| 摘要 |
AN ARC RETRACT CIRCUIT FOR USE IN A PLASMA ARC SYSTEM WITH A TORCH (10) HAVING AN ELECTRODE (30) AND A NOZZLE (34), A POWER SUPPLY (20) FOR PROVIDING A D.C. CURRENT, A POWER CIRCUIT (12) FOR CONNECTING THE POWER SUPPLY (20) ACROSS SAID ELECTRODE (30) AND A WORKPIECE (40) TO BE CUT , A POWER SWITCH (72) FOR CONNECTING THE NOZZLE (34) TO THE POWER SUPPLY WHEN IN A CLOSED CONDITION DEFINING A PILOT ARC MODE OF THE OPERATION AND FOR DISCONNECTING THE NOZZLE (34) FROM THE WORKPIECE (40) WHEN IN AN OPEN CONDITION DEFINING A CUT MODE OF OPERATION, AMPLIFIER MEANS (100) FOR REGULATING SAID POWER SUPPLY (20) TO A FIRST SET CURRENT (1P) WHEN IN THE PILOT ARC MODE AND A SECOND SET CURRENT (1C) WHEN IN THE CUT MODE, AND AN ARC RETRACT CIRCUIT (80) FOR SHIFTING THE POWER SWITCH (72) FROM THE OPEN CONDITION TO THE CLOSED CONDITION , WHICH ARC RETRACT CIRCUIT (80) INCLUDES CURRENT SENSING MEANS FOR CREATING A FIRST SIGNAL REPRESENTING THE ACTUAL CURRENT APPLIED BY THE POWER SUPPLY (20)TO THE POWER CIRCUIT (12) , MEANS (224) FOR CREATING A SECOND SIGNAL (222) REPRESENTATIVE OF A CURRENT LEVEL BELOW THE SECOND SET CURRENT (1C), AND SWITCH OPERATIONS MEANS (220,124) FOR CLOSING THE POWER SWITCH (72) WHEN THE FIRST SIGNAL (104) IS SUBSTANTIALLY EQUAL TO THE SECOND SIGNAL (222).MOST ILLUSTRATIVE DRAWING:FIGURE 1
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