Defect Location for Cables Based on Frequency Modulated Continuous Wave

The broadband impedance spectroscopy (BIS) method, a commonly used method for locating cable defects, is a method based on measuring the amplitude of reflected signals at different frequencies. However, noise may seriously interfere with the amplitude measurement and cause errors. Therefore, this article presents a novel method based on the frequency modulated continuous wave (FMCW) to precisely locate defects in a cable. This method measures the frequency difference between incident and reflected electromagnetic waves in a coaxial cable within a bandwidth of tens of MHz. The anti-noise interference performance of frequency difference measurement is better than that of amplitude measurement. The noise power that the FMCW method can withstand is 7 dB greater than that of the BIS method. The experimental results show that FMCW method is effective for locating and detecting defects. For the minor defects prepared in this experiment, the effective location range of FMCW is greater than 800 m, while BIS is less than 700 m. The defect location deviation of the FMCW method is better than 0.5% and the locating accuracy of the FMCW method is not inferior to that of the BIS method. FMCW method can be a very sensitive defect locating tool usable for real cable systems.