Apparatus for providing regulated direct current to magnetizing coils for non-destructive magnetic testing

A current regulating apparatus for providing regulated direct current within a predetermined range for non-destructive magnetic testing and detecting of welding defects in pipe, comprising:

• a. variable transformer means for receiving current from an alternating current power source and providing varying output alternating current levels;
• b. means for converting the alternating current output from said variable transformer means into direct current;
• c. detecting means for detecting the magnitude of direct current from said means for converting, said detecting means including:
• 1. means for establishing a predetermined critical range of current magnitudes to a range of current magnitudes between lower and higher limits which are sufficiently low to maintain a high signal-to-noise ratio for detecting defects and sufficiently high to permit detection of welding defects in the pipe while the pipe is moving at variable speeds;
• and
• 2. control means for forming a control signal when the direct current magnitude is at either said lower or higher limit of the predetermined critical range of current magnitudes;
• d. means responsive to the control signal formed by said control means for adjusting the direct current from said variable transformer means until the direct current magnitude is within the predetermined critical range to thereby regulate the direct current to the predetermined critical range;
• and
• e. magnetizing coil means electrically connected to said converting means for receiving the regulated direct current therefrom to thereby form a magnetic field for non-destructive magnetic testing and detecting of welding defects in pipe.