capab. term. def

8/17/2019 Capab. Term. Def

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Pp

The Pp index is used to summarize a system's performance in meeting two-sided

specification limits (upper and lower). Like Ppk it uses actual sigma (sigma of the

indi!iduals) and shows how the system is actually running when compared to the

specifications. "owe!er it ignores the process a!erage and focuses on the spread. #f the

system is not centered within the specifications Pp alone may $e misleading.

The higher the Pp !alue...

...the smaller the spread of the system%s output. Pp is a measure of spread only. & process

with a narrow spread (a high Pp) may not meet customer needs if it is not centered within the

specifications.

#f the system is centered on its target !alue...

...Pp should $e used in conunction with Ppk to account for $oth spread and centering. Pp

and Ppk will $e eual when the process is centered on its target !alue. #f they are not eual

the smaller the difference $etween these indices the more centered the process is.

Ppk

Ppk is an index of process performance which tells how well a system is meeting

specifications. Ppk calculations use actual sigma (sigma of the indi!iduals) and shows how

the system is actually running when compared to the specifications. This index also takes

into account how well the process is centered within the specification limits.

#f Ppk is .*...

...the system is producing ++., of its output within specifications. The larger the Ppk the

less the !ariation $etween process output and specifications.

#f Ppk is $etween * and .*...

...not all process output meets specifications.


...Ppk should $e used in conunction with the Pp index. #f the system is centered on its target

!alue Ppk and Pp will $e eual. #f they are not eual the smaller the difference $etween

these indices the more centered the process is.

Pr

The Pr performance ratio is used to summarize the actual spread of the system compared to

the spread of the specification limits (upper and lower). The lower the Pr !alue the smaller

the output spread. Pr does not consider process centering.

/hen the Pr !alue is multiplied $y ** the result shows the percent of the specifications that

are $eing used $y the !ariation in the process. Pr is calculated using the actual sigma (sigma

of the indi!iduals) and is the reciprocal of Pp. #n other words Pr 0 1Pp.


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Cp

The 2p index is used to summarize a system's a$ility to meet two-sided specification limits

(upper and lower). Like 2pk it uses estimated sigma and therefore shows the system's

potential to meet the specifications. "owe!er it ignores the process a!erage and focuses on

the spread. #f the system is not centered within the specifications 2p alone may $e

misleading.

The higher the 2p !alue...

..the smaller the spread of the system%s output. 2p is a measure of spread only. & process

with a narrow spread (a high 2p) may not meet customer needs if it is not centered within the

specifications.


2p should $e used in conunction with 2pk to account for $oth spread and centering. 2p and2pk will $e eual when the process is centered on its target !alue. #f they are not eual the

smaller the difference $etween these indices the more centered the process is.

Cpk

2pk is a capa$ility index that tells how well as system can meet specification limits. 2pk

calculations use estimated sigma and therefore shows the system's 3potential3 to meet

specifications. 4ince it takes the location of the process a!erage into account the processdoes not need to $e centered on the target !alue for this index to $e useful.

#f 2pk is .*...

...the system is producing ++., of its output within specifications. The larger the 2pk the

less !ariation you will find $etween the process output and specifications.

#f 2pk is $etween * and .*...

...not all process output meets specifications.


...2pk should $e used in conunction with the 2p index. 2pk and 2p will $e eual when the

process is centered on its target !alue. #f they are not eual the smaller the difference

$etween these indices the more centered the process is.

Cpm

The 2pm index indicates how well the system can produce within specifications. #ts

calculation is similar to 2p except that sigma is calculated using the target !alue instead ofthe mean. The larger the 2pm the more likely the process will produce output that meets

specifications and the target !alue.


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Cr

The 2r capa$ility ratio is used to summarize the estimated spread of the system compared to

the spread of the specification limits (upper and lower). The lower the 2r !alue the smaller

the output spread. 2r does not consider process centering.

/hen the 2r !alue is multiplied $y ** the result shows the percent of the specifications that

are $eing used $y the !ariation in the process. 2r is calculated using an estimated sigma and

is the reciprocal of 2p. #n other words 2r 0 12p.

capab. term. def

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