Automatic motor control

Of the various systems for controlling electric motors, none surpass in interest and economic importance those which make use of electrically actuated switches controlled by automatic or semi-automatic means. A few years ago the drum controller was quite sufficient for any motor then in use. Since then the use of larger motors and the need for automatic features, unattainable in a simple manner with drum controllers, have resulted in the development of a great variety of magnetically controlled switches, and of various means for operating them in control systems.