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Prep notes for ASQ Certified Reliability Engineer exam ISSN 2165-8633
The CRE Preparation Notes series provides you with short practical tutorials on all the elements that make up the ASQ CRE body of knowledge. The articles provide introductory material, basics, how-tos, examples, and practical use guidance for the full range of reliability engineering concepts, terms, tools, and practices.
Keep your knowledge fresh by regularly reviewing topics and tools that make up reliability engineering.
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You will find the most recent tutorials in reverse chronological order below.
Let’s start by understanding the difference between engineers and engineering designers.
The work we do as reliability engineers may require a different approach when working with these different types of engineers. [Read more…]
The ability to assemble a system to meet the functional requirements is constrained by the design, the materials, and the tolerances.
Some designs are impossible to assembly. While other designs take little effort to build. The discipline of design for assembly, DFA, applied during the design process can enhance the manufacturing process. [Read more…]
People build, transport, use, maintain and dispose of equipment or products.
Thus the creation of these items should include consideration of the humans involved. In order to fully benefit from the functional capability of an item or system, we, as humans, have to interact with an item’s interface, displays, sounds, etc.
Whether a smartphone or bottling machine, the ability to provide commands or direction, the ability to recognize and understand responses, and the ability to correctly identify faults or outputs all combine to permit humans to place calls or fill juice bottles.
It is in the design stage that the elements of a piece of equipment (hardware or software) thwart or enable efficient human interaction. [Read more…]
In 1968 NASA explored where machines and humans would best achieve tasks primarily during space missions. Many of the findings are true today, and in some areas, the differences are blurring.
Machines created by humans continue to improve and take on complex tasks, that once only humans could do. For example, parking a car, now a feature of newer car models. Autonomous driving is happening and continuing to improve. The ability to reason, to foresee and evaluate risks, once thought to be strictly in the domain of human capability is now being done by machines. [Read more…]
Just back from a trip to Patagonia and catching up with emails and writing this morning. Posting an article for this list is due today along with a touch of travel weariness, decided to share a part of a question received concerning data analysis.
My thought is to post an actual question one of our peers is facing, and meet the deadline for this post. [Read more…]
If a human is going to build, install, monitor, use, operate, repair, or dismantle, then the design team must consider human factors.
According to Wikipedia
Ergonomics (or human factors) is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance.
Maintaining high reliability or availability is a marked advantage for any system. A system that achieves the ability to avoid system downtime due to a single failure event, is essential in many applications. Yet, the fault tolerant capability comes at a price.
A system that achieves the ability to avoid system downtime due to a single failure event, is essential in many applications. Yet, the fault tolerant capability comes at a price.
Here is a short list and brief description of fault tolerant design disadvantages:
The nature of a fault tolerance design is to continue to operate normally even with a component failure.
Thus if the ability to detect a component failure relies on a loss of function or capability, it may be difficult to detect the failure. This sets the stage for a second component failure to cause a system downing event. [Read more…]
In the article, Hypothesis Tests for Proportion, the comparison is between a given value and the sample. In this case, let’s compare two populations. We take a sample which provides a proportion representing each population and determines if the populations are different from each other based on the two samples.
The exact solution uses the Binomial distribution, yet when np and 1 – np are greater than 5, then we can use a normal approximation for the test statistic and critical value. [Read more…]
In the previous article, What is Reliability Optimization, we defined the concept. One of the elements of optimization is identifying which elements of a system to focus improvement efforts on.
Simply improving every element of a design may provide an overall improvement of reliability performance.
Given constraints such as time or funding, selecting the specific few elements that would provide the most improvement is key. [Read more…]
Delivering the best reliability performance within the various constraints imposed.
Without constraints such as budget, time to market, customer expectation, product functional capabilities, and product weight, you certainly could design and deliver a highly reliable product.
There always are constraints.
In the Oliver Wendall Holmes poem, The One Hoss Shay, the deacon procures the strongest oak, the supplest leather, and the best of best materials. Cost was not a constraint. And the shay lasted 100 years to the day.
If the technology permits there may be stronger or more durable components available for a price, yet cost is often a limiting factor. [Read more…]
In some circumstances, it is desirable to ensure the system continues to operate even if there is an internal failure. An aircraft navigation system should be able to operate even if an internal dc-dc regulator fails, for example.
Not everything within some systems benefits by being fault tolerant.
For example, a failure of a cabin reading light over a passenger seat is not critical to the safe operation of the aircraft, thus is likely not created to be fault tolerant. One criterion to determine what should be fault tolerant is the criticality of the function the system provides.
This also applies to specific subsystems within a system allowing some elements to be created fault tolerant and others within the system not. [Read more…]
Fault tolerance is a system that is reliant to the failure of elements within the system. It also may be called a fail safe design.
A fault tolerant system may continue to operate just fine, after one of the power supplies fails, for example. Or it may operate in a reduced or degraded state.
Other systems may have a ‘limp home’ condition, allowing the system to save critical data or allowing you to drive to a safe place to change a flat tire. [Read more…]
Concurrent engineering is a common approach that pairs the development of the product design and it’s supporting manufacturing processes through the development process.
Design engineers may require the creation of new manufacturing processes to achieve specific material properties, component performance, or mechanical, electrical or software tolerances. [Read more…]
A product or system’s actual reliability performance is a function of the design, assembly, and use.
Decisions made during design predominately create the inherent reliability capability performance.
The selected components, manufacturing, transportation and installation all can add variability and errors to the product, often reducing the actual reliability performance.
The use conditions and maintenance add another layer of variability, again reducing reliability capability. [Read more…]
System engineering is a superset of the other engineering fields (mechanical, civil, electrical, software, etc.) as the system engineers work to bring all the various elements of a system together into a final and cohesive whole. [Read more…]
