For AC-GTAW of Aluminum Alloys,... most of the significant advances focus on new ways to manipulate the AC wave form. These advances largely result from using inverter-based power sources, which allow a welder to extend the balance control, adjusting output frequency and independently controlling current in each AC halt cycle. New inverter-based GTAW machines extend EN balance control, allowing duration from 50 to 90 percent. Making the EN portion of the cycle last longer:* Allows greater weld penetration* May permit increasing travel speeds by as much as 20 percent.* Narrows the weld bead* May permit using a smaller-diameter tungsten electrode to more precisely direct the heat or deposit a narrower weld bead

This article is the story of our experiences developing and running the iWRS AI control system.The Early YearsBy 1995, the AI controls team had been working with several groups in the Crew and Thermal Systems Division (CTSD), building Al control systems in support of CTSD''s investigations in advanced life support (ALS). In 1995, they put a man in an airlock linked to a 10-foot-diameter chamber full of wheat (Laifook and Ambrose 1997). For 15 days, the man lived, worked, and exercised in the chamber as the wheat crop took in his carbon dioxide and produced oxygen for him. The control system--our first for ALS--monitored and provided caution and warnings for the climate and nutrient environment of the wheat crop.

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