How Pasd Works

The AMMTIAC Quarterly, Volume 1, Number 2 3 INTRODUCTION Detecting and locating insulation defects in wiring systems is a nontrivial challenge. Ideally, the diagnostic should be nondestructive, capable of detecting a variety of insulation defects, such as cracking, chaffing, and abrasion, and be able to locate the defect accurately to reduce potential inspection and maintenance costs. The diagnostic should also have a low rate of false detection. Complicating this quest is the nature of complex wiring systems. For example, aircraft wiring systems are comprised of harnesses containing periodically bound single wire pairs* which create highly non-uniform impedance characteristics due to the varying distance between wire pairs. Insulation defects may also be physically small, resulting in an immeasurable change in the impedance at the defect site. These characteristics tend to render impedance measuring or conventional time-domain-reflectometry (TDR)† concepts ineffective. Other approaches such as partial discharge or DC breakdown techniques may detect some types of insulation defects, but cannot locate them in complex impedance wiring systems (Figure 1).