Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-11-29
2001-08-14
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S623000, C204S404000, C205S775500
Reexamination Certificate
active
06275050
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to detecting corrosion in metal junctions, and, in particular, relates to detecting corrosion in metal junctions where corrosion affects current flow.
Corrosion is a significant problem for both military and commercial systems. Corrosion can cause structural failure of the corroded member. In electronic equipment, corrosion can distort or disrupt the electrical signal that propagates through a metallic connector, that is, a conductor susceptible to corrosion. Corrosion is also a significant source of Electromagnetic Interference (“EMI”) that can disrupt nearby systems. Damaging levels of corrosion can be hard to detect because the corrosion may be inaccessible or imperceptible on visual inspection. The effect of corrosion on electrical transmission is generally not linear.
The failures caused by corrosion in the path of an electrical signal are often intermittent. Factors such as temperature, humidity, amount and type of use, mechanical stresses on the point of corrosion—all influence both the degree of corrosion and its effect on current flow. The rate of growth of corrosion also depends on what is corrosive in the surrounding medium. Thus, even if one knows that corrosion is present, neither the rate of growth of corrosion nor the time a system will start to fail can be predicted.
Current techniques that address corrosion fall into two categories. The first includes techniques that detect corrosion directly. The chief technique is visual inspection. X-rays can also detect the presence of foreign material, sometimes including corrosion, in metal junctions.
Visual inspection may be inadequate to identify adverse degrees of corrosion on metallic structures. The corrosion can be inaccessible, or it can be invisible to the naked eye. In electromagnetic systems even slight surface corrosion at metallic junctions can impede current flow. When one disconnects at these junctions to inspect them, friction of the corroded spots against each other, or against an uncorroded piece, can temporarily remove the corrosion. This process explains why turning a battery in its slot can make the battery work better temporarily. The corrosion on the battery (or on the connections to it) was invisible, but the corrosion limited current flow until the surfaces rubbed together. Similarly, in other electromagnetic systems, the corrosion could easily be erased temporarily when connectors are unmated prior to inspecting them. For a technique to be effective at identifying corrosion that inhibits current flow, it must detect corrosion prior to unmating the connectors.
X-ray methods are expensive, and the foreign materials they detect in metal junctions may not be corrosion. Further, x-ray methods are not practical for routine testing of field equipment.
The second category includes techniques that attempt to detect the adverse effects caused by corrosion. Two techniques predominate. A Loop Resistance Tester (“LRT”) can detect very small resistance in electrical cables and connectors. A Time-Domain Reflectometer (“TDR”) can detect discontinuities in electrical conductors, some of which could be caused by severe corrosion.
A LRT cannot identify corrosion as the cause of increased resistance in the current path. Since corrosion problems are often intermittent, resistance measurements generally fail to identify a corrosion problem as it develops.
Thus there exists a need for apparatus and methods for detecting non-intrusively the presence of corrosion in metal to metal junctions.
OBJECTS AND SUMMARY OF THE INVENTION
Therefore, one object of the present invention is to provide apparatus and method to specifically detect the existence of corrosion in metal junctions.
Another object of the present invention is to provide apparatus and method that are non-intrusive to specifically detect the existence of corrosion in metal junctions.
Briefly stated, the present invention provides apparatus and method to detect corrosion in metal junctions. Corroded metal junctions are usually discovered by visual inspection. The present invention detects corrosion in metal junctions when it is not visually apparent. A corroded metal junction acts as a nonlinear device. It generates harmonics and other nonlinear products (such as intermodulation) of any signals applied to the junction. The presence of relatively high level harmonics and/or intermodulation products indicates directly that corrosion has occurred. To detect corrosion in a metal junction, one couples a fundamental frequency signal (f
0
) into the junction and tests for harmonics of that frequency, especially the third harmonic. Harmonic frequency signals that are relatively large (i.e., above the harmonics generated by the testing system) indicate the presence of corrosion. Measurements to determine if a metal junction is corroded are performed without disturbing the junction.
In an extension of this technique to detect corrosion, couple two (or more) signals into the junction being evaluated and check the output signal for intermodulation products of these signals. Such intermodulation products indicate corrosion on the junction.
According to an embodiment of the invention, apparatus to detect corrosion in a metal-to-metal junction comprises: a signal generator capable of generating at least one electrical signal; a signal injector for injecting the at least one electrical signal into said metal-to-metal junction; a detector effective for detecting the amplitude of the at least one electrical signal, wherein the signal has passed through the metal-to-metal junction, the detector further comprises: an ability to detect the amplitude of at least one selected electrical output signal produced by the non-linear property of a corroded metal-to-metal junction, wherein the presence of a detectable selected electrical output signal amplitude produced by the non-linear property indicates the presence of corrosion; and a signal receiver for receiving the detected amplitude of the at least one electrical output signal from the metal-to-metal junction and for receiving the detected amplitude of at least one selected electrical output signal produced by the non-linear property of a corroded the metal-to-metal junction.
According to a feature of the invention, apparatus to detect corrosion in a metal-to-metal junction comprises a signal generator effective for generating multiple electrical signals each of which has a different frequency; a signal injector for injecting the multiple electrical signals into the metal-to-metal junction; a detector effective for detecting the amplitude of the multiple electrical signals, where the signals have passed through said metal-to-metal junction, the detector further comprises: an ability to detect the amplitude of at least one selected output harmonic of the multiple electrical signals, the selected output harmonic produced by the non-linear property of a corroded metal-to-metal junction, wherein the presence of a detectable output harmonic indicates the presence of corrosion; and a signal receiver for receiving the detected output amplitude of the multiple electrical signals upon being passed-through the metal-to-metal junction and for receiving the detected amplitude of at least one selected output harmonic of the multiple electrical signals produced by the non-linear property of a corroded the metal-to-metal junction.
According to another feature of the invention, a method for detecting corrosion in a metal-to-metal junction comprises the steps of: generating at least one electrical signal; injecting the at least one electrical signal into the metal-to-metal junction; detecting the output amplitude of the at least one electrical signal, wherein the step of detecting further comprises: detecting the amplitude of at least one electrical output signal produced by the non-linear property of a corroded metal-to-metal junction, wherein the presence of a detectable output signal amplitude produced by the non-linear property indicates the presence of corrosion; a first step of receiving t
Born Frank H.
Dodge John E.
Duff William G.
Reynolds Laurence J.
Turner, Jr. Arlie G.
Brown Glenn W.
Burstyn Harold L.
Mancini Joseph A.
The United States of America as represented by the Secretary of
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