An electric gage for measuring the inside diameter of tubes
Abner Brenner, Eugenia Kellogg · Journal of research of the National Bureau of Standards · 1949
An electric gage has been developed for measuring the bores of small guns or tubes of about )~-inch inside diameter.Its operation depends on the mutual inductance of b 'o coils.The instrument has a solenoid mounted on each p rong of a fork .The current induced in the seco ndary vari es inversely with the distance between the p rimary and seco ndary coil~.The gage is calibrated with rings of known diameter, and the diameter of a tube o r gun bo re is read directly on the dial of the instrument.