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This two-part paper presents precise measurements of the ion currents passing between the torch and work piece of the preheat flame of an oxyfuel cutting torch as a means for replacing contemporary sensing suites. Part II presents the results of a novel spinning disc Langmuir probe technique to construct spatially resolved measurements of the flame's ion density distribution. A bias voltage is applied to a .254mm diameter wire protruding from a spinning disc, and as the wire is passed through the flame, the measured currents (on the order 10uA) are collected. The process is repeated with incremental wire depths in the flame to construct the entire planar cross-sectional ion density. Measurements reveal intense ion concentrations in the inner cones that rapidly decay by an order of magnitude in the surrounding flow. The outer cone forms a hollow cylinder of weak ion concentration that declines with distance from the inner cones in a manner consistent with recombination. 

This two-part paper presents precise measurements of the ion currents passing between the torch and work piece of the preheat flame of an oxyfuel cutting torch as a means for replacing contemporary sensing suites. Part I shows that the current-voltage characteristic of the flame exhibits sharp discontinuities common to semi-conductors that we study in various configurations including preheat, pierce, cut, and loss-of-cut. Standoff measurements are made by applying a sinusoidal current signal between the torch and work piece while the resulting voltage amplitude is an indication of flame resistance. Uncertainties are estimated to range from 0.5mm to 1mm (.02in to .04in). Signals for ready-to-pierce and precursors for loss-of-cut are also produced due to the generation of secondary ions from chemical activity at the work piece.