A device for maintaining isochronism in low-power electric motors

In connection with the driving of a wireless direction finding rotating beacon it was found necessary to devise means of controlling a motor so as to obtain accurate constancy of speed over wide ranges of mains variation. In the first instance experiments were made with a governor such as that used in the Baudot printing-telegraph system, but it was found that it did not absorb sufficient power to enable it to be used on the direction-finding rotating beacon. With a view to diminishing the amount of power that need be absorbed by the governor, an electric circuit arrangement for the supply of power to the electric motor used to drive the beacon was devised, and finally an eddy-current governor with clock control was designed. The clock control is intended to enable two beacons to be run with alternate periods of transmission, without the possibility of serious overlapping of these periods. The accuracy of the governor control is of the order of 0.05 per cent with 30 per cent mains-voltage fluctuations, while the clock control limits the cumulative error to less than 1 degree of azimuth.