Patent GB-501581-A (GB)
Title: An improved method of and apparatus for detecting foreign metallic matter in non-metallic materials
IPC: A24C5/34
Filed: 1937-06-01
Abstract: 501,581. Electric and magnetic tests. INTERNATIONAL CIGAR MACHINERY CO. June 1, 1937; No. 15178. Convention date, Jan. 16. [Class 37] Metallic matter in non-metallic material such as foodstuffs, cigars, &c. is detected by automatically passing the material into or through the electromagnetic field of an energized coil or coils included in an impedance bridge, any metallic material present upsetting the balance of the bridge to produce a signal voltage which may be used to separate or divert the portion of metal-containing material. The material or articles A, Fig. 1, are passed through coils 12, 11, 13. The coil 11 is energized with high frequency current from an oscillator 10 and induces equal e.m.f's in the similar coils 12, 13 connected in opposition in a balanced bridge circuit so that the presence of metallic matter in any article A upsets the balance and produces an e.m.f. across points 15, 20 preferably connected by a resistance 16, the e.m.f. being amplified at 22 and passing through a diode-triode detector-amplifier 30 to actuate momentarily a relay 32 which closes contacts 34 to operate a solenoid 36 to divert the faulty article. The coils 12, 13 are tuned by variable condensers 18, 19 to a frequency slightly different from that of the oscillator 10 to enhance the sensitivity of the bridge, and the rectified output of the detector portion of valve 30 is preferably coupled by a condenser 38 to the triode amplifying portion thereof so that the relay 32 will not react to slow voltage changes in the resistance 16 due to variations in humidity, temperature. Alternatively, the amplifier 22, Fig. 3, may be coupled to' a Thyraton (Registered Trade Mark) rectifier 43, in which case the relay 32 when operated remains so until released by the opening of interrupter contacts 48. Coil unit assembly. The similar coils 12, 13, are wound on insulating tubes 50, Fig. 5, secured in metallic end discs 51 spaced by an earthed metallic tube 52, and the coil 11 is mounted on an insulating tube 49 carried by an insulating disc 53 secured at 54, and at 55 held by a collar 57 on an axially adjustable rod 56 whereby the coil 11 may be adjustably positioned for exact symmetry with respect to coils 12, 13. An insulating tube 58 carries a layer of fine copper wires 59 longitudinally arranged around its periphery and secured to metal end rings 60, for screening the coils 11, 12, 13 electrostatically from metallic material in the articles under test as they pass through the coils, and earthed wires 61 radially arranged on one or both sides of discs 62 prevent the adjustment of the inductive balance of the coils from affecting their electrostatic balance. The tube 52 shields the coils from external interference. The coils 12; 13 may alternatively be mounted in separate cylinders and the articles to be tested passed through only one of them. In the application of the invention to the detection of metal particles in cigars delivered from a cigar making machine, the finished cigars C, Figs. 7, 9, are delivered from arerolling device 64 and guide 68 on to an endless band 66 driven from a shaft 76, which conveys them through a detecting unit 82 as shown in Fig. 5. Perfect cigars C<SP>1</SP> after passing through the unit are deflected by a plate. 67 down a slope 81 to a tray 65. Should a metal particle be detected in a cigar, however, the consequent operation of solenoid 36, Figs. 1, 9, rocks the deflector plate 67 against the action of a spring 88 to the dotted position, the faulty cigar C<SP>11</SP> thereby being conveyed to a separate receptacle. Since, in the case of the circuit shown in Fig. 1, the energization of solenoid 36 is only momentary, a locking circuit is provided therefor over contacts 90 closed by the operation of the solenoid armature 83, the solenoid remaining energized until a cam 93 on the shaft 76 breaks the locking circuit at interrupter contacts 48, Fig. 7, when the deflector plate is returned to normal. With the circuit shown in Fig. 3, using a gas-filled discharge tube, the locking circuit is unnecessary, the interrupter contacts 48 being connected directly in the circuit of relay 32.