Patent GB-710784-A (GB)
Title: Improvements in or relating to arrangements for controlling electrically-driven machines
IPC: B04B11/04
Filed: 1951-12-12
Abstract: 710,784. Centrifugal separators. SIEMENS SCHUCKERTWERKE AKT.-GES. Dec. 12, 1951 [Dec. 13, 1950; Aug. 20, 1951], No. 29126/51. Class 23 [Also in Group XXXVII]  Relates to the control of the electric drive of sugar centrifuges and the like means of a tachometer generator which is responsive to the speed of the driving motor and is adapted to provide control signals so that the machine is driven at a number of different set speeds at the respective phases of the working cycle. Actuation of a manual push-button switch energizes a relay SI and connects the A.C. motor driving a centrifuge to a low frequency supply source, a relay SPI being energized at the same time to change over the syrup-separating device until a mechanically operated contact kI is opened. When the motor speed reaches 220 r.p.m., tachometercontrolled contacts BI, BII, close and a magnetic valve MVI is energized to initiate the filling operation which is terminated by means of a manually operated switch which also causes the motor to be connected to a higher frequency supply, the relay SI being opened and the relay SII closed. In addition, a magnetic valve MVII is energized to close the massecuite slide valve, whereupon a. mechanical contact F, is operated to disconnect the valve MVII and energize a time delay relay ZI. Upon termination of the time delay, the magnetic valve MVII is re-energized so that the feed filling shoot is raised. A contact C is closed when the motor reaches a speed of 700 r.p.m. and the magnetic valve MVIII responds to provide washing water for a period determined by a time delay relay ZII. At the end of this interval, a relay SPII is energized so that the syrup-separating device is changed to the position for the discharge of the mother liquor until a mechanical switch k2 breaks the circuit of the relay. When the driving motor reaches a speed of 1200 r.p.m. contacts DI, DII are closed to energize a rotor relay LI for shortcircuiting a starting resistance, and to operate a time delay relay ZIII which is set in accordance with the' required centrifuging time. At the end of this period, a magnetic valve MVIV responds and serves to withdraw air from the vessel controlling the water feed for a period set by a relay ZIV. 'In addition. the relay SII is opened and the relay SI closed to re-connect the driving motor to the low frequency supply, the rotor resistance being again placed in circuit. When the motor speed falls to 500 r.p.m. a contact E operates to open relay SI and close relay SIII for regenerative braking, a signal lamp LII being energized during this period. The contact BI opens at a motor speed of 110 r.p.m. to de-energize relay SIII, and the signal lamp is extinguished to indicate that emptying can commence. A mechanical contact G is actuated by the emptying device so that contact A serves to control the relay SI in such a manner that the motor speed during emptying varies between 30 and 70 r.p.m. The driving motor may have either a slip ring or short-circuited rotor, and, in the latter case, the speed is controlled by resistors or chokes in the stator circuit. The output of the tachometer generator is rectified. if necessary, and smoothed, the relay controlled by this generator being of the weak current type and their sensitivity adjusted by means of resistors or saturable reactors..