Patent GB-191849-A (GB)
Title: Improvements in and relating to electrical transmissions for direction purposes
IPC: G08B5/22
Filed: 1921-10-25
Abstract: 191,849. Evershed & Vignoles, Ltd., and Needham, J. C. Oct. 25, 1921. Order apparatus ; tell-tale apparatus.-Relates to signalling systems of the kind in which rheostats at the two stations are connected on the bridge system, and the receiver contact arm is moved until the nul position of a galvanometer in a diagonal of the bridge indicates that the receiver and transmitter are in agreement; and consists in providing for finer adjustments by employing two or more contact arms at each station so geared that.a complete turn of one arm corresponds to a single step of the next arm, separate galvanometers being used for each contact arm. Fig. 1 shows a circuit arrangement and Fig. 3 a construction of transmitter or receiver. Referring to Fig. 1, resistances c, h are connected across D C leads a at each station. Tappings on these resistances are taken to studs which are swept over by arms b, g, which bear also on rings o, r. A galvanometer coil m connected between these rings is placed near the receiving-operator, who by watching the pointer and adjusting his arm g is able to keep that arm in step with the transmitting-arm b. At each station a further pair of resistances e, f and j, k is connected in parallel across the leads a, and each pair is arranged so as to present jointly a complete circle of contacts for the arms d, l. A contact ring p is engaged by the arm d and a two-part ring s, t by the arm The ring p is connected through a galvanometer n to the ring s and through a reversely-wound coil to the ring t. At each station the operator's handle &c. is connected or geared to the spindle u carrying the arm d (or l), and this spindle is connected by a Geneva gear to the spindle u<1> of the other arm b (or g). The gear comprises two pins w placed at diametrically-opposite points on a disc v secured to the spindle u and engaging in notches in the rim of a Geneva wheel which rotates with a pinion y geared with a toothed wheel z on the spindle u<1>. Thus at the completion of each half-turn of the arm d, the arm b is advanced through a small arc from one contact stud to the next. At intermediate positions of the arm d, the Geneva wheel. is locked by segmental :flanges b<1> on the disc v engaging pins c<1> on the Geneva wheel. When the transmitting instrument has been operated, the receiving-operator turns his instrument in the direction indicated by the pointer of the galvanometer m until that pointer returns to central position. Fine adjustment is then obtained by similarly bringing the pointer or galvanometer n to central position. The divided ring s, t and double coil n are necessary because the advance of arms l beyond the in-step position gives a potential at the receiving end greater or less than that at the transmitting end according as the arm d is on resistance e or resistance f. In a modification, the ring p is divided similarly to the ring s, t, corresponding sections being connected by two leads, both of which include a single coil winding n. Intermediate resistances may be arranged between the. primary set e, f and the final set, their contact arms being geared up to the arm of the primary set and down to the arm of the final set. Such intermediate resistances are in pairs similar to e, f and their contact rings (similar to s, t) are divided at one or both stations and are associated with a third galvanometer.