Patent GB-494103-A (GB)
Title: Improvements in or relating to the grading of electric resistances and articles comprising the same
IPC: F42B3/198
Filed: 1937-04-19
Abstract: 494,103. Wire resistances ; resistance measurements. ASHCROFT, D. G., TAYLOR, W., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. April 19, 1937, No. 11178. [Class 37] Resistance elements are graded according to their resistance values by conveying them in sequence to a collecting system comprising a plurality of collectors each corresponding to a particular range of resistances, applying a potential to each element, and causing the resulting current through the element to direct it to the appropriate collector. A driving shaft 1 carries cams 3, 4, 5 operating respectively a contact-breaker, a lever 6 pivoted at 7, and a cutter 8. The lever 6 at each operation rotates a ratchet-wheel 18 through a quarterturn. This ratchet-wheel is fixed on a shaft 14 which also carries a four-segment contactbreaker 21 and a pair of four-armed metal spiders 15, 16, Figs. 3 and 4, which are mounted on an insulating boss 17, one on each side of a fixed insulating cam 12. This cam has contact strips 23, 24 on opposite sides and is sufficiently broad to keep the tips of the opposed arms of the spiders 15, 16 apart except for a segment corresponding to the gap in the strips 23, 24, where the rim of the cam is narrowed so as to allow the tips of the arms to meet. The apparatus is particularly applicable for grading fuse-head resistances, which are made by coating a sheet of nonconducting material on both sides with metal foil and stamping to form a comb, each tooth of which is subsequently formed into a separate fuse-head. Resistance wire is wound spirally round each comb so that it crosses the head of each tooth and is then soldered to the foil on each side. The excess of wire is removed, leaving a bridge across the tip of each tooth. The teeth are then dipped in an ignitable composition so as to form a bead round each bridge-wire. The comb is fed through a slot 27 and pressed against a stop on the cutter 8 when this is in its advanced position, the spiders being in the position shown in Fig. 3. The cam 4, through the lever 6 then rotates the ratchet-wheel 18 so that the spiders 15, 16 rotate in a clockwise direction. The lower descending arms move off the broad part of the cam and the edges close on the end fuse-head of the comb. The cam 5 then advances the cutter 8, which severs the fuse-head from the comb. The spiders then carry the fuse-head forwards and the contact-breaker 21 makes contact at 22 and applies testing voltage to the strips 23, 24, and thence through the spiders to the fuse-head. Further rotation of the shaft 14 causes the contact-breaker 21 to open the testing circuit and carries the spider arms on to the broad rim of the cam 12 so that the fuse-head is released into the main shoot 33 and is then directed by traps and delivery shoots into its appropriate container as determined by its measured resistance. In series with the fuse-head under test is a dead-beat reflecting galvanometer, the reflected beam of light from which sweeps over a rank of photoelectric cells, each connected by amplifiers and relays to a solenoid operating one of the traps in the main shoot, so that a trap is opened corresponding to the galvanometer deflection.