Siemens-Allis, Inc.

Conrad F Williams

Frederick A Stich

John C Culligan

Carl J Laplace, Jr

A method and a device for monitoring instantaneous electrical parameters of a power distribution system under load utilizing digital control means. An analog signal equivalent to such a parameter is sensed and rated down for processing by solid state components. This signal is converted into a binary coded digital signal having n digits. A plurality of digital signals is sampled and squared values with a format of 2n digits are derived from each sample. The squared values of one sampling period are accumulated to a sum value composed of 2n+m digits and the square root comprising n+k digits of the sum is taken. This value is rescaled to a true root mean square value by performing k left shifts as an accurate measurement result. The core of such device is represented by a microcomputer with built-in analog-to-digital converter.

Method and apparatus for monitoring instantaneous electrical parameters

A system for controlling current flow to the actuating coil of a contactor or the like. A solid state switch is provided for gating current flow to the coil, and operated by an oscillator stage. A time delay causes the oscillator to operate at a high duty cycle when power is initially applied, allowing a relatively high current to flow to the contactor coil to operate the contacts. Subsequently the control causes the oscillator to operate at a low duty cycle, wherein the solid state switch passes a significantly lower current flow to the coil to maintain the contacts in position.

Time ratio control circuit for contactor or the like

A control for an AC circuit protection system which is capable of monitoring either single phase or polyphase current flow. The composite current envelope is periodically sampled and the sample values converted into digital form. Succeeding current signals are tested to determine whether they deviate from previous samples by a given amount. Non-deviant samples increment a first counter, while deviant samples increment a second counter. The ratio of the counts is used to recognize current imbalance and control system parameters are adjusted to compensate for the imbalance.

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New Orleans, LA, United States of America

Conrad F Williams