Torch operation interlock device
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United States of America Patent
Stats
-
Apr 29, 1986
Grant Date -
N/A
app pub date -
Jul 20, 1983
filing date -
Jul 20, 1983
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
The present invention minimizes shock hazard in using a touch start plasma torch. The resistance between the torch tip and the workpiece is compared to a predetermined value set by estimating the resistance between a person's hand to ground under the most unfavorable conditions. In the preferred embodiment, such comparison is performed by supplying an AC voltage to a resistor in series with a torch tip, the resistor having a resistance equal to the predetermined value. The peak voltage at a point in the circuit connection between the resistor and torch tip is sensed and if such peak is less than half of the peak voltage of the AC voltage supplied to the resistor and torch tip, the resistance between the torch tip and ground is less than the predetermined value and a control signal will be generated. A relay will switch on the power supply supplying high voltage between the cathode and the workpiece only when it receives the control signal indicating that the resistance between the torch tip and ground is below the predetermined value.
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