2, April 2001
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the Reliability of Complex Systems
1 - Analytical Techniques
A complex system is one that cannot
be broken down to groups of series and parallel components. Due to
this, it can sometimes be difficult to determine the reliability of
the system as a function of the component reliabilities. There
are two general strategies when solving for system reliability:
analytical techniques and simulation. In
this article, we will look at some of the analytical techniques that
can be employed to determine system reliability. With component-level reliability information
available, it then becomes necessary to determine how these component values are combined to determine the reliability for the
overall system. This article discusses the decomposition, event
space, and path tracing methods of analyzing complex
In next month's
issue, we will look at using simulation to determine system
read more, see http://weibull.com/hotwire/issue2/hottopics2.htm
purpose of this section is to offer background and advice to the novice
Product Failure Definitions
Before life data can be analyzed or even
collected, the definition of failure must be established. While this
may seem like a simplistically obvious piece of advice, lack of
generally accepted definitions for performance-related failures can
result in misunderstandings over validation and reliability
specifications, wasted test time, and squandered resources. The
process of characterizing the reliability and defining the failures for a
product is directly related to the product's mission. Essentially, reliability can be defined as the ability of the product
to perform its intended mission without failing.
The definition of reliability springs directly from the product
mission, in that product failure is the inability of the product to
perform its defined mission.
To read more, see http://weibull.com/hotwire/issue2/relbasics2.htm
Tool Tips section addresses helpful hints and frequently asked questions
about ReliaSoft software products.
Can I speed up the data entry process in Weibull++ and ALTA?
What do I need to know before analyzing data from an Accelerated Life Test with two types of stresses?
How do I get the latest software updates?
When reinstalling older versions of software on a PC that is running Windows
2000, I get an error message saying that I need a service pack for Windows
NT. What can I do to fix this?
To read more, see http://weibull.com/hotwire/issue2/tooltips2.htm
Simulation Tool Available -
ReliaSoft is pleased to offer a new free
simulation tool to our customers. SimuMatic allows you to automatically perform large numbers of Monte Carlo
simulations, analyze the resulting data sets, and tabulate
results of interest. This tool is perfect for calculating
bootstrap confidence intervals, evaluating potential test
designs, and other simulation-based analyses. See http://www.weibull.com/freetools
for downloading instructions. (NOTE: SimuMatic requires Weibull++
6 to be installed on the user's PC. To download an evaluation copy for use with SimuMatic,
Seminar in Tucson, June
4-8 - The next ReliaSoft
"Master the Subject, Master the Tools" seminar will be
held in Tucson from June 4-8, 2001 at the Sheraton Tucson Hotel
and Suites. Topics for this five-day seminar include Life Data
Analysis, Accelerated Life Testing, and System Reliability,
Maintainability and Availability. For more information on
course content and how to register, see http://www.reliasoft.com/seminars.
at the SAE Show -
ReliaSoft attended the 2001 Society of Automotive Engineers (SAE)
World Congress March 5-8, 2001. We want to thank everyone who came by our
BlockSim and RAC's PRISM tool integration -
latest service release of BlockSim includes the integration of
the Reliability Analysis Center's (RAC) PRISM software, thus allowing access to RAC's extensive electronic failure rate database (included in PRISM) as an
integrated add-on to the BlockSim application. To use this
functionality, you must have both PRISM and BlockSim installed on
your computer. Both products are available as a bundle from
Announces the Beta Release of ALTA-PRO - It
has been said that development of a software package capable of analyzing accelerated test data from tests conducted using time varying stress levels would be a major undertaking requiring a team of engineers, statisticians and programmers. It was, and it did!
After years of R&D, ReliaSoft officially announced the Beta release of ALTA-PRO, the first commercial software package capable of analyzing accelerated data form specimens subjected to time varying stresses. ReliaSoft's first version of ALTA enabled engineers to get estimates for the population
cdf, confidence intervals, and other quantities of interest (such as the
MTTF) at use level from data obtained through an accelerated test, and where the stresses applied to the units were not a function of time. ALTA-PRO expands this ability, allowing engineers to perform the same analysis utilizing data gathered from accelerated tests where the stress profile is varying with time (i.e., step-stress, ramp-stress or with any other quantifiable stress profile).
consulting now available through ReliaSoft Professional Services
- ReliaSoft Professional Services now offers expert consulting
help. For more information, see http://www.reliasoft.com/consulting/index.htm.
quarter, ReliaSoft publishes Reliability Edge, a printed journal
that includes articles and information related to the field of
reliability engineering. Articles of interest in the current edition:
Reliability Analysis Using Simulation - This article uses simulation
to explore reliability analysis methods and theory. ReliaSoft's new
SimuMatic utility, which allows users to automatically perform a
large number of reliability analyses on data sets created using
Monte Carlo simulation, is used to demonstrate the concepts. See http://www.reliasoft.com/newsletter/1q2001/simumatic.htm.
- A High
Value of Beta is Not Necessarily a Cause for Concern - Although
often viewed with fear and loathing by reliability engineers, this
article demonstrates that a high value of the shape parameter for
the Weibull distribution (beta) is not necessarily a cause for
concern if the value of the scale parameter (eta) is high enough to
meet the reliability specification. See http://www.reliasoft.com/newsletter/1q2001/beta.htm.
As always, your
feedback and contributions are appreciated. ReliaSoft is able to provide the most
user-friendly reliability software packages and support because we
listen to our customers. This applies to our newsletters and
publications as well. We welcome any suggestions or contributions you may
have for Reliability HotWire.
If you have a topic or
article that you think would be useful to the readers of Reliability
HotWire, feel free to contact us.
Copyright 2001 ReliaSoft
Corporation, ALL RIGHTS RESERVED