Some many years ago I ran across a data sheet for a cooling fan (used to cool a desktop computer, for example) that listed the fan’s life as 50,000 hours MTBF. The big bold lettering was on the data sheet and was the only use of bold on the entire data sheet. One couldn’t miss it. The computers we used these fans within had a one year warranty, plus were expected to operate for a home computer user for about 5 years. Thus, we would expect the fan to also operate for five years without failure. Continue reading Datasheet MTBF
Category Archives: MTBF
MTBF Eradication
After a discussion with a client this morning, and their motor vendor’s reliability engineer asked for a reference for a sample size calculation formula I recommended, I had a short email exchange with said reliability engineer. In my note with the references, I included an aside with a link to this site. He liked the site and agreed that MTBF was often Continue reading MTBF Eradication
Pakistan budgets with MTBF
Now for something completely different. Roaming the net looking for an interesting advertisement or data sheet with a ‘great’ (i.e. bad) example of the mis use of MTBF, ran across that MTBF is actually being used by at least one government for department budgeting.
This is bad. Continue reading Pakistan budgets with MTBF
The Worst Reliability Requirement
Most of us have seen reliability specified using a requirement like the following:
The Zeus 5000 SUV shall have an MTBF of 144,269.5 miles with a 90% confidence.
Some readers may not have seen reliability requirements specified in any other way. What they have always seen has read something like: The widget shall have an MTBF of X with a Y% confidence. This reliability requirement structure is rather ubiquitous Continue reading The Worst Reliability Requirement
I must not MTBF. MTBF is the mind-killer. MTBF is the little-death that brings total obliteration. I will face my MTBF. I will permit it to pass over me and through me. And when it has gone past I will turn the inner eye to see its path. Where the MTBF has gone there will be nothing. Only Reliability will remain.
- Bene Gesserit Litany Against Fear. (with apologies)
Role of parts count prediction
Great note [response to comment on Drain in the Bathtub Curve on NoMTBF Linkedin Group] – yes, there is a place for parts count prediction — not to determine the mtbf, to encourage proper derating, thermal engineering, and parts reduction, etc. It’s a start and as you note only one part of the reliability program. Continue reading Role of parts count prediction
An excellent short white paper by Craig Hillman that is worth reading. It underscores whey I claim HALT is the second worst 4 letter acronym in our profession. See the paper at http://www.dfrsolutions.com/uploads/white-papers/Why_HALT_Is_Not_HALT.pdf
Shaping Organizational Behavior
When conducting a Human Reliability Assessment (HRA) we use the terminology: errors of commission or errors of omission. It behoves every professional to question why we focus upon one metric in preference to all others, in an objective and constructive manner in order to discern whether we are exposing our organization to errors of professional omission or commission. Obviously the other conclusion is that we are doing the right thing and this is also an empowering piece of knowledge. Continue reading Shaping Organizational Behavior
What should we use instead of MTBF?
Giving a presentation last week and asked if anyone uses an 85/85 type test, and a couple indicated they did. I then asked why?
The response was – just because. We have always done it, or it’s a standard, or customers expected it. The most honest response was ‘I don’t know’.
They why is the test being done? Who is using the information for a decision? What is the Continue reading What should we use instead of MTBF?
Use the right fit
I’ve often railed on and on about the inappropriate use of MTBF over Reliability. The often cited rationale is, “it simpler”. And, I agree, making simplifications is often required for any engineering analysis.
It goes to far when there isn’t any reason to knowingly simply when the results are misleading, inaccurate or simply wrong. The cost of making a poor decision based on faulty analysis is inexcusable. Continue reading Use the right fit
The language we use matters
During RAMS this year, Wayne Nelson made the point that language matters. One specific example was the substitution of ‘convincing’ for ‘statistically significant’ in an effort to clearly convey the ability of a test result to sway the reader. As in, ‘the test data clearly demonstrates…’
As reliability professionals let’s say what we mean in a clear and unambiguous manner.
As you may suspect, this topic is related to MTBF. Simply saying Continue reading The language we use matters
Do not want equipment failures
I am a rock climber. Climbing relies on skill, strength, knowledge, a bit of luck, and good gear. Falling is a part of the sport and with the right gear the sport is safe.
I do not know, nor want to know, the MTBF (or MTTF) of any of my climbing gear. Not even sure this information would be available. And, all of the gear I use does have a finite chance of failing every time the equipment is in use. Part of my confidence is the that probability of failure is really low. Continue reading Do not want equipment failures
MTBF free Availability
The classic formula for availability is MTBF divided by MTBF plus MTTF. Standard. And pretty much wrong most of the time.
Recently working for a bottling plant design team we pursued the design options to improve availability and throughput of the new line. The equipment would remain basically the same, filler, capper, labeler, etc. So we decided to gather the last 6 months or so of operating data which included up and down time. Furthermore the data included time to failure and time to repair information. Continue reading MTBF free Availability
true, beneficial and timely
How Good is MTBF as a Metric?
A bolted hanger along a rock climbing route is often a very welcome site. It provides the climber with safety (by clipping the rope to the bolt); with direction (this is the way); and, with confidence. Does MTBF as a metric do the same for your organization?
As climbers we count on the bolts to provide support in case something goes wrong or we need to rest along the route.
A reliability metric is often used in the same way as a climbing bolt. The measure, whether MTBF or Reliability or Failure Rate, provides a sense of assurance that the product in question is performing as expected.
The organizations profits are or will be safe. The development team uses the measures as a guide for design and supply chain decisions. And, the measure provides confidence to the organization related to meeting customer expectations around reliability. Continue reading true, beneficial and timely
First Impressions
At first MTBF seems like a commonly used and useful measure of reliability. Trained as a statistician and understanding the use of the expected value that MTBF represented, I thought, ‘cool, this is useful’.
Then the discussions with engineers, technical sales folks and other professionals about reliability using MTBF started. And the awareness that not everyone, and at times it seems very few, truly understood MTBF and how to properly use the measure.