Patent GB-860589-A (GB)
Title: Electrical remote control systems
IPC: G08C25/02
Filed: 1957-03-08
Abstract: 860,589. Electric selective signalling systems. WESTINGHOUSE AIR BRAKE CO. March 8, 1957, No. 7740/57. Class 40 (1). In a signalling system of the kind having a central office and one or more field stations (only one being shown) each signal transmitted to a field station by the central office is substantially immediately re-transmitted by the field station back to the central office where, in the event of a fault in the system, its absence causes the transmission of further signals by the central office to be prevented. In a first embodiment, Fig. 1, the central office (lower portion of Figure) and a field station are linked in a duplex manner by two uni-directional channels having carrier frequencies F1 and F2. A signal is sent from the central office to the field station by causing normally energized relay TC to be temporarily de-energized, thereby shunting the F1 carrier transmitter, and the signal's significance is determined by its duration which can be either short or long. Any such signal causes, at the field station, the de-energization of a normallyenergized relay FC, which relay, corresponding to the relay TC at the central office, immediately causes the signal to be transmitted back to the central office where it is received by a relay OC. Thus normally relay OC should follow relay TC, changing its condition just after relay TC changes its condition (the delay being the time taken for the signal to travel from the central station to the field station and back again). The central office also includes a checking relay CD which has two hold circuits one via the back contacts a of relays OC and TC and one via their front contacts to the positive terminal of a battery, indicated by a B+. Relay CD is also selectively shunted by a diode Q causing it to be slow to release. In operation relay CD is normally energized via one of its holding circuits. Energization or de-energization of relay TC (i.e. the beginning or end of a signal) breaks the operative hold path and prepares the other and immediately after this relay OC operates to complete this other hold path, the relay CD being maintained energized by the diode shunt. Thus if the system functions correctly relay CD remains energized. Once the other hold path has been completed, contact b of relay OC causes a relay MCP to switch over the shunt Q1. A fault can be of two kinds, either relay OC does not operate immediately after relay TC, whereupon after a short delay caused by the shunt Q1 the relay CD falls out, or relay OC can operate without relay TC having just operated (e.g. when a spurious pulse is induced in the F2 channel) whereupon the relay CD falls out immediately with no delay, the shunt Q1 then being ineffective. A second embodiment is described (Fig. 3, not shown) for signalling by means of long pulses only and modifications of both embodiments (Figs. 2 and 4, respectively, not shown) are described in which the communicating channels are formed by two direct D.C. lines, normally positive and negative when carrying no signal. It is stated that each field station could be provided with similar checking relays. Specification 753,928 is referred to.