5.6 Statistical Calculation Functions
62
Function
Description
The mean, maximum, minimum, overall standard deviation, standard
deviation of sample and process capability indices are calculated and
displayed for up to 30,000 measurement values.
The calculation formulas are as follows:
• In these formulas, n represents the number of valid data samples.
• Hi and Lo are the upper and lower thresholds of the comparator.
• The process capability indices represent the quality achievement
capability created by a process, which is the breadth of the
dispersion and bias of the process' quality. Generally, depending on
the values of Cp and CpK, process capability is evaluated as
follows:
Cp, CpK>1.33................... Process capability is ideal
1.33
≥ Cp, CpK>1.00........ Process capability is adequate
1.00
≥ Cp, CpK................. Process capability is inadequate
5.6 Statistical Calculation Functions
Mean
Overall standard deviation (=
σ
n
)
Standard deviation of sample (=
σ
n-1
)
Process capability index
(dispersion)
Process capability index
(bias)
n
x
x
∑
=
n
xnx
∑
−
=
22
σ
1
22
−
−
=
∑
n
xnx
s
1
6
−
−
=
n
LoHi
Cp
σ
1
6
2
−
−+−−
=
n
xLoHiLoHi
CpK
σ
• When only one valid data sample exists, standard deviation of
sample and process capability indices are not displayed.
• When σ
n-1
is 0, Cp and Cpk are 99.99.
• The upper limit of Cp and CpK is 99.99. Values of Cp and
CpK>99.99 are displayed as 99.99.
• When the BIN function is enabled, Cp and CpK are calculated
using the upper and lower thresholds of the comparator.
• Negative values of CpK are handled as CpK=0.
• Values measured by the Temperature Conversion function (∆t)
cannot be used in statistical calculations.
• Changing settings for the Comparator, BIN or Temperature
Correction functions while performing statistical calculations
invalidates calculation results.
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