SENG 421 Reliability Demonstration Chart

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SENG 421Reliability Demonstration Chart
Department of Electrical Computer Engineering,
University of Calgary B.H. Far (far_at_ucalgary.ca) h
ttp//www.enel.ucalgary.ca/People/far/Lectures/SEN
G421/
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Reliability Demo Chart /1

• An efficient way of checking whether the FIO (?F)
  is met or not.
• It is based on collecting failure data at time
  points.
• Vertical axis failure number (n)
• Horizontal axis normalized failure data (Tn),
  i.e.,
• failure time ? ?F

Figure from Musas Book
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Parameters Involved /1

• Discrimination ratio (?) Acceptable error in
  estimating failure intensity.
• Customer risk (?) Probability that the
  developer is willing to accept of falsely saying
  the failure intensity objective is met (i.e.,
  acceptance) when it is not.
• Developer risk (?) Probability that the
  developer is willing to accept of falsely saying
  the failure intensity objective is not met (i.e.,
  rejection) when it is.

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Parameters Involved /2

• For ? 10 and ? 10 and ? 2
• There is 10 risk (?) of wrongly accepting the
  software when its failure intensity objective is
  actually equal or greater than twice (? 2) the
  failure intensity objective.
• There is 10 risk (?) of wrongly rejecting the
  software when its failure intensity objective is
  actually equal or less than half (? 2) the
  failure intensity objective.

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Reliability Demo Chart /2

• A changes rapidly with customer risk but very
  slightly with developer risk and it determines
  the intercept of accept boundary with the
  horizontal line n0
• B changes rapidly with developer risk but very
  slightly with customer risk and it determines the
  intercept of reject boundary with the vertical
  line Tn0

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Reliability Demo Chart /3

• Boundary between accept and continue regions

(? is the discrimination ratio)

• Boundary between reject and continue regions

(? is the discrimination ratio)
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Reliability Demo Chart /4

• Values of intercepts of boundaries with various
  horizontal and vertical axes

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Reliability Demo Chart /5

• Values of A and B for various consumer and
  supplier risk levels

Table from Musas Book
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Reliability Demo Chart /6

• When risk levels (? and ?) decrease, the system
  will require more test before reaching the accept
  or reject regions, i.e., the continue region
  becomes wider.
• When discrimination ratio (?) decreases, the
  system will require more test before reaching the
  accept or reject regions, i.e., the continue
  region becomes wider.

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RDC Example /1

• Consumer risk
• ? 5
• Supplier risk
• ? 5
• Discrimination
• ratio ? 2

Figure from Musas Book
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RDC Example /2

• Consumer risk
• ? 1
• Supplier risk
• ? 1
• Discrimination
• ratio ? 2

Figure from Musas Book
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RDC Example /3

• Consumer risk
• ? 0.1
• Supplier risk
• ? 0.1
• Discrimination
• ratio ? 2

Figure from Musas Book
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RDC Example /4

• Consumer risk
• ? 10
• Supplier risk
• ? 10
• Discrimination
• ratio ? 1.2

Figure from Musas Book
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Example 1
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Example 2
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Example 3

• We are going to buy a new colour laser printer
  for our department. We have borrowed the printer
  for the test run and we are going to conduct
  certification test on it. Makers data shows that
  we need to change the toner every 10,000 pages.
  We would like to have the system running without
  any failure between the two consecutive toner
  changes and in the worst case having only one
  failure during the period.
• a) What shall be our failure intensity objective
  for the system?

?F 1/10000 pages
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Example 3 (contd.)

• b) We observe that failures occur at 4,000 pages,
  6,000 pages, 10,000 pages, 11,000 pages, 12,000
  pages and 15,000 pages of output. Using the
  reliability demonstration chart, what can we
  conclude about this printer?

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Example 3 (contd.)

• Because of failing the certification test we will
  reject the printer.