Richardson's handbook of projection (1927)

609 HANDBOOK OF PROJECTION FOR CONTROLLER MOTOR. ClRCUt) Gr. Figure 208. In Figure 208 we have intended merely to illustrate what has been already set forth, without regard to constructional details. A is a solenoid, connected "across the arc, through binding posts B B. It is wound with fine, insulated wire. C is a small bar of iron, called an "armature." It is hinged at its lower end. At its upper end are the make-and-break contacts of the motor circuit — one wire of the circuit only, of course. E is the tension spring, controlled by thumbscrew F. As you will readily understand, when the pull of solenoid A becomes strong enough, by reason of rising arc voltage, to cause the pull of spring E to be overcome, armature C will be moved over against contact G, which will bring contact points G-H together, thus closing the motor circuit. When the carbons are fed together sufficiently to lower the arc voltage to a point where spring E overcomes the pull of the solenoid, armature C is pulled back, and thus contacts G and H are broken and the controller motor stopped. That is the operating principle, though of course, as we have said, the actual construction of such a device is very different from that shown, the idea being merely to show you, in simple, easily understood form, the principle upon which such devices operate. Note: For another type of controller see Strong lamp equipment, page 878.