Plasma insensitive height sensing

1. A method for determining a distance between a first piece and a second piece, using a processor or an electronic circuit, the method comprising:

directing a laser beam or a plasma arc onto a first or a second piece;

generating a source electrical signal by switching between two or more DC voltage levels, the source electrical signal establishing a source DC offset having a value different from zero;

applying, using the processor or electronic circuit, at one or both of the first and second pieces, the source electrical signal;

measuring, using the processor or electronic circuit, at one or both of the first and second pieces, a measured electrical signal, the measured electrical signal including a measured DC offset; and

determining the distance between the first and second piece, based on the measured electrical signal by eliminating a plasma resistance using the measured DC offset and the source DC offset.

2. The method of claim 1 , wherein the first piece comprises a torch component and the second piece comprises a workpiece.

3. The method of claim 2 , wherein the torch component comprises a laser nozzle.

4. The method of claim 1 , wherein determining the distance comprises:

calculating a gap capacitance between the first piece and the second piece based on the measured electrical signal; and

determining the distance based on the gap capacitance.

5. The method of claim 4 , wherein determining the gap capacitance is based on: a frequency of the electrical signal, a magnitude of the electrical signal, a magnitude of the DC offset, or any combination thereof.

6. The method of claim 4 , wherein determining the distance comprises:

using a calibration data set to determine the distance, the calibration data set comprising data values associated with: the frequency of the electrical signal, a magnitude of the electrical signal, a magnitude of the DC offset, or any combination thereof.

7. The method of claim 1 , wherein the electrical signal comprises: a current signal or a voltage signal.

8. The method of claim 1 , wherein measuring the electrical signal comprises passing the electrical signal through a high pass filter, the high pass filter attenuating the DC offset.

9. The method of claim 8 , wherein measuring the electrical signal comprises measuring the DC offset by passing the electrical signal through a low pass filter.

10. The method of claim 1 further comprising determining a plasma resistance between the first piece and the second piece based on the measured electrical signal.

11. The method of claim 1 , wherein the source electrical signal comprises: a current source signal or a voltage source signal.

12. The method of claim 1 , wherein the source electrical signal is a square wave.

13. The method of claim 1 further comprising passing the source AC signal through a source band-pass filter before applying the source electrical signal to one or both of the first and second pieces, the source band-pass filter including a cut-off frequency above a fundamental frequency of the source electrical signal.

14. The method of claim 1 , wherein the step of determining the distance comprises:

using a calibration data set to determine the distance, the calibration data set comprising data values associated with: a frequency of the electrical signal, a magnitude of the electrical signal, a magnitude of the DC offset, a magnitude of the source electrical signal, a magnitude of the source DC offset, or any combination thereof.

15. The method of claim 1 , wherein measuring the electrical signal comprises measuring the electrical signal at a position after a known electrical element, the known electrical element being located between the position and a source of the source electrical signal.

16. A system for determining a distance between a first piece and a second piece, the system comprising:

a switched-signal generator that generates a source electrical signal by switching between two or more DC voltage levels, the source electrical signal establishing a source DC offset having a value different from zero;

a source that applies, at one or both of the first and second pieces, the source electrical signal;

a measuring device that measures, at one or both of the first and second pieces, a measured electrical signal, the measured electrical signal including a measured DC offset; and

a signal processing device that determines the distance between the first and second pieces, based on the measured electrical signal and the source electrical signal by eliminating a plasma resistance using the measured DC offset and the source DC offset.

17. The system of claim 16 , wherein the first piece comprises a torch component and the second piece comprises a workpiece.

18. The system of claim 16 further comprising:

a high pass filter that attenuates the DC offset; and

a low pass filter that passes the DC offset.

19. The system of claim 16 , wherein the switched-signal generator comprises a switch coupled to two voltage levels.

20. The system of claim 16 further comprising a source band-pass filter that passes the source signal from the switched-signal generator to the source, the source band-pass filter including a cut-off frequency above a fundamental frequency of the source electrical signal.

21. The system of claim 16 , wherein the measuring device measures the electrical signal at a position of a known electrical element, the known electrical element being located between the position and the source.

22. A system for performing a capacitive distance measurement between a first piece and a second piece, the system comprising:

signal generator means for generating a source electrical signal by switching between two or more DC voltage levels, the source electrical signal establishing a source DC offset having a value different from zero;

source means for applying, at one or both of the first and second pieces, the source electrical signal;

measuring means for measuring, at one or both of the first and second pieces, a measured electrical signal, the electrical signal including a measured DC offset;

signal processing means for determining the distance between the first and second pieces, based on the measured electrical signal by eliminating a plasma resistance using the measured DC offset and the source DC offset.

23. The system of claim 22 , wherein the first piece comprises a torch component and the second piece comprises a workpiece.

24. The system of claim 22 further comprising:

high-pass filtering means for attenuating the DC offset; and

low-pass filtering means for passing the DC offset.

25. An apparatus for determining a distance between a first piece and a second piece, the apparatus comprising a processor or electronic circuit that performs the method steps:

directing a laser beam or a plasma arc onto a first or a second piece;

generating a source electrical signal by switching between two or more DC voltage levels, the source electrical signal establishing a source DC offset having a value different from zero;

applying, using the processor or electronic circuit, at one or both of the first and second pieces, the source electrical signal;

measuring, using the processor or electronic circuit, at one or both of the first and second pieces, a measured electrical signal, the measured electrical signal including a measured DC offset; and

determining the distance between the first and second piece, based on the measured electrical signal by eliminating a plasma resistance using the measured DC offset and the source DC offset;

the apparatus further comprising a computing system including a back-end component, a middleware component, or a front-end component.