Technology Study And Instrument Development For Online Predicting Structure Return Loss Of Data Cable

Non-homogeneity of impedance is one of important factors for transmission properties of data communication cable. Structure Return Loss (SRL) is an important parameter to periodical non-homogeneity of impedance along length, which is one of characteristic parameters to evaluate cable transmission quality. With the increasing of transmission frequency of data communication cable, the requirement of predicting SRL online became urgent according to the demand in last 100m of broadband user access network. Insulation periodical non-homogeneity was tested using capacitance in water and SRL was predicted in this paper, which is the key to reduce rejection ration and raise productivity in terms of requirement of data cable in information society.This paper discussed the influence of impedance non-homogeneity on transmission property. Online detecting periodical non-homogeneity has become one of new technology of cable quality control. The principle of predicting SRL by capacitance in water was analyzed mathematically, which was simulated to prove the relationship between periodical non-homogeneity and SRL using MATLAB. In this paper, some methods of capacitance measurement were described. Also a hardware system for measuring capacitance in water online and a system of data acquisition in lab for measurement parameter were developed. Digital processing methods to ac parameters were analyzed. By contrasting calculation precision between Fast Fourier Transform (FFT) and Root Mean Square (RMS), RMS was adopted to compute a. c. voltage. Several kind of digital filter technology was simulated. Average filter was used to remove random noise, and Morphological filter was used to dispose of pulse disturbance. It used VC++6.0 to compile the course of data acquirement and processing.