Patent GB-411831-A (GB)
Title: Electric control systems
IPC: G05F1/32
Filed: 1932-12-02
Abstract: 411,831. Electric signalling systems. FITZGERALD, A. S., 433, Warwick Road, Wynnewood, Pennsylvania, U.S.A. Dec. 2, 1932, Nos. 34208/32 and 14683/33. [Class 40 (i).] Selection is performed by the ratio of direct current potentials fed to two opposing windings of a number of electro-responsive devices connected with all the first windings in one circuit and all the second windings in a second circuit. As described the devices are saturable re-actors having third windings fed with alternating current, the current for the direct current windings being derived from an alternating current source. The selection is transmitted to the control point by varying one of the direct current potentials, by varying both direct current potentials or by supplying a variable direct current and a variable alternating current over a single channel, the alternating current being rectified at the receiving point to give the necessary two direct currents. Further saturable re-actors may be provided between the receiving re-actors and the controlled units. As shown in Fig. 2 the reactors are provided with alternating current windings 13, 23, 33, 43, with direct current windings 14, 24, 34 and 44 which are of like number of turns and additional saturating windings S of unlike number of turns or of like turns but shunted by resistances to provide different ampere turns. The windings 14, 24, 34 and 44 are fed through resistance T which is adjustable to vary the current in the circuit, a different one of the re-actors becoming unsaturated with the resistance tapped at the different positions shown. There is substantially no volt drop across the A.C. windings of the saturated re-actors but the re-actance winding of the unsaturated re-actor will have a voltage drop across it and the device 10, 20, 30 or 40 in parallel with this re-actor will be actuated. The resistance N maintains the current through the re-actance windings at a substantially constant value. As shown in Fig. 3 the current to both direct current circuits is varied by closing one of the switches 100, 200, 300, 400, the potential being fed to the re-actors 16, 26, 36, 46 over three line wires 51, 52, 53. When a re-actor becomes unsaturated the current flow through the corresponding rectifier bridge is increased and unsaturates the associated re-actor 12, 22, 32, 42 to allow the devices 10, 20, 30, 40 to be selectively controlled. In order to decrease the number of line wires to two the arrangement in Fig. 4 may be used. Here the transmitter is supplied with alternating current 90 which is fed to transformers 55, 550 in a ratio determined by the position of switches 100-400. The current over 55 is fed to the line over rectifier bridge 60 so that a combined direct and alternating current reaches the receiver. At the receiver a further rectifier bridge 63 rectifies the alternating current so that two direct currents are fed over terminals 5, 6, 7, 8 to equipment of similar type to that shown in Fig. 3. By providing a reversing switch for the D.C. supply and an additional rectifier bridge at the receiver a selection between two sets of controlled units can be performed. Specifications 312,338, [Class 40 (i)], 342,681; and 404,034, [Group XXXIX], are referred to.