Patent GB-567964-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1943-10-26
Abstract: 567,964. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and CHRISTIAN, D. A. Oct. 26, 1943, No. 17618. [Class 40 (iv)] A cross-bar switch acting as a call-finder, group selector, or P.B.X. final selector is controlled by a common circuit including a highspeed hunting switch or a group of discharge tubes arranged to hunt for an idle or calling line. The common circuit is only employed for a fraction of a second, the registration of the digits in the case of numerical switches being taken care of by registers individual to the conversation switch. First system ; call finder, Fig. 1. When a call is made, line relay L energizes start relay SN and marks an individual terminal in one of ten levels forming the A1 section of a common searcher with which a cross-bar conversation switch has been associated by a preselecting allotter FA. Latch magnet SL is operated and the switch runs round to the position of the marked terminal, being stopped there by one of ten test relays STA ... STK. This bridges the wipers of the corresponding one of ten pairs of further wipers. The terminals engaged by the latter form the A2 section of the searcher and are multipled vertically and horizontally as shown, so that a circuit is completed from the middle winding of a relay H for one of ten select magnets HMA ... HMK of the conversation switch, in accordance with the position in which the searcher stopped, in series with one of ten relays SMA ... SMK in accordance with the level in which the marked terminal appears. The latter relay disconnects all the similar relays to its right and locks up over a second winding and their back contacts in series with one of ten pull-down and hold magnets VMA ... VMK, at the same time disconnecting the locking circuits of all the similar relays to its left. The energized pull-down magnet locks itself over a de-energizing winding of H which, however, continues to be held over its right-hand winding and the private wire. Operation of the cross-bar magnets switches the +, - and p wires through and cut-off relay K operates over a holding winding of L. Shortly after the operation of H, the allotted moves off in search of an idle conversation switch. The select magnets and the common relays are released. First system ; group selector, Figs. 2 and 3. The digit is repeated by the line relay A to a minor switch D. As soon as the common searcher is available, T pulls up in series with start relay SN and shunts its upper winding to prevent operation of other T relays, energizes .1 to associate the conversation cross-bar switch with the searcher and applies a marking over the minor switch to a group of terminals in the Al section of the searcher. This group may occupy some or all of the terminals in one or more positions. In response to the operation of SN, the searcher advances and is stopped in a marked position, if there is an idle line, by the operation of one or more test relays STA from the common marking ground over the individual t wires of the idle outlets. These relays complete circuits over terminals in the A2 bank for the select-magnet such as HMA corresponding to the position in which the switch stopped in series with the middle winding of relay H and with relays SMA ... SMK that correspond to idle outlets. Only one of these, however, can operate and this one locks and energizes the corresponding pull-down magnet VMA &c. over a chain circuit which ensures that only one magnet can be operated even if more than one relay SMA ... SMK is energized. The pull-down magnet locks over a de-energizing winding of H which remains held over its left-hand winding. Operation of H releases T and cuts off A, which falls, followed by B and the minor switch and searcher go home. If all outlets are busy, the searcher is stopped in its last position by a circuit over sn3 and the O/O contact of the cross-bar switch is actuated to hold A after the operation of H. The pulldown magnet in this case remains locked and busy tone is sent over contacts closed by it and by the pull-down magnet. First system ; modified group selector, Fig. 6 (not shown). The group selector shown in Figs. 2 and 3 may be modified by doubling the number of positions in the searcher and halving the number of its wipers. Each group appears in the A1 bank once in the first ten and once in the second ten positions, the first five relays SMA ... SMK being operated over the A2 bank in the first ten positions and the second five in the second ten positions. First system ; final selector, Figs. 4 and 5, set to ordinary line. The digits are repeated to the switch DM. At the end of the first, a circuit is made over its wiper DA for one of the select magnets HMA &c. over relay G. HMA locks up over a de-energizing winding of G, which, however, remains locked up. The digit switch then goes home, energizing change-over relay S so that, at the end of the second digit, a circuit is made over wiper DB for one of the pull-down magnets VMA ... VMK. H is operated in this circuit, releasing G and the select magnet and connecting up the test relay P. If the line is idle, P shunts its high-resistance winding to seize it and ringing current'is sent out in known manner. If the line is busy, the relapse of G sends back busy tone. First system ; final selector, Figs. 4 and 5, set to P.B.X. line. All P.B.X. first lines have a particular tens digit, 1 in the case shown, and when this digit is dialled, relay X is energized instead of a select magnet and locks. In consequence, the units control is transferred to wiper DC and, at the end of the units digit, relay T pulls up as soon as the common searcher is available, seizes it and energizes the associating relay J. At the same time, the start relay SN is operated and the searcher runs round until it is stopped by one of the test relays STA ... STK when a position containing an idle line of the marked group is reached. As shown by the multipling in bank A1, the lines, other than first lines, may occupy any positions in the final selector not wanted for ordinary lines. Select and pull-down magnets corresponding to the idle line, or the first (left hand) idle line if there are two or more in the position in which the searcher stopped, are energized as in the group selector and the call is completed as in the case of ordinary lines, relay P being operated locally. If no idle line is found, the searcher proceeds to 11th terminals, over which STA is actuated, and operates relay Z to cause the busy signal to be sent. Operation of H releases the searcher as in the group selector. Second system, Figs. 7, 8, and 9 (not shown). The talking-circuit switches are similar to those in the first system and are not shown, but the searcher is replaced in every case by a field of cold-cathode discharge tubes which come into action one row at a time and control row and column relays, the latter being organized so that only one can be operated at a time. In the finder control circuit, Fig. 7, a calling line relay L energizes start relay SN and, since T, Q are operated except when the allotter is hunting, this cuts off SQ, connects up the anode and cathode potentials through row and column relays respectively and connects up the primary potential to the electrodes I in the first row. If the calling line is connected to the electrode G of one of the tubes in the row, the tube breaks down, causing the operation of a column and a row relay which control corresponding cross-bar magnets. If not, tube PT breaks down after an interval and energizes sequence relay LA which prepares the next row. If the searcher fails to find a calling line, the relapse of SQ closes an alarm circuit. In the group selector control circuit, Fig. 8, the digit switch individual to the conversation switch applies its marking over terminals MT. A group may occupy more or less than a row, the marking being transferred from row to row, if necessary, by the sequence relays SLA, SLB, &c. If a line is seized, SZ operates and prevents release of SQ which was disconnected when the starting relay SN pulled up. Otherwise, SQ falls and energizes the O/O relays SHK, SVK to give a busy signal. The common control circuit for the P.B.X. final selector, Fig. 9 (not shown), is similar to that of the group selector, except that when no idle line is found, the relapse of SQ operates a busy relay in the individual circuit and no circuit is made for the conversation switch magnets.