GMS 401 Chapter Notes - Chapter 4: Preventive Maintenance, Mean Time Between Failures
DepartmentGlobal Management Studies
Course CodeGMS 401
ProfessorWally Whistance- Smith
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Chapter 4 Supplement- Reliability
Reliability: The ability of a product, part, or system to perform its intended function under a prescribed set of
In effect, reliability is a probability – (If an item has a reliability of .90, this also means that it has a 90%
probability of functioning as intended
The probability that it will fail (its failure rate) is 1- .90 = .10/10%. This means that the item will fail once in
every 10 trials
N ormal Operating Conditions: the set of conditions under which an item’s reliability is specified
Reliability is used in two ways;
1. Instantaneous Reliability: the probability that the product or system will function when activated
-Focuses on one point in time, often used when an item must operate for one or a few number of times
2. Continuous Reliability: the probability that the product or system will function for a given length of time
-Focuses on the length of service
Probability Rules: used to determine whether a given product will operate successfully
Determining the probability when the product consists of a number of independent components requires the use
of the rules of probability for independent events. Independent Events have no relation to the occurrence or
non-occurrence of each other.
If two or more events are independent and the success is defined as the probability that all of the events occur,
than the probability of success is equal to the product of the probabilities of the events
-Even though the individual components of a system might have high reliability, the system as whole can
have considerably less reliability b/c all components that are in a series must function.
(Example: One lamp has .90 reliability while the other has .80. Therefore the probability that both will
work becomes .90 x .80 which equals .72)
- As the number of components in a series increases, the system reliability decreases.
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