Given the specification limits and the process mean and sigma, computes the process capability index (Cp, also known as the PCI, or the process capability ratio PCR), the Cpk index, the Cpkm index and the estimated process fraction non-conforming in parts per million (ppm). Note that the estimated process fraction non-conforming is only valid if the process is normally distributed. Normally, sigma tolerance is 6.0. Cp = (upper spec. limit - lower spec. limit)/(sigma tolerance x process sigma) CpU = (upper spec. limit - process mean)/(0.5sigma tolerance x process sigma) CpL = (process mean - lower spec. limit)/ (0.5 sigma tolerance x process sigma) Cpk = MIN { CpU, CpL } Cpkm = (upper spec limit - lower spec limit)/(sigma tolerance x tau). tau = sqrt(process sigma^2 + (process mean - (upper spec limit - lower spec limit)/2)^2)


icon

Inputs/Outputs

  • cenum.png mode (0:two sided) —

    (U16) - Selects whether to calculate two-sided, one-sided upper only or one-sided lower only process capability and fraction non-conforming. By default, mode is two-sided. If upper only, or lower only is selected, the Cpk and fraction non-conforming output are the corresponding one-sided values.

  • cdbl.png upper spec limit —

    (DBL) - The upper specification limit of the process.

  • cdbl.png lower spec limit —

    (DBL) - The upper specification limit of the process.

  • cdbl.png process mean —

    (DBL) - the estimated process mean. See the Process Mean & Sigma VI.

  • cdbl.png process sigma —

    (DBL) - the estimated process sigma. See the Process Mean & Sigma VI.

  • cdbl.png sigma tolerance (6) —

    (DBL, default = 6.0). The sigma multiplier to use in the process capability calculations. If left unwired, a value of 6.0 is used which is the tolerance spread most commonly used for process capability calculations.

  • inclst.png CpU & CpL —

  • idbl.png CpU —

  • idbl.png CpL —

  • idbl.png Cp —

    (DBL) - the process capability index, also known as PCI or the process capability ratio PCR. Cp = (upper spec. limit - lower spec. limit)/(sigma tolerance x process sigma) Normally, the sigma tolerance = 6.

  • idbl.png Cpk —

    (DBL) - the Cpk index. Cpk = MIN {CpU, CpL}, mode = two sided = CpU, mode = upper only = CpL, mode = lower only

  • idbl.png Cpkm —

    (DBL) - a centered process capability ratio. Cpkm = (upper spec limit - lower spec limit)/(sigma tolerance x tau). tau = sqrt(process sigma^2 + (process mean - (upper spec limit - lower spec limit)/2)^2) normally sigma tolerance = 6.0.

  • idbl.png fraction non-conf (ppm) —

    (DBL) - the estimated process fraction non-conforming in parts per million based on a normal process distribution. NOTE: if your process distribution is not normal, this is an invalid estimate. fraction non-conf = fraction > USL + fraction < LSL, mode = two sided = fraction > USL, mode = upper only = fraction < LSL, mode = lower only

  • inclst.png U & L fraction non-conf (ppm) —

    fraction non-conf (ppm) is the estimated fraction non-conforming in parts per million based on a normal process distribution.

  • idbl.png fraction > USL —

    fraction non-conf (ppm) is the estimated fraction non-conforming in parts per million based on a normal process distribution.

  • idbl.png fraction < LSL —

    fraction non-conf (ppm) is the estimated fraction non-conforming in parts per million based on a normal process distribution.