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Archive Of The Category "General"
Confidence and “Confidence”

Confidence and “Confidence”

Adam / September 27, 2017

Confidence is used in reliability to give a probabilistic value to the likelihood that a taken measurement will represent a full population.  It is determined by measuring a sample size and then using a selected statistical distribution table to translate to a likelihood. Emotional confidence is how one feels about making a decision based on known information at a specific point in time.   Similar but different. But it is important to connect them.  This is why.

Unless we are running the production equivalent product in the actual user, or perfectly simulated environment we are including assumptions.  This means that any…

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My Favorite Reliability Phrases

My Favorite Reliability Phrases

Adam / September 20, 2017

I like the occasional good catchphrase.  I typically tend to speak in analogies and anecdotes and many of my customers and colleagues have suggested documenting them.  So on occasion, I will write them in my notebook.  Here are a few.

  1. Language is the tragedy of Reliability
  2. The “5 Why” root cause analysis works so well because it is intuitive.  Ever have a 4-year-old ask you about how something works?
  3. Bad data is like driving with a dirty windshield
  4. A completely clean data set is a fake data set
  5. Statistics is a language.  Take the time to learn the vocabulary
  6. Stress margin… Read More
Estimating time to demonstrate Reliability

Estimating time to demonstrate Reliability

Adam / September 12, 2017

One of the most difficult challenges of incorporating reliability activities with program planning is estimating the time it will take to demonstrate reliability.  Demonstrated product reliability is typically measured as a confidence in a product’s capability to achieve a reliability goal. At product release, the business unit may feel comfortable with their target market and warranty goals with a demonstration of a 90% confidence in the products reliability goal of 99.1%.

Achieving a demonstrated 90% confidence in a product is in direct opposition with any “time to market” goal that has been established, no matter what the product or technology…

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Is It Faster to Demonstrate Component Reliability at the System Level?

Is It Faster to Demonstrate Component Reliability at the System Level?

Adam / September 05, 2017

Here is a common situation that is considered when reliability testing is being planned. Let’s use letters to designate depth in a product component structure. The top level product is level “A” and a component in top sub assembly is “B”. A sub assembly, of a sub assembly, of a sub assembly, is at level “D”.  So is it more efficient to test the component at level “E” or at level “B”?

Question: Is it more efficient to test the component at level “E” or at level “B” to demonstrate it’s individual goal?

An allocation model is used to derive goals…

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What is Weibull?

What is Weibull?

Adam / August 29, 2017

Weibull analysis is a tool that is used for characterizing the behavior of a data set.  The value of characterizing a data set is being able to make predictions of failure rate for the same or a similar population. Input to the Weibull analysis is time to fail for all failed units and running time for operating units. The assumptions for the data set are critical to ensuring the right information is included in the analysis.  This may include root cause analysis of the failures so they can be characterized as wear-out or use stress related. It would be…

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The History of Reliability

The History of Reliability

Adam / August 22, 2017

 

If you had to section the history of reliability into only two periods I believe the dividing point would be around 1950.  The first section, stone age to 1950, the “Robust” era; 1950 to today,  the “Margin” era.   In the Robust era, reliability concerns were addressed by creating a design that was orders of magnitude stronger than required, “over-engineered”.  This protected against the variability of fabrication, use, and environment.  If it was made sloppily with low tolerances, it still worked;  Used for an unintended purpose, still worked; Left out in the snow, dropped in the river, run over…

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Mission profile

Mission profile

Adam / August 15, 2017

Mission profiles are fundamental to any reliability prediction being valid.  Without clearly defined environmental and use profiles there will be a long chain of inaccuracy that accumulates into significant errors within a product. 

This is what occurs at the following stages, or tools, if the mission profile or environment profile changes after its completion.

  • DFMEA: Failure modes may be excluded.  Critical failure modes may be ranked low for occurrence and not be addressed
  • DOE:  Stresses may not be included in the matrix.  Resulting singular and interaction failure modes will not be discovered in advance.
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