Abstract: An apparatus (10) for controlling the height of one or more cutting torches (12) above a workpiece (14). The apparatus (10) senses the actual height of the torch (12) above the workpiece (14) and compares the actual height with a desired reference height. The apparatus (10) moves the torch (12) up or down until the actual height and reference height are substantially equal. The apparatus (10) is operable in a manual mode, a semi-automatic mode or a fully automatic mode allowing an operator to select a desired degree of control during a cutting operation.

Abstract: A torch height sensing apparatus (10) is provided for generating information representative of the spacing between a cutting torch (12) and an associated workpiece (14). The apparatus (10) drives a preselected current from the torch (12) through the torch flame to the workpiece (14) so that electrons flow from the workpiece (14) through the flame to the torch (12). The output current biases the flame into the linear region of the preselected voltage-current characteristic at a positive torch (12) to workpiece (14) current. Biasing the torch (12) for positive current flow from the torch (12) to the workpiece (14) insures that flame height sensing occurs in the positive linear region where the sensitivity is greatest due to the availability of thermally emitted electrons at the workpiece.