The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 29, 1986
Filed:
Jul. 20, 1983
Raymond G Wilkins, Hanover, NH (US);
Bruce O Hatch, Lebanon, NH (US);
Thermal Dynamics Corporation, West Lebanon, NH (US);
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.