Your Reliability Engineering Professional Development Site
A point estimate of the mean of a population is determined by calculating the mean of a sample drawn from the population. The calculation of the mean is the sum of all sample values divided by the number of values. [Read more…]
Asking the right question is important.
During a review meeting (informal or formal) asking a few reliability questions may reveal weaknesses, strengths, or uncertainty. The design team has many priorities and reliability is often difficult to estimate, yet knowing what is and isn’t known provides a clear picture of risks for decision makers.
If you are a decision maker and need to ascertain the reliability risks of the current design, then asking a couple of questions may provide just the insights you need. It also conveys that reliability is on your mind and that you want to have answers that are meaningful and well thought out.
The basic measures of central tendency are mean, median, and mode.
Given a collection of data, a common question is about where the data resides. Knowing the center or mid-point or average is a starting point as we consider the data. [Read more…]
Selecting a supplier for components or subsystems involves many aspects including the desired reliability performance.
Once selected the ability of the supplier to provide items that meet or exceed the reliability requirements relies on their understanding of the requirements and operational conditions related to the specific item within the system. It also relies on the supplier’s knowledge of their own design and manufacturing processes as it related to the reliability performance. [Read more…]
It is rare that a third party generated FMEA/FMECA has any value. The development or manufacturing teams and supporting staff should comprise the bulk of the study’s team. Team size for a specific study would include 4 to 10 individuals.
The FMEA/FMECA should provide clear action items that may include:
Conduct research or experiments to understand and quantify uncertainty. This may include exploring how an item responds to specific stress, errors or inputs. Or include experiments to estimate the occurrence rating for a specific potential cause of a failure mode. [Read more…]
How do you use the Weibull Distribution?
It’s just one of many useful statistical distributions we must master as reliability engineers.
Let’s explore an array of distributions and the problems they can help solve in our day-to-day work.
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It may be possible to pass the CRE exam knowing one formula.
The math elements of the exam may take a bit of time to solve, and knowing reliability statistics well is a good plan heading into the exam. Knowing the exponential distribution reliability function is one that you should memorize. [Read more…]
Preventive Maintenance or PM is a set of inspections and tasks that help prevent equipment from failing. Keeping equipment operating improves plant capacity and throughput. Avoiding unwanted downtime helps the plant avoid unnecessary expenses and lost productivity.
Checking the oil level in your car’s engine and adding more as needed, along with regular oil changes are examples of PMs. [Read more…]
A reliable product does not fail often. Customers expect to a level of reliability performance and failures that occur too early dash their expectation.
The design and development team work to create a robust product. To meet the customer’s reliability expectations. The team may use a range of tools to detect any reliability problem prior to launch.
Yet, customers do uncover problems that surprise us. This may be a problem with how we identify and resolve risks, yet it could also be the development process didn’t look close enough to find the issues. Or, worse, we saw the issue and ignored it. [Read more…]
A specific reliability plan may include any number of specific tasks. To build an effective plan you need the knowledge of the individual tools and techniques, plus how they may fit together to create an overall plan to achieve your goals.
Of course, this starts with establishing complete reliability goals that include function, environment characterization, probability of success (reliability) and duration.
I recommend setting specific goals for setup/installation (early life), the warranty period and the expected customer use period. [Read more…]
A reliability block diagram is a graphical and mathematical model of the elements of a system permitting the calculation of system reliability given the reliability of the elements.
The model reflects the reliability performance structure including series, parallel, standby and other arrangements of system elements.
Each block in an RBD represents a component or subsystem of the system. The organization and connecting lines represent the reliability structure of the system and may or may not be representative of the system’s functional block diagram. [Read more…]
The reliable performance of a system is important. It is important to the customer, to our business and to us.
Very few argue that we should ignore the reliability characteristics of a product. We also deem cost, time to market or feature set as important also. The trouble is we can measure the latter directly every day, where the reliability performance is often difficult to measure.
A simple assumption in many experiments is to assume the variable act independently on the response.
This means when I change the temperature a little in a polymer dryer silo that time to achieve a certain dryness goes down. And, changing the humidity or airflow rate or pressure either do not change or as they change has no impact on the relationship between temperature and drying time. [Read more…]
The purchase price of a product may be the start of the cost of ownership.
Maintenance and repairs may cost many times the initial purchase price. An efficient maintenance process and low-cost spare parts may help minimize cost, yet a design that optimizes the total cost of ownership is the most effective method. [Read more…]
Coupled with probability is the duration over which the probability applies.
For example, if we desire 99 of 100 to survive, we must state over which period of time this applies. It is proper to state the couplet of 99% reliable over 1 year.
It is not sufficient to define reliability as ‘5-year product’ as it does not contain the information related to how many are expected to survive the 5 years. Likewise, it is not sufficient to say a product has 5 – 9’s reliability (meaning the probability of failure is less than 0.00001) as it does not contain the duration.
If the product has high reliability for only a few seconds, that does not help us make judgments about the first year of life. [Read more…]
