Patent GB-1180140-A (GB)
Title: Automatic Signal Transmission System
IPC: H04M11/04
Filed: 1967-12-07
Abstract: 1,180,140. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 7 Dec., 1967 [12 Dec., 1966], No. 55744/67. Heading H4K. An automatic (e.g. repertory) dialler is common to a plurality of subscriber substations and can be seized for use by any of the substations to make an alarm call to an appropriate station (e.g. police, fire &c.). The dialler described responds to tripping of an alarm circuit at a substation and marks the line circuit of that substation so that it may be identified. In the arrangement shown which is adapted to make one type of call only the dialler AS is located on the subscribers' side of the subscribers' line circuits LC and has its own line circuit ALC adapted for outgoing calls only, via which transmits dialling pulses to the exchange. Each substation includes an oscillator OSC the output of which is connected via an alarm contact K to the conductors of the telephone line. Adjacent the line circuit of this substation is a receiver REC for the oscillator frequency (which is a tone outside the voice frequency range) arranged to operate an alarm relay Ar. The alarm contact K is normally closed and thus the relay Ar and the receiver are normally energized. Filters F 1  and F 2  prevent this frequency interfering with the speech channel. If the alarm is tripped, contact K opens terminating transmission of the tone, relay Ar releases closing a break contact a 2  of that relay marking a terminal e individual to the substation at which the alarm was initiated and applying this marking potential via a diode G as a common start signal for the dialler AS. The dialler initiates operation of an alarm finder AF to hunt for the terminal (e) carrying the marking, and commences to transmit the wanted number to the exchange via its line circuit ALC. When the finder locates the marked terminal it stops simultaneously marking further terminals f and g individually associated with the particular terminal e that is marked. In consequence a relay Br is enabled and held via its make contact b, and opens its break contact b 2  inhibiting initiation of a fresh alarm call, and a terminal d of the line circuit associated with the substation at which the alarm was initiated is marked so that the substation can be identified by the exchange equipment. The number of this substation may be coded at IFC. In a modification the receiver is adapted to receive at least two frequencies and operate different alarm relays. The frequencies correspond to different types of alarm and result in a different number being dialled. A substation oscillator (Fig. 5, not shown) arranged to oscillate at an initial (normal) frequency and adapted to change to one of two alarm frequencies on operation of an appropriate alarm contact is described. A substation which offers an impedance to the line under normal conditions in order that line continuity may be checked and transmits a frequency in the event of an alarm is also described. In another embodiment the dialler does not have its own line circuit. The alarm relay has additional contacts which disconnect the substation from its line circuit and connect the dialler in its place. Additional contacts of the alarm relay on the exchange side of the line circuit interrupt any incoming call. An alarm tone generator transmits an alarm tone to line. A prerecorded message could be sent. In a further modification (Fig. 3, not shown) the receiver is also connected across the line for the reception of an acknowledgment tone. Relay circuits respond to such reception to prevent further action.