Abstract:

A mathematic model of aerospace wire insulation faults and its corresponding simulation model are presented based on time domain reflectometry (TDR) in this article. The characteristic impedances and reflection coefficients are calculated as they vary with the insulation thickness of aerospace wires. Transmissions in a wire are simulated for pulse wave and step wave respectively. The influences of characteristic impedance of a wire and the rise time of incident wave on TDR are studied experimentally. The results show that the rate of reflection coefficient increases with the increase of frayed wire insulation. For the same amount of insulation frayed among the wires, the reflection coefficient of thin insulated wire is larger and its insulation fault is easier to detect than that in other wires. Step wave is better in TDR than pulse wave. Short circuits can be easily found on TDR wave. But the detection of insulation fault by TDR wave is difficult unless the characteristic impedance of a wire is reduced to a certain value. For the detection of small insulation faults of a wire, the shorter the rise time of incident wave is, the more the TDR wave reflects the fault characteristics, but the sampling frequency must be high due to the narrowed reflection pulse. The width of the reflection pulse is increased and its amplitude reduced as the rise time of incident wave delays, which may to some extent be good for the detection of insulation faults.

Key words: aerospace wire, time domain reflectometry, insulation, rise time of incident wave, characteristic impedance