The Cable Crimp Levels Effect on TDR Cable Length Measurement System

Transcription

1 The Cable Crimp Levels Effect on TDR Cable Length Measurement System Jianhui Song*, Yang Yu, and Hongwei Gao School of Information Science and Engineering, Shenyang Ligong University, Shenyang, , P.R. China Abstract. Time domain reflectometry (TDR) technology is an ideal cable length measurement method. The traveling wave propagation velocity is the key to the measuring accuracy of the TDR cable length measurement system. The cable crimp levels effect on traveling wave propagation velocity is analyzed theoretically, and the corresponding experiment is done. The experimental results are match to the theoretical analysis. The experimental results show that the law of the traveling wave propagation velocity influenced by cable crimp levels is different for different types of cable, however, as long as the cable state under test is uniformed, the velocity error can be controlled in a small range. Therefore the measuring accuracy of the TDR cable length measurement system is ensured. Keywords: TDR, propagation velocity, cable crimp level. 1 Introduction All kinds of wires and cables have been widely used with the rapid development of the national economy. The wire and cable industry have developed rapidly, and gradually expanded the production scale and market share. Cable is an important commodity, and its length measurement precision is strictly formulated in the national standard. However, the issue of measuring precision in the wire and cable market becomes more and more prominent. It is significant to measure the cable length precisely, rapidly and economically. Compared with the traditional measurement methods, time domain reflectometry (TDR) technology has an advantage of nondestruction, portability and high-precision, which is an ideal cable length measurement method[1~3]. It is found in practice that the measuring accuracy of the TDR cable length measurement system can be influenced by the cable crimp levels. In order to reduce the cable crimp levels effect on the measuring accuracy of the TDR cable length measurement system, the cable crimp levels effect on traveling wave propagation velocity is analyzed theoretically, and the corresponding experiment is done. 2 Relationship between Velocity and Capacitance of Cable According to the theoretical knowledge of the capacitor plates, the capacity of the capacitor plates can be calculated as formula (1): S. Lin and X. Huang (Eds.): CSEE 2011, Part I, CCIS 214, pp , Springer-Verlag Berlin Heidelberg 2011

2 The Cable Crimp Levels Effect on TDR Cable Length Measurement System 403 ε D l C = (1) d Where, D is the width of the capacitor plates, l is the length of the capacitor plates, d is the distance between the two plates of the capacitor, ε is the dielectric constant. According to the cable length measurement principle of capacity conversion of capacitor, an open end cable is regarded as a capacitor. Two cores of the cable is regarded as two plates of the capacitor. The effective width of the cable core can be approximately interpreted as D in formula (1). The length of the cable can be regarded as l in formula (1). The distance of the cable cores can be interpreted as d in formula (1). For the two core wire cable whose internal structure, ε, D and d is fixed, the capacitances between the two wires of the cable are proportional to the cable length. That is C1 l1 = (2) C l 2 2 The cable length can be obtained by measuring the cable capacitance per unit length[4]. At high frequencies, the propagation velocity of the electromagnetic waves can be calculated as formula (3)[5~7]. 1 v = (3) LC 0 0 Where, L 0 is the distributed inductance per unit cable length. C 0 is the distributed capacitance per unit cable length. It can be seen from formula (3) that the wave velocity is inversely proportional to the square root of the distributed capacitance per unit length. The relationship between the velocity and distributed capacitance can be expressed as follow v 1/ C (4) 0 The distance between the adjacent insulated core decreases and the distribution capacitance of the cable increases as the cable is curled. Therefore the velocity decreases as the cable is curled. However, as long as the cable state under test is uniformed, the distribution capacitance of the cable is also uniformed; therefore, the velocity can be controlled in a small range. 3 Experiment and Analysis In order to further study the law of the traveling wave propagation velocity influenced by cable crimp levels, the measurements were performed on RVV 300/300V PVC insulated cable. The equivalent capacitances and distributed capacitances of different cable length in state of curl and straighten is shown in table 1.

3 404 J. Song, Y. Yu, and H. Gao Table 1. Equivalent capacitances and distributed capacitance of different cable length in state of curl and straighten Cable Equivalent under Equivalent capacitances test(m) capacitances capacitances capacitances Table 2. Equivalent capacitance ratio and length radio of with 6.75m and 30.00m cable length in state of curl and straighten Capacitance ratio Length ratio Capacitance ratio Length ratio Table 3. Velocity and relative error of different cable length and different cable crimp degree Cable under test(m) Cable state velocity(m/s) Relative error(%) The equivalent capacitance ratio and length radio of 6.75m and 30.00m cable length in state of curl and straighten is shown in table 2. The ambient temperature is It can be seen from table 2 that although the values of the equivalent capacitance of the cable are different under different conditions, the capacitances between the two wires of the cable are still proportional to the cable length. In the same state, the equivalent capacitance of the cable is greater as the cable length is longer. But the distributed capacitance per unit cable length is always the same. The comparison of the distributed capacitance in state of curl and straighten, it can be found that the equivalent capacitance and distributed capacitance in state of curl is bigger than the equivalent capacitance and distributed capacitance in state of straighten. It is because the distance between the adjacent insulated wire cores decreases as the cable is curled, therefore the equivalent capacitance and distributed capacitance in state of curl is bigger. The velocity and relative error of different cable length and different cable crimp degree is shown in table 3. It can be seen form table 3 that the relative error of velocity in state of curl and straighten is big. The velocity relative error of the same cable crimp degree with 6.75m and 30.00m cable length is shown in table 4. It can be seen form table 3 and table 4 that the cable crimp degree of RVV 300/300V PVC

4 The Cable Crimp Levels Effect on TDR Cable Length Measurement System 405 sheathed cable has a great impact on the velocity. However, as long as the cable state under test is uniformed, the velocity can be controlled in a small range. The measurements were performed on RVVP multi-core shielded cable. The length of three cores is 40.73m. The length of seven cores is 41.57m. The length of eight cores is 43.1m. The ambient temperature is 1.0 ÂThe equivalent capacitances and distributed capacitance of different cable cores in state of curl and straighten is shown in table 5. The velocity relative error is shown in table 6. It can be seen form table 5 and table 6 that the cable crimp degree of RVVP multicore shielded cable has little impact on the velocity. However, the cable state under test is better to be uniformed to control the velocity error in a small range. The measurements were performed on SYV coaxial cable. The length is m. The ambient temperature is 1.0. The equivalent capacitances and distributed capacitance of coaxial cable in state of curl and straighten is shown in table 7. The coaxial cable velocity relative error in state of curl and straighten is shown in table. Table 4. Velocity relative error of the same cable crimp degree with 6.75m and 30.00m cable length Cable state Velocity relative error(%) Table 5. Equivalent capacitances and distributed capacitance of different cable cores in state of curl and straighten Cable under test Equivalent capacitances capacitance Equivalent capacitances capacitance Three cores Seven cores Eight cores Table 6. Velocity relative error of different cable crimp degree Cable under test Three cores Seven cores Eight cores velocity( 10 m/s) Relative error(%)

5 406 J. Song, Y. Yu, and H. Gao Table 7. Equivalent capacitances and distributed capacitance of coaxial cable in state of curl and straighten Cable under test Coaxial cabel Equivalent Equivalent capacitances capacitance capacitances capacitance Table. Coaxial cable velocity relative error of different cable crimp degree Cable under test velocity(m/s) Relative error(%) 0.02 It can be seen form table 7 and table that the cable crimp degree of SYV coaxial cable has very little impact on the velocity. However, the cable state under test is better to be uniformed to control the velocity error in a small range. 4 Conclusions The cable crimp levels effect on traveling wave propagation velocity is studied. The experiment results show that the cable crimp degree of RVV 300/300V PVC sheathed cable has a great impact on the velocity. The cable crimp degree of RVVP multi-core shielded cable has little impact on the velocity. The cable crimp degree of SYV coaxial cable has very little impact on the velocity. References 1. Dodds, D.E., Shafique, M., Celaya, B.: TDR and FDR Identification of Bad Splices in Telephone Cables. In: 2006 Canadian Conference on Electrical and Computer Engineering, pp (2007) 2. Du, Z.F.: Performance Limits of PD Location Based on Time-Domain Reflectometry. IEEE Transactions on Dielectrics and Electrical Insulation 4(2), 12 1 (1997) 3. Pan, T.W., Hsue, C.W., Huang, J.F.: Time-Domain Reflectometry Using Arbitrary Incident Waveforms. IEEE Transactions on Microwave Theory and Techniques 50(11), (2002)

6 The Cable Crimp Levels Effect on TDR Cable Length Measurement System Shan, L.D., Meng, W.S., Zhang, L.H., Wang, Y.M.: Apply the Principle of Capacity Conversion of Capacitor and Quick Determination the Inside Break Point of Cable. Metal World (4), 46 4 (2006) 5. Mugala, G., Eriksson, R.: Measurement Technique for High Frequency Characterization of Semi-Conducting Materials in Extruded Cables. IEEE Transactions on Dielectrics and Electrical Insulation 11(3), (2004) 6. Oussalah, N., Zebboudj, Y.: Analytic Solutions for Pulse Propagation in Shielded Power Cable for Symmetric and Asymmetric PD Pulses. IEEE Transactions on Dielectrics and Electrical Insulation 14(5), (2007) 7. Oussalah, N., Zebboudj, Y., Boggs, S.A.: Partial Discharge Pulse Propagation in Shielded Power Cable and Implications for Detection Sensitivity. IEEE Electrical Insulation Magazine 23(6), 5 10 (2007)