1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
Dismiss Notice
You must be a registered member in order to post messages and view/download attached files in this forum.
Click here to register.

control limits

Discussion in 'SPC - Statistical Process Control' started by samy aly, Dec 26, 2023.

Tags:
  1. samy aly

    samy aly Member

    Joined:
    Dec 26, 2023
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    how can I determine the control limits (upper and lower limits)
     
    samy aly, Dec 26, 2023
    #1
  2. Andy Nichols

    Andy Nichols Moderator Staff Member

    Joined:
    Jul 30, 2015
    Messages:
    5,110
    Likes Received:
    2,562
    Trophy Points:
    112
    Location:
    In the "Rust Belt"
    Welcome to QFO. One of our SPC wizards will be along to assist you shortly…
     
    Andy Nichols, Dec 26, 2023
    #2
    samy aly likes this.
  3. Bev D

    Bev D Moderator Staff Member

    Joined:
    Jul 30, 2015
    Messages:
    606
    Likes Received:
    664
    Trophy Points:
    92
    Location:
    Maine
    What kind of data are you working with?
    Do you have any training in SPC?
     
    Bev D, Dec 28, 2023
    #3
  4. samy aly

    samy aly Member

    Joined:
    Dec 26, 2023
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    continuous data , length , width , fragmentation of glass , etc
    yes I have training in SPC
     
    samy aly, Jan 2, 2024
    #4
  5. Bev D

    Bev D Moderator Staff Member

    Joined:
    Jul 30, 2015
    Messages:
    606
    Likes Received:
    664
    Trophy Points:
    92
    Location:
    Maine
    If you have had training then you know you need to use the formulas for continuous data. The exact formula is dependent on the subgroup size you are using.
    UCL = Xbar_bar +A2*R_bar and the LCL = Xbar_bar - A2*R_bar.
    X_bar_bar is the grand mean (average of the subgroup averages)
    R_bar is the average of the subgroup ranges (max value - Min value)
    A2 is the factor that is dependent on the subgroup size. A2 can be found in any SPC factor table and is limited to n>2 and n<26. If your subgroup size is larger than that you should use the formulas for subgroup standard deviation instead of the subgroup range.
    Don’t forget the Range chart: UCL = D4*Rbar and LCL = D3*R_bar

    These are simple formulas taught in any legitimate SPC training. They are of course just the tip of a very large iceberg. Is there something that you are still not clear about?
     
    Bev D, Jan 2, 2024
    #5
    Miner likes this.
  6. samy aly

    samy aly Member

    Joined:
    Dec 26, 2023
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    thanx
     
    samy aly, Jan 3, 2024
    #6