| Fig. 262. | Fig. 263. |
The field helices may be wound in the same direction, or a part may be wound in opposite directions.
The connection between the helices and the auxiliary brush or brushes may be made by a wire of small resistance, or a resistance may be interposed (R, Fig. 263,) between the point x and the auxiliary brush or brushes to divide the sensitiveness when the brushes are adjusted.
| Fig. 264. | Fig. 265. |
The accompanying sketches also illustrate improvements made by Mr. Tesla in the mechanical devices used to effect the shifting of the brushes, in the use of an auxiliary brush. Fig. 266 is an elevation of the regulator with the frame partly in section; and Fig. 267 is a section at the line x x, Fig. 266. C is the commutator; B and B', the brush-holders, B carrying the main brushes a a', and B' the auxiliary or shunt brushes b b. The axis of the brush-holder B is supported by two pivot-screws, p p. The other brush-holder, B', has a sleeve, d, and is movable around the axis of the brush-holder B. In this way both brush-holders can turn very freely, the friction of the parts being reduced to a minimum. Over the brush-holders is mounted the solenoid S, which rests upon a forked column, c. This column also affords a support for the pivots p p, and is fastened upon a solid bracket or projection, P, which extends from the base of the machine, and is cast in one piece with the same. The brush-holders B B' are connected by means of the links e e and the cross-piece F to the iron core I, which slides freely in the tube T of the solenoid. The iron core I has a screw, s, by means of which it can be raised and adjusted in its position relatively to the solenoid, so that the pull exerted upon it by the solenoid is practically uniform through the whole length of motion which is required to effect the regulation. In order to effect the adjustment with greater precision, the core I is provided with a small iron screw, s'. The core being first brought very nearly in the required position relatively to the solenoid by means of the screw s, the small screw s' is then adjusted until the magnetic attraction upon the core is the same when the core is in any position. A convenient stop, t, serves to limit the upward movement of the iron core.
To check somewhat the movement of the core I, a dash-pot, K, is used. The piston L of the dash-pot is provided with a valve, V, which opens by a downward pressure and allows an easy downward movement of the iron core I, but closes and checks the movement of the core when it is pulled up by the action of the solenoid.
To balance the opposing forces, the weight of the moving parts, and the pull exerted by the solenoid upon the iron core, the weights W W may be used. The adjustment is such that when the solenoid is traversed by the normal current it is just strong enough to balance the downward pull of the parts.
| Fig. 266. | Fig. 267. |