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Z Value and Process Capability

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Viewing 7 posts - 1 through 7 (of 7 total)
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  • July 26, 2010 at 8:23 pm #53532

    singh
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    Hey Guys

    Can anybody tell me the difference between the Z value and Cp, Cpk?

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    July 26, 2010 at 11:33 pm #190507

    Mikel
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    Member

    Cpk = 3 * z

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    July 29, 2010 at 5:36 pm #190515

    Rivas
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    Participant

    I think that Z=3*cpk.
    Z is sigma level. If the best cpk=2, sigma level = 6

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    July 29, 2010 at 5:42 pm #190516

    Rivas
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    Participant

    Cp= (LSU – LSL) / 6stdv
    _
    Cpku= (LSU – X)/3stdv
    _
    Cpkl= (X-LSL)/3stdv

    Cpk = the lesser of two

    See me Linked In!

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    August 11, 2010 at 3:24 pm #190590

    MBBinWI
    ★★★★★★★★★★
    Participant

    Marcelo caught you on that one Stan.
    However, the answer was incomplete. Z and Cp are not related mathematically (nor is Cpk related to Cp mathematically). Only in the instance where your distribution is perfectly centered between the LSL and USL will Cp = Cpk = Z/3 and this is not a mathematical relation, rather a definitional relation (yes, Stan, I am well aware that you understand this, I’m pontificating for the masses).

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    August 11, 2010 at 3:51 pm #190593

    Furgeson
    ★★★★★★★★★★
    Member

    MBBinWI,

    We have been looking for you. We need to know if you are Stan’s mentor or his legal guardian.

    Please advise,

    t.

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    August 12, 2010 at 6:26 pm #190606

    MBBinWI
    ★★★★★★★★★★
    Participant

    I could be a real smart alec and accept mentorship, but that would probably get me canned.
    And you certainly aren’t going to pin guardianship on me.

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