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process defect

Discussion in 'SPC - Statistical Process Control' started by samy aly, Apr 4, 2024.

  1. samy aly

    samy aly Member

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    we have an argue about calculating process defect ppm , we have three methods of calculation can u help me which one is more realistic
    1- no of defects in samples / no of samples collected*1000000
    2- no of total defects / no of total production * 1000000
    3- ( no of total defects / no of total production for each process * no of processes ) * 1000000
     
    samy aly, Apr 4, 2024
    #1
  2. Bev D

    Bev D Moderator Staff Member

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    Well if you know anything about math then you know Number 3 is wrong. The denominator should be a simple total of all produced units. Regardless of the number of processes…THINK about it: if process 1 produces 1000 units, process 2 produces 10000 units and process 3 produces 5000 units how many units are produced? 16000. You add you don’t multiply.

    Number 2 should only be used if you know how many defects were actually produced in all of the units. (Through 100% inspection or testing).

    If you only know how many defects were in a sample then you use number 1.
     
    Bev D, Apr 4, 2024
    #2
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