Z Value and Process Capability
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 This topic has 7 replies, 1 voice, and was last updated 10 months, 3 weeks ago by subhayu.

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July 26, 2010 at 8:23 pm #53532
Hey Guys
Can anybody tell me the difference between the Z value and Cp, Cpk?
0July 26, 2010 at 11:33 pm #190507Cpk = 3 * z
0July 29, 2010 at 5:36 pm #190515
RivasParticipant@marcelorivas Include @marcelorivas in your post and this person will
be notified via email.I think that Z=3*cpk.
Z is sigma level. If the best cpk=2, sigma level = 60July 29, 2010 at 5:42 pm #190516
RivasParticipant@marcelorivas Include @marcelorivas in your post and this person will
be notified via email.Cp= (LSU – LSL) / 6stdv
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Cpku= (LSU – X)/3stdv
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Cpkl= (XLSL)/3stdvCpk = the lesser of two
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0August 11, 2010 at 3:24 pm #190590
MBBinWIParticipant@MBBinWI Include @MBBinWI in your post and this person will
be notified via email.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).1August 11, 2010 at 3:51 pm #190593
FurgesonMember@t.Furgeson Include @t.Furgeson in your post and this person will
be notified via email.MBBinWI,
We have been looking for you. We need to know if you are Stan’s mentor or his legal guardian.
Please advise,
t.
0August 12, 2010 at 6:26 pm #190606
MBBinWIParticipant@MBBinWI Include @MBBinWI in your post and this person will
be notified via email.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.0June 20, 2020 at 4:34 am #248471
subhayuParticipant@subhayu Include @subhayu in your post and this person will
be notified via email.I have a follow up question how is it that Z/3 = Cp/Cpk if the process is centered? I understand if the process is centered Cp=Cpk and both values of Cpk will be the same. What I dont get is how will that be equal to Z/3 assuming the Z statistic is Z=[X(mu)]/(sigma)
Will appreciate a response since I am due to take the CSSBB exam next month
0 
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