| 摘要 |
1,203,061. Automatic current control. FMC CORP. Sept.11, 1967 [Sept.14, 1966], No.41410/67. Heading G3R. [Also in Division H2] A circuit for triggering a silicon controlled rectifier comprises a uni-junction transistor TR1, the two bases B1, B2 being coupled across a A.C. supply L10, a Zener diode Z2 being interposed between the A.C. supply and the transistor TR1 so as to convert the A.C. supply into pulses and a phase shifter Fig.3 being included in the connections to the A.C. supply so as to advance the phase of the supply to TR1 relative to that feeding the main thyristors. The phase shifter Fig.3 thus ensures that the main thyristor can be made conductive over a full half cycle even when feeding an inductive load. As described, the main thyristor PSCR-A controls the current in an inductive load formed by a vibratory conveyer feeding a crusher. The current of the three-phase crusher motor is monitored by transformer CT and after rectifying at D10...D13 is used to control the conductivity of a transistor TR2 which in turn controls the firing angle of uni-junction transistor TR1 which provides pulses of appropriate phase to control thyristor CSCR-A which in turn fires power thyristor PSCR-A in such a way as to keep the load constant on the crusher motor. A further alternative control utilizers a permanent magnet Fig.2 fixed to the moving part of the vibratory conveyer adjacent a stationary coil MP57 the output of which is rectified at D21...D24 and used to control the output of a magnetic amplifier comprising high retentivity magnetic rings 47, 48 supplied with A.C. from secondary windings S8 and providing partial half cycles, the negative of which is removed by diode D20, and the leading edge of which is a function of the conveyer output as determined by winding MP57. These pulses are fed to terminal H in Fig.1 so as to control the triggering phase of TR1 and hence that of the main thyristor PSCR-A. The minimum feedrate is set by potentiometer RH1 across a stabilized D.C. supply. Various manual controls RH5... RH9 may be switched in to terminals F, H. An independent load may be controlled by a further main thyristor PSCR-B. |
