Patent GB-105838-A (GB)
IPC: H04M9/00
Abstract: 105,838. Dungey, J. W. July 14, 1916. Intercommunication systems and apparatus.- In an automatic secret intercommunication telephone system of the kind in which each station is connected to each of the other stations by a separate line wire and is provided with a pair of ring- ing leads connected to a common battery, each station is provided with a number of double-winding relays, a switching relay controlling these windings, and a cut-off relay. The calling subscriber is indicated at the called subscriber's station before the latter removes his receiver, and when a lamp is employed in connexion with the indicator, the lamp circuit is broken when the called subscriber removes his receiver. Fig. 1 shows three stations 1<1>, 2<1>, and 3<1> connected by line wires L<1>, L<2>, and L<3> and each provided with three relays R<1>, R<2>, and R<3>. Each relay has a low-resistance winding L and a high-resistance winding H, the terminals of the latter being connected to three spring contacts 4, 5, and 6 adapted to be engaged and operated by a contact mounted on the bell-crank armature 15 of a switching relay E. Each station is provided also with a cut-off relay RE controlling the circuit of the relay E and the circuit of an indicating-lamp. Calling operation and connexions established. When a subscriber at station 1<1> wishes to communicate with a subscriber at station 3' he removes his receiver R from the switch-hook 1, moves a hand selector switch 11 to the contact connected to the line L<3> of the station 3<1>, and depresses a ringing key 12. The removal of the receiver R breaks the hell circuit of station 1<1>, separates the contacts 2, 3 in the circuit of the indicating lamp LP<1>, and closes the contacts 9, 10 thereby placing the winding of the relay RE across the local battery B. The energization of the relay RE breaks the circuit of the relay E at the contacts 16, 17 and connects the home line HL at station 1<1> to the contact 18 of the relay RE. The depression of the key 12 establishes the following ringing and circuit changing connexion :- Positive pole of battery F, contact C, key 12, selector switch 11, low-resistance winding L of relay R<3>, line wire L<3>, home line HL of station 3<1> from which the current divides, part passing through the bell BL and part passing by way of the contacts 16, 17 of the relay RE to the relay switch E and to the negative pole of the battery F. The energization of the relay E at the station 3<1> forces the contacts 4, 5, and 6 into engagement with each other and connects them to the negative pole of the battery F through the armature 15. The operation of the armature 15 of the relay E also closes the contacts 7, 8 thereby placing the cut-off relay RE across the local battery B at station 3'. Before the relay RE operates to break the circuit of the relay E at the contacts 16, 17, the armature A of the relay R' at station 3' is attracted by the energization of the high-resistance winding H as follows :-Positive pole of battery F, contact C and ringing key 12 at station 1<1>, attracted armature A of relay R<3>, primary winding P of induction coil PS, winding of relay RE, contacts 18, 17, home line HL, line L', winding H of relay R' at station 3<1>, contact 4, and armature 15 to the negative pole of the battery F. The armature A of the relay R<1> at station 3<1> is then attracted, and, after the relay RE at station 3<1> has operated, the stations 1<1> and 3<1> are then connected as follows :-One pole of battery B at station 1', primary winding P of induction coil PS, armature A and winding L of relay R', line L<3>, home line HL at station 3<1>, contacts 17, 18 and winding of relay RE, winding P of induction coil PS, armature A and winding L of relay R<1>, line L', home line HL at station 1', contacts 17, 18 of relay RE, hook switch contacts 9, 10 to the other pole of the battery B at station 1<1>. The energized relays at both stations therefore remain energized after the calling current has ceased. Talking - circuits. When the subscriber at station 3<1> removes his receiver, the hook switch contacts 9, 10 are closed to connect the winding of the relay RE across the battery B at station 3<1> and conversation may take place over the lines L', L<3> when the switches in the circuits of the microphones at both stations are closed. Indicators and indicator circuits. The armatures A of the relays R', R<2>, and R<3> are provided with shutters which are operated when the relays are energized, while the circuit of a lamp LP' is closed at the contacts 13, 14 when the relay RE is energized, the circuit of this lamp being completed through the hook switch contacts 2, 3 which are closed when the receiver is on the switch hook and opened to break the lamp circuit when the receiver is removed. In the modification shown in Fig. 2, each relay R<1>, R<2>, and R<3> is provided with an indicating-lamp J<1>, J<2>, and J<3> which is normally short-circuited when the relays are de-energized. If, however, the relays RE and R<1> are energized, the short circuit about the lamp J<1> is removed and the lamp circuit is established as follows :-Positive pole of battery F, hook switch contacts 24, 25, contacts 13, 14 of relay RE, short-circuits about the lamps J', J<2>, lamp J<1>, hook switch contacts 2, 3 and negative pole of the battery F. When the receiver is removed, the circuit of the lamp is broken at the contacts 2, 3 and 24, 25.