CHAPTER II.
CONTACT BREAKERS.
Fig. 18.
The simple form of contact breaker already described is useful up to a certain point, but it has disadvantages. Its rate of vibration is only variable through narrow limits, and it is not suitable for very heavy currents. But as it stands it has done long service, and will be used probably wherever the requirements from it are not exacting. The most desirable form of this simple spring break is shown in Fig. 18. R is the soft iron armature; S, the spring; C, check-nut which holds the adjusting screw A from becoming loose; T, a second adjusting screw used to tighten the spring and so raise its rate of vibration; K is the base to which one wire of the coil is attached; L, base of adjusting device to which battery wire runs at I. Where tightening screw T passes through the pillar of the adjusting screw, the hole therein is bushed with rubber to prevent accidental contact. Both A and T are provided with insulating heads of rubber or ivory. At B are the platinum contacts, which should be fully ⅛ inch in diameter.
One serious defect in the action of the simple spring vibrator (Fig. 19) is the tendency of the spring to vibrate, as it were, sinusoidally. This causes an irregularity in the rate of the vibrations, which affects the discharge of the coil very considerably. By far the better plan is to use a very short thick spring riveted to an arm carrying the armature at its end (Fig. 20). R is the armature, S the piece of spring, and K the point of attachment to the base. The actual width of the portion of the spring which vibrates—the hinge portion, it might be called—should not be over ⅛ inch.
Fig. 19. Fig. 20.
The rate of motion is high; but an erroneous notion has been taken of its performance by many persons in the knowledge of the writer. The rate of vibration is not wholly dependent on the size, or, rather, smallness of its spring; the arm and armature considerably alter this, although they are not pliable, by reason of their mass and the momentum consequent on their mass.