GB965598A - Improvements in communication exchange installations - Google Patents

Abstract

965,598. Automatic exchange systems. ALBISWERK ZURICH A.G. June 12, 1962, No. 22444/62. Heading H4K. In a house satellite of which some at least of the subscribers are connected also to a main exchange, a subscriber's private wire is marked with different potentials according as his line is idle, busy in a local house call or busy in an exchange call, and metering is also effected over the same wire. For testing, the marker ZM includes a saturated core transformer IM. The potential at P1 is - 37 V, and in the case of an idle line the c wire is at - 48 V, whereas for a busy line it is at - 33 V or - 24 V. In the idle condition current flowing through winding W1 reverses the magnetic state of the core. When relay Q1, for example, energizes, current in winding W2 switches back the core and produces a pulse in winding W3 to operate relay C1 and an impulse in winding W1 to operate cut-off relay T. In the event of a wanted satellite subscriber being busy, provision is made for camping, and relay NE controlled by transistor Ts1 operates when the line becomes idle. A further test circuit included in the operator's equipment PS determines whether a wanted line is busy in a local call or in an exchange call. The potential at P3 is - 29 V, and relay HG controlled by transistor Ts2 operates in the former case. When a call is initiated, a marker ZM is taken into use, the calling number is determined by relays T1, H1, Z1, E1 and the line is connected to an idle satellite link HVS. The selection digits are stored in a register RG and a marker ZM is reseized to connect HVS to the wanted line. If, however, the first digit indicates an exchange call, HVS is released and the line is connected instead to an exchange link AVS, from which the subscriber receives dialling tone. In the case of an incoming exchange call, the operator keys the number into the register RG and AVS is controlled by a marker ZM. Identification is initiated from the register RG or from the operator's equipment PS by the discharge of capacitor C through winding W1 of a saturated core transformer Vc, thus giving rise to a pulse of +96V on the c wire and operation of the appropriate relays. In the event of an exchange call, metering pulses of - 20 V are applied over the c wire from AVS to operate meter Z. Further circuits are described, Figs. 2 and 3, for enabling the meter Z to respond to metering pulses but not to identification pulses.