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Glossary of Terms
Characteristic Specification of one particular torque value to be collected. Each
characteristic has a name of up to 14 characters. ETA5 can store up to 48
different characteristics at any one time.
Cp This is a capability index which shows the process capability potential but
takes no account of how centred the process is. This is used for capability
studies and Cp may range in value from 0 to infinity. A large value indicates
greater potential capability and a value of 1.33 or greater is desirable.
CpK This is an index which indicates whether the process will produce units within
the tolerance limits. If the process is centred on the nominal value then CpK
will have a value equal to Cp. For values of CpK between 0 and 1 then some
of the 6 sigma spread will fall outside tolerance limits but for values greater
then 1 these will all be within tolerance. A negative value of CpK indicates
that the process mean is outside tolerance limits. A value of 1.33 or greater is
desirable.
CAM This is an alternative capability index requiring a minimum of 30 readings to
be taken. In this implementation, 5 sub-groups of 6 samples are used for
each calculation. The CAM calculation uses the following formula:
Max -- Min
6
Cp =
(Max and Min are limit values)
(Max -- x )
3
CpK = lesser of
(x-- M in )
3
or
(Max and Min are limit values)
* CAM Factor is taken from a table
(in the case of 5 x 6 samples = 1.910)
Max -- Min x Cam Factor *
6 x Average Sample Value
7529_eng.fm Page 55 Wednesday, November 12, 2003 8:57 AM