Patent GB-121471-A (GB)
Title: Improvements in Automatic Telephone Systems.
Inventor: HULFISH DAVID SHERRILL
IPC: H04Q3/00
Filed: 1918-12-05
Abstract: 121,471. Hulfish, D. S. Dec. S, 1917, [Convention date]. Automatic exchange systems and apparatus.- Relates to a construction of selector and pilot switch in which, after use, the brushes are advanced electro-magnetically to a sub-normal position and are then restored to normal mechanically by a power-driven oscillating member. Circuit connexions are described for effecting the necessary " change-over " after the first set of selecting-impulses, and for restoring the various selectors in such a way as to prevent interference with other lines. The invention is described as applied to a system in which a calling line, Fig. 8, is connected to a desired line over line and group finders 101, 102, Fig. 4, (together forming the equivalent of a two-co-ordinate call-finder), a pilot or controlling switch 103, Fig. 5, a " register " or tens selector 104, Fig. 6, and a " final connector " or units selector 105, Fig. 6. These switches 101 - - 105 are permanently associated and form a connecting " division " or " set." Each switch is set by means of the escapement magnets 121 - - 125, the whole of the controlling-relays being shown in Fig. 7. Construction of switches. Several sets of brushes 201, 202, Fig. 1, are carried by a shaft 203 having a ratchet-wheel 213 engaged by a double pawl 220 secured to the armature 221 of an electro-magnet 225. A spring tends to turn the ratchet 213 clockwise, a movement of a half step occurring when the magnet 225 is energized and also when it is de-energized. The brushes 201, 202 receive current from wipers 205, and may engage the underside of terminals 204, fixed to plates 207 secured to vertical rack bars 208, dowels 255 in the plates 207 passing through holes in the supporting plate 209. In order to restore the switch to normal, a clutch arm 227, pivoted to the ratchet-wheel 213, rests upon a wing 228 of a pivoted guide 226, and is drawn against the guide by a spring 229. In operation, the switch is set to the desired position by the magnet 225, and in order to restore it to normal, further impulses are sent through the magnet 225 to move the switch further in the same direction until a sub-normal position is reached, in which the corner 235 of the clutch arm 227 moves beyond the guide 226 and into the position shown in dotted lines, wherein the spring 229 draws the clutch arm 227 into the path of the clutch tooth 230 secured to an oscillating shaft 231. The clutch tooth then engages the arm 227 and moves it to the position shown in the dot-and-dash line, thus restoring the brush carriage to normal, and opening the normal switch 232 by moving the guide 226 into the position shown in dotted lines. When the tooth 230 recedes, the guide 226 is moved into its normal position, reclosing the normal switch 232. Connexion of calling line 106, Fig. 8, to called line 108, Fig. 6. Figs. 4 to 8 of the drawings form one complete Figure, Figs. 4, 5, and 7 being arranged one below the other, with Fig. 8 to the left of Fig. 4 and Fig. 6 to the right of Figs. 4 and 5. In these Figures, each switch terminal is represented by a circle and each brush by a small rectangle connected by a lead to its feed terminal. Brushes shown between terminals, as in Fig. 6, will engage the terminal at the half step. A terminal is identified hereinafter by giving first the number of the switch, then the level number, and then the terminal number in the level; thus 103-2-6 means the sixth terminal in the second level of switch 103. Similarly, a brush is identified by the location of its feed terminal; thus brush 103-2-25 means the brush, the feed terminal of which is the 25th terminal in the second level of switch 103. Switches 101 and 105 have some of their levels omitted from the diagram. Operation of call-finder, comprising group finder 102 and line-finder 101. When a subscriber 106, Fig. 8, removes his receiver, his line relay 149 puts selectable potential upon his terminal in the line-finder 101, and also upon the group wire 305 connected, say, to terminal 102-1-14. The pilot switch 103 being in its normal position, with its brushes engaging the first and thirteenth vertical rows of terminals as shown in Fig. 5, a circuit is closed through the escapement magnet 122 of the group-finder 102, brush 102-4-25, wire 324, contacts of pilot switch, back contacts of test relay 138, wire 306, and armature of group calling relay 146 to ground. This circuit is interrupted at brush 102-4-25 as the brushes of the group-finder come into their half-step position, being completed again when the full step position is reached. The step-by-step movement of the group-finder brushes thus continues until the test brush 102-1-25 reaches the terminal 14, say, of the group containing the calling line, whereupon the test relay 138 is energized to open the circuit of the escapement magnet 122 and to close the circuit of magnet 123 so as to move the pilot switch into its second position, wherein its brushes engage rows 2 and 14. The escapement magnet 121 of the linefinder 101 is then energized to move its brushes step by step over the line terminals, until its test brush 101-20-0 reaches the test terminal 101-20-4, say, of the calling line, whereupon the test relay 138 is again energized to open the circuit of magnet 121 and to move the pilot switch into its third position, wherein its brushes engage rows 3 and 15. A circuit is then closed from battery over resistance 134, Fig. 5, group and line finders as adjusted, to the cut-off relay 148 of the calling line. (The several sets of terminals in the group-finder 102 are connected to corresponding sets of brushes (not shown) in the line-finder 101 in a manner similar to the connexion of terminals 102-1-2, 102-2-2, 102-3-2, and 102-4-2 to the brushes 101-17-0, 101-18-0, 101-19-0, and 101-20-0). Adjustment of " tens " register 104, Fig. 6. A loop circuit is now closed through the calling line, this circuit including the relays 141, 142, Fig. 7, brushes 103-5-0, and 103-4-0 of the pilot switch, wire 311, 312, brushes of switches 101, 102 as adjusted, and the calling line. The operation of the impulse-sender causes spring 150 to engage spring 151, thus maintaining the circuit of the holding- relay 142, whilst the line circuit is opened a determined number of times by the disengagement of springs 151, 152. These impulses are repeated by the relay 141 to the escapement magnet 124 of the tens register 104, the brushes 104-1-0, 104-2-0, 104-3-0 of which are adjusted to select the desired set of brushes in the final (units) connector; only one set of the latter being shown. At each deenergization of relay 141, an impulse is sent also through the upper winding of a relay 139, Fig. 7, and at each half step of the brushes of switch 104 an impulse is sent by brush 104-6-0 through the lower winding of relay 139, which is thus maintained energized as long as selecting-impulses are received, but when these cease, relay 139 de-energizes and closes the circuit of relay 138 to move the pilot switch into its fourth position, wherein its brushes engage rows 4 and 16. Adjustment of final (units) connector 105, Fig. 6. This is effected in the same way as the adjustment of the tens register 104, and when the selecting-impulses cease, the relay 139 energizes the relay 138 to move the pilot switch into its fifth position, in which its brushes engage rows 5 and 17. Busy test and busy signal. If the selected line is busy, the busy-test relay 137, Fig. 7, is energized over wire 323 and the third brushes of the switches 104, 105 as adjusted, thereby (1) connecting the secondary of the busy transformer 136 over wire 340 to the calling line, and (2) opening the circuit of relay 138 so as to prevent the pilot switch moving at once into its sixth position. When the calling subscriber replaces his receiver, relay 142 de-energizes and closes the circuit of relay 138, thereby moving the pilot switch into its tenth or first release position. Ringing-current. If, however, the selected line is free, the busy-test relay 137 is not energized and the relay 138 moves the pilot switch into its sixth position, wherein its brushes engage rows 6 and 18, and the cut-off relay 107, Fig. 6, of the selected line is energized. When the calling party depresses the ringing-key 153, relay 142 is held energized while relay 141 is short-circuited and energizes the ringing-relay 144, which connects the generator 145 over wire 338 and the switches 103, 104, 105 as adjusted to the selected line, the current returning over switches 105, 104 as adjusted to the wire 337, and then returns to earth through several branched circuits, one of which includes the calling telephone, thereby giving a ringing signal to the calling party. Talking circuit. When the called subscriber replies, he is supplied with microphone current over relay 140 and coil 143, this circuit being connected to the similar circuit of the calling subscriber by means of condensers 131, 132. Restoration of switches. In order to prevent interference with other lines during restoration, the switches are not restored simultaneously. Each switch is advanced electrically to its ultimate or sub-normal position and is then mechanically returned to its normal position: When the calling subscriber replaces his receiver, either after a conversation or at any stage after his line has been seized by the line-finder 101, the relay 142 deenergizes and closes the circuit of relay 138 to advance the pilot switch into its tenth position, wherein the brushes engage the tenth and twentysecond rows of terminals, and all connexions to the calling and called lines are opened. The pilot switch then closes circuits for the escapement magnets of the switches 101, 102, 104, 105, whereby the brushes of the line finder 101 are advanced to position 13 and 25, whereas the brushes of switches 102, 104, 105 are advanced to positions 11 and