⭐️ Testing and Modeling Flashcards
An excellent reference reliability prediction of electronic equipment is ..,.
MIL-HDBK-217
To determine whether failures observed in the test reflect actual use failures are the result of high test stresses,
what must be known?
The mechanism of the failures
A component fails on the average of once every 4 years
with 75% of the failures observed to occur during stormy weather,
what are the failure rates for stormy and good weather respectively?
Apporportion the two failure rates.
a) actual failure in 4 yr
b) actual time in 4 Yr
c) lambda (stormy ; fair)
ESS (Environmental stress screening) is best performed at which stage of the product life-cycle?
Production/Manufacturing
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In Order to determine failure rates of a newly introduced high quality product,
Which method would produce the best short term result?
Accelerated test result
Top-down testing requires which of the followig conditions?
At least one calling module must have been tested previously.
A highly accelerated stress screening (HASS) test can help to detect and seperate units with manufacuring defects
HASS test limits are typically developed from:
Highly accelerated life tests
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Redundant components are used because:
Reliability of parallel components is higher
than the highest reliability component in parallel
A System consist of 4 parallel units each having a reliability of 0.8.
The system can still complete its mission with only 2 units funcioning.
If the failure rate is constant and failures are independent then the system reliability will be:
Active Redundancy, 2 of 4 must work
What component reliability is required to achieve a two component series system reliability of 0.998,
if both components have the same reliability?
R(system) = R2(component) => √R(system)
Realizing a close parallel between injected faults and unknown faults, the software quality assurance group injected 40 errors into a software program. The testing program found a total of 210 faults, 30 of which were injected faults. Assuming all injected faults have been removed,
estimate the number of errors remaining in the software program.
Ratio between injected faults and original faults
The seeding of errors into a program and counting the number of seeded versus identified defects allows the test engineer to estimate the number of:
Defects in the program
Typically statistical distributions or confidence limits can be determined for accelerated tests.
In the case of a step-stress test,
the proper estimated distribution would be?
None, not meaningful
One disandvantage of a full working design prototype is:
The time and cost to create the model
VII - 105
The goal of a design prototype is to …
test products,
before investing in the final product
In order to attain a high order of series reliability …
The number of parts must be kept to a minimum .
A system consists of a large number of different in-series components, none of which individually contribute very heavily to the total failure propability. A particular component that fails during operation is immediately replaced by another of the same type. An appropriate model for the
time between failure distribution for this system is the:
Exponential (VII - 53)
Failure rates in reliability analysis for the exponential case:
Are summed,
to combine independent series elements in reliability analysis
In the logic diagram
RA = 0.90 ; 2 out of 3 and RB = 0.80 ; 2 out of 4
What is the reliability?
System A and system B propabilities can be located from a binominal table.
Then treating the diagram as a series caluculation
R(system) = RA(system) * RB(system)
Electronic assembly screening tests would:
Eliminate manufacturing defects
A steel alloy has a defined endurance limit.
For this material:
Stresses lower than the endurance limit will not cause failure regardless of the number of cycles
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:
This is a binominal based voting system.
n = 4 ; r = 2 ; P = binominal table
The keynote component in the application of Bayes`theorem is:
A component that enhances the reliability of the system by its addition,
but still lets the system operate if it fails
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Equivalence class partitioning is:
A black-box method
that devides the inputs to a program into classes
from which test cases can be derived
A reliability expression for three independent components in parallel with component reliability R is:
3R - 3R - 3R^2 + R^3
In determining the constant failure rate of a system based on test results of components that compromise the
system, why must the individual failure rates be summed instead of dividing total component test times by failures?
The components are assumed to fail independently (VII - 54)
In an S-N diagram,
a point at which failure occurs in one cycle is called the:
Ultimate load
Environmental stress screening has shown to be very effective in a production process.
The levels of defects have dropped form 5% to 25 ppm.
This would indicate:
ESS is still needed, but change the applied stresses.
If all defects have been eliminated ESS may be stopped.
Which theory is customarily used to calculate the life of a part as it undergoes various mechanical loadings over time?
Miner`s Rule
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Die lineare Schadensakkumulation dient zur Beurteilung des Einflusses eines Lastkollektivs auf die Lebensdauer eines Bauteils
If environmental stress screening is required, what precentage of components should be screened?
100% (VII - 12)
The design or discrimination ratio used in PRST (SPRT) is an expression of:
Accpetable MTBF / low limit MTBF
In a software development project,
which of the following elements is essential to ensure a reliable product.
Ensuring that requirements based testing is performed
The effect of increasing the stress level on a component is to:
Decrease the mean wearout life for the component
Which answer mathematically expresses the reliability of an active parallel system
in which all component reliabilites (Ra, Rb, Rc) are unequal?
Solve this algebracally as 1- unreliability
=> Rs = Ra + Rb + Rc - RaRb - RbRc - RaRc + RaRbRc
Which of the following represents a burn-in testing cost?
The burn-in chamber cost for the unit .
If the exponential failure time distribution is assumed,
what is the reliabiliy prediction uncertainty as measure by the standard deviation?
1 / λ = MTBF
.., is the Standard deviation of the exponential distribution.
A classification of tests used for products,
based on the ratio of an acceptable MTBF is:
Propability Ratio Sequential Testing
The Beta distribution is useful for providing a lower confidence limit on a given reliability.
Given three failures,
if the given reliability is 0.90 and the desired confidence is 0.75,
what is the required sample size?
Requires use of Beta table: for 0.75 conf and 3 failures (n-r)
=> look for the lowest sample size that will yield a reliablity of 0.90
The use of reliability data to determine when an individual unit will fail is an example of:
An improper use of reliability data and implications. (VII-98/102)
Reliability data cannot be used to predict when an individual unit will fail.
Reliability data is used to generate statements concerning the propability of a failure at any given time
HASS test limits that are typically derived from previous HALT tests.
Highly accelerated life tests (VII-21)
According to the definition of reliability,
performance over the expected or intended life is one criterion.
In order to obtain a measurement for reliability the actual life (t) must be compared to which of the following?
Required life
Which term is best for defining the reliability of a repairable system such as a personal computer ?
MTBF
The reliability of a complex system can best be improved by:
Including redundant concepts in the design
DoD data indicates that environmental stress screeining can reduce field failure rates by:
20-90%
Failure occur on a system at 75, 79, 83 and 85 hour. Assuming normality, one sided and unbiased,
the lower tolerance limit for 95% reliability with 90% confidence for this sample is:
TL = x̄ - KS
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Calculate the mean (x̄) and sample standrad deviation (s) for the given numbers, based on given dataset
K = a constant found in Section X - 14 of CRE Primer.
In a life test of 4 batteries, failures were observed after 10, 30 and 40 hours. The 4th battery was tested 75 hours without failure, at which time the test was terminated. What are the estimated MTTF (theta) and failure rate (lambda)?
Estimated MTTF = 52 ; Failure rate = 0,019 / theta = T/r ; λ = 1/theta / test terminated means time counted without failure
The purpose of a burn-in operation on parts is to:
Remove weak units from the population
ESS is best performed at which stage of the product life-cycle?
Production/Manufacturing (ESS, is a test or series of test used to pre-screen components druing production to reduce infanct mortality)
Electronic assembly screening tests would:
Eliminate manufacturing defects
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Screening test are used, particulary in electronic assemblies and componets to eliminiate manufacturing defects therby increasing the reliability and decreasing the short term failures in the filed. Screening tests are not used to eliminate design defects. Design defects should be discorvered and eliminated in development testing.
To eliminate potential defects or errors during production, the QE and RE should
Develop pre- production plans
Which type of software testing is performed after modifications are made?
Regression
Which method is best for finding a failure mechanism in a semiconductor device?
Eddy current NDT
When analyzing a design for reliability, which method is used?
Load-stregth analysis
When designing for mechanical reliability, which factor should be included in the study?
Stop / Starts
Which tool is best used to determine if problems are sporadic or chronic problems?
Pareto analysis
A DOE is conducted, which tool is used to analyze the relationship between the factors and the responses?
Main effects plot
If failure times for all of the parts in a life test are analyzed, the resulting data is
complete
Censoring of reliability data indicates which of the following?
Testing has been failure terminated
A weight of 26.581 kilograms would indicate a measurement that is:
Continous and unvariant
The predicted reliability is higher than the long term realized propability. Which of the following is the most likely cause of this difference?
Deterioration of the manufacturing process and procedures
A key element of the prototype process is:
Customer evaluation and feedback
An engineer has determined that the mean diameter of the catheter fittings is always 15 mm. A CRE draws a random sample of nine (9) of the fittings was from stores.
Calculate the value of the appropriate test statistic to test the following: H0: u = 15 cm
xx, xx, ..
t = mean / Sx
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First, put the values into the calculator and get the mean and Sx.
A CRE is using an Arrhenius model and discovers that the activation energy varies with temperature deltas.
What conclusion can be drawn?
The part has multiple failure mechanisms
In the intitial allocation of failure rates, system components are assumed to be
Serially connected
The main reason for categorization in terms of occurence, severity and detection (FMEA) is ..
prioritize the failures for corrective action
A parts-count reliability prediction is based on which model?
Basic series model
In software reliability, an operational profile is used to determine
how the software will be used
Why should a reliability engineer perform a finite element analysis (FEA) simulation to analyze the effect of complex loading situations on various material properties?
The mesh size of the model has an impact on the simulation result.
Which degradation model is distribution free?
Proportional hazards
Which statement is the best desription of environmental stress screening (ESS)?
It`s useful in weeding out defects using either normal or accelerated tests.
The seeding of errors into a program and counting the number of seeded versus identified defects allows a test engineer to estimate the number of:
Defects in the program
A system has three components with reliability values, A, B and C.
The reliability of the system R can be calculated using the equation:
Insufficient information has been provided
White-box testing is distinguished from black-box testing by:
Use of the control structure to derive test cases
Discovery testing is used early in the development cycle to:
Show weaknesses of the design
Which kind of test demonstrates successful operation without failure?
Margin test
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The margin test is designed to demonstrate a unit operates succesfully with a margin of safety.
Which conditions is an example of a non-material failure mode?
Electromagnetic interference
Applied stress divided by rated maximum stress is the formula for calculating a …
safety margin
To eliminate potential defects or errors during production, the QE and RE should …
develop pre- production plans
Which type of software testing is performed after modificatons are made ?
Regression
Which method is best for finding a failure mechanism in a semiconductor device?
Eddy current NDT
When analyzing a design for reliability, which method is used ?
Load-strength analysis
For overall visual understanding, which data is best presented in a graphical format ?
Data Distributions
Which tool is best used to determine if problems are sporadic or chronic problems ?
Pareto analysis
Large sample means tend to be normally distributed and clustered around the the population mean because which theorem ?
Central limit
Which method is used to analyze the effects of residuals for a 2³ or 2ᶰ¯¹ factorial experiments ?
Normal probability plot
A DOE is conducted, which tool is used to analyze the relationship between the factors and the responses ?
Main effects plot
A parts-count reliability prediction,
is based on which model?
Basic series model
If a CRE applies statistical inference techniques to assess the reliability of current software during a system test,
what type of measurement is the engineer using?
Estimation
The main reason for categorizing failures in terms of occurrence, severity, and detection (FMEA) is to …
prioritize the failures for corrective action
Life data that is right-censored and time based time-based reveals failures that …
go beyond the present time
A CRE uses randomization in experiments in order to minimize
bias (Voreingenommenheit)
