Optical Fiber Strain Relief in Steel Pipes

Optical fiber will not act as it is drawn in your picture.

You can have either a gentle curve from mid-tube to the bottom or a loop.

Have you looked at any web sites of vendors?

There are plenty of strain relief glands available for optical fibre use.

This may help you find one.

I've used optical fiber assemblies that used a steel spring as "armor" to protect the fiber inside. The fiber was fairly small, on the order of 100 microns. It had a soft foam filler around it. Next was the steel coil and a vinyl jacket over the steel to make it look pretty and to protect it from moisture. The assembly stayed flexible while protecting the fiber inside.

We used optical SMA connectors, but our supplier offered plenty of other options as well. I can't recall who the supplier was but there are many vendors out there that can do it.

What size(s) of pipe will you be inspecting?

Max and min, but the minimum is the one that will be the most important I feel....also how long?

I would have made a small "trolley", with free running wheels, (or electrically driven if flat piping!) (from a website that supplied parts for modelers), front and back, both sides and the top. Just in case it "falls over".

That is what I made for my USB "Drains" camera with a 25 meter cable, with a strong cord to pull it out.

Mine hasn't up to now fallen over as it has a low center of gravity using a steel weight and the "lower wheels" are mounted high!!....but I made it for drains of 100mm or larger diameter.....though it will still probably fit in a 50mm pipe as well!

It could have been easily made far far smaller.....but I simply had no need....

As mine is for drains, and they tend to have a slope/fall (or at least they are supposed to!), so the trolley runs down the "slope" quite easily being relatively free running, and only needs pulling back up.

But we are only talking a max of 25 meters, I have not needed to try it out on greater distances, usually even (far) less....it was far better than the flashlight and Binocular idea from before!!!

The USB cable is loosely attached to the cord, using cable ties every foot or so holding a small brass ring, putting no strain on the USB cable itself, but preventing it rubbing on the pipe wall. Do find a camera with the small USB connector, mine is the old "A" and I had to find rings big enough....

The cable ties needs to be put through twice from both sides, so as to hold the small ring at right angles to the cord (or use two!)....it makes more sense when you try it out!!

Sadly, I loaned my camera to a relative in the UK till the end of this year, as he needed it for an old hose he is renovating in the UK....so no photos possible.....but it was VERY simple to make one afternoon....(even for me!!)

I'm a bit in question of what you want to achieve with the optical fiber.

Is the fiber a communication between two pieces of electronics?

Then the market is full of solutions.

If the fiber is to be a sensor to pick up light in the pipe I think it will not happen: the light surrounding will not enter the fiber, just as the light inside will not leave it.

If you have created a special fibre that does these things (absorbing surrounding light but not giving it back), great.

But there exist nice FO based measurement systems that can measure temperature and stress/strain based physical phenomenons, so the total system is not that strange and in the blue sky.

Check gas blocking equipment used in blown fiber applications, they are designed to handle fibers as single 250µ elements (the fiber + primary jacket) or 900µ which is an additional mechanical protection which enables handling.

You can't handle smaller fibers than 250µ, the primary jacket is part of the ensemble that delivers the flexibility.

If I had to design this from scratch,I would obtain a tightly wound spring that is

slightly larger than the outside of the fiber, and a piece of Teflon heat shrink that

would fit over the spring.

I would pot the fiber to the inside of the spring using RTV silicon,keeping the fiber

centered in the spring.

After the silicon sets,I would put the heat shrink on the outside of the spring,and heat

slightly to achieve a snug,but not destructive fit,of course being careful not to heat

the fiber excessively.

A standard strain relief with rubber insert gripping the spring area should then

provide the protection from strain that you need.

However,I am sure there are off-the-shelf devices that will do the same thing cheaply

and simpler.

So this optical fiber is for inducing the fluorescence in a taggant or other marker in solution, and you want to seal the fiber against the pipe (rigid part of the probe) and protect the electronics.

It will all depend on two things: (1) the temperature of the process must be low enough to match with materials limits, and (2) the pressure must also be low enough to accomodate the type of seals you will use. Hard seals would be out of the question on fiber optic, so you may have to resort to some cleverness to achieve what you wish.

Have you considered utilizing intrinsically sealed all in one unit with short fiber, but hard wire sealed steel probe vessel (pipe). It might be easier, IDK. For that matter, why is the fiber even necessary? Too little information to base a suggestion upon.

@Lyn You are right the drawing of the fiber is not accurate. I've looked at these websites

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@Spades thank you for your assistance

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@Lo_Volt That sounds great I'll look into that option with the foam, and spring. hat sounds sturdy and very useful.

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@Andy Germany we are look for the smallest possible for our fiber. Under and inch. 7/8 inner diameter at this point for pipe diameter and only a couple of inches long, 6 to 12 inches.

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@Qwen.Stouthuyen There are two fibers, one to transmit light from an LED to a target area and the other to send light from target are to a detector. The goal is to make the fiber durable and protected long term during use in the field and transport. I'll look into the link and gas blocking stuff. The fibers are 2 mm and 4mm diameter. Big stuff for sending light.

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@HiTekREdNek (cool user name) I like this suggestion, my peers are handy with stuff I'll run this by them.

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@James Stewart interesting thoughts I'll consider. My replays above might help with more info.

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I super appreciate all this. Things I might of only stumbled randomly in my internet searches.I had great experience with help on a electronics forum, all about circuits . com and this was also a great experience so far. I have a bunch to read into and think about.

What you found are total sizes of the cable.

In such a 2 mm cable there can be more than one fiber.

We can put up to 12 fibers in one element

The extra thickness is mechanical protection to enable the installation.

Getting the fibers in place without damage is the tricky part.

If you want help send me an inmail message: i work at TE Connectivity for the fiber division. Your question is our speciality