GB166317A - Electromagnetic induction micrometers - Google Patents

Abstract

166,317. Ford, J. M. March 31, 1920. Sounding-apparatus. - Small relative movements or changes of length are measured by causing them to vary the flux density or flux distribution in each of two normally balanced magnetic circuits. The application to a differential pyrometer or thermometer is shown in Fig. 1 in which the rods 2, 1 carry respectively iron cored transformers 4, 5, and armatures 7, 8 through which the magnetic circuits of the transformers are completed. The primary windings 11, 12 of the transformers are connected in series and are supplied with alternating or intermittent current. The secondary windings 14, 15 are connected in opposition to one another and in series with an alternating-current measuring-instrument 16. Normally, the air-gaps in the transformers 4, 5 are equal, consequently the secondary electromotive forces neutralize one another. Any relative motion between the rods 1, 2 causes a decrease of one air-gap and an increase in the other, thereby upsetting the balance of the secondary electromotive forces and causing an indication on the instrument 16, the magnitude of which is a measure of the relative motion. The transformers may be auto-connected. In order to distinguish displacements in one direction from those in the other, the secondary current may be rectified. The secondary windings may be wound on the armatures 7, 8 which two armatures may be replaced by one armature, in the form of a cross, between two inwardly facing E- shaped electromagnets. ln a modification, Fig. 2, the armatures 7, 8 are dispensed with and the secondary winding is a coil 19, normally symmetrically disposed in the fields of two electromagnets 17, 18. Relative motion between the coil 19 and the magnets 17, 18 is thereby indicated. A recording-instrument or oscillograph may replace the instrument 16.