WELD SENTRY 2
Page 29
X & R CONTROL CHARTS & SUMMARIES
-
Select this feature from the SPC menu to calculate,
and display or print, Statistical Process Control (SPC) information for any program with data in
memory.
To
define the data to be evaluated, the following screen is displayed first:
This screen is also used to access the R Control Chart. To change to the R Chart, move the cursor up to the
"X" field and press [CHNG] . The title line will change to R (Range) Control Chart.
After entering the desired schedule number, the "Welds Available in History" line will show the number of
welds which are currently in memory. Enter the number of welds to be included in the SPC calculations and
charts. The count begins with the most recent. In the example above, only the most recent 600 welds will
be evaluated, the first 400 will not be considered. Then. move the cursor to "Sub Group Sample Size".
SUBGROUPS - It is typical in SPC to evaluate sample data in groups to calculate an average and a range
for each group. This produces more statistically reliable results. In the illustration below, data is grouped
into sub groups of 3 welds each. To continue the groupings, sub group #4 would consist of welds 10, 11 &
12. When the "Sampling Period" is CONTINUOUS, weld data is grouped in this way "continuously" until
the total 600 "Welds to use for Calculations" is reached. This would result in a total of 200 sub groups
whose "Sub Group Sample Size" is 3. Refer to the section on SAMPLING MODE, if the sampling period is
PERIODIC.
Enter a "Sub Group Sample Size" from 2 to 25. Press [ENTER] to continue to the summary screen.
If the R Chart were selected, the screen would display “Average R” in place of "Average X". Press
◄
/
►
to
access the summary screen for any of the other Programs A-E for the current schedule. Press [ENTER] to
print the summary screen. Press [CHNG] to continue to the X bar or R Chart.
R CHART X BAR CHART
Summary of Contents for WELD SENTRY 2
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