Differential leakage current measurement for heater health monitoring

1. A system for monitoring a leakage current in a heater connected to a heater power supply by a power cable, the power cable comprising a first power lead conducting an inlet current defining an inlet current direction and a second power lead conducting an outlet current defining an outlet current direction, the outlet current direction being opposite to the inlet current direction, the system comprising:

a differential current electromagnetic sensor, comprising:

a magnetic core defining a center region, wherein:

the magnetic core includes an air gap; and

the power cable is configured to pass through the center region one or more times; and

a magnetic flux sensing device positioned in the air gap, the magnetic flux sensing device configured to provide a magnetic flux signal that is representative of a magnetic flux across the air gap;

wherein:

the magnetic flux across the air gap is indicative of a difference between the inlet current and the outlet current; and

the difference between the inlet current and the outlet current defines the leakage current.

2. The system of claim 1 , further comprising an interface circuit configured to:

provide electrical power to the magnetic flux sensing device;

receive the magnetic flux signal from the magnetic flux sensing device, the magnetic flux signal indicative of the magnetic flux across the air gap; and

produce an output signal that is representative of the magnetic flux across the air gap.

3. The system of claim 1 , wherein the heater power supply provides a direct current to the heater.

4. The system of claim 2 , wherein:

the magnetic flux sensing device is a Hall effect sensor;

the interface circuit provides a bias voltage to the Hall effect sensor; and

the output signal is a voltage representative of the magnetic flux across the air gap.

5. The system of claim 2 , wherein:

the heater power supply provides an alternating current to the heater;

the magnetic flux across the air gap is an alternating magnetic flux; and

the interface circuit is configured to receive an alternating magnetic flux signal from the magnetic flux sensing device.

6. The system of claim 2 , wherein:

the magnetic flux sensing device is a magnetoresistive sensor; and

the output signal is a resistance value representative of the magnetic flux across the air gap.

7. The system of claim 1 , wherein the power cable forms two or more turns around the magnetic core, thereby passing through the center region two or more times, respectively.

8. The system of claim 1 , wherein the heater comprises:

a resistive heating element;

electrical insulation surrounding the resistive heating element; and

a metallic sheath surrounding the electrical insulation;

wherein:

the first current flows into the resistive heating element to provide heat;

the second current flows out of the resistive heating element;

the leakage current flows from the resistive heating element to the metallic sheath; and

the first current is equal to the sum of the second current and the leakage current.

9. The system of claim 1 , wherein the magnetic core is a toroidal core, a square core, or an EI-core.

10. The system of claim 1 , further comprising a polarity selection circuit configured to applying to the heater either a first polarity heater voltage or a second polarity heater voltage.

11. The system of claim 1 , wherein the power cable passes through the center region once.

12. The system of claim 1 , further comprising a clamp fixture, wherein:

the magnetic core further includes a split, thereby defining a first core piece and a second core piece; and

the clamp fixture comprises:

a first clamp piece, the first core piece and the magnetic flux sensing device disposed on the first clamp piece;

a second clamp piece, the second core piece disposed on the second clamp piece; and

a hinge assembly, configured to align the first clamp piece with the second clamp piece, wherein the magnetic core forms a magnetic circuit when the clamp fixture is in a closed position.

13. The system of claim 12 , wherein the clamp fixture further comprises a locking mechanism, the locking mechanism configured to hold the clamp fixture in the closed position.

14. The system of claim 1 , wherein:

the heater is disposed on an aircraft component; and

the aircraft component disposed on an external portion of an aircraft.

15. The system of claim 14 , wherein:

the heater is disposed on an aircraft component;

the aircraft component disposed on an external portion of an aircraft; and

the heater is configured to control ice formation on the aircraft component.

16. A method of monitoring a leakage current in a heater connected to a power supply by a power cable, the power cable comprising a first power lead conducting an inlet current defining an inlet current direction and a second power lead conducting an outlet current defining an outlet current direction, the outlet current direction being opposite to the inlet current direction, the power cable traversing a center region of a magnetic core, the magnetic core including an air gap that is configured to accommodate a magnetic flux sensing device positioned therein, the magnetic flux sensing device configured to provide a magnetic flux signal that is representative of a magnetic flux across the air gap, the magnetic flux indicative of a difference between the inlet current and the outlet current, the method comprising:

supplying electrical power from a power source to a heater via the power cable,

wherein:

the inlet current flows through the first power lead; and

the outlet current flows through the second power lead;

providing electrical power to the magnetic flux sensing device;

receiving the magnetic flux signal from the magnetic flux sensing device, the magnetic flux signal indicative of the magnetic flux across the air gap; and

producing an output signal that is representative of the magnetic flux across the air gap;

wherein the difference between the inlet current and the outlet current defines a leakage current.

17. The method of claim 16 , wherein:

the power source provides direct current to the heater;

the magnetic flux sensing device is a Hall effect sensor;

providing electrical power to the magnetic flux sensing device comprises providing a bias voltage to the Hall effect sensor; and

the output signal is a voltage representative of the magnetic flux across the air gap.

18. The method of claim 16 , wherein the power cable forms two or more turns around the magnetic core, thereby passing through the center region two or more times, respectively.

19. The method of claim 16 , wherein:

the power cable passes through the center region once;

the magnetic core further includes a split, thereby defining a first core piece and a second core piece; and

the clamp fixture comprises:

a first clamp piece, the first core piece and the magnetic flux sensing device disposed on the first clamp piece;

a second clamp piece, the second core piece disposed on the second clamp piece; and

a hinge assembly, configured to align the first clamp piece with the second clamp piece, wherein the magnetic core forms a magnetic circuit when the clamp fixture is in a closed position.

20. The method of claim 16 , wherein the magnetic core is a toroidal core, a square core, or an EI-core.