Current-voltage characteristic curves for a pair of probes inserted in a low plasma concentration zone surrounding the welding arc column have been measured.
The probes made of 1.6 mm φ tungsten wire with holders fixed on the welding torch were set on the right and left side of the arc column.
The results obtained are as follows:
(1) In a case of the welding arc running along the centre line of the groove, the probe current has the same value for both probes at any probe voltage. Then the characteristic curves for the pair of probes coincide with each other.
Otherwise, the running arc deviates left or right of the centre line of the groove. The characteristic curves have different forms intersecting near the floating potential.
(2) The deviation of welding arc from the centre line of the groove is detectable indirectly by a difference in the probe current, if any, between the two probes, because the relation of the deviation of the welding arc to the difference in the probe current has certain regularity, which can be depended on as a sign of the positional deviation of the arc column.
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