Answer 7—After you've identified the leads to each winding with the ohmmeter, feed an asymmetric signal, such as a sawtooth wave, from the signal generator into one winding, again using a resistor if necessary to limit the current. Use a dual-channel oscilloscope to compare the "primary" voltage (even though you might not be driving the actual primary at this point) with the voltages and polarities of the other windings. Regardless of which lead on each winding you start with, you'll be able to identify the correct tap sequence and the relative winding ratios and phases in one pass.

Contributor: Dave Tweed

Published August 2003