GB1172166A - Telephone Exchange - Google Patents

Abstract

1,172,166. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 10 Feb., 1967 [11 Feb., 1966], No. 6518/67. Heading H4K. In a PABX, special links are provided for allowing an operator to set up a connection between an extension and a pre-recordedannouncement machine (e.g. morning alarm call), the operator withdrawing from the connections as soon as it is set-up without waiting for the extension to reply. The link includes a timing circuit which initiates an alarm if the extension does not reply within a preset period. On closing her keys AB and TW at the operator's position AP, relays E and WKI come up in the link AUe. The operator causes operation of the selectors, e.g. W1 and ringing current is sent when the idle called extension is reached. Wk holds over its second winding when the keys are released (after flickering illumination of busy lamp BL) and the magnetic tape announcement machine AG is preparatorily coupled (a still open) via wk5 to the third winding of the link isolation transformer. When the extension replies his line relay A comes up to complete the connection between AG and the transformer. When the extension replaces his handset, a release relay TR comes up to release the link. Timer ZG energizes alarm lamp Al if the extension does not reply within a set time. The operator may use the link for outgoing dialling signals (Z operated) or for an incoming call (e2 operated) while it is in use for automatically calling the extension.