Patent GB-380592-A (GB)
Title: Improvements in or relating to telegraph systems
IPC: H04L12/12
Filed: 1931-09-14
Abstract: 380,592. Telegraph exchange systems. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. Sept. 14, 1931, No. 25764. Convention date, Sept. 16, 1930. [Class 40 (iii).] In a system in which calling and signalling are respectively effected by a change in polarity of the line-potential and by interruptions of normally flowing current, the current is stopped by a condenser in the idle condition of the line and a station is put into the operative condition by a discharge current from the condenser which is then switched off or short-circuited to permit of normal signalling. The subscribers' lines work with single current, and the internal signal-repeating circuits at the exchange with double current. Idle condition. Potential is applied to the line by the central battery as shown at t1, t2, but no current flows owing to.the interposition of subscriber's condenser C. Subscriber calling exchange. On closure of a subscriber's calling switch ET the exchange relay R, individual to the subscriber, cuts in at r the calling lamp AL. The operator inserts a plug VS into the calling subscriber's jack VK, closing a c-wire circuit through relays T and P. Relay T cuts out lamp AL at t3 and at t1, t2 cuts out relay R, reverses the potential applied to the line L, and energizes the receiver relay E so that its armature e moves to its positive contact, its winding I overpowering its winding II. Relay X is cut in at e, p1, and cuts off at x the supervising lamp SL. The calling subscriber's station is prepared for working in the same manner as the called subscriber's station (see below), except that winding I of switching-in relay ER operates .through the calling key ET. Exchange calling subscriber. The conductors a, b are crossed in the cord, and a testing relay X is connected to each of these conductors. When a plug VS is inserted into a jack VK, relays P, T pull up, and the line potential is reversed at t1, t2. Subscriber's condenser C reverses its charge through winding I and reinforcing winding II of switching-in relay ER. Armature er cuts in relay U which cuts in the motor A at u2, u3, and short-circuits the condenser C at u1. Testing-arrangements. If the relay U fails to operate through failure of the mains N at the called station, the exchange relays E, X individual to the jack and plug for that station fail to act, and supervising lamp SL remains alight. Message signals. The subscriber's transmitter-contact SK controls winding I of the exchange receiving-relay E by interruption of the line current. Armature e passes on doublecurrent signals over the a conductor of the sending subscriber, which is the b conductor of the receiving subscriber, to the latter's sending on relay S and so through armature s and line to receiver M. The exchange relay E individual to the receiving subscriber is saved from disturbance by the provision of a substitute resistance W1. At the subscribers' stations the condensers C are short-circuited by contacts u1 in the working state of the line. Clearing. A prolonged interruption of the line current by the clearing key AT causes armature e to cut off relay X long enough for this to release. Lamp SL lights up, and the operator by withdrawing the plug VS restores all parts to the idle condition.