If lamps are in parallel so any one is sufficient and they are repaired
then the MTBF goes up a huge amount. The probability of a surviving
lamp failing while the burned out one is being replaced is then the
concern. For two 1 year MTBF lamps in parallel and a one day repair
time the math works out to about 183 years MTBF for both failed at the
same time. This math is based on steady state failure rates so ignores
infant mortality and wear out failures, but is illustrative of how
reliable parallel redundancy can be when prompt repairs are possible.
However, since filament lamps have finite lifetimes, I think best
practice would be to burn them in to weed out infant mortality and
replace both lamps when one burns out.
Ar redundant system familiar to many computer users is the RAID array,
where the high MTBF is based on a failed drive being replaced promptly.
Grant KZ1W
ref: "System Reliability Engineering", Gerald Sandler
On 1/14/2015 6:02 PM, Patrick Greenlee wrote:
A constant current source in series would make every in-line series
lamp a separate single point of failure which would make the MTBF 1/n
times the MTBF of one lamp where n is the number of lamps. Not a high
reliability approach.
Patrick NJ5G
On 1/14/2015 1:59 PM, Jim Lux wrote:
On 1/14/15 11:52 AM, Jack Brindle wrote:
LED bulbs have power supplies which convert 120/240VAC down to
thecyDC level needed by the LEDs. These components are the major
failure point (for CFLs as well). These are high current power
supplies that generate quite a bit of heat and thus require at least
some of that heat sink capacity as well.
True for replacement bulbs for replacing standard Edison base
incandescent, like the ones you get at home depot.
Not necessarily true for a specialized application. If you were
replacing ALL the bulbs in a tower, there's nothing stopping you from
having a big constant current source at the base, like they do with
streetlights.
It's sort of like replacing incandescents with strobes..
So what kind of climbing harness is required when changing the
external aircraft bulb at altitude??? :-)
- Jack B, W6FB
On Jan 14, 2015, at 10:55 AM, Hans Hammarquist via TowerTalk
<towertalk@contesting.com> wrote:
Replacing a bulb on an aircraft is 'slightly" easier than climbing
1500 feet.
Regarding temperature; the LED do not suffer as for example the
florescent lights. If I remember it right LE-s work better at lower
temperatures, the light output goes down as the temperature
increases. You notice that LED bulbs are equipped with rather large
heat sinks, needed to keep the LED diodes to work properly.
Hans - N2JFS
-----Original Message-----
From: Roger (K8RI) on TT <K8RI-on-TowerTalk@tm.net>
To: towertalk <towertalk@contesting.com>
Sent: Tue, Jan 13, 2015 5:16 pm
Subject: Re: [TowerTalk] Fwd: Now THIS is a tower climb!
There already are, very bright LED strobes in use on aircraft. All
the
exterior lights on mine were solid state, except for the landing
light.
There are LEDs that could have replaced that, but I never saw any that
had been approved.
I don't know at how low a temperature they will still function, but I
flew in temperatures a lot colder than most towers would see.
I would think the new LED strobes would be ideal for towers and
replacements would be few and far between.
73
Roger (K8RI)
On 1/13/2015 12:25 PM, Hans Hammarquist via TowerTalk wrote:
I think the problem is to introduce a "new", long-life, light
bulb. Any,
modern LED bulb would do lifetime wise. I believe, though, there
are several
light bulbs in the assembly that automatically replace the bulbs as
they burn
out. That is used in lighthouses to insure there is a light on all
the time. To
design an assembly that could automatically replace burnt-out LED
bulbs might
not be that simple. You know, everything there has to be approved by
authorities.
Hans - N2JFS
-----Original Message-----
From: Richard Solomon <dickw1ksz@gmail.com>
To: Tower Talk <towertalk@contesting.com>
Sent: Mon, Jan 12, 2015 6:39 pm
Subject: Re: [TowerTalk] Now THIS is a tower climb!
Repairs ??
Looks like he's changing a light bulb !!
Now, invent a really long life bulb and you will sell at least a
hundred !!
73, Dick, W1KSZ
On Mon, Jan 12, 2015 at 4:33 PM, Mike via TowerTalk <
towertalk@contesting.com> wrote:
This is video of a technician climbing 1768 feet to the top of a
transmissions tower for repairs.
It also shows him free climbing and some dialog to go along with
it.
Its a helmet cam so if anyone gets dizzy or has anything that can
give out
watching this stuff while sitting in your chair....be
warned!...DO NOT
WATCH IT!!
https://www.youtube.com/watch?v=INbKYq0G9nU
Mike W2GR
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