Time-Domain Reflectometry (TDR) Square and Pulse Test Signals Comparison

Abstract

It is very important to ensure operational reliability of measurement systems. Every shutdown causes loses. The longer diagnostics and repair of the measurement system last, the higher are the loses and they often build up faster the longer the system is not working. The damage can be caused by many things and all of them have to be checked to be absolutely sure that the line is working correctly. This is where TDR reflectometry comes to the aid. It allows detecting, estimating and defining the type of the cable disruption. Disruptions can occur because of natural aging processes, environmental influence, but also because of careless excavation works taking place where the cables are laid underground or other situations like intentional vandalistic behaviors. In this work the theory of the coaxial cable construction and its connection with the used method was shown. Basics of TDR reflectometry and commonly used test signals were presented. Additionally, other methods of cable length measurements were mentioned. Measurements were conducted using suggested test stand consisting of oscilloscope and function generator. Screenshots from the oscilloscope were added to show typical view of the measurement signal. Discussion about existing errors was performed and comparison of two types of test signals, square and pulse, was conducted. Errors caused by each used signal and ease of their usage were taken under consideration too. It has also been checked if acquired data is statistically different depending on method. Lastly conclusions about uses of discussed method, signals and their limitations were expressed.