you mean the number of distinct categories? if so, you cannot calculate the NDC unless you have the repeatability value.
    If you mean simply the resolution of the gauge vs the tolerance tehn you can and should look a this first. You don't need parts or any measurements to do this.

    Calibration can be done next - but it only establishes 'accuracy' and can be effected by repeatability depending on hwo the calibration is performed. typically calibration is done to a standard and doesn't involve fixturign or any other real part that can effect repeatability...

    Repeatability is the next measurement test. Without establishing repeatability, none of the other calculations are reliable. IF you will be using multiple operators to determine bias, stability, or linearity, you should etablish the reproducibility next.
     
  3. Juggler_IN

    Juggler_IN New Member

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    So, as I understand the flow would be as follows:

    Step 1. Gage Resolution vs. Tolerance
    Step 2. Gage Calibration against a Standard
    Step 3. Gage Repeatability
    Step 4. Reproducibility (with multiple operators)
    Step 5. Bias
    Step 6. Linearity
    Step 7. Stability

    Is this a fair order?
     
  4. Bev D

    Bev D Moderator Staff Member

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    I do refer you to Miner's blogs in the resources section of the forum (see upper left tabs to move from the forums to the resources) as he is an expert in this subject.

    Traditionally, Bias and Linearity are part of calibration. Bias will tell you how 'inaccurate' the device inherently is from a 'gold standard' method or standard object of known geometry or property.
    Linearity will tell you if the bias is consistent across the response of the thing to be measured.
    Typically these two are assessed together as part of the calibration study.

    Stability is how the gauge - or method - changes over time. Some systems will be susceptible to transients such as temperature or humidity or vibration. Some will be susceptible to a systemic temporal forces such as age, wear during use, etc. So stability is typically a larger - and longer study. It can be done after the initial studies are complete that would validate the use of the system. Stability then would cap the length of time, or number of uses, or set limitations on environmental conditions.

    So I might perform these in this order:

    resolution against the tolerance
    calibration against standards (including bias and linearity)
    repeatability
    reproducibility (alternately a single large study can be performed for both repeatability and reproducibility at the same time. this is quite common)
    stability. (unless I have reason to be concerned about stability under typical use conditions...then I might combine repeatability and stability together before approving the system for use. I would do this after the calibration step and then perform reproducibility last)
     
    Mark Paul and Miner like this.
  5. Mark Paul

    Mark Paul Member

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    Thank you for the clarity without getting bogged down!
     

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