On 2024-12-09, David Higton <dave@davehigton.me.uk> wrote:

Do you know what MTBF means?

Yes. Something I don't understand, though, is why so many people use
the term MTBF when the appropriate one would be MTTF, since so few of
the things referred to are repaired.

It does not really matter if you repair or replace - what is important is
that a technician needs to drive to the installed equipment to get it going again, and MTBF helps calculating how often that will be necessary during normal operation.

That assumes that properly repaired equipment is as reliable as comparable, non-failed equipment of the same age, otherwise, the numbers will be skewed.

cu
Michael
--
Some people have no respect of age unless it is bottled.

--- SoupGate-Win32 v1.05
* Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)

On 2024-12-09, The Natural Philosopher <tnp@invalid.invalid> wrote:

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?

remove "electronic" and it makes sense.

https://www.digi.com/support/knowledge-base/understanding-mtbf-mean-time-between-failures

"Furthermore, MTBF specifically excludes wear-out factors"

Total crap.

No. Again, MTBF characterizes failures during normal service life.

Take a fan which usually fails after 5 years of operation due to wearout,
which happens on all of those fans after about the same amount of time -
those 5 years are *not* parts of the MTBF. MTBF characterizes the
statistical mean time between failures *during* those 5 years due to *other* reasons.

So you can have a MTBF of 50 years, and a lifetime of 5 years. If you take
100 of those fans, you can expect 2 failures per year - but after 5 years,
the failure rate will rise rapidly to reach 100%.

What matters is how long the repair or the new fan will last. Not
splitting hairs over MTTF versus MTBF

The important thing is to keep MTBF and lifetime separate - both will lead
to failures, but are separate mechanisms.

cu
Michael
--
Some people have no respect of age unless it is bottled.

--- SoupGate-Win32 v1.05
* Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)

On 12/9/24 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.

Thanks Michael, very instructive. That clears up my misunderstanding. So
MTBF is a random type, rather than a wear type thing. You just have to
assume bits are replaced before they get old.

--- SoupGate-Win32 v1.05
* Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)

On 12/9/24 13:11, The Natural Philosopher wrote:

On 09/12/2024 12:28, Pancho wrote:

On 12/9/24 10:50, The Natural Philosopher wrote:

On 08/12/2024 19:50, David Higton wrote:

In message <vj1d28$31v9g$12@dont-email.me>
           The Natural Philosopher <tnp@invalid.invalid> wrote: >>>>

It's an interesting thought as to why one would use a fan at all.
If its
such a high compute task that you need one, maybe a bigger Pi or an
Intel based machine is indicated.

I dislike fans. They fail.

PC fans run pretty much all the time.  A fan on a RasPi is likely to
run less of the time, and could well last longer overall.

Fans fail.  Disc drives fail.  SSDs fail.  Batteries fail.  Reservoir >>>> capacitors fail.  But before they do, they are very useful.

Such an ArtStudent™ view of life.

Do you know what MTBF means?

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.

For some relatively reliable components, such as people, you initially
see a relatively low failure rate, but come 80 or 90 years they start
dropping like flies, due to wear and tear.

Yup. MTBF of peole is about 70 years.

I read MTBF for people is about 700 years.

For some things like atomic an atomic nucleus, the failure does seem
random, so MTBF seems applicable.

Never used.

Well yes and no,


Given f = failure rate (e.g probability of nuclear decay)

half life = ln(2)/f.
MTBF = 1/f.

Therefore:

half life = ln(2) * MTBF = ~0.69 * MTBF

essentially they are the same, apart from the 0.69 conversion factor.

I don't know which it is for PC fans, but would assume it is more wear
and tear than random.

In general fans fail for one reason only. Bearing failure.  The cheapos
use phosphor bronze plain bushes and these dry out and seize up, wear
out and get noisy and start slowing down  or get clogged with people's cruft.

You can go for sealed ball races if you like, as in hard drives,  but
the price goes up.

In terms of drying out, its time elapsed, not time spent running. Same
for cruft. Only bearing wear is time dependent.

None of these are random., All if them are however dependent on
conditions and maintenance

For a stingy old man like me, yes. I wait till things break. So MTBF is
not particularly useful. I want long average life, not reliability until
they get old.

MTBF is an attempt to get a handle on how long a collection of parts
should stay operational given the spreads of failures in a spread of conditions  of the individual parts

There will always be variations in conditions and manufacturing quality

MTBF is the type of metric used by someone who will replace bits before
they get old.

If I were managing a data centre and I knew human intervention was very
costly (I suspect it is), I might have a policy of replacing parts
before the failure rate became high due to old age.

I know the companies I worked for hated investigating failure, or fixing
stuff. They much preferred replacement. Essentially components were
cheap, human intervention was not.

Obviously if the equipment is expensive, or you have cheap slave labour,
the equation may change.

My experience of cheap fans is that 5 years was about the MTBF.

--- SoupGate-Win32 v1.05
* Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)

On 12/9/24 13:11, The Natural Philosopher wrote:

On 09/12/2024 12:28, Pancho wrote:

On 12/9/24 10:50, The Natural Philosopher wrote:

On 08/12/2024 19:50, David Higton wrote:

In message <vj1d28$31v9g$12@dont-email.me>
           The Natural Philosopher <tnp@invalid.invalid> wrote: >>>>

It's an interesting thought as to why one would use a fan at all.
If its
such a high compute task that you need one, maybe a bigger Pi or an
Intel based machine is indicated.

I dislike fans. They fail.

PC fans run pretty much all the time.  A fan on a RasPi is likely to
run less of the time, and could well last longer overall.

Fans fail.  Disc drives fail.  SSDs fail.  Batteries fail.  Reservoir >>>> capacitors fail.  But before they do, they are very useful.

Such an ArtStudent™ view of life.

Do you know what MTBF means?

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.

For some relatively reliable components, such as people, you initially
see a relatively low failure rate, but come 80 or 90 years they start
dropping like flies, due to wear and tear.

Yup. MTBF of peole is about 70 years.

I read MTBF for people is about 700 years.

For some things like atomic an atomic nucleus, the failure does seem
random, so MTBF seems applicable.

Never used.

Well yes and no,


Given f = failure rate (e.g probability of nuclear decay)

half life = ln(2)/f.
MTBF = 1/f.

Therefore:

half life = ln(2) * MTBF = ~0.69 * MTBF

essentially they are the same, apart from the 0.69 conversion factor.

I don't know which it is for PC fans, but would assume it is more wear
and tear than random.

In general fans fail for one reason only. Bearing failure.  The cheapos
use phosphor bronze plain bushes and these dry out and seize up, wear
out and get noisy and start slowing down  or get clogged with people's cruft.

You can go for sealed ball races if you like, as in hard drives,  but
the price goes up.

In terms of drying out, its time elapsed, not time spent running. Same
for cruft. Only bearing wear is time dependent.

None of these are random., All if them are however dependent on
conditions and maintenance

For a stingy old man like me, yes. I wait till things break. So MTBF is
not particularly useful. I want long average life, not reliability until
they get old.

MTBF is an attempt to get a handle on how long a collection of parts
should stay operational given the spreads of failures in a spread of conditions  of the individual parts

There will always be variations in conditions and manufacturing quality

MTBF is the type of metric used by someone who will replace bits before
they get old.

If I were managing a data centre and I knew human intervention was very
costly (I suspect it is), I might have a policy of replacing parts
before the failure rate became high due to old age.

I know the companies I worked for hated investigating failure, or fixing
stuff. They much preferred replacement. Essentially components were
cheap, human intervention was not.

Obviously if the equipment is expensive, or you have cheap slave labour,
the equation may change.

My experience of cheap fans is that 5 years was about the MTBF.

--- SoupGate-Win32 v1.05
* Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)