Abstract An alternative to the conventional weld penetration sensing methods in pulsed gas tungsten arc welding is proposed for implementation at manufacturing sites. The fluctuation amplitude of arc voltage in the peak duration (ΔUk) reflects the weld penetration status in a single-weld spot; a fully penetrated weld spot is obtained in the step-by-step welding process when the abrupt change of ΔUk (denoted as ΔU’k) is above the threshold (1.50 V herein). A full penetration control system that employs ΔU’k as the feature signal for step-by-step pulsed gas tungsten arc welding can be easily installed at the manufacturing sites.