iSixSigma

SPC Xbar-RChart

Viewing 2 posts - 1 through 2 (of 2 total)
  • Author
    Posts
  • #253163

    Chemron9400
    Participant

    Hi everyone. I am new here. I am new with SPC. In our lab we are using certified reference material to check our instrument. Means it has a certified value with uncertainty in the certificate. Now, with our SPC the control limit is even outside the certified value +/- uncertainty. Should i set the limit fixed according to the certificate value to make sure that i do necessary adjustment or correction? If i will follow the control limit calculated then some data are out of the certificate value range. Pls help.

    0
    #253167

    Robert Butler
    Participant

    No, the variability identified by your SPC chart is the ordinary variation of your process. If you try to use control limits that have nothing to do with your process all you will do is add to the process variation and make everything worse – this is known as over control.

    Usually a reference material is some kind of gold standard and you use it to give yourself some sense of how your process is operating relative to the reference. If your ordinary process variation is greater than the gold standard and if the object of your effort is to have a process whose ordinary variation is equal to or less than the gold standard you will need to study your process to identify sources of variation that, when removed, will reduce the accepted ordinary process variation.

    0
Viewing 2 posts - 1 through 2 (of 2 total)

You must be logged in to reply to this topic.