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OC curve for Continuous Sampling Plan CSP-1

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  • #37871

    Whitehurst
    Participant

    OC curve for Continuous Sampling Plan CSP-1 old MIL STD 1235
     
    Hello Experts
     
    I have a feeling this may have been answered before, but I couldn’t find it.  If you have already beaten this to death, please just point me to the thread.
    I have inherited a CSP-1 plan (old MIL STD 1235). We x-ray castings using this plan. It was set up before my time by someone who is no longer with the company. I now have to try to justify its use to a customer.
    It seems to me that the way we use this plan is overly “producer friendly”. It also appears to me to have a very high consumer risk. I want to determine the consumer risk for this plan. And that is a problem for me.The copy of the standard I have is almost illegible. I can’t easily read the OC curves.I would like to develop my own OC curve, but I don’t know what distribution this plan is based on. I’m confused by the use of a sampling frequency instead of sample sizeIt seems that I first select a sampling frequency code letter based on the number of units in the production interval (Table I). For example for 501-1200 units I can select code letters A through F.This then lets me select sampling frequency “f” from ½ all the way to 1/10 (Table II-A).For example if we had 750 units in the production interval at a frequency of 1/10 my sample size is 75? Can I then make an OC curve using this sample size and Binomial method?
     
    Or does anyone know how the OC curves for CSP-1 were determined?
    Any help is appreciated.

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    #112544

    Mikel
    Member

    Hypergeometric – easy to do in Excel.
    Post the sampling plan if you want help.

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    #112565

    Mike Carnell
    Participant

    Joe,Get a copy of Grant and Levenworth.Good luck

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    #112580

    Whitehurst
    Participant

    Mike
     
    Thanks for the lead, does Grant and Levenworth specifically deal with the CSP plans?
     
    Stan
     
    Here is the plan as it exists. This is a CSP-1 plan, page 101-4 of the old MIL STD 1235.
     
    Sampling frequency code letter based on the number of units in the production interval (Table I). We are at about 1000 units. So for 501-1200 units it appears I can select code letters A through F.
     
    We are using a sampling frequency “f” of 1/25 and a clearance number “i” of 10.
     
    From  Table II-A it appears we should have selected “i” of 14 for an AQL of 10% and an AOQL of 11.46%!
     
    There is a note at the bottom of this table which states : AQLs are provided as indices to simplify use of this table, but have no other meaning relative to the plans.
    Thanks
     

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    #112582

    Mikel
    Member

    I have the sixth edition of Grant and Leavenworth and it deals with Acceptance Inspection of Continuos Production in chapter 16. It specifically deals with Dodge’s AOQL plan CSP-1 and modifications to them CSP-2 and CSP-3.
    They also give you instruction on how to construct OC curves.
    The correct distribution is hypergeometric – sampling from a finite population.

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    #112589

    Mike Carnell
    Participant

    Joe,Your welcome.Stan already got the rest of the answer.Good luck.

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    #112598

    Whitehurst
    Participant

    Mike & Stan
    Thanks!  I will order a copy of Grant and Leavenworth.  It seems to be a definitive reference, I keep seeing it referred to, time I got a copy.
    Joe
     

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