Reliability
189
1. During the Korean War less than 30% of the combat airplane
electronic equipment was operational. Later similar equipment
is over 70% operational. (The Korean War was fought with almost
half the planes and virtually all the ships of World War II
Vintage.)
2. In 1958 only 28% of all United States satellite launchings were
successful, whereas in 1962, 83% of all United States launchings
were successful.
3. In 1959 passenger-car Warranties were for a period of 90 days or
4000 miles whichever came first. In 1997, 100,000 mile warranties
are offered.
It is understood that Reliability is "the probability that a device will
perform its specific function for a specific time under specific operating conditions." Note that to define Reliability
1. satisfactory performance must be stated
2. time is involved (either calendar time or number of operating
cycles)
3. operating conditions must be stated
4. then after testing the probability can be estimated
There are several areas of interest in reliability for engineers:
1. designing with reliability in mind
2. measuring reliability
3. management or organization of systems for high reliability
4. prediction of reliability
by means of mathematics
II. RELIABILITY FOR A GENERAL FAILURE CURVE
The best possible way to discuss Reliability would be to start with the basic
part of its definition-probability.
There are various distribution curves for failure data which are not
necessarily Gaussian. These alternative distributions are approximated
by curve-fitting the failure data. Some of the distributions which can be
found in handbooks [4.10] are:
Binomial distribution
Geometric distribution
Poisson distribution
Triangular distribution
Normal distribution
189
1. During the Korean War less than 30% of the combat airplane
electronic equipment was operational. Later similar equipment
is over 70% operational. (The Korean War was fought with almost
half the planes and virtually all the ships of World War II
Vintage.)
2. In 1958 only 28% of all United States satellite launchings were
successful, whereas in 1962, 83% of all United States launchings
were successful.
3. In 1959 passenger-car Warranties were for a period of 90 days or
4000 miles whichever came first. In 1997, 100,000 mile warranties
are offered.
It is understood that Reliability is "the probability that a device will
perform its specific function for a specific time under specific operating conditions." Note that to define Reliability
1. satisfactory performance must be stated
2. time is involved (either calendar time or number of operating
cycles)
3. operating conditions must be stated
4. then after testing the probability can be estimated
There are several areas of interest in reliability for engineers:
1. designing with reliability in mind
2. measuring reliability
3. management or organization of systems for high reliability
4. prediction of reliability
by means of mathematics
II. RELIABILITY FOR A GENERAL FAILURE CURVE
The best possible way to discuss Reliability would be to start with the basic
part of its definition-probability.
There are various distribution curves for failure data which are not
necessarily Gaussian. These alternative distributions are approximated
by curve-fitting the failure data. Some of the distributions which can be
found in handbooks [4.10] are:
Binomial distribution
Geometric distribution
Poisson distribution
Triangular distribution
Normal distribution