norbar T-Box 43236, Руководство оператора

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SPC Calculations
Term Mathematical equation Comment
No readings N The number of readings
Minimum The smallest reading.
Maximum The largest reading.
Mean Sum of readings / N This is the average reading.
Sigma
The square root of:
Σ(reading-mean)² / (N-1)
Also known as standard deviation, this shows how
close together the readings are.
Cp (3 sigma)
(Upper limit – Lower limit) /
6 sigma
This is the capability index, showing the process
capability potential. It takes no account of how
centred the process is.
A value of 1.33 or more is desirable.
Cpk (3 Sigma)
lesser of:
(Upper limit-mean) / 3 sigma
or
(mean – Lower limit) / 3 sigma
This indicates whether the process will produce
units within tolerance.
If the process is centred on the nominal value then
Cpk will have a value equal to Cp.
A negative value shows mean is outside tolerance.
A value of 1.33 or more is desirable.
Cp (6 sigma)
(Upper limit – Lower limit) /
12 sigma
This is the capability index, showing the process
capability potential. It takes no account of how
centred the process is.
Cpk (6 Sigma)
lesser of:
(Upper limit - mean) / 6 sigma
or
(mean – Lower limit) / 6 sigma
This indicates whether the process will produce
units within tolerance.
If the process is centred on the nominal value then
Cpk will have a value equal to Cp.
A negative value shows mean is outside tolerance.
The SPC calculations depend on the number of readings selected and if a Target with limits was used.