1. Copyright © 2014 by McGraw-Hill Education (Asia). All rights reserved. 4S Reliability

2. 4S-2 Learning Objectives  Define reliability  Perform reliability computations  Explain the purpose of redundancy in a system

3. 4S-3 Reliability  Reliability : The ability of a product, part, or system to perform its intended function under a prescribed set of conditions  Failure : Situation in which a product, part, or system does not perform as intended  Normal operating conditions: The set of conditions under which an item’s reliability is specified

4. 4S-4  Probability that the product or system will:  Function when activated  Function for a given length of time  Independent events  Events whose occurrence or nonoccurrence do not influence each other  Redundancy  The use of backup components to increase reliability Reliability Is a Probability

5. 4S-5 Rule 1.90.80 Lamp 1Lamp 2.90 x.80 =.72

6. 4S-6 Rule 2.90.80.90 + (1-.90)*.80 =.98 Lamp 1 Lamp 2 (backup)

7. 4S-7 Rule 3.90.80.70 1-[(1-.90)*(1-.80)*(1-.70)] =.994 1 – P(all fail) Lamp 1 Lamp 2 (backup for Lamp1) Lamp 3 (backup for Lamp 2)

8. 4S-8 Example 4S-1: Reliability Determine the reliability of the system shown.98.90.92.95

9. 4S-9 Example 4S-1: Solution The system can be reduced to a series of three components.98.90+.90(1-.90).95+.92(1-.95).98 x.99 x.996 =.966

10. 4S-10 Failure Rate Figure 4S.1 Few (random) failures Infant mortality Failures due to wear-out Time, T Failure Rate

11. 4S-11 Exponential Distribution Reliability = e -T/MTBF 1- e -T/MTBF TTime Figure 4S.2

12. 4S-12 Normal Distribution Reliability 0z Figure 4S.3

13. 4S-13 Availability  The fraction of time a piece of equipment is expected to be available for operation MTBF = mean time between failures MTR = mean time to repair

14. 4S-14 Improving Reliability  Component design  Production/assembly techniques  Testing  Redundancy/backups  Preventive maintenance procedures  User education  System design