# GMS 401 Lecture Notes - Lecture 3: Standard Deviation, Exponential Distribution, Preventive Maintenance

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29 Jul 2016
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Chapter 3S: Reliability
RELIABILITY:
“is a measure of the ABILITY of a product, part, or system to perform its intended
function under a prescribed set of conditions over a period.”
It can have an impact on:
Repeat sales
The product’s image
FAILURE:
a situation in which the product or service DOES NOT perform as intended.
Either substandard performance or failure to perform AT ALL.
In effect: Reliability = PROBABILITY!
E.g. given that an item has a reliability of .90
It thus has a 90% or .90 probability of functioning AS INTENDED.
The probability that this item will FAIL is 100-90 = 10% or 1.00 - .90 = .10.
Similarly a reliability of .985 implies an average of 15 failures per
1000 parts or trials.
Reliability is a Probability
Probability is used in TWO ways:
1. The probability that the product or system WILL FUNCTION when activated.
This focuses on ONE POINT IN TIME
Used when a system MUST operate for ONE TIME or a relatively
FEW number of times.
2. The probability that the product or system WILL FUNCTION for a given length
of time.
This focuses on the length of service.
Independent events
The PROBABILITY that a system or a product WILL OPERATE as planned is an important
concept in system and product design.
Determining THAT probability when the product or system 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.
Redundancy
The USE of probability Rules:
RULE #1:
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