Bowers-group Sylvac D100S Readouts Manuel d'utilisateur télécharger pdf (Page 24)

Following display:

-3σ =

X - 3σ = lower regulation or intervention limit

+3σ =

X + 3σ = upper regulation or intervention limit

-NG = number of stored values smaller than lower tolerance

+NG = number of stored values greater than upper tolerance

%Def = percentage of defective stored values =

Cp = process capability =

Cm = machine capability = s given for a sample at time t.

A high Cp will indicate a small dispersion of measured values inside the tolerances:

High Cp Low Cp:

Cmk = center capability = the smaller value of the 2 formulas and

Cpk = process capability in relation to spec mean = the smaller value of and

Cmk/Cpk will formulate capability in a manner that indicates shifts (skewing) in the mean of the distribution away from

the midpoint:

Good Cmk/Cpk: Poor Cmk/Cpk:

Cp >= 1.33 corresponds to a capable process

Note: some users require a Cp >= 1.66 which corresponds to 10.

These indices of capability are certainly an efficient way of taking decisions but their importance must not be exaggera-

ted. Without process analysis, i.e. without knowing the dispersion, random factors and system influences, the indices

are only of limited value and may lead to erroneous decisions being taken.

-3 σ = 9.994

+3 σ = 10.006

-NG = 1

+NG = 0

%DEF = 0.893

Cp = 1.3311

Cpk = 1.3102

Cm = 1.3252

Cmk = 1.3068

(- NG) + (+ NG)

x 100

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Bowers-group Sylvac D100S Readouts Manuel d'utilisateur Page 24