| 摘要 |
A detection unit ( 8 ) is disposed for detecting the magnitudes of f<SUB>1 </SUB>and f<SUB>2 </SUB>frequency components of a composite signal which is passed through a center electrode cable ( 4 ). A detecting signal generating unit ( 9 ) generates a detecting signal corresponding to a gap between a nozzle ( 5 ) and a workpiece ( 6 ) from the magnitudes of the f<SUB>1 </SUB>and f<SUB>2 </SUB>frequency components of the composite signal, which are detected by the detection unit ( 8 ). As a result, even if plasma occurs in the gap between the nozzle ( 5 ) and the workpiece ( 6 ), the gap can be detected with a high degree of precision.
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