Sujet : Re: Pi-FAN for RPi4 with 4 (instead of 3) cables?
De : tnp (at) *nospam* invalid.invalid (The Natural Philosopher)
Groupes : comp.sys.raspberry-piDate : 09. Dec 2024, 16:51:51
Autres entêtes
Organisation : A little, after lunch
Message-ID : <vj73mo$f8rj$3@dont-email.me>
References : 1 2 3 4 5 6 7 8 9 10 11
User-Agent : Mozilla Thunderbird
On 09/12/2024 13:47, Michael Schwingen wrote:
On 2024-12-09, The Natural Philosopher <tnp@invalid.invalid> wrote:
I was surprised you'd use MTBF for a component which is expected to
steadily deteriorate due to wear and tear.
>
I though MTBF was more a random failure thing.
>
No it isnt that at all.
MTBF is a measure for the rate of failures *during normal lifetime* - ie.
1 / failure rate
It is *not* the lifetime of a component. MTBF is a measure for failures
during the flat part of the bathtub curve. Failures due to end of lifetime
(like normal, not-premature wearout on a fan) are not part of MTBF.
Well yes and no. There is no guarantee that the failures will be (economically) repairable.
MTBF is a stochastic emergent property of a bunch of items all of which have a lifetime.
A fan has items inside it, like its bearings.
https://www.vitecpower.com/technische-daten/the-difference-between-mtbf-and-lifetime/
"According to the information provided earlier, the primary distinction lies in one encompassing the failure rate of all components, while the other exclusively focuses on the lifespan of electrolytic capacitors."
https://www.rs-online.com/designspark/why-l10-life-expectancy-is-key-for-fan-durability-over-mtbf-ratings
This is full of bullshit
"MTBF estimates the lifespan of a fan’s electronic components, expressed in millions of hours. In contrast, L10 Service Life, measured in thousands of hours, is based on the durability of the bearings and lubrication grease."
So a fan with no electronic components has no MTBF?
https://www.digi.com/support/knowledge-base/understanding-mtbf-mean-time-between-failures
"Furthermore, MTBF specifically excludes wear-out factors"
Total crap.
"Mean time between failures (MTBF) describes the expected time between two failures for a repairable system. For example, three identical systems starting to function properly at time 0 are working until all of them fail. The first system fails after 100 hours, the second after 120 hours and the third after 130 hours. The MTBF of the systems is the average of the three failure times, which is 116.667 hours. If the systems were non-repairable, then their MTTF would be 116.667 hours."
"In general, MTBF is the "up-time" between two failure states of a repairable system during operation "
It is an academic nicety to make a distinction between repairable and irreparable subsystems.
In a Triggers broom sort of way a replacement is simply a repair of all components
I could for example clean the cruft out of a seized fan Or oil its bearings. Or completely replace it.
What matters is how long the repair or the new fan will last. Not splitting hairs over MTTF versus MTBF
-- Gun Control: The law that ensures that only criminals have guns.