Slashdot Mirror
Electricity Over Glass
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."
But what if power could be delivered over optical fiber instead of copper wire, without fear of short circuits and sparks?
You're stilling bringing as much power into the fuel tank. High-power beams of light aren't any safer, a laser can cut inch thick steel.
At least electricity is very well understood, we know how to insulate the wire, we know how much voltage will spark in a given medium, and the low voltage for sensors is very safe.
High energy lightbeams are not at all well understood. Will the fiber heat up? What about light leakage, will that cause an explosion? What if the fragile fiber breaks while the beam is on?
Who even says that the sensor necessarily needs to be fully electronic? You can have a mechanical piece that sticks in the fuel tank and have an electronic control piece that's outside of the fuel tank. In fact, this is exactly how the gas gauge in your car works. This design has, quite frankly, worked well for decades. Sure there's a few disadvantages, but, uh, who cares?
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There is nothing wrong with running wires into petrol tanks for sensors... Take a good look at how badly made the rheostats in everyone's pertol tanks are made. Most engineers freak out when they see them for the first time.
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
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What, no one ever heard of vacuum lines? Or maybe pressurized lines?
I'm no rocket scientist either, and I'm sure that those rocket scientists has already consider those options you've mentioned. Perhaps because it is on an airplane going over 500mph and you have all sorts of physics and temperature considerations that vaccuum/pressurized lines are just not best suited for.
Speaking as a former USAF Avionics Specialist, who worked on C-5's, C-141's, and C-130's, and who personally saw a parked C-141 burst into flames on the ramp because of a fuel probe maintenance accident, let me explain things simply.
Design considerations:
JP4, the fuel that makes most jets run, is difficult to ignite. It needs a heat source. You could run a bare wire into a full tank and not have a problem. However, heat that wire up, and get the fuel/air mixture just right, and you have a problem. Big Boomba Problem, to quote JJB.
The big problem is the mostly empty tank and exposed heat sources. The C-5 has a nitrogen purging system. Basically, as fuel empties from a tank, it is replaced by nitrogen. The only way that wing is going to explode is if something other than a bare wire acts on it. Then, you've got bigger problems.
The big problem comes when you open the tank for maintenance. So, there are massive safety considerations. The C-141 that exploded in the mid-90's at Travis AFB in California blew because a jackass tech did not follow lockout/tag out procedures. The 141 doesn't have the nitrogen purge, but the tanks were open anyway. Two senior specialists were standing on top of the aircraft when the wing blew. Several others were in the cargo box. Luckily, aside from bumped elbows and bruised body parts, everyone got out o.k. We towed nearby aircraft to safer distances. There was precious little left of the burnt aircraft that identified it as such.
Most amatuers could make a good guess at a practical design for fuel sensors, but most of the solutions developed as such will end up being to costly, too heavy, will introduce other problems such as high maint., or simply won't work in 3-d, or extreme temperatures.
Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly and applying the wrong fix.
OLD: The deal was finished on May 26, 2005 . The article referenced by the Slashdot story is from October 2005.
NOT NEW TECHNOLOGY: They are merely piping light using fiber optics, and then using the light with photocells to create small amounts of power for use with measuring devices. The measurements are communicated back through the fiber optics, using a different wavelength.
PATENTS? The article says, "Photonic Power owns key patents..." Can the generation of power using light be patented again? Can sending information using fiber optics be patented again? Maybe the company has patents, considering that the U.S. government has become corrupt, but it is difficult to believe that any patents could be valid.
IGNORANT: See this quote from the article referenced in the Slashdot story: "... the company's fastest growing sector is currently electric power transmission. One important application is eliminating the transformers used to step down high currents and voltages to measurable levels."
The article should have said, "... the company's fastest growing sector is currently powering and connecting the measuring devices used in electric power transmission."
The writer does not understand that the idea does not change the measuring system, only the method of transmitting the data. If step down transformers are part of the method of measurement, they will still be required. The "senior research analyst" who was quoted, Vincent Lui, doesn't understand that, either, apparently.
REALITY RULES: If you play video games too much, your brain will become partly useless for other things, and, if then try to be a Slashdot editor, you won't be able to do a good job. (This is a theory that seems to fit the facts.)
This is a useful idea for computer professionals in some cases where voltage isolation is needed, but the Slashdot story was mishandled, as often happens.
Most jets (the largest quantity number of them, civilian commercial and private aircraft including everything from jetliners to small turboprops) burn Jet-A, which is a completely different formulation from the old JP-4. JP-4 had a significant amount of lighter molecular weight hydrocarbons (e.g. more of the constituents of gasoline) blended in.
JP-4 was also phased out of use by the USAF over ten years ago. JP-8 is used now, which is a completely different formulation from JP-4 and has much higher flash point than JP-4. JP-4 was a naptha-based fuel and JP-8 is a kerosene-based fuel. Today's Jet-A and JP-8 have very similar base formulations, but they have very different additive packages blended in. JP-8 has a much higher flash point than Jet-A too, since it is tailored for use in military aircraft that need to handle supersonic operations.