Patent GB-685205-A (GB)
Title: Improvements in circuits for embodiment in automatic telephone exchange and like systems
IPC: H04Q3/42
Filed: 1949-04-19
Abstract: 685,205. Automatic exchange systems. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. April 19, 1949 [April 20, 1948], No. 10351/49. Class 40 (iv). In a system in which an idle link circuit VC seized upon the occurrence of a call is connected to the calling line over a finder OZR1 and a direct first finder OZ1d or indirect first and second finders OZ11, OZ21 in tandem, a common marker KS allots an idle route by applying potential at points A1d or All, B21 to the test wires of the finders, a direct route being chosen in preference to an indirect one. If the circuits VC are arranged in groups, a further marking at C1 ensures the seizure of a circuit that can be connected to the calling line. A common call detector OD controls an impulse generator IG to send starting impulses over wire SL and an allotting circuit KR to an idle control circuit SR. The wire SL is opened at contact u1 or u2 if no idle route exists. Call detector OD and control circuits SR, Figs. 2, 3. The subscribers' lines are associated with resistances R1, R2, R3 so that a calling condition produces at Oa a negative potential which cuts off valve B of the call detector OD and releases relay S, thereby opening the holding circuit of relay I. With I back, valve B2 is made conductive by the grounding of its control grid and I reoperates after a time determined by a shunt condenser C4. Charging of a condenser C2 then reduces the grid bias and cuts off B2. Thus, as long as I has no holding circuit, impulses are sent over wire SL, at. intervals of about 1 second. When the first linefinder is seized, relay H (not shown) therein connects a charged condenser C3 to the grid to cut-off B2. The various start wires SL are distributed over the inlets E of a closed chain of contacts controlled by relays M of the control circuits SR. The duration of the starting impulse is such that only one circuit is seized, and its repetition prevents loss of the call if all the control circuits are busy. During an impulse, a condenser C12, Fig. 3, is charged, and if the impulse is too long, rectifier g4 passes current and cuts off a common valve B3 and releases an alarm relay AL. During a calling condition, a condenser C11 is charged, and if the condition persists for an excessive time, e.g. 15-20 seconds, rectifier g3 passes current and cuts off B3. If there is no idle route to the calling line, the marker KS opens wire SL at u<SP>1</SP>1 or u<SP>1</SP>2 and the charging circuit of the condenser C11 at u<SP>2</SP>1 or u<SP>2</SP>2. Marker KS, Fig. 4. The release of relay S, Fig. 2, applies potential over a chain of contacts to one of the points A1d ... Amd, A11 ... A1n to allot an idle first finder, the contacts being controlled by relays H (not shown) of the finders and being so arranged that all the direct finders OZ1d, Fig. 1, are allotted before the indirect finders OZ11. When an indirect first finder is allotted, the marking potential is extended via P<SP>1</SP>3 and an inlet P3 of a closed contact chain to one of the points B21 ... B2n to allot a second finder OZ21 Fig. 1. The closed chain has different inlets for the various groups of first finders. When all the first finders are in use, relay U1 energizes and opens the start wire SL, Fig. 2. When all the second finders are in use, relay M releases and removes ground from the control grid of a normally-conducting pentode B4. If an indirect first finder is now allotted, negative potential applied to the grid from P<SP>1</SP>3 cuts off B4 and releases anode relay U2 which opens the start wire SL. The circuits of B4 are arranged for rapid cut-off and rapid reoperation. If the finders OZR1, Fig. 1, also require marking, a third chain allotting circuit is employed. Modification employing double-wiper first and second finders, Figs. 5, 6 (not shown). The first finders each have access to two groups of lines, and the arrangement is such that each group is served by first-choice finders without wiper-switching and second-choice finders with wiper-switching. The second finders are similar. The marker KS therefore includes chain circuits for controlling the operation of the wiper-switching relays when necessary. As in the previous arrangement, indirect first finders are allotted only when all the direct first finders are in use.