Resonant circuit with two partial inductances

Claim 1

In a control circuit for measuring the distance between a workpiece and a sensing element which is formed as inductance and is part of a resonant circuit as a frequency-determining element whereby the frequency variations of the resonant circuit for producing voltage and/or current changes which are proportional to a distance are connected to a measuring circuit, the improvement being said resonant circuit having at least two partial inductances, one of said partial inductances being represented by said sensing element and the other of said partial inductances being a stationary resonant circuit coil arranged at a distance from said sensing element and in immediate influence sphere of the workpiece, in combination therewith, wherein sensing element is part of a cutting torch and said workpiece is metallic, and said sensing element being arranged concentrically around the cutting torch beam, said sensing element being connected to a switching-off device connected to torch control means for inactivating the cutting action of the cutting torch, a capacitance diode being connected to said sensing element, an auxiliary voltage source being connected to said sensing element and said capacitance diode for adjusting a capacitance value to be determined, and said workpiece being connected to the axuiliary voltage source in such a way that when said sensing element and workpiece touch each other the voltage at the capacitance diode and its capacitance value is variable.