| 摘要 |
1,225,838. Control of D.C. motors. ETABS. JOUAN. 4 June, 1968 [2 June, 1967], No. 26611/68. Heading H2J. [Also in Divisions G2-G3] A series-field D.C. motor 1 is started by the control circuit shown, in which a thermistor 10 in series with the motor controls a relaxation oscilator III whose trigger pulses determine the firing instants of silicon controlled rectifiers 3, 4 in the motor power supply, the progressive decrease in thermistor resistance with increasing motor current providing a corresponding increase in speed up to the normal running value set by a variable resistor 16. The oscillator comprises a uni-junction transistor 12 controlling a pulse transformer 13, 14, 15 and being controlled by a transistor 11 to whose base is applied a signal from the thermistor 10 (via members 18, 19) and a signal from the A.C. part of the motor supply (via change-over switch 32 and members 34, 35). In a starting operation the switch 32 is arranged to be in its upper position when A.C. mains switch 33 is closed, so that a voltage is applied to the base of transistor 11 to block it and prevent the firing of rectifiers 3, 4. Switch 32 is now changed over to unblock transistor 11 and allow the oscillator to transmit trigger pulses corresponding to the thermistor resistance, which produces minimum conduction of the rectifiers 3, 4. Thereafter a positive feedback action produces heating of the thermistor, decrease in its resistance, further increase in current and so on until the normal running speed has been reached. The motor may be stopped by changing the switch 32 back to its upper (transistor blocking) position. A currentlimiting resistor 9 is provided and speed control may be effected (see Divisions G2-G3) by feeding to transistor 11 an additional signal representative of the motor speed. |
