Patent GB-209044-A (GB)
Abstract: 209,044. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Stehlik, R. F.). Dec. 23,1922, [Convention date]. Automatic exchange systems.-In a system employing call-finders two independent circuits are provided for starting up an idle finder on the initiation of a call. Two starting relays 42, 43. Fig. 1, are used, either or both of which when energized closes a circuit for initiating the operation of an idle finder F preselected by an allotting switch FA. The relay 42 is normally shunted by a chain circuit including normallyclosed contacts of all the line relays, whilst the other relay 43 is adapted to be energized over a normally-open contact of any line relay. Each finder F is furnished with an auxiliary set of bank contacts 23 - - 25 associated with a common relay group RG, which is so connected that if a fault develops in the chain shunt circuit and a finder is started hunting by the response of the relay 42. when the wipers encounter the auxiliary contact set a second time, the finder is stopped and an attendant's signalling device is operated. The finder, however, is not thereby prevented from hunting for a line which initiates a call before the fault has been attended to, but the fault signal is repeated when the call has been dealt with. Means are also provided for signalling the attendant if, owing to a fault, no current flows in the starting circuit when either or both of the relays 42, 43 pull up. On a calling sub. scriber A taking down his receiver, the line relay 13 disconnects earth from the test contact 27, energizes the starting relay 42 by opening the chain shunt circuit at armature 16, and at armature 17 closes a circuit for the other starting relay 43. The starting wire 99 is thus earthed at both armatures 49, 50 and a relay 44 is energized in series with the line relay 82 of the allotting switch FA. The relav 44 opens an alarm circuit simultaneously closed over an attendant's lamp L<1> and a relay 49<1>, which operates a buzzer 50<1>. If, owing to a fault in the starting circuit (such as an imperfect contact at armature 59 or 89), no current flows therein, the relay 44 remains inert and the attendant is signalled. The line relay 82 closes a series circuit for the test relay 84 and the stepping magnet 94 of the idle finder F, the test wiper 73 of which is connected over armatures 97, 85 to a point between the relay 84 and the magnet 94. The finder F now rotates in well-known manner until the calling line terminals 26 - - 28 are engaged, on which the test relay 84, being no longer shortcircuited, pulls up and energizes the stepping magnet 81 of the allotting switch FA, which being of the kind which steps on the release of the stepping magnet does not advance its wipers. The test relay 84 also closes parallel circuits for the allotting switch cut-off relav 83 and the finder switching relay 95. The relay 95 earths the holding wire, extending earth to the private normal 22 and energizing the calling line cut-off relay 14, which locks up and disconnects the line relay 13, causing the relapse of the starting relays 42, 43. The relay 83 de-energizes the line relay 82, which after an interval relapses and breaks the circuit of the test relay 84. The test relay 84 de-energizes the stepping magnet 81 which advances the wipers of the switch FA to the bank contacts associated with the next finder. The stepping magnet 81 continues to operate over its interrupter contact until its test wiper 93 engages an unearthed test contact associated with an idle finder, when the cut-off relay 83 de-energizes and connects up the line relay 82 to the starting wire 99. If, due to a fault developing in the chain shunt circuit, the relav 42 pulls up when no subscriber is calling, a finder F is started as before by the grounding of the wire 99 at the armature 49, but a circuit is also completed at the armature 50 for a. relay 45, which connects the test contact 24 of the auxiliary contact set 23 - - 25 to a low resistance relay 46. When the test wiper 73 engages the test contact 24 of the auxiliary contact set, the relay 46 is energized in series with the stepping magnet 94 of the finder F over the wipers 92, 91 of the allotting switch FA, and connects a marginal relay 47 in parallel with themagnet 94, but on account of the relative resistances of the relay 46 and the magnet 94 the relay 47 does not respond at this time. The resistance of the relay 46 is not sufficiently high to prevent the operation of the stepping magnet 94 which continues to advance the finder F. When the wiper 73 passes off the contact 24, the marginal relay 47 is energized in series with the relay 46 and pulls up, and at armature 54 connects the test contact 24 to the upper winding of a relay 48. When the wipers of the finder engage the auxiliary contact set for the second time, the upper winding of the relay 48 is energized in series with the stepping magnet 94. The resistance of the upper winding of the relay 48 is such that the stepping magnet 94 is prevented from operating in series and the marginally-adjusted test relay 84 is prevented from operating in parallel. The relay 48 locks up over its lower winding and disconnects the starting wire 99, causing the relapse of the relays 44, 82, 83. The relay 44 closes a circuit over armatures 51, 57 for the attendants' lamp L and the alarm buzzer relay 49<1>. If a subscriber should call whilst the above signalling operations are taking place, or before the attendant has responded to the alarm, the apparatus is not tied up since the response of the second starting relay 43 opens any of the relays 45 - - 48 which may have become energized. If, when a call is made, the starting relay 43 does not energize owing to an imperfect contact 17, and the finder wipers pass over the auxiliary contact set on their way to the calling line contacts, the relays 45 - - 47 are energized as described above, but when the calling line contacts are reached, the relapse of the relay 42 opens the circuit of the relays 45 - - 47 and restores the relay group RG to its normal condition.