| 摘要 |
1279838 Control of D.C. motors CABLEFORM Ltd 12 Oct 1970 [28 Oct 1969] 52679/69 Heading H2J A motor, which has an armature A associated with diode D1 and field winding F, is supplied from battery B through thyristor switch S, a unit, responsive to pulses of armature voltage, starting to count from zero each time a fieldreversing switch FR moves into or through an "off" position. A relay RLA restricts the motor current when the counter operates between zero and a predetermined number, but permits full current at other times. The pulses of armature voltage are applied to a network R4, Z1, which ensures constant amplitude pulses. The counter comprises small capacitor C1, large capacitor C2, diode D2, and resistor R3 so that the charge on capacitor C2 increases with each pulse until diode D3 breaks down and transistor T1 conducts to energize relay RLA. The capacitor C2 is discharged through transistor T2, the transistor T1 being held conductive through resistor R1. Contacts RLA2 then change over the control voltage for the switch S from a low range to a high range, ensuring that the motor is stopped before a high range of current is applied. The relay RLA is de-energized when the switch FR passes through the "off" position, the control range being changed to low values suitable for braking. |
