Patent GB-189912279-A (GB)
Title: Improvements in Electric Telegraphs for Ships and other Purposes.
Filed: 1899-06-13
Granted: 1900-06-13
Abstract: 12,279. Evershed & Vignoles and Evershed, S. June 13. Order or alarm apparatus, for sbips and other purposes, based on that described in Specification No. 8784, A.D. 1891. The transmitter is a divided resistance switch, arranged to supply current from one pole of a battery to two conductors in varying ratios. A common return conductor leads to the other pole of the battery. The resistances may be equal, and connected in series between the two conductors, the switch arm moving along them, and also including more of an auxiliary resistance in circuit as it moves away from a middle position, to reduce the total current. Or the switch arm may move along two series of resistances, each connected at one end to one conductor, and arranged in steps of increasing resistance to the other end, to keep the total current constant. The switch arm may move circularly on a numbered or order dial, and be provided with a latch, which is linked to a plain switch on the switch spindle so that the battery circuit is opened when the switch is locked. The receiver consists of a series of polarized electromagnetic movements such as that shown in Fig. 1, each having two windings A, B, one included in each of the two conductors mentioned above, and acting differentially. The ratio of the numbers of turns in the two windings differs in the successive electromagnets. The resultant polarity in each depends on the ratio of the currents in the two conductors. In the form shown in Fig. 1, the two windings are on an iron core having pole-pieces f<1>, f<2> acting on an armature n, pivoted on one pole of a polarizing- magnet N. The armature carries an arm R between stops J<1>, J<2>, and is retained magnetically against either of these after the current in the coils ceases. When a long series of electromagnetic movements is used, they are preferably made without iron cores, and, unless a constant current is used, the arms R are retained, after the current ceases, by catches on two bars previously raised by an electromagnet. In one form of receiver, each arm R of the series carries a coloured indicator shutter behind a slotted plate marked with numbers or orders. Two or more such plates, each carrying ten digits may be placed parallel, and their series of electromagnets controlled by separate pairs of conductors from transmitters arranged to send numbers containing two or more figures. A circular dial receiver is shown in Fig. 5. The arms R are situated radially so that their inner ends lie in either of two small circles. A central shaft and a sleeve a<2> carry notched arms D', D<2> in these circles, and are movable oppositely by a coiled spring so far as the radial arms R or stops h', h<2> permit. A dial pointer I' is carried by another shaft A, having a bent arm r interposed between and movable by the notched arms D<1>, D<2>. When a signal is received, the notched arms D', D<2> are first returned to stops h<1>, h<2>, in opposition to the spring, by an electromagnet M in the return conductor turning armatures K', K<2>, toothed sectors S', S<2>, and pinions on the shaft and sleeve a<2> ; in such return motions, any displaced arms R are moved to a middle position by the arms D<1>, D<2>. The arms R then set in accordance with the ratio of the currents passing through the movements, and, when the current ceases, the spring turns the notched arms D<1>, D<2> against two of the radial arms R, setting the pointer I' to its new position.