GB421741A - Improvements in or relating to electric signalling systems - Google Patents

Abstract

421,741. Direct call party - line systems. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. June 30, 1933, No. 18635. Convention date, July 1, 1932. [Class 40 (iv)] [See also Group XL] An impulse-transmitting contact is connected to a signalling line through a transformer so that the beginning and end of an impulse cause pulses of opposite polarity which at the receiving station effect the striking and extinguishing or vice versa of a gas-discharge tube such as a neon lamp. A change in condition of the tube automatically controls the priming voltage so that restoration to the original condition may take place with the minimum energy. The invention is described as applied to a party-line system in which each station calls any other station by transmitting a characteristic number of impulses which are received by selectors at all the stations. In the arrangement shown, the neon tube GL is normally maintained by a variable tapping VS at a voltage just below the striking voltage. The closure of impulse contact nsi in series with the primary winding of transformer U2 causes a pulse of current to flow over line VL and at each station the tubes GL coupled to the line through a second transformer U1 are caused to strike. Relays J, H operate, transmitting an impulse to the local selector and removing a short-circuit around a resistance W1 whereby the priming voltage is reduced to a value just above the extinguishing voltage so that when a pulse in the opposite direction is generated in the line VL by the opening of contact nsi the tube is extinguished and relays J, H release. The primary winding of transformer U1 must be of high impedance which may be increased by the addition of a condenser C1 of such a value that the frequency of the oscillatory circuit thus formed is equal to the impulse frequency of the contact nsi. In a modification, the line windings of transformers U1, U2 are connected in series and are alternately shunted by switch-hook contacts so that the selector at the transmitting station does not respond to the outgoing impulses. The tube GL is normally alight and is extinguished as a result of the closure of contact nsi. In a third arrangement, the discharge-tube circuit is directly bridged across the line, priming voltage being obtained from a battery at a central station and adjusted by a variable resistance in shunt with the tube.