IE40933L - Manual telephone system - Google Patents

Abstract

1446691 Telephone exchanges STANDARD TELEPHONES & CABLES Ltd 31 Jan 1974 04567/74 Heading H4K A manual exchange, e.g. a PMBX employs a crosspoint matrix at each crosspoint element of which is a relay in series with a diode, the junction therebetween being connected to a hold wire via a contact of the relay, the arrangement being such that a crosspoint relay is operated in response to manual actuation of row and column marking keys is maintained over a path independent of the keys in a manner such as to reverse bias the associated diode so that that crosspoint cannot be taken into use for a second connection, and is automatically broken down when one of the subscribers releases. As described the crosspoint elements are sealed contact reed relays. The ringed crosses shown are lamps or light emitting diodes associated with extensions, connectors and exchange lines. When due to a call initiation an exchange line or extension lamp is lit, a buzzer or bell sounds and the operator responds closing a locking key SWE1 to SWE8 associated with the exchange line or a non-locking key (not shown) associated with the extension, switch SW1 being automatically set to connect to the selected line. The operator ascertains the connection required and presses a non-locking key or a locking key associated respectively with the called extension or connector to be taken into use. In the case of an incoming or outgoing main exchange call the appropriate crosspoint responds, the connection is complete and the operator withdraws from the connection by releasing the locking key. In the case of an internal call a cross-point of the access half A of a local connector responds when the locking switch SWC1 to SWCN associated with the selected connector is operated and the operator operates the non- locking key associated with the called extension thus operating a crosspoint of the connect half C of the connector before releasing the non- locking key. A feed bridge (Fig. 3, not shown) is detailed which supplies ringing signals and causes release of the crosspoints relays involved when either party releases. A tone is introduced on the line if the operator remains in circuit while both parties are off hook. Under fault or night service conditions the operator's set connects automatically to the first exchange line. [GB1446691A]