In GTAW, the high-frequency may be set so that it behaves differently for DC and AC. Which pairing is correct?

• A. It is kept on continuously for DC and automatically cuts off after the arc is established for AC
• B. Automatically cuts off after the arc is established for DC and is kept on continuously for AC
• C. Is kept on continuously for both DC and AC
• D. Automatically cuts off; goes off after one minute

Answer: (B)

High-frequency is used to strike the TIG arc and can be left on or turned off depending on the polarity. For direct current, once the arc is established, the high-frequency is typically cut off to avoid continuous RF energy feeding back into the welding circuit and to reduce interference with equipment. Direct current maintains the arc with steady polarity, so ongoing ionization from high-frequency isn’t necessary.

For alternating current, the arc tends to extinguish at each zero-crossing as the current reverses. Keeping the high-frequency on continuously helps re-ignite the arc at each half-cycle and keeps the arc stable as the polarity switches.

So the pairing that matches this behavior is: high-frequency is cut off after arc establishment for DC and kept on continuously for AC. The other patterns don’t reflect the practical use of high-frequency in TIG welding, where DC benefits from turning HF off after start and AC benefits from keeping HF on to sustain arc during polarity changes.