Patent GB-546304-A (GB)
Title: Improvements in or relating to electrical signalling systems
IPC: B66B19/06
Filed: 1941-01-04
Abstract: 546,304. Identifying calling signalling station. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., PREIST, T. P., and THOMPSON, G. W. Jan. 4, 1941, No. 157. [Class 40(i)] In a system in which signals can be given to a central station from any one of a number of points along a pair of conductors 'by connecting the conductors together, as in a mine, it is arranged that a resistance-measuring operation occurs at the central station in response to a call, to ascertain the point at which the call was made and a characteristic lamp glows. In response to the operation of a key, the original lamp circuit is broken but the registration of the position of the calling point is held by magnetically locking relays and the lamp is now operated in a flashing circuit. On the reception of a further signal from the same point, the lamp again glows continuously. It may be arranged that only long signals set the identifying circuit into action. Current operations.-Operation of one of the contacts 1SK ... 10SK energizes, through one or more of a number of line resistances LR1 ... LR9, the line relay R which is followed by its relief relay RR. A short circuit is thus removed from resistances YAA ... YAF and a bridge circuit, of which three of the arms are formed by resistances YC, YB, YD and the fourth by the resistances YAA ... YAF and the line resistances LR1 ... LR9, is completed. At the same time, a circuit is completed whereby relays A ... F, operating in the manner of a counting chain, cut out the resistances YAA ... YAE in turn, then resistance YAF, replacing YAA ... YAD, and then YAA ... YAD. This operation stops, owing to the operation of a detector relay BR, when the combined resistance of the line resistance LR1 ... LR9 that have not been byepassed and the resistances YAA ... YAF that have not been short-circuited reaches a predetermined value. Relay BR energizes WS which locks, lights one of a number of lamps 1 ... 10 selected by the relays A ... F and connects negative battery and YE to the windings of a group of relays AF ... FF which are normally held by permanent magnets in the opposite condition to that shown. The flux produced when the lower end of the windings is connected to negative opposes that of the permanent magnets and in consequence those relays that are connected up by the corresponding relays A ... F change over to the condition shown. A slow-to-operate relay FK opens the energizing circuits shortly afterwards without effect on the relays. In response to a bell signal given by RR and to the lighting of the selected lamp, the engine man stops the engine and operates a key KCA. By this time the initiating signal will have ended and relays R, BR, RR will have fallen back and the operation of the key releasesWS and the operated relays A ... F. The original circuit for the lamp is thus broken but a flashing circuit is made for it over contacts of the relays AF ... FF and of relay FJ which interacts with FK to produce flash impulses on the energization of FH which results from the relapse of WS. To give the start signal, the man in the haulageway gives two rings with the key 1SK ... 10SK. The relays A ... F operate as before to identify the calling point and if this is the same as the original calling point the lamp which was previously flashing now glows steadily. No action takes place on the relays AF ... FF because FH is energized. The apparatus is restored to normal by the operation of key KCB which releases A ... E and WS and re-energizes such of the relays AF ... FF as have been de-energized. These relays in operating open their own circuits but are held by their permanent magnets. When they are all energized, relays FH, FJ, FK are released. Had the second signal come from another point, the key KCA would have been operated to cancel it. In the case of a permanent loop, neither KCA nor KCB is able to cancel the signal and KCW is pressed to remove a shunt from CW which thereupon lights a special fault lamp. Relays BR, R, fall back owing to the increased resistance of the line circuit and are followed by the other operated relays. To verify the location of the fault, key KCS is thrown to cause the appropriate lamp to glow through contacts of the relays AF ... FF on which the faulty signal has remained registered. Specification 515,529, [Group XXXVII], is referred to.