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As an embedded systems developer, I have developed mistrust to statistical reliability figures. These days you quite often come across components and subassembl

by varjag 7y ago

As an embedded systems developer, I have developed mistrust to statistical reliability figures. These days you quite often come across components and subassemblies with MTBF stating (sometimes tens of) millions of hours. When you try to clarify with the vendor how they arrive at these figures there is nothing but general handwaving about using industry tools and statistical models. But sorry, just can't seriously take it on faith that your product is going to last 11 centuries at 20C.

Quequau 7y ago
Yeah there's a few degrees of separation between the people who wrote the claims (and have to defend/support them) and the people that did the testing... and then substantially more between those that did the testing and those who did the original work showing that the statistical proofs on accelerated ageing were reasonable things to depend on. By the time it gets to the marketplace nobody knows anything and we're all acting like the monkeys in the story with banana and the ice-water spray.
jacquesm 7y ago
Any MTBF longer than that particular industry has existed should be suspect or invalidated absent an existence proof (which will take some time...).
Hunisgung 7y ago
A couple of years ago, I was working on the verification team for a (non-critical) avionics system for a large commercial aircraft. I noticed one of the components seemed to have more failures than expected. I reported the issue and the systems architect waved it off arguing that his analysis of the supplier data had proven that the MTBF for this component was over 500 thousand hours. Few months later, a task force was established by the project management to look for an alternate supplier for this component after it became obvious that its failure rate was significantly higher than advertised.
- jhayward 7y ago
  Much, perhaps most, of the effect we have as individuals in large organizations is indirect and hard to see or quantify. It's not always as simple as we think and changing course of a group almost always takes time, education, repetition, and some redundant effort. It's still worthwhile and effective. It is entirely possible that this is a success story of a lower-level engineer raising an issue that the higher levels then addressed. Just because no one immediately jumps and say "by golly, we have to get rid of component X right now!" doesn't mean that the issue didn't begin percolating vertically and horizontally, ultimately resulting in a large-scale corrective effort.
  - treypitt 7y ago
    in my experience this is by far the less likely scenario, but I would like to hear from OP whether his initial work contributed to the ultimate decision
    - Hunisgung 7y ago
      For more context, I was 99% sure they there was an issue with the component and that a hardware rework would have to be made sooner or later. The systems architect had some seniority over me but I could have pushed the issue hard enough for it to be addressed. Then I did not take the high road. The guy was very obnoxious and I had other issues to address. So I let it slide to maintain my "this is important" quota for other matters. And a couple of months later, when some units failed on the test aircrafts (I insist on the fact that this was not a critical system), I had an issue report showing that the issue was observed during supplier-side tests and then ignored.
londons_explore 7y ago
I really wouldn't be surprised if some components don't last that long... Take a regular ceramic resistor. I'd bet that if you kept it in a temperature controlled sealed box, it would last 2000 years. I would possibly even reckon it might last 200,000 years. Ceramics are so so so inert, and as are metals as long as they're away from oxygen.
- deleted 7y ago
  [deleted]
- varjag 7y ago
  The 11 century MTBF example was a complete SoM.

by varjag 7y ago

Quequau 7y ago

Yeah there's a few degrees of separation between the people who wrote the claims (and have to defend/support them) and the people that did the testing... and then substantially more between those that did the testing and those who did the original work showing that the statistical proofs on accelerated ageing were reasonable things to depend on. By the time it gets to the marketplace nobody knows anything and we're all acting like the monkeys in the story with banana and the ice-water spray.

jacquesm 7y ago

Any MTBF longer than that particular industry has existed should be suspect or invalidated absent an existence proof (which will take some time...).

Hunisgung 7y ago

A couple of years ago, I was working on the verification team for a (non-critical) avionics system for a large commercial aircraft. I noticed one of the components seemed to have more failures than expected. I reported the issue and the systems architect waved it off arguing that his analysis of the supplier data had proven that the MTBF for this component was over 500 thousand hours. Few months later, a task force was established by the project management to look for an alternate supplier for this component after it became obvious that its failure rate was significantly higher than advertised.

jhayward 7y ago
Much, perhaps most, of the effect we have as individuals in large organizations is indirect and hard to see or quantify. It's not always as simple as we think and changing course of a group almost always takes time, education, repetition, and some redundant effort. It's still worthwhile and effective. It is entirely possible that this is a success story of a lower-level engineer raising an issue that the higher levels then addressed. Just because no one immediately jumps and say "by golly, we have to get rid of component X right now!" doesn't mean that the issue didn't begin percolating vertically and horizontally, ultimately resulting in a large-scale corrective effort.
- treypitt 7y ago
  in my experience this is by far the less likely scenario, but I would like to hear from OP whether his initial work contributed to the ultimate decision
  - Hunisgung 7y ago
    For more context, I was 99% sure they there was an issue with the component and that a hardware rework would have to be made sooner or later. The systems architect had some seniority over me but I could have pushed the issue hard enough for it to be addressed. Then I did not take the high road. The guy was very obnoxious and I had other issues to address. So I let it slide to maintain my "this is important" quota for other matters. And a couple of months later, when some units failed on the test aircrafts (I insist on the fact that this was not a critical system), I had an issue report showing that the issue was observed during supplier-side tests and then ignored.

londons_explore 7y ago

I really wouldn't be surprised if some components don't last that long... Take a regular ceramic resistor. I'd bet that if you kept it in a temperature controlled sealed box, it would last 2000 years. I would possibly even reckon it might last 200,000 years. Ceramics are so so so inert, and as are metals as long as they're away from oxygen.

deleted 7y ago
[deleted]
varjag 7y ago
The 11 century MTBF example was a complete SoM.