GB555530A - Telephone or similar systems for establishing connections with a switching arrangement, comprising one or more stages with group selector switches - Google Patents

Abstract

555,530. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). April 3, 1942, No. 4476. [Class 40 (iv)] In a system employing register-controllers and single-motion selectors, a selector sends to the register-controller for each outlet or each idle outlet it encounters an A.C. signal characteristic of the group to which the outlet belongs and the driving circuit is opened when the signal received agrees with a reference current selected by the relevant register. In the register-controller, Fig. 1, the dialled digits are repeated by relay Isr to registers SM1 ... 3 which are brought into use in turn by relays Dirl ... 3 under the control of in-sequence switch IM. Upon seizure of the first selector, Fig. 2, relay Ar energizes over wire b and the normal contact of SM1 and locks over wire d, and as soon as the register SM1 moves offnormal the power magnet P operates over wire a. As the selector rotates, A.C. signals picked up by wiper d are fed back over wire c to a transformer HC1, while A.C. current selected by SM1 is fed to a transformer HC2. When these currents are in phase, the output from the transformers is such as to ionize a cold cathode tube T2, controlled through an amplifier T1 and rectifier RE, thereby energizing relay Vtr which opens the driving circuit. Relays Ftr, Fhr pull up in turn and release relay Chr momentarily to extinguish the tube T2, after which relay Vtr reoperates provided the selector is still on the tested outlet. Relay Str energizes and closes a test circuit over relay Tr, b wire, relay Br wiper c to battery. Relay Tr pulls up and connects in parallel marginal relay Dtr which guards against double connections and allows relay Br to operate. The latter relay locks, switches through and grounds wiper d to guard the selector. Meanwhile, relay Sar energizes, advances out-sequence switch OM and prepares for the control of the second selector, in which relay Ar operates over wire b and locks to ground at the first selector. If relay Vtr fails to reoperate, relay Kir pulls up momentarily to release relays Ftr, Fhr and replace the original A.C. test circuit. If the direct current test fails owing to the selector having passed the tested outlet or for any other reason, relay Gbr energizes, remakes the driving circuit and connects wire b to a cold cathode tube T3 which ionizes and operates relay Fsr when any idle outlet is reached. This relay restores the original driving circuit and the A.C. test circuit. As shown, the selector moves from a normal position as soon as the register SM1 receives the first impulse. Relay Chr which controls the anode potential of the tube T2 follows impulse relay Isr, however, so that the selector cannot stop definitely on an outlet until the digit is complete, when Chr is held by Dir1. Moreover, the direct current test circuit is ineffective until the ground for relay Dtr is provided by the release of series relay Lmr, which controls in-sequence switch IM, and subsequently by Dirl. Alternatively the selector may be of the no-normal type, in which case, preferably, it does not start to move until the first digit is fully registered. As shown the characteristic A.C. potential is disconnected when a second selector is seized, so that a hunting selector stops only on idle outlets, but it may instead be permanently connected, the D.C. test being then applied to all outlets of the wanted group. In a modified selector having one relay only, the functions of relay Br are performed by contacts of the magnet P.