Nonlinearity detection using fault-generated second harmonic

Test apparatus for determining the existence of nonlinearity faults in a conductor under test, which conductor is connected by probes to the test apparatus, characterized by:

• (a) a test signal generator having a composite test signal node and means to provide at the composite test signal node a composite test signal including a direct current signal of known characteristics and an alternating current signal of known characteristics including a fundamental frequency, and having a fundamental frequency node for providing the fundamental frequency;
• (b) connecting means, for connecting the composite test signal node to a device under test in such fashion that nonlinearity anomalies in the device under test provide fault signals including second harmonics of the fundamental frequency;
• (c) test signal filtering means, connected to said composite test signal node, to pass only the second harmonic signal from the device under test;
• (d) frequency doubling means connected to the fundamental frequency node of said test signal generator to produce second harmonic test signals;
• (e) phase detection means having inputs including an input connection from said filtering means for accepting second harmonic signals from the device under test and having further input means for accepting the second harmonic test signals from said frequency doubling means, for detecting fault signals separate from conductor signals differing in phase;
• and
• (f) output means for providing an indication of fault in the device under test.