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The following information is provided
by the American Society for Quality (ASQ):
Certification Requirements
Education and/or Experience
You must have eight years of on-the-job experience in one or more of the
areas of the Certified Reliability Engineer Body of Knowledge. A minimum of three years of
this experience must be in a decision-making position. Decision-making is
defined as the authority to define, execute, or control projects/processes and to be
responsible for the outcome. This may or may not include management or supervisory
positions.
If you are now or were previously certified by ASQ as a Quality Engineer,
Quality Auditor, Software Quality Engineer, or Quality Manager, experience used to qualify for
certification in these fields often applies to certification as a Reliability Engineer.
If you have completed a degree* from a college, university, or technical school with
accreditation accepted by ASQ, part of the eight-year experience requirement will be
waived, as follows (only one of these waivers may be claimed):
- Diploma from a technical or trade schoolone year will be waived
- Associate degreetwo years waived
- Bachelors degreefour years waived
- Masters or doctoratefive years waived
*Degrees/diplomas from foreign educational institutions must be
equivalent to degrees from U.S. educational institutions.
Examination
Each certification candidate is required to pass a written examination
that consists of multiple choice questions that measure comprehension of the Body of
Knowledge. The Reliability Engineer examination is a one-part, 150-question, four-hour
exam and is offered in the English language only.
Examinations are conducted twice a year, in March and October,
by local ASQ sections and international organizations. All examinations are
open-book. Each participant must bring his or her own reference materials. Use of
reference materials and calculators is explained in the seating letter provided to
applicants.
Please Note: The Body of Knowledge for certification is affected
by new technologies, policies, and the changing dynamics of manufacturing and service
industries. Changed versions of the examination based on the current Body of Knowledge are
used at each offering.
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Body of
Knowledge
|
The topics
in this Body
of Knowledge
include
additional
detail in
the form of
subtext
explanations
and the
cognitive
level at
which the
questions
will be
written.
This
information
will provide
useful
guidance for
both the
Examination
Development
Committee
and the
candidates
preparing to
take the
exam. The
subtext is
not intended
to limit the
subject
matter or be
all-inclusive
of what
might be
covered in
an exam. It
is intended
to clarify
the type of
content to
be included
in the exam.
The
descriptor
in
parentheses
at the end
of each
entry refers
to the
highest
cognitive
level at
which the
topic will
be tested. A
more
comprehensive
description
of cognitive
levels is
provided at
the end of
this
document.
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- RELIABILITY MANAGEMENT (18
Questions)
- Strategic management
- Benefits of
reliability engineering
Describe how reliability
engineering techniques and
methods improve programs,
processes, products, systems,
and services. (Understand)
- Interrelationship of
safety, quality, and reliability
Define and describe the
relationships among safety,
reliability, and quality.
(Understand)
- Role of the
reliability function in the
organization
Describe how reliability
techniques can be applied in
other functional areas of the
organization, such as marketing,
engineering, customer /product
support, safety and product
liability, etc. (Apply)
- Reliability in
product and process development
Integrate reliability
engineering techniques with
other development activities,
concurrent engineering,
corporate improvement
initiatives such as lean and six
sigma methodologies, and
emerging technologies. (Apply)
- Failure consequence
and liability management
Describe the importance of these
concepts in determining
reliability acceptance criteria.
(Understand)
- Warranty management
Define and describe warranty
terms and conditions, including
warranty period, conditions of
use, failure criteria, etc., and
identify the uses and
limitations of warranty data.
(Understand)
- Customer needs
assessment
Use various feedback methods
(e.g., quality function
deployment (QFD), prototyping,
beta testing) to determine
customer needs in relation to
reliability requirements for
products and services. (Apply)
- Supplier reliability
Define and describe supplier
reliability assessments that can
be monitored in support of the
overall reliability program.
(Understand)
- Reliability program
management
- Terminology
Explain basic reliability terms
(e.g., MTTF, MTBF, MTTR,
availability, failure rate,
reliability, maintainability).
(Understand)
- Elements of a
reliability program
Explain how planning, testing,
tracking, and using customer
needs and requirements are used
to develop a reliability
program, and identify various
drivers of reliability
requirements, including market
expectations and standards, as
well as safety, liability, and
regulatory concerns.
(Understand)
- Types of risk
Describe the relationship
between reliability and various
types of risk, including
technical, scheduling, safety,
financial, etc. (Understand)
- Product lifecycle
engineering
Describe the impact various
lifecycle stages
(concept/design, introduction,
growth, maturity, decline) have
on reliability, and the cost
issues (product maintenance,
life expectation, software
defect phase containment, etc.)
associated with those stages.
(Understand)
- Design evaluation
Use validation, verification,
and other review techniques to
assess the reliability of a
product’s design at various
lifecycle stages. (Analyze)
- Systems engineering
and integration
Describe how these processes are
used to create requirements and
prioritize design and
development activities.
(Understand)
- Ethics, safety, and
liability
- Ethical issues
Identify appropriate ethical
behaviors for a reliability
engineer in various situations.
(Evaluate)
- Roles and
responsibilities
Describe the roles and
responsibilities of a
reliability engineer in relation
to product safety and liability.
(Understand)
- System safety
Identify safety-related issues
by analyzing customer feedback,
design data, field data, and
other information. Use risk
management tools (e.g., hazard
analysis, FMEA, FTA, risk
matrix) to identify and
prioritize safety concerns, and
identify steps that will
minimize the misuse of products
and processes. (Analyze)
- PROBABILITY AND STATISTICS
FOR RELIABILITY (27 Questions)
- Basic concepts
- Statistical terms
Define and use terms such as
population, parameter,
statistic, sample, the central
limit theorem, etc., and compute
their values. (Apply)
- Basic probability
concepts
Use basic probability concepts
(e.g., independence, mutually
exclusive, conditional
probability) and compute
expected values. (Apply)
- Discrete and
continuous probability
distributions
Compare and contrast various
distributions (binomial,
Poisson, exponential, Weibull,
normal, log-normal, etc.) and
their functions (e.g.,
cumulative distribution
functions (CDFs), probability
density functions (PDFs), hazard
functions), and relate them to
the bathtub curve. (Analyze)
- Poisson process
models
Define and describe homogeneous
and non-homogeneous Poisson
process models (HPP and NHPP).
(Understand)
- Non-parametric
statistical methods
Apply non-parametric statistical
methods, including median,
Kaplan-Meier, Mann-Whitney,
etc., in various situations.
(Apply)
- Sample size
determination
Use various theories, tables,
and formulas to determine
appropriate sample sizes for
statistical and reliability
testing. (Apply)
- Statistical process
control (SPC) and process
capability
Define and describe SPC and
process capability studies (Cp,
Cpk, etc.), their control
charts, and how they are all
related to reliability.
(Understand)
- Statistical inference
- Point estimates of
parameters
Obtain point estimates of model
parameters using probability
plots, maximum likelihood
methods, etc. Analyze the
efficiency and bias of the
estimators. (Evaluate)
- Statistical interval
estimates
Compute confidence intervals,
tolerance intervals, etc., and
draw conclusions from the
results. (Evaluate)
- Hypothesis testing
(parametric and non-parametric)
Apply hypothesis testing for
parameters such as means,
variance, proportions, and
distribution parameters.
Interpret significance levels
and Type I and Type II errors
for accepting/rejecting the null
hypothesis. (Evaluate)
- RELIABILITY IN DESIGN AND
DEVELOPMENT (26 Questions)
- Reliability design
techniques
- Environmental and
use factors
Identify environmental and use
factors (e.g., temperature,
humidity, vibration) and
stresses (e.g., severity of
service, electrostatic discharge
(ESD), throughput) to which a
product may be subjected.
(Apply)
- Stress-strength
analysis
Apply stress-strength analysis
method of computing probability
of failure, and interpret the
results. (Evaluate)
- FMEA and FMECA
Define and distinguish between
failure mode and effects
analysis and failure mode,
effects, and criticality
analysis and apply these
techniques in products,
processes, and designs.
(Analyze)
- Common mode failure
analysis
Describe this type of failure
(also known as common cause mode
failure) and how it affects
design for reliability.
(Understand)
- Fault tree analysis
(FTA) and success tree analysis
(STA)
Apply these techniques to
develop models that can be used
to evaluate undesirable (FTA)
and desirable (STA) events.
(Analyze)
- Tolerance and
worst-case analyses
Describe how tolerance and
worst-case analyses (e.g., root
of sum of squares, extreme
value) can be used to
characterize variation that
affects reliability.
(Understand)
- Design of
experiments
Plan and conduct standard design
of experiments (DOE) (e.g.,
full-factorial, fractional
factorial, Latin square design).
Implement robust-design
approaches (e.g., Taguchi
design, parametric design, DOE
incorporating noise factors) to
improve or optimize design.
(Analyze)
- Fault tolerance
Define and describe fault
tolerance and the reliability
methods used to maintain system
functionality. (Understand)
- Reliability
optimization
Use various approaches,
including redundancy, derating,
trade studies, etc., to optimize
reliability within the
constraints of cost, schedule,
weight, design requirements,
etc. (Apply)
- Human factors
Describe the relationship
between human factors and
reliability engineering.
(Understand)
- Design for X (DFX)
Apply DFX techniques such as
design for assembly,
testability, maintainability
environment (recycling and
disposal), etc., to enhance a
product’s producibility and
serviceability. (Apply)
- Reliability
apportionment (allocation)
techniques
Use these techniques to specify
subsystem and component
reliability requirements.
(Analyze)
- Parts and systems
management
- Selection,
standardization, and reuse
Apply techniques for materials
selection, parts standardization
and reduction, parallel
modeling, software reuse,
including commercial
off-the-shelf (COTS) software,
etc. (Apply)
- Derating methods and
principles
Use methods such as S-N diagram,
stress-life relationship, etc.,
to determine the relationship
between applied stress and rated
value, and to improve design.
(Analyze)
- Parts obsolescence
management
Explain the implications of
parts obsolescence and
requirements for parts or system
requalification. Develop risk
mitigation plans such as
lifetime buy, backwards
compatibility, etc. (Apply)
- Establishing
specifications
Develop metrics for reliability,
maintainability, and
serviceability (e.g., MTBF, MTBR,
MTBUMA, service interval) for
product specifications. (Create)
- RELIABILITY MODELING AND
PREDICTIONS (22 Questions)
- Reliability modeling
- Sources and uses of
reliability data
Describe sources of reliability
data (prototype, development,
test, field, warranty,
published, etc.), their
advantages and limitations, and
how the data can be used to
measure and enhance product
reliability. (Apply)
- Reliability block
diagrams and models
Generate and analyze various
types of block diagrams and
models, including series,
parallel, partial redundancy,
time-dependent, etc. (Create)
- Physics of failure
models
Identify various failure
mechanisms (e.g., fracture,
corrosion, memory corruption)
and select appropriate
theoretical models (e.g.,
Arrhenius, S-N curve) to assess
their impact. (Apply)
- Simulation
techniques
Describe the advantages and
limitations of the Monte Carlo
and Markov models. (Apply)
- Dynamic reliability
Describe dynamic reliability as
it relates to failure criteria
that change over time or under
different conditions.
(Understand)
- Reliability predictions
- Part count
predictions and part stress
analysis
Use parts failure rate data to
estimate system- and
subsystem-level reliability.
(Apply)
- Reliability
prediction methods
Use various reliability
prediction methods for both
repairable and non-repairable
components and systems,
incorporating test and field
reliability data when available
(Apply)
- RELIABILITY TESTING (24
Questions)
- Reliability test
planning
- Reliability test
strategies
Create and apply the
appropriate test strategies
(e.g., truncation,
test–to-failure, degradation)
for various product development
phases. (Create)
- Test environment
Evaluate the environment in
terms of system location and
operational conditions to
determine the most appropriate
reliability test. (Evaluate)
- Testing during
development
Describe the purpose, advantages,
and limitations of each of the
following types of tests, and use
common models to develop test plans,
evaluate risks, and interpret test
results. (Evaluate)
- Accelerated life tests
(e.g., single-stress,
multiple-stress, sequential
stress, step-stress)
- Discovery testing (e.g.,
HALT, margin tests, sample size
of 1),
- Reliability growth testing
(e.g., test, analyze, and fix (TAAF),
Duane)
- Software testing (e.g.,
white-box, black-box,
operational profile, and
fault-injection)
- Product testing
Describe the purpose, advantages,
and limitations of each of the
following types of tests, and use
common models to develop product
test plans, evaluate risks, and
interpret test results. (Evaluate)
- Qualification/demonstration
testing (e.g., sequential tests,
fixed-length tests)
- Product reliability
acceptance testing (PRAT)
- Ongoing reliability testing
(e.g., sequential probability
ratio test [SPRT])
- Stress screening (e.g., ESS,
HASS, burn-in tests)
- Attribute testing (e.g.,
binomial, hypergeometric)
- Degradation
(wear–to-failure) testing
- MAINTAINABILITY AND
AVAILABILITY (15 Questions)
- Management strategies
- Planning
Develop plans for
maintainability and availability
that support reliability goals
and objectives. (Create)
- Maintenance
strategies
Identify the advantages and
limitations of various
maintenance strategies (e.g.,
reliability-centered maintenance
(RCM), predictive maintenance,
repair or replace decision
making), and determine which
strategy to use in specific
situations. (Apply).
- Availability
tradeoffs
Describe various types of
availability (e.g., inherent,
operational), and the tradeoffs
in reliability and
maintainability that might be
required to achieve availability
goals. (Apply)
- Maintenance and testing
analysis
- Preventive
maintenance (PM) analysis
Define and use PM tasks, optimum
PM intervals, and other elements
of this analysis, and identify
situations in which PM analysis
is not appropriate. (Apply)
- Corrective
maintenance analysis
Describe the elements of
corrective maintenance analysis
(e.g., fault-isolation time,
repair/replace time, skill
level, crew hours) and apply
them in specific situations.
(Apply)
- Non-destructive
evaluation
Describe the types and uses of
these tools (e.g., fatigue,
delamination, vibration
signature analysis) to look for
potential defects. (Understand)
- Testability
Use various testability
requirements and methods (e.g.,
built in tests (BITs),
false-alarm rates, diagnostics,
error codes, fault tolerance) to
achieve reliability goals
(Apply)
- Spare parts analysis
Describe the relationship
between spare parts requirements
and reliability,
maintainability, and
availability requirements.
Forecast spare parts
requirements using field data,
production lead time data,
inventory and other prediction
tools, etc. (Analyze)
- DATA COLLECTION AND USE (18
Questions)
- Data collection
- Types of data
Identify and distinguish between
various types of data (e.g.,
attributes vs. variable,
discrete vs. continuous,
censored vs. complete,
univariate vs. multivariate).
Select appropriate data types to
meet various analysis
objectives. (Evaluate)
- Collection methods
Identify appropriate methods and
evaluate the results from
surveys, automated tests,
automated monitoring and
reporting tools, etc., that are
used to meet various data
analysis objectives. (Evaluate)
- Data management
Describe key characteristics of
a database (e.g., accuracy,
completeness, update frequency).
Specify the requirements for
reliability-driven measurement
systems and database plans,
including consideration of the
data collectors and users, and
their functional
responsibilities. (Evaluate)
- Data use
- Data summary and
reporting
Examine collected data for
accuracy and usefulness.
Analyze, interpret, and
summarize data for presentation
using techniques such as trend
analysis, Weibull, graphic
representation, etc., based on
data types, sources, and
required output. (Create)
- Preventive and
corrective action
Select and use various root
cause and failure analysis tools
to determine the causes of
degradation or failure, and
identify appropriate preventive
or corrective actions to take in
specific situations. (Evaluate)
- Measures of
effectiveness
Use various data analysis tools
to evaluate the effectiveness of
preventive and corrective
actions in improving
reliability. (Evaluate)
- Failure analysis and
correction
- Failure analysis
methods
Describe methods such as
mechanical, materials, and
physical analysis, scanning
electron microscopy (SEM), etc.,
that are used to identify
failure mechanisms. (Understand)
- Failure reporting,
analysis, and corrective action
system (FRACAS)
Identify the elements necessary
for a FRACAS to be effective,
and demonstrate the importance
of a closed-loop process that
includes root cause
investigation and follow up.
(Apply)
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NOTE: Approximately 20% of the CRE exam will require candidates to perform
mathematical functions.
Levels of Cognition
based on
Bloom’s Taxonomy – Revised (2001)
In addition to content
specifics, the subtext for each topic in
this BOK also indicates the intended
complexity level of the test
questions for that topic. These levels are
based on “Levels of Cognition” (from Bloom’s
Taxonomy – Revised, 2001) and are presented
below in rank order, from least complex to
most complex.
Remember
Recall or recognize terms, definitions,
facts, ideas, materials, patterns,
sequences, methods, principles, etc.
Understand
Read and understand descriptions,
communications, reports, tables, diagrams,
directions, regulations, etc.
Apply
Know when and how to use ideas, procedures,
methods, formulas, principles, theories,
etc.
Analyze
Break down information into its constituent
parts and recognize their relationship to
one another and how they are organized;
identify sublevel factors or salient data
from a complex scenario.
Evaluate
Make judgments about the value of proposed
ideas, solutions, etc., by comparing the
proposal to specific criteria or standards.
Create
Put parts or elements together in such a way
as to reveal a pattern or structure not
clearly there before; identify which data or
information from a complex set is
appropriate to examine further or from which
supported conclusions can be drawn.
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Back to Top
Sample
Questions
- Which of the following is best defined as the practice of using
parallel components and subsystems?
- Maintainability
- Reliability
- Optimization
- Redundancy
- Balancing a reliability requirement against other design parameters
such as performance, cost, or schedule, and then analyzing the consequences of placing
special emphasis on one of these factors is called
- reliability allocation
- reliability predictions
- trade-off decisions
- system modeling
- Software reliability planning includes all of the following EXCEPT
- selecting models for data analysis and prediction
- modeling acquisition of computer software systems
- trade-offs of general purpose programs vs. commercially available
programs
- trade-offs involving cost, schedule, and failure intensity of software
products
- The lifetime of a mechanical lifter is normally distributed with a
mean of 100 hours and a standard deviation of 3 hours. What is the reliability of the
lifter at 106 hours?
- 0.0228
- 0.0570
- 0.9430
- 0.9772
- In an analysis of variance, which of the following distributions is
the basis for determining whether the variance estimates are all from the same population?
- Chi square
- Student's t
- Normal
- F
- A full factorial design of experiments has four factors. The first
factor has two levels, the second factor has three levels, the third factor has two
levels, and the final factor has four levels. How many runs are are required for this
analysis?
- 16
- 48
- 192
- 256
- In a certain application, two identical transducers are used to
measure the vacuum in a system. The system is considered to have failed if either of the
vacuums read by the transducers varies from the standard by more than 10 mm Hg. Which of
the following is the correct reliability logic block diagram for the transducer assembly?

- On the basis of the fault tree below, what is the likelihood of the
top event occurring?
- 0.0044
- 0.2600
- 0.3000
- 0.5200
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- Assuming perfect switching and perfect starting, which of the
following systems has the longest mean life if each system consisits of n units
with identical reliability?
- A series system
- A parallel system
- A k out of n system
- A cold standby system
Questions 10-12 refer to the following situation:
A high incidence of failures has developed during aircraft acceptance
testing over the last several months. The identified failure is that an instrument panel
light has malfunctioned on 6 of the last 10 aircraft tested. This problem needs to be
investigated and a Failure Reporting and Corrective Action System (FRACAS) needs to be
completed without stopping aircraft production.
- The first step of the investigation should be to
- collect additional data on similar events over the last two years
- conduct failure analysis to determine the failure mode and mechanism
- conduct surveillance testing on suspect components
- establish a cross-functional team to brainstorm on the cause and effect
- If the cause of the failure is determined to be a faulty
subassembly manufactured only by a single supplier, and this situation is threatening to
shut down aircraft production, the next step should be to
- visit the supplier to assist in determining the root cause of the problem
- initiate a supplier corrective action and return all of the unsorted
inventory
- issue a Government and Industry Data Exchange Program (GIDEP) alert
- update the inspection instruction and retrain receiving inspection
- If a corrective action notice was sent to the supplier of a
faulty subassembly, and the supplier's response states that the root cause is simply an
operation error, the next step should be to
- accept the response and close the FRACAS
- visit the supplier to develop a better understanding of the root cause
- issue a Government and Industry Data Exchange Program (GIDEP) alert
- being looking for a new supplier
- Which of the following is an appropriate use for experimental design?
- Establishing product requirements
- Developing a fault-tree analysis
- Ensuring the robust design of a product
- Analyzing customer complaint reports
- Which of the following is NOT considered good practice in reliability
design?
- Using proven parts
- Using series design
- Using failure mode and effects analysis (FMEA)
- Simplifying item configuration
- According to Taguchi, robustly designed experiments should employ all
of the following techniques EXCEPT
- inner and outer arrays
- signal-to-noise ratios
- linear graphs
- fold-over capabilities
- Which of the following measures can be used to find a quick
approximation of the availability of a system?
- Mean time to failure (MTTF) and mean time to repair (MTTR)
- Failure rate and failure mode
- Mission time and failure rate
- Downtime and time to repair
- The investment in automated test equipment is often justified under
which of the following circumstances
- Numerous tests must be performed.
- Repair times must be short.
- Conformance records are required.
- Traceable records are required.
- For a company operating multiple units of production equipment, the
observed failure rate is 42 x 10-6 failures per operating hour, and the
preventive maintenance rate is 320 x 10-6 actions per hour. What is the mean
time between corrective and preventive maintenance (MTBM)?
- 2,688.2 hr
- 2,762.4 hr
- 2,840.9 hr
- 26,935.0 hr
- All of the following are purposes of a production reliability
assurance test (PRAT) EXCEPT
- detect significant shifts between the as-built reliability requirements
and the as-assigned reliability requirements
- assess performance against reliability requirements
- assess actual product reliability against reliability requirements
- minimize the need for specific process controls
- The primary aim of sequential-life testing is to determine
- the probability density function of failures
- the mean time between failures (MTBF)
- whether a lot meets the reliability goal
- whether the stress-level variation is significant
- A small sample from a product population is subjected to multiple
levels of elevated stress. Which of the following could be used to model the life of the
product?
- Poisson process
- Pascal expansion
- Pareto rule
- Inverse power law
- Which of the following are important elements of the concept of risk?
- Frequency
- Schedule
- Damage
- I and II only
- I and III only
- II and III only
- I, II, and III
- Which of the following tools is used to analyze the safety of a
system?
- Fault-tree analysis
- Failure reporting and corrective action system
- Reliability allocation
- Environmental stress screening
- System-safety analytical techniques included all EXCEPT
- hazards analyses
- fault tree analyses
- logic diagram analyses
- design readiness reviews
- A component fails on the average of once every 4 years with 75% of the
failures observed to occur during stormy weather. If there are 12 hours of stormy weather
to every 240 hours of good weather, what are the failure rates for stormy and good weather
respectively?

- A go/no-go device is tested until it fails. If X is the number of
tests to first failure with no wear out present, and the probability of success on each
test is .99, then the probability that X is greater than 5 is:
- .9310
- .9410
- .9510
- .9610
- The best way to set an overall reliability goal is to
- write a specification calling for a product to have high realiability and
incorporate it into a contract
- put down specific numerical requirements for reliability, statements of
operating environments, and a definition of successful product performance
- insist that the goal be expressed in terms of mean-time-between-failures
for all components and assemblies
- indicate who would be at fault if the desired reliability is not obtained
during the warranty
- Weibull analysis is a way to quickly and easily analyze field data or
interval test data. The limits of the use of this technique include having a good estimate
for the:
- MTBF
- expected life
- shape parameter
- average quality of the production lots
- A system consists of 4 parallel units each having a reliability of
0.80. The system can still complete its mission with only 2 units functioning. If the
failure rate is constant and failures are independent then the system reliability will be:
- 0.4096
- 0.5376
- 0.8192
- 0.9728
- Given a reliability growth test in progress having accumulated 4
failures during 5000 test hours. Assume a growth rate of 0.3, what is the expected MTBF at
25,000 hours?
- 1250 hrs
- 1895 hrs
- 2026 hrs
- 3856 hrs
- Successful operation of System S, illustrated below, requires that at
least 1 out of 3 through paths be good. The 3 paths are ABC, AEF, and DEF.

If A and D have predicted reliability of .95, and B, C, E, and F each have a predicted
reliability of .99, find the predicted reliability (Rs) of the system.
- .996
- .997
- .998
- .999
- A Weibull distribution has been found to describe the reliability
distribution with characteristic life= 12,000 hrs., and shape parameter
If these are good parameters, at what time will
reliability decrease to .85?
- 2204 hrs
- 3503 hrs
- 4838 hrs
- 5254 hrs
Answers: |
| 1. d |
6. b |
11. a |
16. a |
21. d |
26. c |
31. a |
| 2. c |
7. a |
12. b |
17. a |
22. b |
27. b |
32. d |
| 3. b |
8. a |
13. c |
18. b |
23. a |
28. c |
|
| 4. a |
9. d |
14. b |
19. d |
24. d |
29. d |
| 5. d |
10. b |
15. d |
20. c |
25. a |
30. c |
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