Patent GB-162739-A (GB)
Abstract: 162,739. Automatic Telephone Manufacturing Co., Ltd., and Savin, J. Jan. 23, 1920. Automatic exchange systems.-In a system for small exchanges, two step-by-step switches, the movements of which are controlled solely by their own stepping-magnets, are connected together in such a manner that one of the switches is adapted to move from the line of the party previously calling, to the line of the next calling party, while the other switch is adapted to act as a selector, and on the completion of the conversation return to the normal position under the control of its stepping magnet. The selector switches are provided with two banks of contacts and two sets of wipers mounted on a common shaft, the numbers allotted to one bank being all prefixed by the digit 1. After the dialling of 1, upon the deenergization of a slow-acting relay, the connection of the switch is transferred from one set of wipers to the other. In order that access may be had to more than 60 subscribers on each bank, the dialling of 0 (ten impulses) steps the wipers to a dead set of contacts, and subsequent dialling rotates them to further sets of contacts. In the arrangement shown, the capacity of the system is 39 local lines and 4 exchange lines. Line-finder. Two line-finders B, B<1> are allotted to each of the two sets of lines dealt with by the upper and lower wipers respectively of the selectors. The removal of the receiver at substation A, Fig. 1, energizes the lower winding of cut-off relay 5 and both windings 9, 10 of a group relay 11, which short-circuits its high-resistance winding 10. The current through the lower winding of cut-off relay 5 is thereby increased and the armatures 23 and 4, which are controlled by lighter springs than the armature 8, are attracted. The armature 23 removes earth from the private contact in the line-finders, but although contact is made between the armature 4 and its front contact its movement is insufficient to break the contact at the other springs, thereby maintaining the relay 5 energized. The relay 13 is also energized over the armature 14, and causes the actuation of the slow-acting relay 3, which completes a circuit through the stepping magnet 20 and the high-resistance relay 19, substitutes earth over the back contact of armature 4 by earth over its front contact, and connects the private wiper 22 with the junction of the stepping magnet 20 and the relay 19. As long as the wiper 22 is earthed, the relay 19 is short-circuited and the stepping magnet 20 ceases to operate on account of the high resistance of the relay 19. The actuation of relay 19 connects the line wipers 24 and 25 to the selector switch C, and earths the private normal 38 over armature 21. Cut-off relay 5 is now fully energized and effects the relapse of group relays 11 and 13. On the release of relay 3 the starting wire 16 is transferred to the starting wire 37 of the next line-finder. If a call is made and both line-finders are in use, a metering relay 40 is actuated over the armatures 41, 41<1>, in order that the number of times this occurs may be recorded. The Provisional Specification states that the 25 contacts of the line-finder may be connected to the lines of ten subscribers to which the line-finder is allotted by the group relay 11, the lines of ten subscribers of an adjacent group, and five selected lines of the next group. Selector. Connection having been established with a selector C, Fig. 2, the line relay 28 and the release relay 30 are actuated, the latter maintaining the line-finder relays 19 and 36 energized over armature 31 after the release of relay 3. Assuming that connection is desired with substation 108, on sending the first digit the line relay 28 will be denergized once and the stepping magnet 50 will be energized in series with the slow-acting relay 45 to rotate all the wipers one step from the normal. The discriminating wiper 51 is thereby earthed, and on the release of the slow-acting relay 45 the relay 53 is actuated to take in use the lower set of wipers 61, 62, 63 over the armatures 55, 56, 57. If the first digit had been other than 1, the relay 4 would have remained energized during the transmission of impulses, the relay 53 would not have been actuated, and the upper set of wipers 58, 59, 60 would have been used. On dialling the next digit 0, the wipers are rotated ten steps further, thus bringing the lower wipers to rest on a dead contact, when nothing happens and the subscriber can dial again. Eight impulses are now sent and the switch is rotated a further eight steps so that the lower wipers make connection with the contacts of substation 108. The 11th and 21st contacts of the upper bank are dead in order that when this bank is taken into use three digits can be dialled without any " switch over." Connection having been established, if the called party is not engaged the ringing relay 47 is locked energized and closes the ringing circuit through the called station at armatures 76 and 77. Upon the called party removing his receiver the relay 69 is locked energized, and connects the called line to the calling line over armatures 81 and 68, speaking current being supplied to the called subscriber's circuit over the upper winding of relay 49. Busy test for ordinary lines. If the called party is engaged and the test wiper 63 or 60 rests on an earthed contact, upon the de-energization of the slow-acting relay 45 the relay 49 is locked energized over the resting contacts of armature 66, and at its armature 72 connects the busy tone transformer 73 to a line conductor. Calls to main exchange. The number 100 is allocated for exchange lines of which four are fitted on the lower bank. Substations which are not allowed access to the exchange lines are allotted an earthed contact in the bank wiped over by the auxiliary wiper 84 of the line-finder B. Consequently if 100 is dialled the relay 65 energizes over a circuit including the wipers 84 and 51, earth is substituted for wiper 63 at armature 64, and the relay 69 is locked up to give the busy signal. If the substation is allowed exchange facilities, relay 33 is actuated but relay 65 is not, and the first exchange line being idle the ringing relay 47 is energized as when a local subscriber's line is seized. Should the first exchange line be engaged, the series relay 45 is maintained operated and stepping magnet 50 is actuated over a circuit from earth at armature 95 of relay 94.'If the next line is engaged a similar circuit is closed over armature 97 of relay 98, the magnet 50 thus being continuously operated until an idle trunk is found. Busy test for exchange connection. If all exchange lines are engaged, no armature being provided for last relay 101, the last contact wiped over by the wiper 74 will not be earthed and the stepping magnet 50 will cease to operate. Wiper 63, however, will be earthed and the busy signal will be sent. Release. This is under the control of the calling subscriber, who, on hanging up his receiver,. effects the de-energization of the line relay 28 and series relay 30. The removal of the holding earth at armature 31 causes the relapse of all the remaining relays in operation. Armature 31 connects earth to all contacts in the bank swept over by wiper 74 except the first, so that stepping magnet 50 continues to operate until the wiper 74 reaches the normal unearthed contact. Conference calling. The number 004 is allocated for this purpose. An impedance 102 is placed across the line contacts swept by wipers 58, 59, and a permanent potential is placed on the corresponding private contact 103. The line is thus always accessible and as many parties may confer as there are selectors in the system.