Fun with Fiber

There was Tom Swift Sr and TS Jr. Junior did the wilder stuff.

I did a physics project, measuring projectile speeds, beaking wires and oscilloscope. A couple of the Tom Swift Junior books were about right to stop a

I skimmed the Tom Swift books. I became inspired by electronics reading the Carl and Jerry series in Popular Electronics. I don't have any of the old issues. I recycled my magazines and gave away my collection of science fiction books long ago. About every 10 years or so, I purge my bookshelves, in order to make room for new books.

I think people are using raman backscatter or something to measure the temperature profile all along a length of fiber. I recall that being done in setting concrete.

or something like this:

:p

-Lasse

There have been an enormous number of fibre optic sensor papers written, for at least 30 years. They've been found much more effective in generating grants and theses than in doing anything very useful in practice. Those fibre optic smart structures gizmos sound great--people use fibre catheters and stuff in medicine, why not in civil engineering?

The basic problem is that it requires construction folks to be as skillful as doctors. Good luck with that. (There are a few other issues, of course, e.g. needing a temperamental $50k laser with a grad student attached in order to read out $10 worth of fibre.)

Cheers

Phil Hobbs

I do not know spit about raman backscattering, but you are prolly right. My best guess as how the temperature profile was obtained was a radar-like system and maybe swept FM. Swept FM was tried in the Navy but it prolly did not last because nobody could conceptually figure how it really worked - meaning repair almost did not exist. Hell, there was a story that 2 waves of engineers from the manufacturer were unable to fix the damn thing. What is so hard about delta-f being an analog of distance? After all, a pulse allows delta-t to be an analog of distance.

Well, the continuous temperature VS length measurement scheme is used in down-hole tools. Remember, in the oil patch, everything is a tool: a pipe, a lifting rod, exotic instruments, fiber temp measurements, 3-axis MEMS accelerometers, etc.

Sure. I've done a bit of downhole stuff myself, a year or two back. Everything in fibre is a temperature sensor and a vibration sensor. The trick is to get it to be _just_ a temperature or vibration sensor. ;)

Cheers

Phil Hobbs

I think I have related before that while I was working on toll roads, my nominal employer's main line of business was fiber optic networks. One of the questions that had come up was weighing trucks while in motion, and wondered if you could embed a fiber optic sensor in a rubber strip in the road and weigh them that way. After a few months, and probably a million or so dollars of prototyping, then finally decided that they couldn't - too much drift in the sensors. They then tried just to detect vehicle presence with the sensors, and it still didn't work. The rubber strip around the sensors was too sensitive to temperature. In cold weather (this was Omaha in winter!) they couldn't detect a thing as the rubber was too stiff.

Yup. You virtually never see a fibre sensors paper that does any sort of comparison, let alone apples-to-apples, against an all-electronic or cost-reduced bulk optic solution. There's a reason for that.

Cheers

Phil Hobbs

Intro:

In short, throw radiation at stuff, see what happens. Apparently, on the ppm level, most materials aren't just regular mirrors!

Tim

A "simple" strain gauge was insufficient?

Spot on. Of course the 150K instrument reads out in temperature, so that a civil ungineer can use it, and the "special" fibers cost over a 1$ a foot and they use it by the hundreds of feet to thousands of feet regularly. A real boondogle.

Not that anyone might care, i have use of the TIA-498 set fiber specifications and the three matching ICEA cable specifications. I convinced my employer that i needed them to rationalize the current splattered FO cable specifications that we do use.

?-)

Many approaches have been tried. The two successful technologies that i know of for weigh-in-motion is a steel strain plate and a load cell type scale. Both need to be calibrated for the particular location. The nearby pavement needs to be ground to be very smooth as well.

?-)

Good find, but no Carl and Jerry stories. It looks like they picked out some of the better technical articles, apparently by reader requests. I skimmed through a few of them and recall that I tried to build some of the construction projects, with variable success. Ah, nostalgia.

There's at least one:

Cheers

Phil Hobbs

Thanks. The link at the bottom of the page eventually leads to a five volume collection of the Carl and Jerry (John T. Fry) stories: At $16/ea, I don't think I'll be buying any of the books.

It's scarey to think that much of what I knew about electronics, upon entering High Skool, came from Popular Electronics and Carl & Jerry stories.