| 摘要 |
1358292 Control of motors F K PREIKSCHAT 22 June 1971 [13 July 1970] 29079/71 Heading H2J [Also in Division G3] A process variable is controlled by a motor driven actuator, e.g. an arrangement for restricting a tube to regulate fluid flow or a continuously running, variable speed, conveyer. (See Division G3.) Two motor control systems are described. In Fig. 3, the motor 34 is a synchronous stepping motor which moves one step per cycle of an A.C. supply. Its direction depends on whether L1 or L2 is energized directly, the other winding being energized via capacitor C6, and this is determined by the triggering of triac TR1 or TR2. Triggering is effected by the respective transistors Q1 ... Q6 for a time dependent upon the difference between a control signal B and a current feedback signal via R17 (which depends only upon the control signal, not the motor speed or current). The difference is applied to an integrating operational amplifier A4. As the motor runs the control signal (process error) diminishes until the transistors turn off. LS1 is a manual override switch and LS2 a limit switch. In Fig. 4, the armature of a D.C. motor is energized for rotation in a direction and at a speed determined by the instant of triggering a triac TR3 in series with an A.C. supply. This is effected in the required half cycle by transistors Q7, Q9 or Q8, Q10. Q7, Q8 emitters are connected to the output of an integrating operational amplifier A5 whose input is the difference between a control signal B and the back e.m.f. of the motor via R37. The base of these transistors receive a biased sine wave from potential divider R38, R41, C9, R43 and their conduction thus depends upon the magnitude and polarity of the output of A5 relative to this sine wave. LS3 are limit switches; L3 is the motor field. The circuits have a dead band when TR3 is not triggered, to ensure that the motor is not energized in both directions at once. |
