Nonlinearity detection using fault-generated second harmonic

• US 4,496,900 A
• Filed: 04/30/1982
• Issued: 01/29/1985
• Est. Priority Date: 04/30/1982
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Di Stefano, Thomas H., Halperin, Arnold
• Primary Examiner(s): Krawczewicz, Stanley T.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US06/373,318
• Time in Patent Office: 1,005 Days
• Field of Search: 29/574, 324/51, 324/52, 324/64, 324/71 R
• US Class Current: 324/71.1
• CPC Class Codes: G01N 27/20 Investigating the presence of flaws
• CPC Class Codes: G01R 31/281 Specific types of tests or tests for a specific type of fault, e.g. thermal mapping, shorts testing G01R31/2818 takes precedence
• CPC Class Codes: Y10T 29/49004 including measuring or testing of device or component part

Abstract

The tester and method for nondestructively detecting nonlinearity faults in conductors includes the application of a composite AC and DC drive signal to the device under test in such manner that nonlinearities in the device under test produce fault signals including second harmonics, due to local changes of resistance caused by ohmic heating. Electronic filters are used to select out and amplify the second harmonic only, eliminating the direct current and fundamental frequency components of the initial test pulse, plus third and subsequent harmonics. The filtered second harmonic signals from the device under test are then phase-compared to a phase-shifted second harmonic signal produced by a frequency doubler from the test signal generator oscillator to cancel out the second harmonic signals from the good conductor; the remaining phase anomaly signals control a threshold detector remaining to provide fault indication.

Claims

1. 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.

2. Test apparatus according to claim 1, further characterized by:

(g) a continuity detector connected to said composite test signal node; and

(h) disabling means connected to said continuity detector and to said test signal filtering means to prevent passage of spurious test signals when continuity is not made.

3. The method of testing an electrical conductor for nonlinearity faults, characterized by:

(a) probing the device under test with a composite signal including a DC signal and an AC signal at a characteristic test signal fundamental frequency, whereby nonlinearity faults in the conductor under test generate second harmonic nonlinearity signals at a first phase relationship, and whereby resistance characteristics of the conductor under test itself generate relatively large second harmonic conductor signals;

(b) phase-sensitive-demodulating such fault-generated second harmonic nonlinearity signals using a predetermined standard signal at second harmonic frequency and phase shift to null the second harmonic conductor signals and identify as faulty a device under test having second harmonic nonlinearity signals differing from the standard signal.

4. The method of claim 3, further characterized by:

(c) disabling the detecting of spurious second harmonic signals during periods except when continuity has been established.

5. The method of claim 3, further characterized in that the characteristic test signal fundamental frequency of said composite test signal is selected within the range of optimum frequencies above the frequency at which second harmonic signals caused by heating and cooling along the conductor length diminish because of integration, and below the frequency at which second harmonic signals caused by heating and cooling of defects of the expected type begin to diminish.