Statistical Quality Control-Control Charts (ISS (Statistical Services) Statistics Paper IV): Questions 23 - 25 of 31

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Question number: 23

» Statistical Quality Control » Control Charts » Variable

Essay Question▾

Describe in Detail

a) What is major difference between X bar Chart and R chart?

b) What is OC plot?

c) What is Average outgoing Quality (AOQ)?

d) What is Average Total Inspection (ATI)?

Explanation

a) Equation is used to control the process mean, R chart is used to control process variation. Equation reveals undesirable variations between samples as far as their averages are concerned while the R chart reveals any undesirable variations within samples.

b) Operating Characteristic (O. C. ) curve is a graphic

… (250 more words) …

Question number: 24

» Statistical Quality Control » Control Charts » Attributes

Essay Question▾

Describe in Detail

a) In welding of seams, defects included pinholes, cracks, cold laps, etc. A record was made of the number of defects found in one seam each hour and given below. Obtain the 3-σ limits for number of defects.

Finding limits for number of defects

Finding limits for number of defects

1/12/1983

8 A. M.

2

12 A. M.

6

9 A. M.

4

1 P. M.

4

10 A. M.

7

2 P. M.

9

11 A. M.

3

3 P. M.

9

12 A. M.

1

3/12/1983

8 A. M.

6

1 P. M.

4

9 A. M.

4

2 P. M.

8

10 A. M.

3

3 P. M.

9

11 A. M.

9

2/12/1983

8 A. M.

5

12 A. M.

7

9 A. M.

3

1 P. M.

4

10 A. M.

7

2 P. M.

7

11 A. M.

11

3 P. M.

12

b) The number of daily customer complaints are monitored at a telephone exchange. Complaints have been recorded over the past twenty days. Develop three-sigma control limits for the following data.

Number of days and complains per day

Finding control limits for the given data

Days

No. of complaints

Days

No. of complaints

1

2

11

1

2

3

12

3

3

1

13

2

4

3

14

1

5

3

15

1

6

2

16

1

7

3

17

3

8

1

18

2

9

1

19

2

10

3

20

4

Explanation

a) Average number of defects per sample is

Equation

Equation

Equation =6+Equation =13.35

Equation =6-Equation

Since number of defects cannot be negative, Equation can be considered as zero.

b) Average number of defects per sample is

Equation

Equation

Equation =2.2+Equation =6.65

Equation =2.2-Equation →0

Since number

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Question number: 25

» Statistical Quality Control » Control Charts » Variable

Essay Question▾

Describe in Detail

A machine is manufacturing mica discs. Samples of size 5 are drawn every hour and their thickness in units are recorded as follows. Based on Equation chart, Check whether the production is under control?

Find whether production is under control for R chart

Find whether production is under control for mica discs

Sample No.

Observstions

1

8

9

15

4

11

2

7

10

7

6

8

3

11

12

10

9

10

4

12

8

6

9

12

5

11

10

6

14

11

6

7

7

10

4

11

7

10

7

4

10

10

8

8

11

11

7

7

9

8

11

8

14

12

10

12

9

12

17

11

11

7

7

9

17

13

12

9

9

4

4

11

13

10

12

12

12

12

14

8

11

9

6

8

15

10

13

9

4

9

16

9

11

8

5

11

Explanation

Find whether production is under control for R chart - mica Total, Mean and Range

Find whether production is under control for mica discs

Sample No.

Observations

Sample Range

1

8

9

15

4

11

11

2

7

10

7

6

8

4

3

11

12

10

9

10

3

… (148 more words) …

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