Practical Data for Metallurgists - Timken

CONTROL CHARTS FOR ATTRIBUTES
The u Chart
u – total nonconformities
5
total units inspected
_
3√u
UCLu 5 u – 1
√n
3√u _
LCLu 5 u – 2
√n
The p Chart
p
The c Chart
c 5 The count (number) of
nonconformities within a
sample
–
c 5 Average number of nonconfomities
per sample
UCLc 5 c 1 3 √ c
LCL c 5 c 2 3 √ c
– number of rejects in subgroup
5
number inspected in subgroups
3√p _ ( 12 p _ )
UCLP 5 P – 1
√n
3√ p _ ( 12 p _ )
LCLP 5 P – 2
√n
The np Chart
np 5 Number of non-conforming
units within a sample
np – 5 Average number of
nonconforming units per
sample
UCLnp 5 np – 1 3 √ np – ( 1 2 p – )
LCL np 5 np – 2 3 √ np – ( 1 2 p – The u Chart
total nonconformities
u =
)
__________________
total units inspected
3√ u
UCLu = u + _____
√n
3√ u
LCLu = u - _____
√n
The p Chart
number of rejects in subgroup
p =
The u Chart
c = The count (number) of
nonconformities within a
sample
c = Average number of nonconfomities
per sample
UCL = c + 3 √ c
c
LCL = c - 3 √ c
c _________________________
number inspected in subgroups
______
3√ p ( 1- p )
UCLP = P + _________
√n
3√ p ( 1- p )
LCLP = P - _________
√n
_
_ _
_
_
_ _
_
_
_
_
_
The np Chart
np = Number of non-conforming
units within a sample
_
np = Average number of
nonconforming units per
sample
_ _ _
UCL = np + 3 √ np (1 - p )
np
_ _ _
LCL = np - 3 √ np (1 - p )
np
_
One or
More Points
Outside
Control
Limits.
A Run Of
7 Or More
Points
Decreasing.
IDENTIFICATION Identification OF of OUT-OF Out-of Control CONTROL Conditions CONDITIONS
(Each point is a subgroup)
128
A Run Of
7 Or More
Points
Increasing.
A Run Of
7 Or More
Points On
Either Side
Of Aim Size.