GB394585A - Improvements in or relating to telephone systems - Google Patents

Abstract

394,585. Manual exchange systems. STANDARD TELEPHONES & CABLES, Ltd. and HARDWICK, J. R., Connaught House, Aldwych, London. Dec. 5, 1932, No. 34354. [Class 40 (iv).] Calling and supervisory arrangements between two stations, e.g. a police box and a police station, comprise a calling lamp at the box and a lamp at the station which is signalled in a distinctive manner from the box until the call is answered or cancelled. To call the box B, the operator at police station P plugs in and sends momentary ringing current to operate relay B which is followed by C and E. On cessation of ringing, B and C relapse but E holds over D which also pulls up. A relay interrupter group G, H, I intermittently loops the line to flash line lamp S at the police station, it being assumed that the operator has unplugged while attending to other calls (the cord lamp would, otherwise, be flashed). The lamp KL at the box is, as shown, lit by relay E but it may be flashed by interrupter relay I. When the call is answered, A pulls up, disconnects the relay equipment, and lamp S glows steadily. The lamp KL and interrupter group can only be restored to normal by operating relay F which may be done by key K accessible only to the police (the public may use the box) or by sending a pulse of ringing current from the police station to operate B and C. If the public use the box during a police call from the station, the interrupter relays are disconnected from the line by relay A until the public call is terminated. Operating current may be derived from D.C. or A.C. mains.