| 摘要 |
1,144,931. Automatic control of speed. MULLARD Ltd. March 10, 1966, No. 10569/66. Heading G3R. In a system in which the speed of a D.C. motor 1 is kept constant by regulating its power supply in response to the back e.m.f. on line 7, compensation for variations in the field 2 current is provided by a control element 6 which alters the response of the system when the field current, monitored at 3, changes above a predetermined value. The speed control circuit is as described in Specification 1, 144, 762 and comprises a thyristor whose firing angle is determined by the conduction of a transistor 12. This is modified by the conduction of transistor 6, which depends upon the amount that the voltage tapped at 3 exceeds that of a Zener diode 5. Resistors 15, 17 and capacitors 16, 18 are for smoothing purposes. In an alternative embodiment the connection between transistors 6 and 12 includes a second Zener diode which conducts if the field current falls to a large extent, thereby causing the thyristor to be triggered late and so avoiding the large motor current which would otherwise occur. |
