Patent GB-683005-A (GB)
Title: Improvements in or relating to circuits for use in automatic telephone-exchange and like systems for operating numerical selectors
IPC: H04Q1/18
Filed: 1950-10-27
Abstract: 683,005. Automatic exchange systems. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Oct. 27, 1950 [Oct. 31, 1949], No. 26250/50. Class 40 (iv). Each outlet of a single-motion final selector is marked by a voltage and a resistance representing the tens and units digits respectively and the switch is positioned by comparing the markings with a voltage and a resistance selected by a register, a test of a marking resistance occurring only if a successful comparison is first made of the associated marking voltage. In this arrangement, individual and P.B.X. outlets may be connected to non- consecutive outlets. As shown in Fig. 1, the tens and units digits are registered on switches MS1, MS2 which provide 'comparison voltage and resistance markings Vm and Rm respectively, and a differential relay T pulls up immediately and starts a final selector S. At each outlet, a marking voltage Vx is compared with the comparison voltage Vm over a high resistance device NW which normally biases off a grid-controlled gas tube 33, but permits the tube to fire if Vx equals Vm. The gas tube thus becomes conductive only at final selector outlets associated with the registered tens digit and applies current determined by the value of marking resistance Rx to the second winding of relay T. At the particular outlet required Rx equals Rm and relay T is disabled and stops the switch. Engaged outlets are marked by a potential such as earth potential (not shown) which neutralizes the marking voltage. A timing device (not shown) then determines that a required outlet is engaged by detecting continuous rotation of the switch. Alternatively, separate busy marking contacts may be used. In a modification, Fig. 2 (not shown), the marking resistances and voltages are determined by suitable potentiometers connected between common potential sources. An alternative arrangement, Fig. 3, comprises a rectifier gl which becomes conductive when the gas tube fires so that the current through Rx is derived from a common potential V3. The register is also modified, the comparison resistances being connected to a common potential instead of to the comparison voltages over switch MS1. Another embodiment, Fig. 4, comprises a trigger-pair of thermionic valves B1, B2, valve B1 controlling a series circuit including the marking and comparison resistances Rx, Rm. Valve B2 is normally conducting and biases valve Bl to a non-conducting condition. The marking potential Vx at each outlet is compared with the register comparison voltage Vm over a circuit comprising resistors R9, R10 and a high resistance potentiometer R7, R8, shunting valve B1. When Vm and Vx are equal, the potentials Vp and Vq correspond and a high resistance voltage - comparison device NW changes the grid potential of valve B1 over rectifier g2. Valve B1 now conducts and cuts off valve B2, and current through Rx and Rm causes the potential Vp to change except in the particular case when Rm and Rx are equal. The bridge conditions at the outlet required therefore remain balanced so that the device NW is undisturbed. The circuit of the driving magnet DM is then disabled by the zero device after an interval determined by the time to effect both the voltage and the resistance test. In either embodiment, the gas tube or the trigger-pair is restored to normal as the switch wipers move to the next outlet in the event of an unsuccessful resistance test. Specifications 662,215, 664,658, [both in Group XXXVI], and 675,069, [Group XL (c)], are referred to.