Precise speed control for D-C machines

In this paper a circuit is described that holds the average speed of a d-c shunt-wound machine as constant as the standard reference used (for which the most precise standard known can be employed) and holds the instantaneous speed very close to standard speed if there are not sudden changes of load or applied voltage. The machine is positively indexed in phase with respect to the standard. In addition to its precision, the method is characterized by its simplicity and general applicability over a considerable part of the range of d-c machine speed and capacity.