Electricity Over Glass 187
guddan writes "Running a live wire into a passenger jet's fuel tank seems like a bad idea on the face of it. Still, sensors that monitor the fuel tank have to run on electricity, so aircraft makers previously had little choice. But what if power could be delivered over optical fiber instead of copper wire, without fear of short circuits and sparks? In late May, the big laser and optics company JDS Uniphase Corp., in San Jose, Calif., bought a small Silicon Valley firm with the technology to do just that."
Intrinsic Safety. (Score:5, Interesting)
However the design is what is known as "Intrinsically Safe"... ie, it can't cause an explosion.
Currents, voltages are limited. Components are overrated by a set amount.
I've never heard of any intrinsically safe circuit igniting gasoline.
So what if you use fiber optics to provide the power. It's still electronic circuits in the tank, except now they are a whole lot more complicated and have power generation and regulation circuits, which make it a whole lot more dangerous...
And please don't just say encapsulate the dangerous stuff, because I'm sure that won't explode with a pressure build up if a component dies (as they tend to do in regulated power circuits).
It really scares me how such "great" ideas like this seem sane, when the original technology was probably safer.
GrpA
Ok, so I read the article... (Score:2, Interesting)
Say what?!? Ok...so, yes, I'd much rather have the manufacturer disclaim that they can't be sure that their product won't explode (thusly guaranteeing all hands lost), than use wires that have have never caused a problem in the manner in which the manufacturer of said bomb-like device.
Still...there might be some application for this device, but it certainly WON'T be in a fuel tank.
By the way, millions or even billions of fuel level sending units have been in use in anything with gas gauge for years. How many users of such devices have been killed due to electric failures? I'm guess very very VERY few, if any at all.
I agree with another commenter when they said that they don't want frickin' lasers pointing at their frickin' gas tanks.
How much Power? (Score:3, Interesting)
Current ATEX regs make it awkward to supply anything above about 1Watt at 6V.
Most people resort to pneumatics and/or keeping the computational logic outside the zoned areas.
Disappointingly for IEEE, he article is sparse in terms of technical details, such as the power/size ratio.
Re:Intrinsic Safety. (Score:3, Interesting)
It also bugs me, as an engineer, when people want better, faster, cheaper, but then refuse change. I hear numerous stories from my coworkers who used to design parts for the automotive industry. Apparently they had to come up with improvement plans and present them only to have the "what we have works, why change it?" mentality. Follow this with, now do it for less because we are going to buy the same system for less money each year...but remember, don't change or improve anything. Sounds dumb? Obviously the company no longer makes those parts.
Re:Intrinsic Safety. (Score:3, Interesting)
Intrinsic Safety [wikipedia.org] is better explained on the Wikipedia that I did in the post.
And the insulation doesn't exist in the rheostat - just wires rubbing together in the presence of fuel and air, but as I mentioned, it's extremely rare for car fuel tanks to spontaneously explode, which is probably a good example of why intrinsic safety designs work so well
I designed some intrinsically safe stuff for a company I worked for once... Sensors that were designed to sit inside the petrol tank and relay information through RFID to an external reader... Which is even lower power than lasers, and actually worked quite well (Credit card information located in the fuel tank or near the filler to be read by the pump handle).. In the end I think they just went with straight commercial stuff, which would have been IS also..
GrpA
High Transmission Lines? (Score:2, Interesting)
For an idea of the scale of loss versus cost of power: some power companies are currently willing to take the hit in lost power by using aluminium lines instead of copper, because they can engineer the towers holding the lines up to use less steel. (ie: This is possibly an argument against doing this). The cost savings in the tower construction outweighs the power lost in the lines.
Formidably silly article (Score:5, Interesting)
Re:Is this needed? (Score:3, Interesting)
I think it happened a few months after 9/11 and happened to a plane leaving JFK airport, so everyone initially assumed it was terrorists. (Just to help jog anyone's memory, not making a point here)
IIRC the power cables that went into the fuel tanks weren't at a high enough voltage to cause sparks, which is what makes sense of course. The problem was that there were two short circuits; one was a short circuit in the instruments in the fuel tank, and the other was a short circuit in the main power cables which run down the plane.
One of the short circuits caused there to be a higher voltage in the fuel tank, and this caused the spark.
By itself even this wouldn't be enough to cause an explosion because liquid jet fuel won't ignite with just a spark, it needs to be in vapor form, but doesn't vaporize until it gets hot.
As it happened the plane was waiting in the airport for a very long time before takeoff and had the air-conditioners running, and the air-conditioning units were underneath the fuel tanks. Staying on the ground for far too long on a hot day with the A/C on caused the fuel to heat up enough to vaporize, so that soon after takeoff when the two short circuits caused a spark there was something to ignite.
Moral of the story; if you think four unlikely things won't happen one after the other to cause a disaster you're dead wrong. Any extra fail-safes are a very welcome addition to an aircraft's design.
I don't think a relative of someone who died in that crash would agree that the people working on this new tech are just making work for themselves. It's hard to think of any other area where a single failure in 20 years and thousands of uses isn't acceptable.
What about capacitance fuel sensors? (Score:4, Interesting)
And for all of the people asking how often sparking inside a fuel tank causes a tank to explode, yes, it *does* happen sometimes. The final NTSB report on the airliner that crashed off New York about a decade ago (you know, the one that the conspiracy theorists said was shot down by a hand-held SAM) was due to sparking inside the fuel tank. I'd link to it, but I can't recall the flight number, and I don't have time to search for it right now...
Re:Is this needed? (Score:4, Interesting)