3 Recent Questions and Comments Concerning MTBF

Trying to Respond to All Questions and Comments Concerning MTBF

Over the past couple of days, like most days, have received questions and comments concerning MTBF. I do try to respond to all questions and acknowledge the comments.

Glad to help in anyway I can, so please feel free to send me your questions. Certainly do appreciate the supporting comments, or any comments for that matter.

Let’s take a look a few such discussion that occurred over the past two days.

Which Parts Count Method to Use Today?

The question:


I have a basic question and request you to clarify. Which method should i follow ( MIL 217 F or Telcordia) for MTBF and Failure rate calculations for Automotive application electronics part.

Thanks in advance !!


My response:

Neither – 217 is little more than a random number generator and is over 20 years old based on data and technology the is even older.

Telcordia is likewise little more than a random number generator concerning the expected future reliability performance, and based on telecommunication system failure data. Not suitable for automotive applications at all.

If you are simply comparing design options and not attempting to estimate future reliability field performance then use your own field data supplemented with vendor or internal testing data.

If trying to estimate field performance, parts count predictions is not the right tool.

Cheers, Fred

So, was the an appropriate response or was I bit too harsh?

Directed to Calculate MTBF

Hello Fred,
How are you and hope this email meets you well.
Please I have a question concerning MTBF.
Our international reliability department just sent us an updated memo for calculating MTBF for both operational units and standby units.
I do not agree with their calculation because they divide the number of hours by the total number of failures.
Please what do you think?
Thanks for your help.
Kind regards,
My response:

HI … ,

First the reliability department should know better than to use MTBF at all. My opinion is MTBF is a very poor measure, and only measures the average of the inverse failure rate, thus providing very little useful information. It is often mis-used and mis-understood, too. See nomtbf.com for many more reasons to avoid using MTBF.
Second, the total hours divided by total number of failures is a common way to calculate MTBF.
Third, using MTBF for your situation is most likely not helpful. If you have to report to this department, send them both MTBF and a Weibull Plot or reliability over a duration that is meaningful. Send both, only use the time to failure or reliability, R(t) information for managing your reliability program.
Hope that helps.

Again, was that the appropriate response? Did I miss something?

Someone That Wants to Learn More

The comment:
Hi, I came across your “No MTBF” website on the internet, and would like to connect to your group, to learn more from experts and professionals in the field of Reliability Engineering. Thank You & Best Regards,
My response:
Hi … , you may also enjoy accendoreliability.com which has many more articles, webinars, and podcasts on a wide range of reliability engineering topics. cheers, Fred
Oh, and just received this comment:
Thanks Fred! Thank you for all the great information you always give us!
My immediate response to both of these was a broad smile. Glad to help and appreciate the kind words that you provide.

What Questions do You Have?

Finally, as I’ve stated many times, if you have a question or comment, just let me know and I’ll try to respond in a meaningful and helpful way.
Understanding reliability is a lifelong endeavor. Asking questions is a natural part of what we should be doing. Also, use the comments section below to show how you would respond to the above questions.

About Fred Schenkelberg

I am an experienced reliability engineering and management consultant with my firm FMS Reliability. My passion is working with teams to create cost-effective reliability programs that solve problems, create durable and reliable products, increase customer satisfaction, and reduce warranty costs.

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