LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – STATISTICS

YB 48

FOURTH SEMESTER – April 2009

ST 4806 – STATISTICAL PROCESS CONTROL

 

 

 

Date & Time: 21/04/2009 / 9:00 – 12:00 Dept. No.                                                     Max. : 100 Marks

 

 

SECTION – A

 Answer ALL the questions                                                                                         10×2 =20

1. Define quality improvement
2. Explain six-sigma quality
3. Discuss the statistical basis underlying the general use of 3 – sigma limits on control charts.
4. How is lack of control of a process is determined by using control chart technique? .
5. Write down the expression for process capability ratio (PCR) when only the lower specification is known.
6. What information is provided by the OC curve of a control chart?
7. Give an expression for AOQ for a single sampling plan.
8. Write a short note on Multivariate Quality Control.
9. Define a) Specification limits b) Natural tolerance limits.
10. Explain double sampling plan.

SECTION- B

Answer any FIVE questions                                                                                      5 x 8= 40

11. What are the major statistical methods for quality improvement? .
12. A normally distributed quality characteristic is monitored by a control chart with K sigma

control limits. Develop an expression for the probability that a point will plot outside the

control limits when the process is really in control .

13. Sampes of n=6 items are taken from a manufacturing process at regular interval. A normally

distributed quality characteristic is measured and x-bar and S values are calculated for each

sample. After 50 subgroups have been analyzed, we have

 

1. a) Calculate the control limits for the x-bar and S control charts.
2. b) Assume that all the points on both charts plot within the control limits .What are the natural

tolerance limits of the process? .

14. Write a detailed note on the moving average control chart.
15. In designing a fraction non-conforming chart with CL at p =0.20 and 3-sigma control limits,

what is the simple size required to yield a positive LCL? What is the value of n necessary to

give a probability of 0.50 of detecting a shift in the process to 0.26?.

16. Consider the single – sampling plan for which p₁ = 0.01, a = 0.05, p₂ = 0.10 and b = 0.10.

Suppose that lots of N = 2000 are submitted. Draw the AOQ curve and find the AOQL.

 

 

17. What are acceptance and rejection lines of a sequential sampling plan for attributes?. How

are the OC and ASN values obtained for this plan? .

18. What are chain samplings and skip-lot sampling plans?

 

SECTION- C

 

Answer any two questions                                                                                            2 X 20 = 40

 

19. a) Describe the procedure of obtaining the OC curve for a p-chart with an example .
20. b) Explain process capability analysis with an illustration.                               ( 12+8 )

20.a) What are modified control charts?. Explain the method of obtaining control limits for these

charts.

1. b) A control chart for non-conformities per unit uses 0. 95 and 0.05 probability limits .The

center line is at  u=14. Determine the control limits if the size of the sample is 10.     (14+6)

21.a) Discuss the purpose of cumulative sum chart .

1. b) Outline the procedure of constructing V-mask.                                 (8+12)
2. a) Explain with an illustration the method of obtaining the probability of acceptance

for a triple sampling plan.

1. b) What are continuous sampling plans?. Mention a few situations where these plans are

applied.                                                                                                                      (10 + 10)

 

 

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