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Pre-control is an alternative to control
charting. A chart is prepared with the span
between the specification limits (not the
control limits) divided into colored bands:
Individual items are taken
from the process, measured and plotted on
the charts. The initial process adjustment,
and subsequent patterns are based on the
pattern of points:
Initial Adjustment (Qualification):
| 5 parts in a row are in the green |
OK to run |
| 1 part in the yellow |
restart the count |
| two consecutive parts in the yellow |
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| one part in the red |
adjust the process and restart
the count |
Operation:
| take 2 consecutive parts from the
process |
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| first part checked is green |
continue operation |
| first part checked yellow |
check the second part |
| second part green |
continue operation |
| second part yellow or either part
red |
stop and adjust the process |
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