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x-R CONTROL CHART
This application requires a plotter-printer.
l~t·Zthiul•ttOm
Control charts are used mainly for quality con-
trol and analysis of processes. They are useful
for obtaining an overall view of particular data.
The
x
-R chart
is
typical of various control
charts based on measured values. The
x -
chart
represents the change
in
the mean value
in
the
distribution of data and the R-chart represents
the change
in
the range of the data.
Input data can be preserved on cassette tape.
The results of processing are output
in
the form
of charts (graphs) and a table. This application
requires the FP-1011 PL plotter-printer.
••WlM,tl
A Chart preparation process
(1) Collected data is arranged according to the time of measurement or lot number,
then divided into groups, which are input one at a time. The sizeun of a group (the
number of data items comprising a group)
is
from 2 to 6. The value of n should
be predetermined.
·
(2) For each group, the mean value
x
and the range
Rare
calculated.
Mean value
x
=
"i:,x/n
Range
R=
xmax -Xmin
(xmax:
maximum value,
Xmin:
minimum value);
(3) The total mean and the average range are calculated.
Total mean
x
= "i:,x/k
A verange range
R
=
"i:,R / k
k: Number of groups.
4) The control limits forx and R charts are calculated.
Control limits for
.x-chart
CL =x
UCL =x
+
A2R
LCL =x - A2R
Coefficients of
A 2/D4
Control limits for R-chart
CL=-~
UCL= D4R
( LCL = DJR is not used.)
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5) Graphs and a table are prepared based on the results of processing.
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