Patent GB-567032-A (GB)
Title: Improvements relating to code-operated electric remote control systems
IPC: B61L7/08
Filed: 1940-02-19
Abstract: 567,032. Electric selective signalling systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. Feb. 19, 1940, No. 3124. Convention date. March 25. 1939. [Class 40 (i)] [Also in Group XXX] In a code - operated electric system for selective control of a number of remote stations from a central control point, the stations form two or more groups, the code impulses appropriated to one group having electric character different from that of the code impulses for the other group or groups. Thus one group may respond only to impulses having one polarity, and the other group only to impulses of the opposite polarity, or one group may respond only to direct current code impulses and the other on others only to coded A.C. of predetermined current frequency. The invention is particularly described as applied to a centralized traffic-control system for railways of the kind described in Specification No. 415,787. The OT, OR, R, M, E, T, relays shown function as in the prior specification, OT relays transmitting the desired code from a central office O to lines Y, Z, relays OR at the office and R at the stations responding to the code. As a result relay M at the selected station picks up, breaking the line connection between more remote stations and the office, and connecting contacts of relays E, T at the selected station to the office line. Relay T can then be used to transmit a signal or indication code from the selected station to the office. Other relays of the prior system are not shown. The invention as described introduces additional relays PO, V, and the arrangement of the stations in two groups 1A ... 35A, 1B ... 35B, each group responsive only to code current of predetermined electrical character, allows code to be sent between stations in each group and the office, in either direction, simultaneously and without interference, thus increasing the number of stations which can be served over the same lines, or increasing the rate at which operations can be effected. Fig. 1 shows a transformer 4 supplying A.C. of commercial frequency from source BX, CX over front contacts of relay PO, back contacts of office transmitting relays OTA, OTB and windings of relays ORA, ORB in parallel, to lines Y, Z. Rectifiers 1, 2 in circuit with the relay contacts are reversely arranged so that positive half waves send positive current over upper OTA contact to line Y with return from line Z over lower OTA contact, whilst negative half waves send positive current over lower OTB contact to line Z with return from line Y over upper OTB contact. Thus operation of relay OTA sends " positive " code impulses to " A " stations, and operation of relay OTB sends " negative " code impulses to " B " stations. Relay PO is of direct current type fed from transformer 4 through rectifier 3, its contacts being normally picked up as shown, but, on failure of source BX, CX, releasing to connect a direct current source B, C to the winding of a reed or other vibrator relay V, the contact of which operates to send current from source B, C through the half-windings of the primary winding of transformer 12 alternately. Release of relay PO contacts disconnects transformer 4 from line, and in lieu connects secondary winding of transformer 12 to line, the arrangement thus providing a stand-by source of code current. Station 1A is connected to lines Y, Z through rectifiers 1, 2 (arranged to pass " positive " code impulses only), the back contacts of relay M at that station completing line circuit to the line continuations Y1, Z1 leading to other stations. The station circuit is bridged by rectifiers 7, 8 which by-pass negative code impulses direct to lines Y1, Z1. " B " stations may be similarly connected to line in series with " A " stations, except that rectifiers 1, 2 would be interchanged and the " B " station relays connected to the Z line, which rectifiers 7, 8 bridging a " B " station would be reversed to by-pass positive code impulses. As shown, however, stations 1A ... 33A only are assumed to be connected in series with the line up to wires Y33, Z33, beyond which the line branches, stations 34A, 35A being connected in one branch through rectifiers 11, 12 passing only positive code impulses, and stations 1B ... 35B in the other branch through rectifiers 9, 10 passing only negative code impulses. At stations 35A, 35B most remote from the office relays M complete the line circuit directly by a back contact, or through contacts of relays E, T by a front contact. Relays ORA, ORB at the office and relays R at the stations are of biased polar type shunted by rectifiers 5 to prevent chattering of their contacts with code frequency but not distorting their response to code impulses. Fig. 2 shows a similar system in which the " A " and '' B " stations are connected in series in the lines Y, Z, the former responding only to D.C. code impulses and the latter only to A.C. impulses of predetermined current frequency. The D.C. code impulses are sent to line from a battery OB through contacts of office transmitter OTA and winding of office relay ORA. A.C. current is provided from a D.C. source by an arrangement of vibrator relay V and transformer 12 similar to that shown in Fig. 1 and under control of relay OM, the current being coded by contacts of relay OTB, which are normally open. Similar vibrator and transformer arrangements are used at each " B " station under control of the station relay M to send A.C. current to line for giving indication code to the office under control of the selected station transmitting relay T and for locking out more remote stations as referred to below. A low-pass filter 14 is included in the circuit between the'contacts of each " A " transmitter (OTA or T) and the line. The continuity of the line is normally maintained over back contacts of the station relays M in succession, but each " A " station is bridged by a high-pass filter 15 to maintain line continuity for A.C. when its relay M is picked up, and each " B " station is bridged by a low-pass filter 13 to maintain line continuity for D.C. when its relay M is picked up. Relays R at " A " stations are directly connected in the line, but relays R at " B " stations are supplied through rectifiers 19 from coils 17 which, together with condensers 18, provides circuit elements tuned to the frequency of the A.C. source, and protect the relays from D.C. codes. As in the prior Specification 415,787 each transmitter is controlled by the associated line relay so that codes can be initiated only when the line is free. Indication codes are initiated by energizing the station master relay M and to deal with the event of two or more codes being initiated at the same time each control code is arranged to begin with a relatively long impulse and each indication code with a relatively short one. Each station relay E is selectively responsive to a long first impulse, and requires to be energized to condition the station apparatus for selective response to the control code. Energization of a " B " station relay M causes the associated V relay to impress steady alternating voltage on the lines leading to more remote stations, energizing the remote station E relays, which, as explained in said prior specification, releases the relay M at any more remote station which attempts to transmit code at the same time. Stations between a transmitting station and the office are more responsive to a short first impulse of an indication code. Alternating current used with the system shown in Fig. 2 may, in place of frequencies which can be generated by a vibratory relay V, have higher frequencies, such as may be generated by vacuum tube oscillators, so rendering the lines available for telephone communication. An arrangement of this kind is described in which a vibratory relay V and transformer such as is shown in Fig. 2 is used to provide high voltage for the plate circuit of a vacuum tube oscillator, the plate circuit being inductively coupled to the line circuit and a tuned circuit similar to the arrangement 17, 18 of Fig. 2, associated with each line relay R, and connected across the output terminals of the source 1 is used to control an intermediate relay which in turn controls the station relay M, this arrangement being used to delay operation of relay M until the tube is sufficiently heated and the requisite line voltage and frequency available, as indicated by the energization of the intermediate relay.