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Control charts

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  • #47116

    Whitehurst
    Participant

    Hello – can anybody point me towards a guide showing when to use specific types of control charts for different applications?
    Thanks for your help
    Joe

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    #156741

    BritW
    Participant

    Decent, but basic flowchart for chart selection:
    http://www.qualityadvisor.com/library/controlchartselection.php
     

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    #156742

    Fake Gary Alert
    Participant

    Control  Charts  for  variables:for  temp.,size,weight,sales,volume,etc
    Types: Xbar-R cHARTS (when  data  is  readily  available)
    Run Charts (limited single-point data)
    MXbar-MR Charts (limited  data-moving average/moving  range)
    Xbar-S Charts (when  sigma  is  readily  available)
    Median Charts
    Short  Run  Charts (when  the  production lot  size  is  extremely small
    (10–20) pieces or  when  the  sample  size under  typical operating   condition  is  small).
    (2) Control  Charts  for  attributes:# of  complaints per  order,# of  orders on  time,absenteeism  frequency,# of  errors  per  letter,etc
    Types:
    P  Charts (for  defectives-sample  size varies)
    np Charts (for  defectives-sample  size  fixed)
    c Charts (for  defect – sample  size  fixed
    u Charts (for  defects-sample  size varies)
    Short Run Varieties of  p,np,c and  u  charts
    Important  note:The  most sensitive  attribute chart is  the p chart.The  most  sensitive  and  expensive  chart  is  the  Xbar-R.
    Hope  that  helps   

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    #156743

    Savage
    Participant

    There’s a good one on this site:
    https://www.isixsigma.com/st/control_charts/
    Good luck.

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    #156744

    Whitehurst
    Participant

    Thanks for your help on this.
    cheers

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    #156745

    Fontanilla
    Participant

    What is the difference between “defect” and “defectives”
    cheers

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    #156746

    accrington
    Participant

    Why is the Xbar – R chart the most expensive chart, and why is it more sensitive than, say an Xbar – s chart, or maybe a cusum chart?

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    #156747

    BC
    Participant

    A unit can have multiple defects.  The unit itself is either defective or not defective.

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    #156748

    newbie
    Participant

    What does the question “Can the data being collected be larger than the subgroup` mean?  Thanks!!

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    #156750

    BritW
    Participant

    Basically means deciding if you are counting attribute data or workin gwith classifications of data.  If you count items, then go the direction of the u and c chart. If you have a classification of data or are workin g with rates/percentages, go the p and np route.

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    #156759

    Fake Gary Alert
    Participant

    Defects:
    A product may  have   many  defects
    Does  not  prevent  the product  from  functioning
    Defectives:
    The  product is  not  usable
    Hope  that  helps 

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    #157108

    sathish chandran
    Member

    Hi,
    The type of control chart depends on what type of data is being measured.
    For continuous type of data we have the following options;
    1) I & MR Chart – where it is induvidual data points
    2) X bar r chart where you have a sub group and its size is less than 8
    3) X bar s chart where you have a sub group and its size is more than 8
    For discrete type of data we have the following options – when you are measuring defectives
    1) NP chart for a constant sub group size
    2) P chart for a varying sub group size
    For discrete type of data we have the following options – when you are measuring defects
    1) C chart for a constant sub group size
    2) U chart for a varying sub group size
    Point to remember in Control Charts
    1) nDo not apply SPC tools to processes that are known to be out on control
    2) nDo not compare control limits with specification limits
    3) nDo not ignore ‘out-of-control’ signals if your ‘Y’ is meeting the specifications & ‘X’ is meeting the operating limits
    4) nDo not plot them for the sake for it, act on it
    5) Ensure that observations are independent of each other
    6) nIt’s quite possible that ‘X’ is under control, but ‘Y’ is out-of-spec’s
    hope this helps you
    with regards
    sathish chandran
     

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