NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
TDR Using Autocorrelation and Varying-Duration PulsesIn an alternative to a prior technique of time-domain-reflectometry (TDR) in which very short excitation pulses are used, the pulses have very short rise and fall times and the pulse duration is varied continuously between a minimum and a maximum value. In both the present and prior techniques, the basic idea is to (1) measure the times between the generation of excitation pulses and the reception of reflections of the pulses as indications of the locations of one or more defects along a cable and (2) measure the amplitudes of the reflections as indication of the magnitudes of the defects. In general, an excitation pulse has a duration T. Each leading and trailing edge of an excitation pulse generates a reflection from a defect, so that a unique pair of reflections is associated with each defect. In the present alternative technique, the processing of the measured reflection signal includes computation of the autocorrelation function R(tau) identical with fx(t)x(t-tau)dt where t is time, x(t) is the measured reflection signal at time t, and taus is the correlation interval. The integration is performed over a measurement time interval short enough to enable identification and location of a defect within the corresponding spatial interval along the cable. Typically, where there is a defect, R(tau) exhibits a negative peak having maximum magnitude for tau in the vicinity of T. This peak can be used as a means of identifying a leading-edge/trailing-edge reflection pair. For a given spatial interval, measurements are made and R(tau) computed, as described above, for pulse durations T ranging from the minimum to the maximum value. The advantage of doing this is that the effective signal-to-noise ratio may be significantly increased over that attainable by use of a fixed pulse duration T.
Document ID
20080048025
Acquisition Source
Kennedy Space Center
Document Type
Other - NASA Tech Brief
Authors
Lucena, Angel
(NASA Kennedy Space Center Cocoa Beach, FL, United States)
Mullinex, Pam
(NASA Kennedy Space Center Cocoa Beach, FL, United States)
Huang, PoTien
(NASA Kennedy Space Center Cocoa Beach, FL, United States)
Santiago, Josephine
(NASA Kennedy Space Center Cocoa Beach, FL, United States)
Mata, Carlos
(ASRC Aerospace Corp. United States)
Zavala, Carlos
(ASRC Aerospace Corp. United States)
Lane, John
(ASRC Aerospace Corp. United States)
Date Acquired
August 24, 2013
Publication Date
December 1, 2008
Publication Information
Publication: NASA Tech Briefs, December 2008
Subject Category
Electronics And Electrical Engineering
Report/Patent Number
KSC-12856
Distribution Limits
Public
Copyright
Public Use Permitted.
No Preview Available