Patent GB-479314-A (GB)
Title: Improvements in and relating to circuit arrangements for telegraphic selector installations
IPC: H04L12/00
Filed: 1936-12-16
Abstract: 479,314. Telegraph exchange systems. SIEMENS & HALSKE AKT.-GES. Dec. 16, 1936, Nos. 34600, 34601, and 34602. Convention dates, Dec. 16, 1935, Jan. 3, 1936, and July 20, 1936. [Class 40 (iii)] If, during an established connection in an automatic exchange system, a release condition is set up due to a fault, the switches are liable to be re-set on another line by the telegraphic impulses. To obviate this, a signal of the same nature as the release signal is sent back when a connection is made to a line and means, which normally prevent the signal from effecting release, are provided for responding to the signal in the case of a normally set-up call to permit communication or indicate that it may be commenced, the circuits then being conditioned so that subsequent receipt of such a signal breaks down the connection. In some arrangements the calling key or a contact thereof is held operative until the calling party receives the signal which indicates connection to the wanted party, the operation of the key preventing the signal from effecting release. The calling party then restores the key to make the connection effective and permit release if a signal is subsequently received. In other arrangements, these functions are performed automatically by relays at the calling subscriber's line switch. In the arrangement shown in Fig. 1, a subscriber makes a call by pressing key Rt which operates R(i) to start line switch VW. The connection is set up over group and final selectors in the usual way, but when changeover relay UR at the final selector LW operates to connect up rotary magnet D, relay F pulls up and maintains positive battery TB on the b wire over rotary off-normal contact w. When test relay P operates on an idle line, it replaces +TB on the b-wire by -TB maintained for the period of successive slow release of relays UR and F which finally switches through. The negative battery or the b wire would normally cause release by energizing winding (i) of relay L in opposition to the normally energized winding (ii). The relapse of L normally releases R which opens the holding circuit over the c-wire at the line switch. In the present arrangement, a calling party maintains key Rt operated so that R(i) still holds over the loop after the relapse of L. To signal the calling party when he may release key Rt (which also shunts his teleprinter EM, SK), the reversal of loop current by the release of L releases E previously operated to energize M which started the motor AM, but when L re-operates after the negative battery signal has been removed. the motor starts again. The stopping and starting of the motor constitutes the signal to the calling party. In the case of an undesired connection being set up during telegraph transmission, (key Rt normal), the connection would be released and the teleprinter at the calling station stopped, the loop being opened by the release of M. Modification, Fig. 2 (not shown). The calling key has an additional contact grounding the b wire and remaining closed after the other (loop) contact which opens when the key is released. The additional contact which has to be released manually when the calling party receives the signal referred to in the preceding paragraph operates one winding of a differential relay the other winding of which is in the a wire so that the relay is not operated by loop current alone. In this modification relay R is released by L when the negative battery signal is received but this is prevented from opening the c wire on genuine connections by an operated contact of the differential relay arranged in parallel to contact r4, Fig. 1. Modification, Fig. 3, involving a repeater FTA between a distant subscriber TS and the exchange. This arrangement also uses a calling key Rt with a grounded holding contact in the b-wire as described in the preceding paragraph but operates differently. Relay Rl operated by the calling key moves ER1 to the spacing position to send a spacing signal over trunk FL to ER at the exchange whereby R(ii) energized in aiding relation to R(i) starts the line switch VW. Spacing current sent back over the switch train is repeated back by SR to SR1 so that T1(i,) and (ii) are in aiding relationship and T reverses the current in the calling loop to start the teleprinter. When the connection has been set up, -TB (marking) connected up temporarily at the final selector as previously described, is repeated back by SR, SR1 to release TI, but as R1 is held by key Rt, ER1 remains in spacing position so that ER at the preselector remains in spacing position, R remains operated and the line switch is not released. If however, an unwanted connection is established in error during telegraphic transmission (Tr not operated) ER1 changes over in response to the negative battery signal, and ER at the line switch follows to release R and the unwanted connection. This arrangement may be modified, Fig. 5 (not shown) by the provision of relay H as described in the next paragraph. Fig. 1 modified in accordance with Fig. 4. A relay H is provided, one winding (i) being energized on operation of R by the calling key so that winding (ii) is connected to the b wire and held by + ve battery normally connected thereto when the line switch extends the connection, winding (i) being then de-energized. The calling key is not held operated in this modification. The + ve battery on the b wire also operates L so that L(i) and SR are disconnected from the b-wire and connected to + ve battery in a local circuit. When the negative signal is sent back H(ii) is released slowly to reconnect L(i) and SR to the b-wire but the -ve battery condition is removed before L can relapse. In the case of an unwanted connection being set up during telegraphic transmission, as H(ii) is not now connected to the b-wire whereas L(i) is, L is released by the signal, reverses the current in the calling loop to stop the teleprinter, and releases R to release the connection. In a further modification, Fig. 6 (not shown) the negative battery is applied to the b wire of the line switch of the wanted party by a normally operated sluggish relay so that negative battery is sent back immediately the final selector switches through, the normally operated relay being released to terminate the signal when the switching relay at the wanted subscribers' line switch operates.