Chapter 4 Supplement Reliability 1Saba Bahouth – UCO
2 Reliability: the probability that a manufactured good, piece of equipment, or system performs its intended function for a stated period of time under specified operating conditions. Several ways to looking at reliability: First view: Related to the probability of working properly when needed. Second view: Related to the life of the product (How long does it work before it breaks) Probability of a product serving longer than a specified period of time
R P = 0.98 R L = 0.95 R F = Saba Bahouth – UCO
Example of Overhead Projector R P = 0.98 R L = 0.95 R F = 0.97 R bL = 0.96 R s = Saba Bahouth – UCO
Probability of first component working + Probability of second component working x Probability of needing second component R ss = R ss = R m + { (1-R m ) x R b } Providing Backups 5Saba Bahouth – UCO
Average Reliability of all Components (Percent) Reliability of the System (Percent) n=1 n=10 n=50 n=100 n=200 n=300 n=400 System Reliability - Components in Series 6Saba Bahouth – UCO
Basic Rule [(1-.90)*(1-.80)*(1-.70)] = – P(all fail) Lamp 1 Lamp 2 (backup for Lamp1) Lamp 3 (backup for Lamp 2) 7Saba Bahouth – UCO
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 8Saba Bahouth – UCO
Infant mortality Regular failureWear-out failure Failure rate Lifetime 9Saba Bahouth – UCO
Improving Reliability Component design Production/assembly techniques Testing Redundancy/backups Preventive maintenance procedures User education System design 10Saba Bahouth – UCO
Exponential Distribution Reliability = e -T/MTBF 1- e -T/MTBF TTime 11Saba Bahouth – UCO
Normal Distribution Reliability 0z 12Saba Bahouth – UCO