Improvements in the automatic correction of synchronous electric clocks or like time-indicating or time-recording devices operated from a.c. supply mains

摘要

767,581. Automatic speed control systems. ELLIOTT BROS. (LONDON), Ltd. Jan. 29, 1952 [Jan. 29, 1951], No. 2240/51. Class 38 (4). [Also in Group XVIII] The synchronous electric clocks 1 are normally supplied from the A.C. supply means 6, 7, 8 via a frequency changer comprising a stator 3 and a rotor 4 the single-phase winding 9 of which is connected to slip rings 10, 11. The rotor 4 is normally stationary and is coupled to a three-phase motor 14. A selected synchronous electric clock is located in an error detector 17 and is therein continuously compared with a standard clock 16. The arrangement is such that an output signal is produced from the detector 17 when the error of the selected synchronous clock reaches a predetermined maximum so that the motor 14 is energized to drive the rotor 4 for a predetermined number of revolutions which is the product of the maximum error in seconds and the desired. frequency, in cycles per second, of the A.C. supply. The rotor 4 is driven in the appropriate direction to reduce the error by increasing or decreasing the frequency of the A.C. supply to the clocks 1. An auto-transformer may be connected across the slip rings 10, 11 so that the voltage of the supply to the clocks is automatically corrected when the frequency changer 2 is in operation. The error detecting means 17 may comprise a differential gear the sun-wheels of which are respectively driven by the standard clock and the selected synchronous clock and the planet carrier of which moves if the standard clock and synchronous clock are not in agreement.