Patent GB-412302-A (GB)
Title: Improvements relating to telephone systems
IPC: H04M3/523
Filed: 1933-01-13
Abstract: 412,302. Exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, London, GRINSTED, W. H., Under the Plane, London Lane, Bromley, Kent, CHRISTIAN, D. A., Morven, Charlton Road, Charlton, and PETERS, C. L., 51, Verdant Lane, Catford, both in London. Jan. 13, 1933, No. 1240. [Class 40 (iv).] Calls are extended in order of arrival by forwardly hunting switches which first set themselves to positions indicative of the order of arrival, and subsequently hunt in the same order for circuits over which the calls are to be extended as and when these become free. The invention is described for the distribution of calls to toll positions in connection with the system described in Specification 401,394, but is generally applicable to the distribution of calls to call indicators, registers &c. Calls from ordinary subscribers, operators and, it may be, coin boxes, come into the demand circuit shown in Fig. 1 which terminates in distributer switch A the last contacts of which give access to a further distributer B. The earlier positions of A (the first 7 as shown) give access to recording and indicating circuits shown in Fig. 2 common to the demand circuits, which the remaining positions on A and B give access to operators' connecting circuits. On arrival of a call, L pulls up, shunts out the re-ringing contacts of RR, and operates BB which connects ground over CO(ii) to the incoming holding wire. CO(ii) is merely a choke coil to prevent short circuiting the tone lead TT and does not effect the operation or holding of relay CO. Switch A is self stepped by magnet DMB and, assuming no previous call over the demand circuits, the first six of the leads l d from bank AS are open and the switch stops on the seventh (last) lead l d when test relay T pulls up in series with A, Fig. 2, which lights lamp CL2. If another call comes in, the switch A of another demand circuit will step to lead ld1 and relay B will light lamp CL2. Further calls also operate corresponding switches to positions indicative of the order of arrival, the sixth call operating relay F and lighting lamp CL6. If any further demand circuits are now seized, their switches take one step to lead ld1 where they remain held since their T relays operate to battery on this lead. When a T relay operates it connects up S in parallel to apply informatory ringing tone from RS to the calling party. S also connects up booster battery over ballast resistances and L(1) to improve speaking conditions. Assuming now that an operator answers a call by throwing key CA in the position circuit OPC, Fig. 3 (unnecessary details omitted), CA1 closes before CA2 so that differential relay CN remains inert. CA2 operates ST over a high resistance winding which does not upset the balance of CN until ST closes a holding circuit over which battery is applied to CN(i) to unbalance the relay which holds over CA2. Relay ST operates SR and opens the circuit of " first call " relay A so that this relay falls back slowly and the relays S, T of the first called demand circuit falls back. The switch A therefore steps off in search of the connecting circuit CCE, Fig. 4, marked by the operator over key CA3. The relapse of relay A releases ST whereupon the " second call " relay B falls back slowly, the relays S, T of the corresponding demand circuit fall back and its switch A takes one step to lead ld7 whereupon S, T pull up again in series with relay A. In a similar manner, the switches of each of the other demand circuits of the first six calls move on a step whereupon battery is removed from ld1 so that the switches A of any other waiting demand circuits are re-started. One of these seizes ld2 and the unsuccessful ones step on to last contacts where CO operates, locks up, disconnects magnet DMA and releases T and S which operated in series with CO. Magnet DMB thereupon steps switch B and, assuming that no connecting circuit happens to be assigned, B proceeds to last contacts where TCO operates in series with T, and S pulls up. TCO releases CO which releases T and S while B steps to normal followed by A which releases TCO and immediately takes a first step to ld1 and then hunts for the earliest idle indicating circuit if absence of battery on ld1 signifies that one is idle. Reverting to the point at which the first called demand circuit hunts for the assigned connecting circuit CCE, T operates when this is found and holds in parallel with a further circuit in CCE completed by BA. Relay BA corresponds to relay B in Fig. 3 of Specification 401,394 and the other relay contacts shown in CCE correspond to relays described in that Specification. As wiper A7 has stepped off the grounded leads ld, SS is no longer shortcircuited and pulls up to release T. If the call is from an ordinary subscriber or an operator, contacts of TCD in the speaking circuit are replaced by the dotted connections and the call is switched through to the operator. Coin freed systems. If, however, the demand circuit is connected to coin box levels of a preceding selector, the full line connections are used and the operator receives informatory dialling tone from DT and switches through by operating TCO from her connecting circuit, the connection being held by SS under the control of S held from the operator's position. In some cases it is necessary for the operator to unbalance the lines to improve the reception of coindepositing tone-signals, and for this purpose she operates RR over the positive wire to shunt out L(ii), L(i) being held. Re-ringing a calling party. The operator energizes RR over the positive wire to connect ringing from R to a party who has cleared (L unoperated). Attracting attention of operator. Interrupting the calling loop flashes relay L but BB holds. The relapses of L connect S(i) and (ii) in parallel and the resulting variations in the resistance in the third wire unbalance a differential relay at the operator's position to flash a lamp. Routine testing of lamp circuits, Fig. 2. Key RTK is thrown to operate RT which grounds leads ld2-7 so that the call recording relays A-F pull up in turn and light the lamps CL, the ground connected by F to ld1 lighting lamp TL after a successful test.