GB946581A - Improvements in or relating to electric control systems - Google Patents

Abstract

946,581. Automatic speed control. LANCASHIRE DYNAMO ELECTRONIC PRODUCTS Ltd. March 17,1960 [March 17, 1959], No.9221/59. Heading G3R. [Also in Division H2] In a speed control system for an electric motor M a transistor Tr1 is arranged to generate driving pulses at twice mains frequency under the control of rectifiers MR8 and MR9, the amplitude of the pulses being regulated by a transistor Tr2 in accordance with an error signal obtained by comparing the rectified output from a tachometer generator G with a reference voltage derived from a Zener diode Zn1. The driving pulses are transmitted to transistors Tr3, Tr4 and Tr5 and associated delay circuits whereby pulses having a phase delay with respect to the mains voltage are delivered from transistor Tr5, which phase delay depends on the error or deviation. These phase controlled pulses are amplified by a further transistor Tr6 feeding pulse transformers T1, T2 whose primary windings are connected in parallel so as to produce two separate coincident current pulses for firing two full-wave connected silicon controlled rectifiers Sr1 and Sr2 supplying direct current to the armature circuit or motor M. Each rectifier Sr1 and Sr2 is thus fired with a variable delay so that the current supplied to the motor is regulated by the amplitude of the pulses occurring at the collector of Tr1.