Development of a Cable Shield Tester for In-Situ Hardness Surveillance of Cables

Abstract

A conceptual model of a shielded cable tester, capable of measuring the surface transfer impedance of cables installed on an aircraft or other system, has been experimentally demonstrated. The objective of this program was to develop a shielded cable tester to measure the electromagnetic performance of shielded cables while they were installed on aircraft. In addition, the tester had to use methods that were simple to perform and to interpret, produce data for predicting the rate of degradation and be a credible measurement directly related to electromagnetic hard­ ness. The tester was required to have sufficient sensitivity so that cables could be evaluated that had transfer impedances that are a factor of two less than those associated with a typical double braid. This would require measuring transfer resistances of 2 mS2 and transfer mutual inductances of 30 pH. This corre­ sponds to a shielding effectiveness of about 95 dB at 10 MHz. The initial design analysis led to an approach in which the cable surface transfer impedance was measured by inductively injecting a C.W. current on the outside of the cable shield (with both ends attached to the aircraft), measuring the ratio of the voltage on the conductors to the shield current, calculating the shield resistance and mutual induc­ tance and comparing the measured values to a hardness acceptance criteria. Measurements using brass calibration samples showed that sensitivity require­ ments were met with a factor of five margin. Measure­ ments made on a wide variety of cables demonstrated that the electromagnetic quality of the cable could be quantitatively evaluated in spite of variations in length and load impedances.