GB729817A - Improvements in or relating to apparatus for detecting the presence or absence of a conducting or magnetic object - Google Patents

Abstract

729,817. Electric tests. GENERAL ELECTRIC CO., Ltd., DAVIS, G. E., and IRVING, H. D. April 10, 1953 [Jan. 10, 1952; April 10, 1953], No. 23631/51. Class 37. Apparatus for indicating the presence of a magnetic or electrically conductive body comprises an H-shaped core 10 (Fig. 1), having an A.C. energizing winding 11 on the centre limb, and similar secondary windings 12 on the other limbs connected in series opposition to give no resultant output voltage at terminals 13 except when the flux distribution is disturbed by the presence of such a body 14. The detector may be used to sense over-shooting of a reciprocating table, e.g. of a planing machine, to effect reversal of the direction of movement, or to effect operation of a cutter when a predetermined length of steel bar is extruded on to rollers. Two such detectors may be located along the line of travel of a body to determine its speed by noting the time interval between responses in the detector, and may be used to control braking equipment. As shown (Fig. 2), a detector 20 when affected by a passing body fires a thyratron 21 to energize a relay 22 and close contacts 25, thereby initiating the charging of a condenser 32, so that after a certain time interval a thyratron 26 also fires to energize relay 27 and open contacts 34. A further detector 44 is located in the path of the body, which, when affected, fires a thyratron 42 to energize relay 41 and close contacts 40, which are connected in series with contacts 34 to terminals 45 and a brake control circuit. If thyratron 42 fires before thyratron 26, contacts 34, 40 are simultaneously closed, and a brake is brought into action. A third detector 46 is located beyond the normal end position of the moving body, so that the brake is applied if the body overshoots its desired final position. The invention may be applied to the lift cage in a mine, or to the movement of tubs on a rail. In a further embodiment (Fig. 6) one' detector 124 senses the end of a metal strip 120 passing through strip rolling and reeling machinery, and a second detector 128 is located near the reel 122 on which the strip is being wound, to stop the driving motor 123 at a predetermined diameter of material on the reel.