eatyourguitar wrote: we do not need to multiply (footswitch failure)*(relay failure) to get the total failure probability.
woah easy. that would not be the way to do it anyways. ie if p(fail) of the switch was .5 and p(fail) of the relay .5, you say the p(fail) of the system is only .25? i don t think so. (if they are independent it would be p(fail) = .75 in this case for example).
the cases for failure are: just the switch fails. just the relay fails. both fail. with the numbers above each of those occur with .25 probability. so the probability of failure is .75 not .25 (under the assumption of independence).
its not just both pfails multiplied together, although if you think of probability of success, in this case it would be the 2 probabilities of success multiplied together, then you can do 1 - p(success) = p(fail) and get the same result. Because for a successful switch the relay has to succeed AND the switch has to succeed, if independent -> implies multiplication.
do some Bernoulli trials and find out what the expected trial number of the first failure is....
the relay is not a human interface device. it is also protected from accidental damage since it is inside the case. we can not compare them like apples to apples. so with all that in mind, the 400,000 cycles for the relay is most likely the only spec that matters. since we can not in our life time ever use a pedal that much, you can pretty much assume that it will not fail at all. so now if we can find a footswitch that is more reliable than the blue 3PDT,
yes i think you see my point then. if the footswitch you have sucks, why does it matter what the spec of the relay is? you would still be repairing that 36 year old pedal. you sort of say well 400,000 is alifetime, if only we had a foot switch that would last that long. total circular reasoning. i mean sure the setup might last longer but you are still at the mercy of a mechanical component, which probably wont go 400,000. that is all i was saying.