## measure the diameter of a tube

hello!

lets say we have a long tube with variable diameter and with variable direction

is it possible to measure the diameter of its walls in each point of its lenght, by sending waves or something from its edge towards inside it ?

imagine it is not possible to access the outside of the walls of the tube

thanks
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 You should provide more info:Diameter of tube. Length of tube. Tolerance of measurement. If you cannot access the outside wall surfaces of the tube, then have the case of a hole measurement. There are many devices and methods to measure the inside diameter of a hole.
 I cannot provide the diameter of the tube, this is what i want to measure! I am thinking of sending specific waves inside the tube, that will run inside its whole length and they will reflect to its walls, and by this procedure, to calculate the diameter The tube is very labyrinthine and very thin (.000 of mm)

## measure the diameter of a tube

I have used both TDR's and OTDRs (Time domain reflectometer) to measure Coax and fiber optic cables.
http://en.wikipedia.org/wiki/Optical..._reflectometer.
You can construct both easily with an oscope and some electronics.
The OTDR would send a pulse of light down your tube, the reflections will tell you
"things" about your tube. (What those "things" mean, is up in the air, as no one hase modeled your tube before.)
So lets say for example you put a reflector at the far end of the tube, and send in a quick pulse of light. The reflected light you get back in time may tell you how many
turns, or restriction are in the tube, and how far away they are.
If you model it with tubing you do have access to, you can learn to interpret what you see.
If the tube is insulated and made of a conductor, you may be able to do the same thing by sending an electrical pulse down the walls of the tube.
 that is very interesting the problem is if it can be applied inside a biological tube, like vessel or bronchiol in vivo their walls have unique properties and their content is not void is there something that we could do to overcome such obstacles?
 I agree with tygerdwg you need to provide considerably more information before sensible discussion can proceed. You are beginning to do this but more is needed. It seems you want to measure the diameter of small biological fluid vessels. Are these in a living organism? Where do you want to measure the diameter in relation to the entry point What access do you have? What fluid is in the vessel? Are you interested in the fluid bore or the total bore of the vessel if partly obstructed? and so on.
 I imagine placing a probe inside a human vessel in vivo (so with blood running in it) that probe will send waves that will refract on its walls for some distance from the probe and this way (given that the probe will also act as sensor) the information about the diameter of the vessel in each point of its lenght will be measured
 I see no feedback maybe you know a more appropriate place to discuss such things?
 This sounds a lot like some research I read about in 1985. I want to say HARC was doing the work,(Houston Area Research Counsel) They were looking at optical reflective spectroscopy with intravenous fiber optics. I don't know much about where they took the research, as I moved to another field.
 This may not be a practical solution but here is an idea similar to fundamental calculus. If you fill the tube with a liquid -say water- and can measure the volume of the container (i.e. it is not infinite); then empty the tube while measuring the rate of flow of the liquid out, you may be able to measure the rate of change of volume of the tube. The only variable causing the increase/decrease in volume would be the diameter of the tube, assuming we kept each Δlength constant and the shape cylindrical. This situation reminded me of the "trough problem" from calculus, except we're working backwards by measuring the rate of flow and calculating the change in volume. Unfortunately, this solution probably isn't viable in a situation where the tube is as small as you're describing.