Author Topic: First official mobile app from OS  (Read 4189 times)

Skills4Survival

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Re: First official mobile app from OS
« Reply #15 on: January 20, 2013, 06:23:49 PM »
very comforting :-)
Ivo

captain paranoia

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Re: First official mobile app from OS
« Reply #16 on: January 21, 2013, 06:36:53 PM »
A simple multiplicative approach is only valid if you require failures of all three redundant items to constitute a system failure.

if you need a 2 out of 3 multiple vote; it's a much higher probability than that because you're only allowed one failure.  For an individual element reliability, R =(1-Pf), and all three elements being identical, the resulting 2 of 3 redundant reliability is given by

Rs = R^3 + 3.R^2.(1-R)

For P =0.1, Rs = 0.972, so Ps = 0.028, 28 times higher than Pf^3

And the smaller the Pf, the larger this ratio becomes.

I fear we're getting off the navigation track here, though...

Skills4Survival

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Re: First official mobile app from OS
« Reply #17 on: January 21, 2013, 07:11:31 PM »
getting there...slowly but steady. Message, think of the whole system?
Ivo

captain paranoia

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Re: First official mobile app from OS
« Reply #18 on: January 22, 2013, 12:51:07 PM »
It's a long time since I've done reliability calculations, and I'd forgotten just how silly some of the numbers become...  I looked back at some work last night, and was reminded of the measure 'Failures In Time' (1 FIT = 1 failure in 10^9 hours).  Small sections of circuitry might have a figure measured in tens of FITs (e.g. a small memory system), corresponding to an MTBF in the order of 10^7 to 10^8 hours, and equipments might have MTBFs measured in tens of thousand hours.

Running the numbers for the triple-redundant system, it looks like you'd need an individual MTBF of about 55,000 hours to achieve the one billion hours system MTBF.  That's within the bounds of sanity.

Sorry; should have run the numbers first.  No delusion going on...

Paracat

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Re: First official mobile app from OS
« Reply #19 on: February 21, 2013, 10:50:56 PM »
Re the I phone apps, Im sure that I have read that the I phone or its competitors should not be relied on as a primary GNS system for the walkers and climbers in the UK I think that LB also mentions that fact in the NAV Manual?