⭐️ 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