LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

YB 30

B.Sc. DEGREE EXAMINATION – STATISTICS

SIXTH SEMESTER – April 2009

ST 6602 – STATISTICAL PROCESS CONTROL

 

 

 

Date & Time: 23/04/2009 / 9:00 – 12:00   Dept. No.                                                  Max. : 100 Marks

 

 

PART A

 

Answer ALL the questions:                                                                           (10 x 2 = 20)

 

1. Define Total Quality Management.
2. Mention the basic concepts in quality improvement.
3. How will you model the process quality?
4. Define quantile plot.
5. Distinguish between control charts for attributes and control charts for variables.
6. What are the advantages of control charts?
7. Define the purpose of process capability analysis.
8. What are slant control charts?
9. Mention an application where continuous sampling plan can be used.
10. Explain multiple sampling plan for attributes.

 

PART B

 

Answer any FIVE questions:                                                                         (5 x 8 = 40)

 

1. Examine the need for quality control techniques in production.

 

1. Explain the chance and assignable causes of variation in the quality of manufactured product.

 

1. The sample given below represents the number of defectives found in batches of a production line. Construct a stem and leaf display with stem labels 1,2,3,4,5,6,7,8,9 and leaves ordered.

258	639	739	839	579	679	588	688	654	673
838	412	638	619	369	759	859	679	779	628
728	659	471	571	671	534	693	738	106	206
465	608	708	808	908	998	639	739	489	674
556	656	329	567	509	523	428	528	628	495

 

1. What is a control chart? Explain the basic principles underlying the control charts.

 

1. A machine produces spark plugs to tolerance limits of 25 thousandths of an inch ± 2 thousandth of an inch. Plugs outside this range would give erratic running of the engine. It is decided to set up control charts for the machine. Records reveal that the average range for sample of 5 items is 1 and the mean of the means is 25.1. Setup the mean and range charts.

(d₂ = 2.326, D₃ = 0, D₄ = 2.11)

 

1. Explain the basic principles underlying the slant control charts.

 

1. Explain the terms: (i) Producer’s and consumer’s risks

(ii) AQL and LTPD

 

1. Discuss the relative merits and demerits of single and double sampling plans.

 

PART C

Answer any TWO questions:                                                                                     (2 x 20 = 40)

 

1. a) Explain the need and utility of Total Quality Management.                                  (10)

 

1. b) Batches of 100 components were taken at fixed interval of time from a production line and tested. The following figures are the number of components found to be non-conforming in each of the batches:

4

3

2

0

7

5

2

4

1

3

4

6

Calculate the mean proportion rejected. Draw a quality control chart for samples of 200 such that the inner limit is equal to the mean plus one standard error and the outer limit is equal to mean plus two standard error.                                                                        (10)

 

1. a) Explain histogram and frequency distribution as methods of describing quality variation.

(10)

 

1. b) Draw a suitable control chart for the following data pertaining to the number of coloured threads considered as defects in 15 pieces of cloth in a certain synthetic fibre and state your conclusions:

7	12	3	20	21	5	4	3	10	8
0	9	6	7	20					(10)

 

1. a) Explain the underlying principle and working of CUSUM chart                           (10)

 

1. b) Explain in detail the item by item sequential sampling plan (10)

 

1. a) What is meant by acceptance sampling procedures? What are its advantages?     (10)

 

1. b) Describe single sampling plan. Obtain the OC and AOQ curves for this plan. (10)

 

 

 

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