Patent GB-454739-A (GB)
Title: Improvements in telephone systems
IPC: H04M3/523
Filed: 1935-09-16
Abstract: 454,739. Electric signalling systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, Westminster, GRINSTED, W. H., Under the Plane, London Lane, Bromley, Kent, and HUMPHRIES, H. E., 61, Rochester Way, Blackheath, London. Sept. 16, 1935, No. 25652. Addition to 401,394, [Group XXXIX]. [Class 40 (i)] [See also Group XXXIX] In a system such as that described in the parent Specification in which toll operators extend calls by means of automatic switches which, in the case of congestion, extend calls to a storage circuit, the number of calls so stored being shown on an indicator controlled by a self-balancing bridge circuit, the bridge comprises a differential transformer T to the mid-point of the primary of which a connection is made periodically, the resulting transient impulse in the secondary winding causing, with the help of a thermionic valve V the operation of a relay at make or at break according to the direction of the unbalance, the relay actuating a counting chain A.. D to restore the balance and to control an indicator over wires C1 .. C9. When the last of a group of junctions is taken into use earth is taken off the wire WG leading to the corresponding storage circuit and relay G energizes Q and disconnects interrupted earth on WE from wire WS to give a signal to the operators, Q connects up the valve heater, earths wire WB to start the pulsing machine and connects R to wire WP which carries the pulses. R at each operation makes a fleeting circuit for a high speed relay X of the kind described in Specification 405,436, [Group XXXVII], and while there are fewer than five waiting calls energizes a relay K. X locks up at the first impulse and nothing further happens in response to repeated operations of R until a connection is attempted. The group selector attempting the call runs to 11th terminals and connects battery to WN over a resistance (not shown) and next time R receives an impulse a circuit is completed through the upper primary winding of T and then broken. The direction of the resulting pulse of current in the secondary is such that at make the valve V becomes conductive and Z is operated over its winding (i) the pulse being prolonged by the regenerative action of winding (ii) which is included in the grid circuit. Since R and Z are now operated together a circuit is made for the first of the counting relays A.. D in series with X and Y. Y and A pull up and A locks at a light armature a<1> and then at a<3> holds Q and itself independently of G and M. It also connects battery over YA to the lower primary winding of T to balance the bridge and extends the impulse circuit to B. Contact a<2> however in changing over drops X and Y so that the impulse circuit is not complete when it is extended and B is not operated. Before R is released Z has fallen back, its release having been hastened by the connection of battery to the lower primary winding of T. On falling back R again makes a fleeting circuit for X which re-operates. If no more attempts have been made to extend calls over this group of junctions the opening of contact r<3> does not interrupt any current flow since the bridge is balanced. If congestion has increased the impulse is in a direction to prevent the operation of Z. If it has been reduced Z is operated at a time when R is de-energized and the impulse goes to the releasing winding (iii) of the last operated counting relay. When next relay R pulls up, if the bridge is balanced, no effect other than the re-operation of M is produced. If congestion has increased the direction of unbalance is such that Z is re-operated and the chain is built up a further step as before. Assuming a progressively increasing state of congestion the chain builds up to relay K which energizes L and arranges for K to be de-energized while R is up and energized while it is back. L lights the first four busy lamps independently of the counting relays and also a fifth lamp and holds up Q, and K, in addition to the functions described above, connects up YK which is equivalent to five resistances such as YA .. YD in parallel. If congestion continues to increase, the impulses from Z now break the counting chain down beginning at D by acting on releasing windings (iii). When A has been released the ninth lamp is operated and a circuit made whereby operation of key DW energizes O to give an appropriate signal to the supervisor. If at any stage the testing operation by relay R finds less conjestion instead of more contact r<3> at make produces no effect but at break causes a momentary operation of Z. As the result a counting relay is energized or de-energized according to whether the chain is being broken down or built up by increasing congestion as indicated by the condition of L. Progressive reduction of congestion after L has been operated causes in due course the release of K and so of L and thereafter the breakdown of the counting chain. As soon as a junction becomes available G falls but Q is held at a<3> or l<6> to keep the pulse machine running so that a signal may be given over WS.