Patent GB-232699-A (GB)
Abstract: 232,699. Siemens Bros. & Co., Ltd., and Humphries, H. E. Jan. 26,1924. Automatic exchange systems.-The impulse relay of a group selector acts also as a stepping relay to effect, in conjunction with the rotary magnet, the automatic hunting movement over the selected level. For this purpose, the relay is disconnected from the speaking .conductors at the end of the group-selecting impulses and is connected over front contacts of the rotary magnet to the test wiper. If all the trunks in the selected level are busy, the impulse relay may be re-connected to the speaking conductors when the last contact in the level is reached, special provision being made for giving a busy tone signal to the calling subscriber or a busy flash signal to the distant operator if the call originates at a manual exchange. A statistical meter may record the number of times no idle trunk is available. Five arrangements of selector circuits are described in detail. First arrangement, Fig. 1. Windings 1 and 2 of the impulse relay A are connected normally to the b- and a-wires respectively over vertical normal contacts k3, k2, and relays A, B operate upon the seizure of the selector. Dialling tone may be thansmitted, if the switch is a first selector, from leads DS, a condenser and resistance spark-quenching device connected in shunt to the battery-connected winding 2 serving also to reduce the impedance of the dialling-tone circuit. The first impulse is repeated at back contact a1 over normal contacts k1 and contact b3 to the vertical magnet VM in series with winding 1 of the change-over relay C, which operates to maintain the connection of the impulse relay to the a- and b-leads during impulsing and to complete a new circuit over off-normal contacts k1 and front contacts b2, c1 for the transmission of the remaining impulses to the magnet VM. At the end of the impulses, the relapse of relay C disconnects relay A from the speaking conductors and completes a circuit for the rotary magnet RM. Just before completing its stroke, magnet RM closes its contact rm which connects winding 2 of relay A to the test wiper C<0> so that, if the first trunk is busy, relay D is short-circuited and relay A operates to break the rotary magnet circuit at armature a1, the rotary magnet in turn breaking the circuit of relay A. The rotation thus continues, relay B remaining operated owing to the intermittent operation of armature a1, until an idle trunk is reached, when relay D energizes in series with relay A which does not energize, locks up in series with magnet VM and relay C, neither of which operates, and switches through. All trunks busy. When the wipers reach the last contacts of a level owing to no idle trunk being found, contacts w1, w2, w3 operate and relay D operates as for an idle trunk and completes a circuit for windings 1 and 2 of relay C which operates. Relay A is now re-connected to the a- and b-leads over contacts c2, c3, w1 to maintain relay B operated, a busy signal is transmitted from lead BS, and a meter CM is operated over wiper C‹ and contact w2. When the subscriber hangs up, relays A, B release and unlock relay D, which completes a circuit for the release magnet MM. Second arrangement. The impulse relay is connected to the a- and b-wires over switch contacts which open upon the first rotary step and re-close on the last contact of the level being reached. The arrangement also differs from that shown in Fig. 1 in that winding 2 of relay C is connected to the last terminal in the bank of the test wiper C‹ whilst the meter CM is connected to the last terminal of the wiper A‹ and is operated over a front contact of relay C and the busy tone BS is connected to the last terminal of the wiper B‹. Third arrangement, for use in a selector which when idle has battery connected to its last terminal. In this case windings 1 and 2 of the change-over relay C are connected to the incoming c-wire so that relay C operates as soon as the selector is seized to connect the normallv-disconnected impulse relay to the a- and b-leads. The original circuit of relay C contains a normal contact of the selector, but the relay is maintained over its winding 1 during impulsing in the usual manner. Fourth arrangement. In the arrangement shown in Fig. 1, the means for transmitting a busy signal mav comprise the alternate connection to the lead BS of a grounded transformer winding, to give a tone signal to a calling subscriber, and of grounded battery to flash a supervisory lamp before an operator at an originating manual exchange. The grounded connection effectively short-circuits winding 1 of relay A so that, if the calling subscriber should in error transmit further impulses, relay A may be unable to re-energize properly and irregular release may follow. In the fourth arrangement described, this difficulty is overcome by connecting the busy lead BS to the b-wire over a back con. tact of the change-over relay C and arranging that this relay energizes if any further impulses are transmitted and disconnects the busy signal until the impulses have ceased. The test circuit includes a back contact of relay C which also energizes as soon as the calling subscriber replaces his receiver so that the presence of any other grounded wiper C‹ on the multipled terminals connected to the meter CM does not interfere with release. Fifth arrangement, Fig. 5. This arrangement also overcomes the difficulty referred to in the preceding paragraph. The normal operation is similar to that described above in connection with Fig. 1, If no idle trunk is found, the selector moves to its last contacts and busy transformer BS is connected up in series with winding 1 of relay A. Winding 2 of relay C is connected over contact w1 to a cam-operated spring LF, which is intermittently closed, and at each closure, relay C operates, disconnects busy tone BS and short-circuits the a- and b-leads over contacts c2, c4, the intermittent short-circuiting producing the required flashing signal. Whilst the spring LF is common to a number of selectors, there is no undesirable direct interconnection between selectors as there would be with the arrangement shown in Fig. 1, since the actual transmission of the flash signal is controlled by the relay C which is individual to the selector. Trouble and supervisory signals. The continued illumination at a first selector of a lamp PL which is lit when the selector is seized and flickered during impulses may indicate that no impulses have reached the selector, that impulses received have failed to operate it, or that the subscriber has delayed in hanging up after receiving the busy tone.