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PICList Thread
'[EE] Failsafe vs. Redundant, was Automobile LED he'
2006\11\02@170003 by Mike Hord

picon face
As Russell points out, many people don't know what the difference
between "fail safe" and "redundant" is.

Perhaps as engineers we really should.  I've heard engineers misuse
the terms before.  It's an important distinction.
http://en.wikipedia.org/wiki/Failsafe is a poor explanation of the
concept.  Wikipedia DOESN'T know everything.

Anyone want to take a crack at it?  I don't feel like I have the level
of expertise required to do so.

Mike H.

{Quote hidden}

2006\11\02@190137 by James Newton, Host

face picon face


> -----Original Message-----
> From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu
> [.....piclist-bouncesKILLspamspam@spam@mit.edu] On Behalf Of Mike Hord
> Sent: 2006 Nov 02, Thu 07:09
> To: Microcontroller discussion list - Public.
> Subject: [EE] Failsafe vs. Redundant, was Automobile LED headlights
>
> As Russell points out, many people don't know what the
> difference between "fail safe" and "redundant" is.
>
> Perhaps as engineers we really should.  I've heard engineers
> misuse the terms before.  It's an important distinction.
> http://en.wikipedia.org/wiki/Failsafe is a poor explanation
> of the concept.  Wikipedia DOESN'T know everything.
>
> Anyone want to take a crack at it?

Fail safe means that a failure is possible and even expected, but that when
it happens, it will do so in a way that is the least likely to do damage.
The device "Fails" in a "Safe" way.

Redundant means that there is more than one system for the function required
and some means of switching from one to the other when a failure is
detected.


Some (rather bad) examples include:

Redundant is an electric fuel pump behind a mechanical one with a switch to
turn it on if the main pump fails.

Fail safe is when there is a shroud under the fuel pump that directs leaking
gasoline away from the exhaust headers.


Redundant is when the engine has both air and water cooling.

Fail safe is when the thermostat spring is engineered to corrode away long
before the actuator causing it to fail in the open position rather than
closed.


Redundant is capacitors in series.

Fail safe is capacitors in series with a fuse.


I'm sure someone can improve on that...

---
James.


2006\11\02@191214 by Bob Blick

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> I'm sure someone can improve on that...

We can check with the Department of Redundancy Department!

-Bob


2006\11\02@192553 by Paul Anderson

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On 11/2/06, Bob Blick <bblickspamKILLspamsonic.net> wrote:
>
>
> We can check with the Department of Redundancy Department!
>
>
But wouldn't that be redundant?

--
Paul Anderson
VE3HOP
.....wackyvorlonKILLspamspam.....gmail.com
http://www.oldschoolhacker.com

2006\11\02@192716 by Jinx
face picon face
Redundancy is belt and braces

Failsafe is a Ken doll

2006\11\02@224155 by peter green

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face


> -----Original Message-----
> From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu]On Behalf
> Of Mike Hord
> Sent: 02 November 2006 15:09
> To: Microcontroller discussion list - Public.
> Subject: [EE] Failsafe vs. Redundant, was Automobile LED headlights
>
>
> As Russell points out, many people don't know what the difference
> between "fail safe" and "redundant" is.
>
> Perhaps as engineers we really should.  I've heard engineers misuse
> the terms before.  It's an important distinction.
> http://en.wikipedia.org/wiki/Failsafe is a poor explanation of the
> concept.  Wikipedia DOESN'T know everything.
>
> Anyone want to take a crack at it?  I don't feel like I have the level
> of expertise required to do so.
I always thought the key of failsafe was "if it fails it fails in a safe way" am i wrong?



2006\11\02@224304 by John Ferrell

face picon face
Add "Fail Softly" to your conditions. When the result of a failure leads to
continued but degraded operation. Example: when your car computer cannot
manage closed loop but allows the engine to continue in open loop rather
than leaving you stranded.

John Ferrell    W8CCW
"My Competition is not my enemy"
http://DixieNC.US

----- Original Message -----
From: "James Newton, Host" <@spam@jamesnewtonKILLspamspampiclist.com>
To: "'Microcontroller discussion list - Public.'" <KILLspampiclistKILLspamspammit.edu>
Sent: Thursday, November 02, 2006 7:00 PM
Subject: RE: [EE] Failsafe vs. Redundant, was Automobile LED headlights


>
>
>> {Original Message removed}

2006\11\02@224511 by John Ferrell

face picon face
Add "Fail Softly" to your conditions. When the result of a failure leads to
continued but degraded operation. Example: when your car computer cannot
manage closed loop but allows the engine to continue in open loop rather
than leaving you stranded.

John Ferrell    W8CCW
"My Competition is not my enemy"
http://DixieNC.US

----- Original Message -----
From: "James Newton, Host" <RemoveMEjamesnewtonTakeThisOuTspampiclist.com>
To: "'Microcontroller discussion list - Public.'" <spamBeGonepiclistspamBeGonespammit.edu>
Sent: Thursday, November 02, 2006 7:00 PM
Subject: RE: [EE] Failsafe vs. Redundant, was Automobile LED headlights


>
>
>> {Original Message removed}

2006\11\02@225517 by Charles Craft

picon face
There was a pretty good cold war book, made into a movie, called "Failsafe".
Back in the days of ASR33 Teletype machines.  :-)


{Quote hidden}

>-

2006\11\03@024445 by Wouter van Ooijen

face picon face
> Fail safe means that a failure is possible and even expected,
> but that when
> it happens, it will do so in a way that is the least likely
> to do damage.
> The device "Fails" in a "Safe" way.

> Some (rather bad) examples include:
> Fail safe is when there is a shroud under the fuel pump that
> directs leaking gasoline away from the exhaust headers.

That is an attempt at 1-fail safe: one failure will probably not lead to
a catastrophic result. For realy 1-fail safe there should be indicators
for both leaking and shroud failure. Otherwise one could be driving a
car with a damaged shroud, which would no longer be 1-fail safe.

The robot arm for which I once worked was (designed to be) 3-fail safe
(and 1-fail operational). Here is a description:
http://adsabs.harvard.edu/abs/1998dsa..conf..321B

Note that to realy pin down 'N-fail safe' one must provide a lot of
additional definitions:
- what is catastrophic
- what is independent
- how are your components 'allowed' to fail
- is man-in-the-loop allowed
- how long must the N-fail-safe last (components wear down, especially
in space!)
etc

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\11\03@201956 by Jim Korman

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face
Charles Craft wrote:
> There was a pretty good cold war book, made into a movie, called
> "Failsafe".
> Back in the days of ASR33 Teletype machines. :-)
>
Which was also a culprit in "The Andromeda Strain".

Jim

2006\11\03@234031 by Shawn Wilton

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Wow, what a great book.  Movie sucked though.

On 11/3/06, Jim Korman <TakeThisOuTjkormanEraseMEspamspam_OUTalltel.net> wrote:
>
> Charles Craft wrote:
> > There was a pretty good cold war book, made into a movie, called
> > "Failsafe".
> > Back in the days of ASR33 Teletype machines. :-)
> >
> Which was also a culprit in "The Andromeda Strain".
>
> Jim
> -

2006\11\04@064432 by Howard Winter

face
flavicon
picon face
> On 11/3/06, Jim Korman <RemoveMEjkormanspamTakeThisOuTalltel.net> wrote:
> >
> > Charles Craft wrote:
> > > There was a pretty good cold war book, made into a movie, called
> > > "Failsafe".
> > > Back in the days of ASR33 Teletype machines. :-)
> > >
> > Which was also a culprit in "The Andromeda Strain".
> >
> > Jim

Hey, I wrote my first program (and quite a few afterwards) on an ASR33!  Sat in the little room at the end of the Computer Science lab, with four of
them clattering away (they'd probably issue ear defenders these days) interacting with the Town Hall computer ten miles away, we felt like we were
in a SciFi film!  Ah, those were the days... of course they were completely un-failsafe, especially when storing programs on paper tape (we had a
very small budget for storing programes on the computer itself) and more than one person had to retype parts of their program because the tape had
got mangled.

Cheers,


Howard Winter
St.Albans, England


2006\11\04@165044 by Dave Lag

picon face
Charles Craft wrote:
> There was a pretty good cold war book, made into a movie, called "Failsafe".
> Back in the days of ASR33 Teletype machines.  :-)

Now if you know what ASR stands for you have passed the test
:)
D

2006\11\04@183541 by Howard Winter

face
flavicon
picon face
Dave,

On Sat, 04 Nov 2006 16:51:14 -0500, Dave Lag wrote:

> Charles Craft wrote:
> > There was a pretty good cold war book, made into a movie, called "Failsafe".
> > Back in the days of ASR33 Teletype machines.  :-)
>
> Now if you know what ASR stands for you have passed the test
> :)

Automatic Send/Receive !  There was also KSR (Keyboard Send/Receive) which didn't have the paper tape reader/punch, and was just a
keyboard/printed paper terminal.

What do I win?  :-)

Cheers,


Howard Winter
St.Albans, England


2006\11\04@232141 by Dave Lag

picon face
Howard Winter wrote:
> Dave,
>>
>>Now if you know what ASR stands for you have passed the test
>>:)
>
> Automatic Send/Receive !  There was also KSR (Keyboard Send/Receive) which didn't have the paper tape reader/punch, and was just a
> keyboard/printed paper terminal.
>
> What do I win?  :-)
>
> Cheers,
> Howard Winter
> St.Albans, England


Ummmmmm--- me keeping secret how old you (we) are ?  :o

After a 6 week course and 3 months of tearing them down, dunking in
freon baths and building them back up you were entrusted to go back into
the world with your feeler guages and spring hooks to service the things.
Oh, and the oilcan....

2006\11\06@151850 by gacrowell

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face
I dunno, I've always loved the scene between Peter Sellers and Keenan
Wynn as Col. 'Bat' Guano.  "You're gonna hafta answer to the Coca-Cola
company."

GC

> {Original Message removed}

2006\11\06@153017 by William Couture

face picon face
On 11/6/06, gacrowellEraseMEspam.....micron.com <EraseMEgacrowellspammicron.com> wrote:
>  I dunno, I've always loved the scene between Peter Sellers and Keenan
> Wynn as Col. 'Bat' Guano.  "You're gonna hafta answer to the Coca-Cola
> company."

Actually, that scene is in "Dr. Strangelove -- or how I learned to stop
worrying and love the bomb"

Bill

> GC
>
> > {Original Message removed}

2006\11\06@192518 by Nate Duehr

face
flavicon
face
William Couture wrote:
> On 11/6/06, RemoveMEgacrowellEraseMEspamEraseMEmicron.com <RemoveMEgacrowellspam_OUTspamKILLspammicron.com> wrote:
>>  I dunno, I've always loved the scene between Peter Sellers and Keenan
>> Wynn as Col. 'Bat' Guano.  "You're gonna hafta answer to the Coca-Cola
>> company."
>
> Actually, that scene is in "Dr. Strangelove -- or how I learned to stop
> worrying and love the bomb"

Man, I love that movie.  People don't "get" true satire anymore.  Can
you imagine the protests if such a movie were released today?

:-)

Nate

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