Measure thickness of inner layer of pipe

[dv_sa559]

I wanna make robot which sensing thickness of inner layer of 5 layer pipe .
This pipe consist of 2 layer polymer and 2 layer adhesive and one layer aluminum (centric layer).

In fact on the producing of these pipe sometimes inner layer maybe have insufficiency in the surface and maybe have holes ( this is very bad defect).
I think we can sensing capacitance between device and aluminum or spark test (such as megger testing method)or Electrical field sensing. if device detect defect then we can stop machine and maintenance it.
any idea in this case would be appreciated.

 

[i.esmaili]

Hi
I think the most popular approach in thickness measurment is ULTRASOUND.
As you know the exact metal that used in the pipe, you can find the sound speed in that metal and with a simple physical relation(velocity=distance/time) you find the thickness.
The problem that may occure is that sound can't travel in the air. Maybe you have to fill the pipe with water.But it can be helpfull in your case, beacause hole in the metal is like a air bubble and it's very easy to find this holes with ultrasound.