Abstract: An electrical device such as an electrical contactor interfaces at least one alternating current transformer having an output providing a signal proportional to changes in alternating current and includes at least one filter for filtering the output signal of the transformer. Each of the filters have an input connected to the transformer and an output having a signal proportional to the transformer output signal and inversely proportional to selected frequencies of the alternating current. The electrical device also has means for determining a value related to the alternating current using the output of each of the filters. The filter may have a resistor and a capacitor for filtering the transformer output signal in order that the filter is a low-pass filter. Alternatively, the filter may be a band-pass filter.

Abstract: In an induction motor drive controlled by SCR devices connected in the AC power supply phase lines of the motor, a plurality of channels establish, on a common input to a digital gate pulse generator of the SCR's, various signals occurring in the course of the motor drive operation. These signals relate to motor operating modes, such as soft start tripping, current limit. A central large scale integrated (LSI) chip responds digitally to such common input so as to establish the required firing angle at any instant and for any situation.

Abstract: An energy-saving controller for a multiphase AC induction motor controls the average voltage supplied to the motor windings by the use of a pair of back-to-back SCR's of opposite polarity connected to each winding. The conduction of the SCR's is varied in response to a signal derived from the voltage across each pair of SCR's corresponding to motor slip, the line voltage, and the current flow through each motor winding.

Abstract: A multi-phase motor controller for controlling voltage and power expended by a multi-phase motor comprises a sensing stage for detecting power factor angle, a feedback amplifier stage for comparing the power factor angle with a desired power factor angle, and a control stage for controlling voltage and power expended by the multi-phase motor in accordance therewith. Other features of the motor controller include a current limiting circuit for limiting "in-rush" current during "start up" of the motor controller, a current trip circuit for implementing "instantaneous trip" and "timed trip" capabilities upon detection of corresponding "overload" conditions, and a phase-loss circuit for automatically disabling operation of the motor upon detection of "phase-loss". A further embodiment of the motor controller includes a lead network, connecting the feedback amplifier stage to the control stage, for enhancing the stability of operation of the motor controller.

Abstract: A three-phase shift network includes a single transistor which controls phase shift by introducing a variable resistance into the network as determined by a D.C. control signal supplied to the transistor. The three-phase signals generated from the phase shift network undergo pulse shaping and are subsequently introduced into an opto-coupled pulse amplifier. The amplifier drives large SCR devices, connected as a load.