Non-contact reflectometry system and method
Non-contact reflectometry for testing a signal path is described. The technique includes using capacitive coupling to inject a test signal into the signal path and extract a response signal from the signal path. Reflectometry techniques are used to determine characteristics of the signal path from the response signal. The technique is compatible with performing testing of a signal path carrying an operational signal.
1. A non-contact reflectometry system for testing a signal path comprising:
a) an injection probe comprising a first conductive body shaped to create electrical capacitance between the first conductive body and the signal path when placed in near proximity to the signal path and configured to inject a test signal into the signal path via capacitive coupling to the signal path when placed in near proximity to a first point on the signal path;
b) an extraction probe comprising a second conductive body shaped to create electrical capacitance between the second conductive body and the signal path when placed in near proximity to the signal path and configured to extract a response signal from the signal path via capacitive coupling to the signal path when placed in near proximity to a second point on the signal path; and
c) a reflectometry instrument operatively coupled to the injection probe and to the extraction probe and configured to generate the test signal, accept the response signal, and determine a signal path characteristic from the response signal.
2. The system of claim 1 , wherein the injection probe and extraction probes are each a capacitive coupler.
3. The system of claim 2 , wherein the capacitive coupler comprises a substantially cylindrical conducting body configured for placement substantially surrounding a signal path.
4. The system of claim 3 , wherein the cylindrical conducting body is flexible.
5. The system of claim 2 , wherein the capacitive coupler comprises a flexible, spiral element configured for wrapping around a signal path.
6. The system of claim 2 , wherein the capacitive coupler comprises an extended substantially linear element configured for placement substantially parallel to a signal path.
7. The system of claim 2 , wherein the capacitive coupler comprises a clamp element configured to clamp around the signal path.
8. The system of claim 1 , wherein the injection probe and the extraction probe are provided by a single capacitive coupler.
9. The system of claim 1 , wherein the reflectometry instrument is chosen from the group of instruments consisting of a time domain reflectometer, a frequency domain reflectometer, a standing wave reflectometer, a sequence time domain reflectometer, a spread spectrum reflectometer, a mixed signal reflectometer, and a noise domain reflectometer.
10. The system of claim 1 , wherein the signal path characteristic is the location of an anomaly in the signal path.
11. The system of claim 1 , further comprising an amplifier coupled between the reflectometry instrument and the injection probe to amplify the test signal before injection into the signal path.
12. The system of claim 1 , further comprising an amplifier coupled between the extraction probe and the reflectometry instrument to amplify the response signal after extraction from the signal path.
13. A method of non-contact reflectometry testing of a signal path comprising:
a) generating a test signal;
b) capacitively coupling to the signal path by placing a first conductive body in near proximity to the signal path to create capacitive between the first conductive body and the signal path to inject the test signal into the signal path at a first point;
c) capacitively coupling to the signal path by placing a second conductive body in near proximity to the signal path to create capacitive between the second conductive body and the signal path to extract a response signal from the signal path at a second point; and
d) determining a characteristic of the signal path from the response signal using reflectometry techniques.
14. The method of claim 13 , wherein the first point is located at the beginning of a wire.
15. The method of claim 14 , wherein the second point is located at the end of the wire.
16. The method of claim 13 , wherein the first point and the second point are substantially collocated.
17. The method of claim 13 , wherein the signal path is carrying an operational signal.
18. The method of claim 13 , further comprising compensating for frequency response effects caused by capacitively coupling.
19. The method of claim 13 , wherein determining a characteristic of the signal path further comprises compensating for known characteristics of the signal path.
20. The method of claim 13 , further comprising filtering the response signal.