Block 5 - lecture 3

Question 1

np chart?

Answer 1

number nonconforming chart

counts the number of nonconforming items

Question 2

benefits of the np chart over the p chart?

Answer 2

• easier for operators to understand

- few calculations required

Question 3

problems with a np chart over a p chart?

Answer 3

• don’t work for changing subgroup sizes

Question 4

how to find the number nonconforming from the proportion nonconforming?

Answer 4

multiply by the subgroup size

Question 5

how do the points on a number nonconforming chart differ from the limits and central line?

Answer 5

• points are integers

- limits should also be integers but can be left as fractions to stop points falling on them

Question 6

process capability of an attribute?

Answer 6

the central line

Question 7

who are responsible for the non-conformance levels at the central line and outside the limits?

Answer 7

• at the central line is management responsibility

- outside the limits is normally operator responsibility

Question 8

what must happen if the non-conformance levels at the central line isn’t acceptable?

Answer 8

the process needs to be improved with substantial changes

Question 9

what happens if a point is below the lower control limit for non-conformance?

Answer 9

• due to spike in good quality
• assignable cause should be found so it can be repeated
• might be an inspection error

Question 10

types of charts for count of non-conformities?

Answer 10

c chart (per item / fixed subgroup)
u chart (variable subgroups)

Question 11

what is the type of distribution on conformance charts?

Answer 11

Poisson distribution

Question 12

conditions needed for Poisson distribution?

Answer 12

• average count of non-conformities is much lower than max possible
• occurrences are independent