# 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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