Block 3 - lecture 3

Question 1

steps of using a control chart?

Answer 1

• get preliminary data
• find central line and control limits
• check for values out of control
• remove subgroups with assignable causes of deviation (not part of natural variation)
• repeat

Question 2

what happens when Xdoublebar and Rbar are representative of the process?

Answer 2

they become Xbar0 and R0

Question 3

How to recalculate the central lines?

Answer 3

sum of averages minus sum of discarded averages. Then divide by the new number of subgroups

Question 4

Which subgroups to remove?

Answer 4

either:

1. subgroups with either Xbar and R is out of control with assignable cause.
2. subgroups with both Xbar and R is out of control with assignable cause.

Question 5

how to work out the standard deviation from the average range?

Answer 5

standard deviation (sigma0) = R0/d2
(from sheet, with n=values in each subgroup)

Question 6

what happens to the control limits with each revision?

Answer 6

they become narrower, range limits lower