Patent GB-383314-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1931-08-07
Abstract: 383,314. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and PATTERSON, W. G., 68, Eltham Road, Lee, both in London. Aug. 7, 1931, No. 22405. [Class 40 (iv).] A two-step relay used as a combined line and cut-off relay puts an engaged marking on the final selector multiple immediately the calling line is looped. In one arrangement, two private wires extend to the final selector and the two-step relay whether operated in one-step, or fully, busies the final selector multiple over one of them but is not operated over this wire when the final selector tests the line if idle. The relay is, however, operated over the other wire after a successful test over the first wire. P.B.X. hunting arrangements are also described. In another arrangement, a single private wire is used, the two-step relay being connected directly thereto, and over a two-step contact and resistance to one line wire, the other line wire being normally grounded. In the idle condition of the line, battery over the two-step relay is connected to the final selector multiple but when the line is looped, this is changed to ground over the resistance. First arrangement, Fig. 1. When the calling line is looped, relay L operates one step over a resistance, marks the finder multiple at l2, makes a starting circuit at l3 and at l1 disconnects itself from the final selector multiple in the case of an individual line or last line of a P.B.X. group. If the line is the first or intermediate one, l1 connects up ground directly or over a resistance respectively. When the line is found, L operates fully to disconnect itself from the loop and open the start circuit. The finder shown is a bi-directional one. On incoming calls, the final selector shown has the following relays (contacts only are shown) operated: N when the switch is seized and D, G at the end of the units digit. Testing takes place during the fleeting period between the relapse of D and G. If the line is idle, T operates in series with L which remains inert, TA is connected to the additional wiper, operates L fully, and connects direct ground over the wiper to the call-finder test-multiple. TA switches through and both T and TA lock up over windings (ii). If the line is the first of a P.B.X. group and is busy, PR operates over (i) after the relapse of D and G, energizes PQ, cuts in its high resistance winding (ii), and tests the remaining lines of the group. PR remains operated over the resistance ground of busy intermediate lines but falls back to connect T to the test wiper on an idle one or on the last one whether busv or idle. Relay T operates, during the release period of PQ, as for an individual line. During search over a P.B.X. group the busy signal circuit is opened by PR and PQ and if the final selector is set to an intermediate line by dialling PR does not operate if the line is busy (owing to the resistance connected tothe test multiple) and the busy signal is given. Second arrangement, Fig. 2. Relay L makes marking and starting circuits for the finder as before, but in this case, the looping of the line connects ground over l4, the loop, resistance and l5 to the final selector multiple. The finders and final selectors are rotary switches, the finals being controlled by a common circuit. When the final selector is seized K (not shown) connects up the control circuit. At the end of the units digit relays E. F, G (contacts only shown) are operated in the control circuit, EE is energized and G is operated with its right-hand winding shortcircuited. Dialling relay E falls back slowly and connects up test relay BB during the release period of EE. If the line is idle (battery over L) BB fails to operate and EE connects switching relay H to the test wiper. Relay H confirms the test and switches through, L being fully operated by direct ground over the test wiper. If the line is engaged, BB will operate either (1) to ground at l4 of a calling line not yet found, (2) to direct ground over the call finder test wiper or (3) to direct ground on the final selector multiple. BB removes the short circuit on the right-hand winding of G which is differential and relapses to give the busy signal.