| 摘要 |
<p>1,142,166. Timed switching in electric circuits. MALLORY TIMERS Ltd. May 16, 1966 [July 1, 1965], No. 21583/66. Heading G3T. A step advance mechanism for use in a time sequence switch comprises a motor 11, a rectifier circuit 20, an electronic switch 34, a timing circuit 21 and a cam 37 driven by the motor. The cam 37 is mounted on a shaft 19 and the periodicity of the timing circuit may be adjusted by rotating a shaft 17 of a variable resistor 18. On completion of each period of the timing circuit a unijunction transistor 30 is triggered and supplies a pulse to the electronic switch 34 which comprises a silicon controlled rectifier. The transistor 34 therefore conducts and is held in this state by a capacitor 27. The resistance of circuit 22 thus decreases allowing a large current to flow through and switch on the motor 11. The rotation of the cam closes a switch 36 and the transistor 34 ceases to conduct. The motor, however, continues to rotate until the cam allows the switch 36 to reopen and stop the motor in readiness for the next cycle. Instead of the variable resistor 18 a switch contacting a network of fixed and/or variable resistors may be used or the time interval may be made dependent on the resistance of a temperature sensor.</p> |
