Patent ID: 8869631

Claim:
A method of detecting thickness of walls of elongate hollow bodies of carbon fiber composite material, the method comprising the steps of: a1) providing a hollow manufactured body having at least one wall of non-ferromagnetic material with an outer surface and an inner surface facing a cavity of the body; a2) providing an inner slider and an outer slider, comprising: a first couple of mutually magnetically attracted elements, wherein the first couple includes at least one permanent magnet accommodated in a seat of the inner slider, and at least one second permanent magnet or a second block of ferromagnetic material accommodated in a seat of the outer slider; wherein the element of the first couple of elements, located on the inner slider is accommodated in the seat in a freely slidable manner in a direction which in use is substantially perpendicular to a plane in which the wall extends at the point in question, and in which the seat is open towards the wall to be measured, wherein the element directly contacts the inner surface of the wall; and wherein the seat has, on the side opposite the side open towards the wall, a catch for limiting movements of the element in the seat away from the wall; at least a second couple of mutually magnetically attracted elements, wherein the second couple includes at least one permanent magnet located on the inner slider, and at least one second permanent magnet or a second block of ferromagnetic material located on the outer slider; b1) locating the inner slider on the inner surface of the wall, so that the corresponding element of the first couple of elements is free to contact the inner surface, and b2) placing the outer slider on the outer surface so that the corresponding element of the first couple of elements is free to contact the outer surface due to the magnetic attractive force mutually exchanged with the other element of the first couple; c) manually moving the outer slider across the outer surface to a predetermined point where the wall thickness is to be detected, wherein the inner slider on the inner surface follows the movements of the outer slider due to the magnetic attractive force mutually exchanged between the elements of the second couple; d) measuring, by a transducer device mounted on the outer slider and mechanically connected to the corresponding element of the first couple, the force required to detach the corresponding element of the first couple from the outer surface; and e) deriving, from the measured force, the value of the thickness of the wall in that predetermined point.