Methods and apparatus for detecting leakage current

Patent metadata

Field	Value
Publication number	US-11167366-B2
Application number	US-202016744747-A
Country	US
Kind code	B2
Filing date	Jan 16, 2020
Priority date	May 8, 2017
Publication date	Nov 9, 2021
Grant date	Nov 9, 2021

Abstract

An example apparatus to monitor a welding-type system includes: a test signal generator configured to output a test signal to a monitored circuit; and a lock-in amplifier configured to: receive a reference signal based on the test signal; measure a leakage current in the monitored circuit based on the reference signal; and generate an output signal representative of the leakage current.

First claim

What is claimed is:

1. An apparatus to monitor a welding-type system, comprising:
a test signal generator configured to output a test signal to a monitored circuit; and
a lock-in amplifier configured to:
receive a reference signal based on phase-shifting the test signal;
measure a leakage current in the monitored circuit based on the reference signal; and
generate an output signal representative of the leakage current.

2. The apparatus as defined in claim 1 , further comprising a comparator configured to compare the output signal to a threshold to determine whether at least a threshold leakage current is present in the monitored circuit.

3. The apparatus as defined in claim 2 , further comprising a threshold generator configured to determine the threshold based on the test signal.

4. The apparatus as defined in claim 2 , wherein the comparator is configured to indicate that the monitored circuit is coupled to the test signal generator and the lock-in amplifier when at least the threshold leakage current is present.

5. The apparatus as defined in claim 1 , further comprising a comparator configured to compare the output signal to a threshold to determine whether less than a threshold leakage current is present in the monitored circuit.

6. The apparatus as defined in claim 5 , wherein the comparator is configured to indicate a current leakage fault is present in the monitored circuit when at least the threshold leakage current is present.

7. The apparatus as defined in claim 5 , further comprising a threshold generator configured to determine the threshold based on the test signal.

8. The apparatus as defined in claim 1 , wherein the test signal generator and the lock-in amplifier are capacitively coupled to the monitored circuit via a power supply.

9. The apparatus as defined in claim 1 , further comprising a control circuit configured to enable or disable a power supply in response to the output signal.

10. The apparatus as defined in claim 1 , wherein the monitored circuit is at least one of an inductive heating cable configured to be inductively coupled to a workpiece to be heated, a resistive heating cable, a welding cable configured to provide welding current to a welding torch, a plasma cable configured to provide current to a plasma torch, or an extension cable configured to be coupled between a power supply and the inductive heating cable, the resistive heating cable, the welding cable, or the plasma cable.

11. The apparatus as defined in claim 1 , further comprising a feedback cable configured to be coupled to a workpiece to be worked on using the welding-type circuit and configured to provide the leakage current to the lock-in amplifier.

12. An apparatus to monitor a welding-type system, comprising:
a test signal generator configured to output a test signal to a monitored circuit, wherein the test signal generator is configured to generate the test signal at a first frequency different than a second frequency output by the power supply to the monitored circuit; and
a lock-in amplifier configured to:
receive a reference signal based on the test signal;
measure a leakage current in the monitored circuit based on the reference signal; and
generate an output signal representative of the leakage current.

13. A method, comprising:
generating the test signal at a first frequency different than a second frequency output by a power supply to a monitored circuit;
outputting a test signal from a test signal generator to the monitored circuit;
receiving, at a lock-in amplifier, a reference signal based on the test signal;
measuring, with the lock-in amplifier, a leakage current in the monitored circuit based on the reference signal; and
generating, with the lock-in amplifier, an output signal based on the leakage current.

14. The method as defined in claim 13 , further comprising comparing, with a circuit, the output signal to at least one of a first threshold or a second threshold to determine at least one of: 1) whether at least an upper threshold leakage current is present in the monitored circuit; or 2) whether less than a lower threshold leakage current is present in the monitored circuit.

15. The method as defined in claim 14 , further comprising generating at least one of the first threshold or the second threshold based on the test signal.

16. The method as defined in claim 14 , further comprising outputting a signal indicating that the monitored circuit is coupled to a test signal generator and the lock-in amplifier when at least the lower threshold leakage current is present.

17. The method as defined in claim 14 , further comprising outputting a signal indicating a current leakage fault is present in the monitored circuit when at least the upper threshold leakage current is present.

18. The method as defined in claim 13 , further comprising enabling or disabling a power supply in response to the output signal.

19. The method as defined in claim 13 , wherein the monitored circuit is at least one of an inductive heating cable configured to be inductively coupled to a workpiece to be heated, a resistive heating cable, a welding cable configured to provide welding current to a welding torch, a plasma cable configured to provide current to a plasma torch, or an extension cable configured to be coupled between a power supply and the inductive heating cable, the resistive heating cable, the welding cable, or the plasma cable.

Assignees

• Illinois Tool Works

Inventors

• Salsich Anthony

Classifications

• B23K9/0953 Primary

  using computing means · CPC title

• B23K10/006

  Control circuits therefor · CPC title

• B23K11/257

  the measured parameter being an electrical current · CPC title

• G01R31/52

  Testing for short-circuits, leakage current or ground faults · CPC title

• B23K13/08

  Electric supply or control circuits therefor · CPC title