Patent GB-977392-A (GB)
Title: Telephone switchboard
Inventor: INABA SOHEI
IPC: H04M9/00
Filed: 1961-03-16
Abstract: 977,392. Manual switchboards. MEISEI ELECTRIC CO. Ltd. March 16, 1961, No. 9683/61. Drawings to Specification. Heading H4K. [Also in Division H2] In a manual switch board one two-wire line is connected to another by pressing two non- locking keys, one associated with each line, so that a relay at the cross point between the lines locks up to make and hold the connection. A calling condition on a subscriber's line, which may be connected to an extension or a trunk line, operates a line relay and lights a calling lamp to which the operator responds by pressing a non-locking key particular to the calling line. Actuation of the subscriber's line key energizes a service relay which is particular to the subscriber's line and which locks up to connect the line to the operator's position. Having ascertained requirements the operator actuates a non- locking key which is particular to the wanted trunk or extension line and which has a contact associated with each subscriber's line. The presence of an operated line relay or service relay on the subscriber's line causes the trunk or extension key to operate the appropriate crosspoint connecting relay which locks up subject to release either by the line relay or by an operator's release key. The operator withdraws from the connection by pressing a key to release the operated service relay; this key being replaced by the on-hook condition of the operator's handset if this is provided. Since the service relays are arranged in a chain it is necessary to release the service relay of one call before setting up the next. To ensure that the service relay chain is fully released the actuation of a subscriber's line key may cause the interaction of a pair of relays to restore all service relays before the particular service relay associated with the key is energized. With a number of calls established the operator can establish what trunk or extension a subscriber's line holds in service by pressing a question key particular to the subscriber's line so that, in one embodiment, a busy lamp associated with the connected trunk or extension is extinguished, or in a second embodiment, a lamp is lighted to indicate the junction. A call from an extension line or a trunk line lights a calling lamp and sounds an alarm to signal the operator who responds by pressing the non-locking key particular to the calling trunk or extension. The alarm may be a buzzer or a tone injected into the operator's circuit from a transistor oscillator. Actuation of the trunk or extension line key energizes a service relay particular to line and this relay locks up to make connection with the operator's position. In response to requirements the operator connects a free subscriber's line by operating a line key associated with an extinguished subscriber's line lamp. This brings up the service relay for that line and the appropriate cross-point connecting relay which locks up. When the wanted party replies the line relay operates to hold the connection and the service relays may be cleared down. By employing contacts of the subscriber's line relays in the service relay chain it is arranged that an idle subscriber's line is automatically seized and connected to the operator and a calling trunk or extension. In this event should all line relays be energized any attempt to seize an idle line operates an alarm circuit. The operator may be provided with a key to divert all incoming trunk calls to a so-called " main telephone." A pair of interacting relays may be provided to connect a clearing down signal to the trunk lines whenever a call is released. A construction of push button switch containing lamps is described; see Division H2.