iSixSigma

Control limits

Six Sigma – iSixSigma Forums Old Forums General Control limits

Viewing 3 posts - 1 through 3 (of 3 total)
  • Author
    Posts
  • #49511

    Markert
    Participant

    Dear all Six sigma experts
    I have some control charts (Individuals continuous data = defects produced per month) from a few years ago in industry that have an upper control limit calculated as:
    UCL = Xbar + (Xbar/Rbar)*2.66
    I cant remember why they are not calculated in the traditional way as UCL = Xbar+Rbar*2.66
    Can anybody advise if this is an acceptable calc or if its not right?. It seems to reduce the limit & make the control levels finer thus affecting more control – I used the chart like a zone control or J chart. …It worked the defect rate fell dramatically & it was easy for ‘directors’ to use. Thanks Phil

    0
    #169258

    walden
    Participant

    Can you explain why you think defects/month is continuous data?

    0
    #169274

    Markert
    Participant

    Meters of defective product / day, week or month. (from a constant rate line so there is no value in proportioning it). The real question is about the calc of the limits being:
    Xbar+(Xbar/Rbar)*2.66          Vs            Xbar+Rbar*2.66

    0
Viewing 3 posts - 1 through 3 (of 3 total)

The forum ‘General’ is closed to new topics and replies.