Patent ID: 6720749
Filing Date: 2004-04-13
Classification: H02H

Abstract:
Motor protector apparatus for controlling the state of energization of a three-phase motor through a three-phase power source comprising:first and second toroid current sensors for producing an AC sine wave corresponding to current in first and second power lines of the three-phase power source, a circuit having a 5V rail supply for converting the sine waves of the first and second toroid current sensors to separate square waves amplified close to the 5V rail supply voltage, a microprocessor, inputting the separate square waves to respective channels of the microprocessor for adding the two square waves to provide an ANDed square wave and determining the phase relationship between the two square waves as an indication of current in the third power line of the three-phase source, and a relay for causing energization and de-energization of the motor, the relay controlled by the microprocessor, the microprocessor de-energizing the relay when the duty cycle of the ANDed square wave is less than a selected value.