Ingersoll-Rand ETA5, ETA2 manual Glossary of Terms, Characteristic, CpK

7529_eng.fm Page 55 Wednesday, November 12, 2003 8:57 AM

		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.
							Cp =	Max -- Min
							6
					(Max and Min are limit values)
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.
				(Max --		)		(		-- Min)
		CpK = lesser of			x		or		x
		3					3
		(Max and Min are limit values)
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 x Cam Factor *
			6 x Average Sample Value
		* CAM Factor is taken from a table
		(in the case of 5 x 6 samples = 1.910)

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