METHOD AND APPARATUS FOR MEASURING DETERIORATION IN A SHIELDED CABLE BY HIGH FREQUENCY PULSE INJECTION

• US 3,803,484 A
• Filed: 11/30/1972
• Issued: 04/09/1974
• Est. Priority Date: 11/30/1972
• Status: Expired due to Term

• Current Assignee: Robert F. Gray
• Original Assignee: Robert F. Gray
• Inventors: Gray, Robert F.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/310,732
• Time in Patent Office: 495 Days
• Field of Search: 324/51,52,54,58.5A,58A,127
• US Class Current: 324/544
• CPC Class Codes: G01R 31/08 Locating faults in cables, transmission lines, or networks
• CPC Class Codes: G01R 31/58 Testing of lines, cables or conductors testing of electric windings G01R31/72

Abstract

A generator injects a current pulse to a coaxial driver that is slipped over one end of a shielded cable undergoing test. The current pulse is divided between the cable shield and the cable bundle. A capacitive trough is positioned along an intermediate length of the cable, adjacent the cable shield, and serves as a high-frequency current return. Remaining low frequency current is returned through the total length of the cable. Instrumentation is provided to compare the ratio of the internal bundle current to the external shield current with known standards, over a frequency spectrum thereby permitting the detection of connector and cable deterioration.

Claims

1. A method for testing a shielded cable consisting of the steps of:

subjecting the shield of the cable and the Internal conductors thereof to an input current pulse;

measuring the conductor current amplitude as a function of frequency;

measuring the input current amplitude as a function of frequency;

forming a ratio relationship between conductor current and input current at particular frequencies thereby defining the cable transfer function; and

comparing the transfer function of the tested cable with that of known standard cable, deviations between the transfer functions being determinative of cable deterioration.

2. A system for testing a shielded cable having connectors at opposite ends thereof, the system comprising:

means for generating an input current pulse;

conductor means for conducting the input current pulse to at least one internal conductor and the cable shield via a first connector;

means for separately measuring the input current and the current flowing through the internal conductor as a function of frequency to enable the determination of the ratio of internal conductor current to input current for particular frequencies thereby defining a cable transfer function to be compared with a standard cable function; and

means for completing a return circuit path from the internal conductor and the shield, via a second connector to the generating means;

deviations between the transfer functions being indicative of cable deterioration.

3. The structure of claim 2 wherein the cable includes a plurality of internal conductors to form a cable bundle, and further wherein means are provided to short circuit the individual conductors at both ends of the bundle to enable parallel conduction of current through the individual conductors.

4. The structure as defined in claim 2 wherein a high frequency driver is coaxially mounted over a cable end, the driver being connected between the generator and the cable shield.

5. The structure of claim 2 together with a capacitive trough located adjacent an intermediate length of the cable shield;

and means for connecting the trough to the generator to complete a high frequency current bypass to the generator, the remaining low frequency current being conducted along the entire length of the shield and the conductor.

6. The subject matter defined in claim 2 wherein the cable is looped while undergoing testing to improve the wide frequency bandwidth of current conduction through the cable.