Patent GB-171498-A (GB)
Abstract: 171,498. Automatic Telephone Manufacturing Co., Ltd., and Mercer, R. Aug. 21, 1920. Automatic exchange systems and apparatus.- In a forwardly hunting switch of the kind having a number of sets of wipers adapted to test a number of lines simultaneously, the selection of the particular set of wipers to be used is determined solely by a switching operation brought about by the set or sets of wipers resting on an engaged line or lines. When two or more sets of wipers simultaneously engage idle lines, only a single circuit becomes operative to connect up the set of wipers having precedence, so that other sets of wipers and the lines on which they rest cannot even momentarily be interfered with. The invention is shown as applied to a group selector having two sets of wipers 20, 21, 22 and 23, 24, 25, the private wipers 20, 23 being connected respectively to the test relays 15, 16 over the armatures 29, 30 of the switching relay 6. The upper set of wipers 20, 21, 22 remain connected up over the armatures 34, 35 unless the test wiper 20 rests on an engaged line, in which case the test relay 15 responds and connects up the lower set of wipers 23, 24, 25. When making a call, the vertical magnet 12 is operated by the calling impulses in the usual manner to raise both sets of wipers to a selected level. After the first step, both test relays 15, 16 are energized over the springs controlled by the armature 13 and the offnormal springs 14, and lock up over their upper armatures 18, 19. When the series relay 11 falls back, a circuit is completed for the rotary magnet 28 over the armatures 26, 27 of the test relays, and the wipers are advanced one step in search of an idle line. The energization of the rotary magnet breaks the locking circuit of both test relays which in turn cause the de-energization of the rotary magnet. If both the lines tested are busy, the relays 15, 16 are locked energized and the rotary magnet 28 advances the wipers another step. The alternate energization of the test relays and the rotary magnet continues until one of the wipers 20, 23 engages an idle line, when one of the test relays will not respond and the circuit of the rotary magnet will not be completed. If the wiper 20 engages an idle line first, a short circuit is removed from the upper winding of the switching relay 6, and this winding is energized in series with the upper winding of relay 15. As the windings of relays 15, 16 are of low resistance and those of the relay 6 are of high resistance, the relay 15 does not energize in this circuit. The switching relay 6 responds, extends the line 1, 2 over the armatures 32, 33 to the wipers 21, 22, and a non-selective potential is applied to the wiper 20 over the armatures 29, 31. If the wiper 23 seizes an idle line first, the test relay 16 remains de-energized and the relay 15 is locked energized over both its windings. The lower winding of the switching relay 6 is energized in series with relay 16 (which does not respond) and the line 1, 2 is extended over the armatures 32, 33 and 34, 35 to the lower wipers 24, 25. A non-selective potential is applied to the wiper 23 over the armatures 30, 31. As the circuit of the lower winding of the switching relay 6 is broken at the armature 38, the relay 6 is prevented from energizing simultaneously with the relay 15, thereby ensuring that the line upon which the wipers 21, 22 is resting is not interfered with. If both sets of wipers simultaneously engage idles lines, both test relays 15, 16 remain de-energized and the switching relay 6 is immediately energized over its upper winding and extends the calling line to the upper set of wipers, which in this manner always has precedence. The provision of the armature 38 in the operative circuit of the lower winding of relay 6 prevents this last-named circuit from becoming operative at this time, so that the other set of wipers and the lines upon which they are resting are not influenced in any way. The Provisional Specification states that this result may also be attained by arranging that the relay 15 connects the testing-circuit to the relay 16 so that the tests take place slight y after one another. Release is effected when holding earth is removed from the test wiper 20 or 23 at the switch ahead, the switching relay 6 de-energizing and completing a circuit 5, 7, 10 for the release magnet 37.