| 摘要 |
1,167,189. Control of A.C. motors. EATON YALE & TOWNE Inc. 19 Dec., 1966 [6 June, 1966], No. 56687/66. Heading H2J. [Also in Division G3] A hoist is powered by an induction motor 11, 13 energized through direction relays HR, LR and thyristors Q1, Q2, the triggering of which is dependent upon the difference between a voltage from a tachogenerator and a desired speed voltage obtained from transformers T3, T4 having cores movable by push-buttons P1, P2 which also operate the direction relays. The transformers are energized from a transistor oscillator 23; their output is rectified and compared with the rectified output of A.C. tachogenerator TAC, the difference being arranged to charge a capacitor (C17, Fig. 2, not shown) connected to a Schmitt trigger circuit (Q8, Q9) which in turn switches a monostable circuit (Q10, Q11) which triggers both thyristors via an impulse transformer (T5) having two secondary windings. The capacitor is reset after each halfcycle of the mains supply by a second Schmitt trigger (Q6, Q7). The motor has a running winding 11 and a start winding 13 which may be disconnected by a centrifugal switch CSW. Limit switches LS1, LS2 apply reverse current braking by energizing a plugging relay PR which changes over the directional contacts and applies a rapid charging current to the capacitor (C17) to ensure early triggering of the thyristors. There is an electromagnetic brake S1. |
