Patent GB-648789-A (GB)
Title: Improvements in electrical remote control systems
IPC: H02J13/00
Filed: 1948-02-02
Abstract: 648,789. Electric control systems. ROSS, T. W., SMITH, R. M. A., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Feb. 2, 1948, No. 3030. [Class 40 (i)] A relay responsive to the duration between two electric impulses for switching a load "on" or "off," comprises a motor operated cam which on the reception of the first impulse is driven from a " reset " to a " starting " position, and is driven therefrom on the cessation of the first impulse to the rest position unless during this movement a further impulse is received to stop the drive. Provided the second impulse is received at one or other of two predetermined time intervals after the first, switches rotated by the motor will be in appropriate positions to cause opening or closing respectively of the load circuit by the second impulse. As shown, Fig. 1, a ripple current of the appropriate frequency received over the power lines L1, L2 operates through a series tuned circuit 6, 7 and transformer 5, a resonance relay 1, e.g. as described in Specification 517,971, [Group XXXVII]. The normally short-circuited heater 8 of a quick-acting hot wire switch is thereby energized to throw its switch arm 10 over to contact 12 and energize a constant speed motor 13 which advances a shaft 13a from the " rest " position shown to a " start " position where the motor circuit is broken by a cam 14 on the shaft 13a rocking a snap action contact arm 15 to engage contact 16. When the ripple signal impulse ceases the switch arm 10 reverts to normal, the motor circuit is energized, over contact 16 and, in the absence of a further ripple signal, advances the shaft 13a to the " reset " position shown where the motor circuit is again broken. To operate the contactor 23 controlling a load connected across lines 22, L2, a further ripple signal is sent at a time when one or other of the adjustably fixed radial contact arms 18, 19 has been advanced by the shaft 13a to engage its co-operating contact 20 or 21, when the quick-acting switch 10 again changes over to stop the motor and energize the " open " or " close " actuating coil 24, 25 of the contactor, as the case may be, the motor resetting the shaft at the end of the ripple impulse. The type of control effected " open " or " close " is thus determined by the time interval between the first and second ripple signals. The contacts 18, 19 may be located 'in selected radial notches on a disc 26 secured to the shaft 13a whereby the time interval between the two ripple currents for actuating the contactor 23 may be varied. In a modification, Fig. 2, the cam-operated arm 15 has contacts 11a, 12a co-operating directly with a bimetal strip 10 actuated by the heater coil 8, the strip 10 being out of contact with either contact 11a, 12a in the reset position shown. In this case the appropriate contactor actuating coil is energized from the strip 10 over a contact 12b. The main switch 23 in both Figs. 1, 2 may be of thermal or other slow-acting type in which case the contacts 18, 19 may be connected directly to the line L2. According to the Provisional Specification the cam 14 of the Fig. 2 arrangement carries a pin which, during rotation of the cam, sequentially moves contacts carried on springs into engagement with associated fixed contacts to control various circuits, the appropriate circuit being selected by the time interval as described above. Specifications 574,371 and 648,790 also are referred to.