Abstract
A PAPER by B. M. Thornton and Prof. W. M. Thornton, upon which written discussions are to be sent to the secretary of the Institution of Mechanical Engineers before January 31, 1939, gives a method of measuring the thickness of metal walls from one surface only by electrical means. A reference was made to this device by Prof. Thornton in his contribution to the discussion on non-destructive testing at the Institution of Electrical Engineers on November 25. He states that there is a definite need in the engineering industry for an instrument which will determine accurately the thickness of a metal wall from one side only, especially if it is easy to operate, robust, portable, and independent of external power supply. It is claimed that the instrument described in the paper fulfils all these conditions. The method is essentially that of comparing the resistance of the metal wall under test with that of a similarly shaped wall of the same material, of which the thickness is known. Current, usually less than ten amperes, is supplied by a 12-volt battery to two current contacts held against the wall and usually spaced about three inches apart. The current in the circuit is adjusted by varying the rheostat or the number of cells of the small motor-car battery employed, until the very small potential drop indicated by the deflection of a galvanometer connected to two potential contacts reaches a predetermined fixed value. The instrument was originally designed for measuring the thickness of boiler-tubes, and examples are given showing that its accuracy is within a few thousandths of an inch. It has been found in practice that the instrument can be used to measure the thickness of mild steel plates up to 1 '25 in. and of iron castings up to three inches, with the same order of accuracy. It can also be used for the measurement of engine cylinder walls to detect core shift.
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Thickness of Metal Walls. Nature 142, 1152–1153 (1938). https://doi.org/10.1038/1421152d0
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DOI: https://doi.org/10.1038/1421152d0