Block 3 - lecture 2

Question 1

procedure for creating control charts?

Answer 1

1. select quality characteristic (eg. mass)
2. Choose rational subgroup
3. Collect data
4. Determine trial centre line and control limits
5. establish revised centre line and control limits

Question 2

instant-time sampling method?

Answer 2

take measurements at the same time

Question 3

period of time method?

Answer 3

take measurements randomly over a duration of time

Question 4

reasons for using instant-time sampling method?

Answer 4

minimum variation within subgroup and maximum variation among subgroups

most common - uses a particular time reference (good for assignable cause)

Question 5

reasons for using period of time method?

Answer 5

maximum variation within subgroup and minimum variation among subgroups

better results, more accurate of overall quality

Question 6

how to choose specimens?

Answer 6

All made under the same conditions (same operator, machine, mold etc.)

Question 7

effects of larger subgroup size?

Answer 7

• control limits are tighter
• higher cost per subgroup
• more disruptive/more stock used

Question 8

Subgroup size for R chart?

Answer 8

4-10

>4 distribution is nearly normal

Question 9

Subgroup size for s chart?

Answer 9

> 10 (R more likely to have outliers that affect it more)

Question 10

Calculating the trial centre line for Xbar and R charts?

Answer 10

average of Xbars or Rs

Question 11

What’s n when working out constants?

Answer 11

the subgroup size