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MANAGERS AND PROJECTIONISTS 589
A, B, which connect to the arc lamp circuit, the inside one, A, being the negative and the outside or left hand one B, the positive. The positive must, of course, connect through the projector table switch to the top carbon arm of the lamp, and the negative through the projector table switch to the bottom carbon arm of the lamp. The A. C. leads, H, are seen in Plate 3 at right hand side. These leads connect directly, through a switch and fuse, to the alternating current supply. In the center, at the top of Plate 3, is relay magnet 1, the purpose of which will be explained further on.
THE AUTO-TRANSFORMER, L-L, Plate 3, consists of an iron core with a winding of heavy copper wire. It is similar to an ordinary transformer, except that its connections are such that in effect it has only one winding, whereas the ordinary transformer has two, viz. : a primary and secondary. Its function is to change the voltage of the A. C. supply circuit to the pressure required at the arc. The center point of the winding also forms the negative terminal of the arc circuit, as per 3, 4, 4, in diagram, Plate 5. See Fig. 199, page 546.
REACTANCE COIL.— The reactance coil, Q, Plate 3, is similar in appearance and construction to a transformer. It is connected into the alternating current circuit for the purpose of limiting current flow when the carbons are brought together to strike the arc, to a value that will not be injurious to the tube ; also it operates to insure steadiness of the arc and to prevent any wide fluctuations of the current when the length of the arc is changed. The general effect is to make the arc much easier to handle.
TILTING MECHANISM.— Each rectifier is provided with an automatic tilting device, consisting of parts B, D, K and P, Plate 2. This device is so connected that the closing of the carbons energizes magnet P and thus causes the tube to tilt, which makes the rectifier a self-starter. The mechanism is operated by magnet P, Plate 2, the pull of which is applied to the tube by coil spring B, Plate 2, as shown. A spring is used instead of a rod in order to prevent the tube from being subjected to unnecessary and violent shock.
THE RELAY, 1, Plate 3, is another magnet, used to operate the contacts which open the tilting magnet circuit when the arc is started, thus preventing the tube from tilting at any other time. But for this cutout the tilting magnet would continue to operate, and the tube would be tilted, or rocked continuously.