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You are here: Home / Archives for Fred Schenkelberg

Fred Schenkelberg — Thought Leader

Author of CRE Preparation Notes, Musings", NoMTBF, multiple books & ebooks>, co-host on Speaking of Reliability>/a>, and speaker in the Accendo Reliability Webinar Series.


This author's archive lists contributions of articles and episodes.

by Fred Schenkelberg 2 Comments

Poisson Distribution Calculation

Poisson Distribution Calculation

Let’s say the results of software testing averaged three defects per 10,000 lines of code. The criteria for release is 90% probability of 5 or fewer defects per 10k lines.

If this product ready for release?

The Poisson distribution is appropriate here as it is useful for modeling defects per unit, count per area, or arrivals per hour. If the data, in this case, the defect count per lines of code to be modeled by the Poisson distribution, the probability of an occurrence (defect in this case) has to be proportional to the interval (lines of code in this case). Also, the number of occurrences (defects) per interval must be independent (more on statistical independence in another post). [Read more…]

Filed Under: Articles, CRE Preparation Notes, Probability and Statistics for Reliability Tagged With: Statistics distributions and functions

by Fred Schenkelberg 17 Comments

Calculating Lognormal Distribution Parameters

Calculating Lognormal Distribution Parameters

The lognormal distribution has two parameters, μ, and σ. These are not the same as mean and standard deviation, which is the subject of another post, yet they do describe the distribution, including the reliability function. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Probability and Statistics for Reliability Tagged With: Lognormal Distribution, Statistics distributions and functions

by Fred Schenkelberg 11 Comments

ALT and HALT

ALT and HALT

The other day I got a question about the difference between ALT and HALT. There was some confusion probably because of the similar words in the acronym. ALT is Accelerated Life Test, and HALT is Highly Accelerated Life Test. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Reliability Testing Tagged With: Highly Accelerated Life Testing (HALT), Life testing and accelerated life testing (ALT)

by Fred Schenkelberg 7 Comments

Effective FMEA Principles

Effective FMEA Principles

Failure mode and effects analysis, or FMEA, is a tool for the identification and prioritization of possible ways a product or process can fail. The intent is to use that information to make improvements to the product or process.

I think of FMEA (and related processes like FMECA, dFMEA, etc.) as structured brainstorms that provide a means to focus on what’s important. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Reliability in Design and Development Tagged With: Failure Mode and Effects Analysis (FMEA)

by Fred Schenkelberg Leave a Comment

Reliability Goal

Reliability Goal

The reliability goal is a key element across the entire product lifecycle. From product definition to determining warranty to judging performance, knowing the goal in clear terms sets the stage for a successful product.

Reliability in engineering terms is the probability of satisfactory product performance within a defined environment over a stated duration. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Reliability in Design and Development, Reliability Management Tagged With: Customer and market analysis, Requirements

by Fred Schenkelberg 5 Comments

Sequential Sampling by Attributes

Sequential Sampling by Attributes

There a few different ways to sample a lot (or group) of material to determine if it has an acceptably low failure rate (or proportion that are considered ‘bad’). The following is an example of the sequential sampling method, which happens to be rather efficient by generally using the fewest samples for the same risk protection. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Probability and Statistics for Reliability, Reliability Testing Tagged With: Acceptance sampling

by Fred Schenkelberg 2 Comments

Reading CDF Plots

Reading CDF Plots

First the Question:

Fred,
Early in the FMEA lecture you worked through a homework problem and you mentioned that a cdf may not be linear (hence the reason for giving three points in a reliability goal).  Can you give an example of two of things you’ve seen with non-linear cdf’s?  I’ve only done limited reliability testing at this point, but everything I’ve done and every example I’ve ever seen have had linear cdf’s.
Thanks,
John

And, my response: [Read more…]

Filed Under: Articles, CRE Preparation Notes, Data Collection and Use, Probability and Statistics for Reliability Tagged With: Statistics distributions and functions

by Fred Schenkelberg Leave a Comment

EAM & CMMS Systems, 10 times more data in the system or 10 time less done with the data available?

EAM & CMMS Systems, 10 times more data in the system or 10 time less done with the data available?

10 times more data in the system or 10 time less done with the data available?

EAM & CMMS Systems, 10 times more data in the system or 10 time less done with the data available?.

A nice short article about the problem of data, data, too much data.

Filed Under: Articles, CRE Preparation Notes, Data, Data Collection and Use, Maintainability and Availability Tagged With: CMMS, Data analysis

by Fred Schenkelberg Leave a Comment

More Errata

More Errata

CRE_Errata_9-26-2011_revised

The CRE_Errata_9-26-2011_revised document is in pdf format and contains a couple of typos noted by John Cooper in the Indiana Council CRE prep materials – he has taught the CRE Prep course for Ops A La Carte and is a pretty good teacher and a CRE. [Read more…]

Filed Under: Articles, CRE Prep, CRE Preparation Notes

by Fred Schenkelberg 2 Comments

Series Reliability Question

Series Reliability Question

Recently a colleague sent me a published copy of the first CRE exam. Scanning through the document suggests that a few things have changed and many have not changed at all. I often comment my enjoyment of the reliability engineering profession, as it doesn’t change too fast and even I can keep up. [Read more…]

Filed Under: Articles, CRE Prep, CRE Preparation Notes, Reliability Modeling and Predictions Tagged With: Reliability Block Diagram (RBD)

by Fred Schenkelberg 3 Comments

RBD and Design Process

RBD and Design Process

A reliability block diagram (RBD) for a product that has no redundancy or complex use profile is often very simple. A series system (reliability wise) implies that any one part or element of the product that fails the entire product fails. One might ask if an RBD is even necessary. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Reliability in Design and Development Tagged With: Reliability Block Diagram (RBD)

by Fred Schenkelberg 2 Comments

Top Tips for Probability Analysis

Top Tips for Probability Analysis

This is provided courtesy of Amanda at

Egerton Consulting Ltd
Visit our website at www.egertonconsulting.co.uk

<They have a great newsletter and worth subscribing. Fred> [Read more…]

Filed Under: Articles, CRE Preparation Notes, Probability and Statistics for Reliability Tagged With: Probability concepts

by Fred Schenkelberg 33 Comments

How to Calculate Warranty Failures

How to Calculate Warranty Failures

Let’s say we have a product that most often fails for one major component. Let’s say a fan (it could be anything, and while I don’t have anything against fans, it’s easy to picture).

Ok, this fan has a data sheet with the classic reliability claim of 50,000 hours MTBF. For those that know about my disdain for MTBF (www.nomtbf.com) rest assured I’m not going to get into it here. The basic approach for estimating the number of failure during any [Read more…]

Filed Under: Articles, CRE Preparation Notes Tagged With: Statistics distributions and functions

by Fred Schenkelberg 3 Comments

5 Books for a Professional Reliability Engineer

A part of the preparation for the ASQ CRE is experience and education. These, in my simple way of thinking, means applying what you have learned to solve problems and provide value. Reliability engineering is about two questions: [Read more…]

Filed Under: Articles, CRE Prep, CRE Preparation Notes

by Fred Schenkelberg 5 Comments

Life Testing Question

Life Testing Question

Hi Fred,

I would take this opportunity to ask the reliability guru about bathtub curve for hardware reliability. I am running 27 units for life test for a million cycles around 555 hours. I have one failure at 300,000 cycles, and the rest of the units are running fine. Would this be classified as an early life failure? Also, how do I make a determination of when the early life failure time interval ends and constant failure rate starts in this example based on failure rate of remaining units? Thanks. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Reliability Testing Tagged With: Failure mechanisms, Life testing and accelerated life testing (ALT)

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