Patent GB-516373-A (GB)
Title: Improvements in or relating to telegraph apparatus
IPC: H04L13/10
Filed: 1938-06-23
Abstract: 516,373. Synchronous movements ; code telegraphy. CABLE & WIRELESS, Ltd., and WARBURTON, F. June 23, 1938, No. 18698. [Class 40 (iii)] The line-condition of incoming signal impulses is tested at the middle and end of each revolution of the receiver shaft, and at preferably two other instants during the revolution, for the purpose of correcting synchronism ; and if there is a serious error in synchronism, one revolution of the receiver shaft is missed by the signals, the corresponding signal element taking effect during the next revolution. Construction.-In a cable-code system suitable for incorporation in the printing-telegraph apparatus described in Specifications 463,975, 463,976, and 463,977, a shaft 1, Fig. 1, makes a complete revolution for each impulse, and a synchronism testing magnet 8 responds to both dot and dash impulses but not to spaces. Four switches a, b, c, d, Fig. 3A, are operated by four switch arms 24a .. 24d, Fig. 1, and these are set according to the position in which the armature lies at four instants in the revolution of shaft 1 ; the instants b, c occur at the middle and end of the revolution, respectively, as shown in Fig. 2A, while instants a and d occur approximately at the quarter revolutions but can be varied by adjustment of the eccentrics 2a, 2d, Fig. 1. The setting of the switches 24a, 24d is effected as follows. Levers 4a .. 4d are rocked about their pivot 5 by the action of eccentrics 2a.. 2d, and pivoted at 4w on each lever is a selecting bell crank 6 whose lefthand end 7 abuts upon a lug 19 during a space impulse, so that the crank 6 turns anti-clockwise as its pivot 4w is lowered, and the lug 22 on its vertical arm rides clear of the projection 23 on the switch lever 24 a, b, c or d. During a dot or dash impulse, however, each controlling member 15 lies, to the right with its lug 19 clear of the end 7 of lever 6 ; hence crank 6 is not turned, when its pivot 4w is lowered, and lug 22, by engaging projection 23, sets the corresponding switch lever 24a, b, c or d, which is thereafter latched by a latch such as 30a until the latter is released by the nose 35 of the corresponding crank 6 during a subsequent space impulse. The controlling members 15 are locked in their right-hand positions by engagement of the parts 7, 19, and in their left-hand positions by springs 27 which are carried by the cranks 4a 4d. They are initially set by the armature 9 through arms 10 and springs 17, the springs allowing freedom to the armature when the members 15 have been locked. In the cam of the third switch lever 24c, however, additional mechanism 36, controlled by the second latch 30b is provided ; it prevents the switch lever 24c from being moved into the operative position if the switch lever 24b has already been latched in that position. Operation.-The switches a .. d, operated by the switch-arms 24a .. 24d, are shown in their unoperated condition in Fig. 3A. They are coded so as to control magnets 53, 54, which are adapted respectively to retard and accelerate the shaft 1, in the manner described in Specification 238,622 [Class 40 (iii)]. Retarding corrections are applied when a current impulse, whether dot or dash, follows a space impulse, 'while accelerating corrections are applied when a space follows a current impulse. If a current impulse follows a space at a time when there is strict synchronism, neither of the magnets 53, 54 is affected, Fig. 3A, but if the shaft 1 is fast, switches 24b, 24d are latched up while 24a is missed, and 24c remains unoperated because of the previous operation of 24b. Hence the coded contacts, Fig. 3A, are changed so as to close a circuit through the retarding magnet 53, Fig. 3C (not shown), but this circuit is broken again by the operation of switch a at the end of the received impulse. If the shaft 1 is slow, Fig. 2C, then when a current impulse follows a space, switch a or switches a and b but not c and d are latched up, and the accelerating magnet 54 is energized, Fig. 3D (not shown). If, on the other hand, the shaft 1 is so fast that, when a space follows a current impulse, switches a and bare both missed while switches c and d are latched up, Fig. 2D, the accelerating magnet 54 is energized, Fig. 3E (not shown), so that the received signal impulse misses the revolution of shaft 1 to which it originally corresponded and takes effect in the next revolution. The signal may be so shortened by distortion that it ends before the mid point of that revolution is reached and to provide against this contingency a contact of the switch c is arranged, Fig. 4 (not shown), to close a hold-on circuit for the dot magnet or dash magnet, as the case may be, and the circuit is broken by a cam when the impulse has taken effect. If the current impulse after a space is so late that only switch c is latched up, Fig. 2E, the speed correcting magnets 53, 54 are not energized ; one revolution of the shaft is ineffective and the signal takes effect in the next revolution. To this end the dot magnet or dash magnet is held on over the instant b in the next revolution.