Development Of Cable Fault Tester Based On Time Variable Gain Pulse Reflection Method

The low voltage pulse reflection method is the main method for testing and locating the communication cable fault.The principle is to emit the square wave to the cable,through a certain algorithm to measure the distance between cable failure points.However,due to the natural characteristics of the communication cable like,small diameter,high attenuation,so that the detection distance of cable lines is limited.In addition,due to the changes of frequency components have effect on electromagnetic waves attenuation and propagation speed.So the reflected wave-forms of long distance fault point have the distortion and the starting point is very hard to find,making the accuracy and reliability of fault detection are reduced.So the purpose of this paper is to give countermeasures on how to improve the test distance and accuracy of fault line.This paper presents a wavelet time varying gain test method,or the gain of variable gain amplifier(VGA)is dynamically adjusted with time.The adjustable gain and time of the amplifier are according with certain functional relations,so that the instrument can get the same amplitude test waveforms through all the test length.Relatively to the traditional pulse testing method,the method avoids signal saturation distortion with high gain,also able to overcome the limitations of gain can't be too large by long-distance testing and eliminate signal trailing phenomenon caused by saturation distortion.Using this method,we can easily to understand and adjust the wave-forms and further raise the testing distance.This paper also develops a vision of integration of the traditional pulse test method and time variable gain method,also in the hardware and software discuss how to switch the two methods at any time.When the testing distance is close,we can use the fixed gain of traditional pulse test method.For long testing distance,we can choose adjusting gain with distance from time variable gain test method.So that the instrument can better adapt to different fault location,improve the test length and test accuracy.