Methods and systems relating to AC current measurements

A device comprising:

• a dual stage current transformer coupled to an input port to receive an input signal comprising three magnetic cores, a primary winding, a first secondary winding, and a second secondary winding;
• a processing circuit to generate an output signal in dependence upon an AC input signal coupled to the processing circuit and a DC signal coupled to a correction input of the processing circuit, the processing circuit having a pair of AC inputs configured to receive the AC input signal, wherein a first resistor and a second resistor are coupled in series across the pair of AC inputs;
• the first resistor coupled across only the first secondary winding generating a first voltage in response to the AC input signal applied to the primary winding;
• the second resistor coupled across only the second secondary winding to add a compensating voltage to the first voltage, the compensating voltage generated in response to the AC input signal applied to the primary winding;
• a DC magnetic sensor coupled to a first magnetic core of the plurality of magnetic cores to generate the DC signal proportional to a DC magnetic field within the dual stage current transformer;
• and
• a flux compensation winding coupled to a second magnetic core of the plurality of magnetic cores to generate a magnetic flux to reduce the DC magnetic field within the dual stage current transformer.

A device comprising:

• a dual stage current transformer comprising three magnetic cores, a primary winding configured to receive an AC input signal to be measured, a first secondary winding, and a second secondary winding;
• and
• a DC magnetic sensor coupled to a first magnetic core of the plurality of magnetic cores to generate a DC output signal proportional to a DC magnetic field within the dual stage current transformer, and
• a processing circuit configured to process the DC output signal and an AC output signal from the dual stage current transformer to generate a corrected measurement of an AC signal;
• applied to the primary winding;
• wherein
• a first resistor and a second resistor are disposed in series across a pair of inputs of the processing circuit to generate the AC output signal from the dual stage current transformer;
• the first resistor has a first end coupled to a first end of the first secondary winding and a second end to a second end of the first secondary winding;
• the second resistor has a first end coupled to a first end of the second secondary winding and a second end to a second end of the second secondary winding;
• and
• the second end of the first resistor and the first end of the second resistor are the ends joining the first resistor and second resistor together and the only direct connection between the first secondary winding and the second secondary winding.

A current comparator comprising:

• a dual stage transformer comprising three magnetic cores;
• a primary winding wound around all three magnetic cores;
• a first secondary winding wound around all three magnetic cores;
• a second secondary winding wound around a middle magnetic core of the three magnetic cores;
• a DC magnetic sensor coupled to an outer magnetic core of the three magnetic cores and coupled to a magnetic field generated in dependence upon a first current within the primary winding and a second current within the first secondary winding;
• and
• a first resistor and a second resistor coupled in series with each other;
• wherein
• the first resistor is only coupled across the first secondary winding;
• the second resistor is only coupled across the second secondary winding;
• and
• the primary and first secondary windings are wound around the three magnetic cores directly without a magnetic shield disposed between any of the three magnetic cores, the primary winding, and the first secondary winding.

A current comparator based sensor comprising:

• three magnetic cores;
• a primary winding wound around all three magnetic cores for connecting to an electrical circuit;
• a first secondary winding wound around all three magnetic cores;
• a second secondary winding wound around a middle magnetic core of the three magnetic cores;
• a DC magnetic sensor sensing a magnetic field within an outer magnetic core of the three magnetic cores generated in dependence upon a first current within the primary winding and a second current within the first secondary winding;
• a control circuit configured to generate and apply a magnetization current to at least one of the primary winding and a tertiary winding wound around the three magnetic cores, wherein the magnetization current sequentially cycles the three magnetic cores to saturation in opposite directions;
• and
• a measurement circuit coupled to at least the first secondary winding configured to determine timing information relating to the cycling of the magnetic core and establishing a magnetization field strength therefrom and the current flowing in the primary winding due to the electrical circuit.