Patent GB-674245-A (GB)
Title: Improvements in or relating to electrical telegraph systems
IPC: H01H67/26
Filed: 1949-08-05
Abstract: 674,245. Telegraph exchange systems. TELETYPE CORPORATION. Aug. 5, 1949 [Aug. 13, 1948], No. 20424/49. Class 40 (iii). In an electrical telegraph system comprising a central station connected over a two-way signal transmission path to a plurality of remote stations, each provided with means to initiate transmission of signals from its local transmitter to the central station in response to the reception of a predetermined sequence of signals transmitted from the central station, the predetermined sequence includes a measured pause of predetermined duration during which code signals are not transmitted. The arrangement (Fig. 4), responsive to the station selecting sequence of signals is mainly similar to that described in the Specification 696,541, but also includes means for controlling the timing arrangement and for closing the contacts 36 to complete the circuit of the station transmitter. The elements of a received signal selectively set vanes 41 and selector levers 43 are provided with attached bars 45 having code projections corresponding to the sequential signals for selecting the station. When the levers 43 are lowered at the end of each signal by a bail 47, the selected lever 43 drops so that a shoulder 56 is engaged by a hook 57 which, on the upward movement of the bail 47, raises a lever 58 which is latched by a member 64. The bars 45 are associated with blocking levers 67 and a cam surface 74 on an operated lever 58 engages a lateral stud 71 on the blocking lever 67 associated with the next bar 45 to be operated in the station-selecting sequence. A gate member 72 is manually operated to rock the blocking lever 67 associated with the first code bar 45. The station selecting sequence is constituted by the signals for Blank, Space, a letter, such as A, B, ... designating the station and' the " Letters " signal. The bar 58 operated by the " blank " signal has an extension 61 with a projection 95 which operates a rod 91 and the bar 58 operated by the station-designating letter allows contacts 36 to close for the operation of the tape or like transmitter at the outlying station. The operation of the rod 91 rocks a member 85, Fig. 2, to remove a tooth from engagement with a cam 77 on a sleeve 76 which is released for one revolution and driven at a relatively slow speed from the receiving selector cam-shaft. If signals are not received during the predetermined interval, e.g. one second, which follows the blank signal and is represented by the distance between the low portion of a cam 78 and the end of a follower lever 104, the lever 104 drops off the high portion of the cam 78 and under the action of a spring 122 rocks a lever 107 so that its arm 102 closes contacts 39 to short-circuit the magnet of the printer at the outlying station. If signals are received during the predetermined interval following the blank signal, a lever 135 associated with a cam on the selector cam-shaft is rocked so that a member 131 biased by a spring 142 is free to rotate. A member 127 in turn rocks a latch member 124 out of the path of an extension 123 of a latch member 116 having a hook 118 which prevents a bail 109 attached to the lever 107 from moving forward with the result that the contacts 39 are not closed. A lever 138 has a projection 141 which drops off the high portion of a cam 83 at approximately the end of the predetermined interval, the movement of the lever 138 lowering a bar 143 so that the selecting lever 43 corresponding to " space," which follows " blank " in the station-selecting sequence, can be selected. At the end of the station-selecting signal sequence, the tail portion 145 of the lever 58 operated by a selector bar 45 engages a bar 146 attached to a pivoted member 147 provided with an arm 149 which rocks a lever 153 engaging a lateral extension 154 of the latch member 112 so that the bail 109 is rocked to its normal position to open the contacts 39. The bar 58 finally selected also closes contacts 36. Towards the end of the rotation of the cam 77 a pin 97 engages a tooth 99 on the lever 91 to release the member 85, independently of the restoration of the lever 91 by projection 95, to return to the position in which the cam sleeve 76 is arrested. A number of separate transmitters may be located at a remote station, the selector being provided with a corresponding number of bars 58 provided with tail portions 145 and carrying also the element 66 to actuate the contacts 36 of the associated transmitter. Specification 365,975 and U.S.A. Specification 2,296,845 also are referred to.