| 摘要 |
The present invention features a system and method for determining an overload condition in either DC or AC motors. The system of the invention is non-invasive, in that the impedance of or the current in the line is not affected by the system measurement of the line current being drawn by the motor. A pair of current sensing toroids having variable permeability is placed about the lead-wire(s) of the motor, without interrupting the current path in the line. The sensors each consists of metallic glass that changes its permeability as a function of an external magnetic field. Current in the lead-wire(s) creates a magnetic field. The inductance of the sensors varies in direct proportion to the magnetic field. A controller starts the motor. As the motor starts, the pattern of load current drawn by the motor is measured and stored in memory. The sensors are connected to an oscillator circuit, whose output frequency is proportional to the current drawn by the motor load. The output of the oscillator circuit is connected to a microprocessor controller for determining the current profile of the electric motor being monitored and controlled.
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