| 摘要 |
1279746 Control of A.C. motors SULZER BROS Ltd 5 Feb 1970 [6 Feb 1969] 5601/70 Heading H2J An induction motor 2 drives a valve 4 and is provided with reversing switches 13v, 13r, under the control of push-buttons 16v, 16r. A current-measuring network 11 comprises transformers 21 and provides a signal c, for switching off the motor when the valve reaches a limiting position or encounters an obstruction. A trigger 30 develops an output signal d when the signal c exceeds a reference signal e. An AND gate 31v produces signal fv when it receives the signal d as well as a command signal av for opening the valve. A store 32v is triggered by the signal fv to remove a signal gv from AND gate 18v whereby switch 33v turns off the main switch 13v. The store 32v is returned to its basic position by a command signal ar for closing the valve, thus preventing re-starting of the motor in the previous direction after being switched off by the network 11. Conflicting switching-on signals for both directions of rotation are prevented, a closure command signal hr being inverted and applied to gate 18v. An OR gate 36 receives directional command signals hv, hr, and produces signal m which is applied to delay device 35 having output k forming one input to gate 18v. In this manner, power can be restored to the motor after switching-off only after a certain delay. The signal m is also applied to a further delay device 37 which produces pulse p for making transistor 29 conductive and reducing the signal c by means of the divider 27, 28. This sets a higher current-limit for the motor during the starting period. |
