Method of and means for spacing control of plasma arc torch

Abstract

A method of automatically maintaining a selected spacing for a plasma arc torch from a workpiece is disclosed which takes advantage of the fact that at any given setting of a plasma arc power supply the current in the arc varies inversely and the voltage across the arc varies directly in relation to the spacing of the plasma arc torch from the workpiece. According to such method, the current and voltage of the power supply for the torch are sensed in operation, a signal representative of each comparable to the other is generated and one of such signals is inverted with respect to the other of such signals. The signals are then summed with each other and with a third comparable selectively adjustable signal and the difference signal is used to control the spacing of the torch from the workpiece. A preferred embodiment of the control means for practicing the invention is described as included in a commercial plasma arc apparatus and includes means for shutting down the apparatus if an extreme condition occurs such as reaching the end of the workpiece or extinguishment of the arc. Means for protecting the control means during ignition of the arc, for enabling manual control of the plasma arc torch and for interfacing between the control means according to this invention and prior art control means are disclosed.