GB757051A - A telephone system with satellite exchanges or similar electric systems - Google Patents

Abstract

757,051. Automatic exchange systems. LICENTIA PATENT-VERWALTUNGS-GES. April 27, 1954 [April 27, 1953], No. 12121/54. Class 40 (4). In a satellite exchange, having a common calling relay for all subscribers connected thereto, this relay is connected in common over associated rectifiers to the diagonals of a number of bridge circuits each having a subscriber's loop connected in one arm. By this method the effect of variations in insulation resistance of the loops can be minimized. As shown, subscribers T1 . . . Tn are connectible by a relay switch to the exchange line La, Lb. The calling circuit consists of a bridge comprising ratio arms composed of the resistances M and B (the latter being in fact a relay coil) and bridge arms comprising respectively the subscribers' loops T 1 . . . Tn and a set of resistances W1 . . . Wn in series with the relay D. As is seen each of the resistances is connected to its corresponding loop circuit, the point of connection being connected via rectifiers G1 . . . Gn to the common calling relay An. The resistances are arranged so that the bridge is balanced under almost the worst permissible insulation conditions for the line loops. Under better conditions the bridge is unbalanced in such a direction as to back-bias the rectifiers so that An does not operate. Under slightly worst conditions the rectifiers although slightly forward biased have still a high resistance and An fails to operate. When, however, a calling loop is completed the unbalance is sufficient to put one of the rectifiers in low-resistance condition and An operates. The latter connects low resistance earth through relay D to the wire Lb to effect switching operations at the main exchange. Relay D operates in this circuit and disconnects the normally operated relay A (not shown) from the wire La. A in falling back connects up the wire La to an impulsing circuit (not shown) for the relay switch. The temporary disconnection in the wire La serves as a signal to the main exchange to send im pulses over La to step the relay switch to find the calling line.