1、NEMA Standards PublicationNational Electrical Manufacturers AssociationANSI/NEMA WC 61-2005 (R2015)Transfer Impedance TestingANSI/NEMA WC 61-2005 (R2015) American National Standard for Transfer Impedance Testing Secretariat: National Electrical Manufacturers Association Approved: February 13, 2015 A
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20、n any form, in an electronic retrieval system or otherwise, without prior written permission of the publisher. Printed in the United States of AmericaANSI/NEMA WC 61-2005 (R2015) Page ii 2015 National Electrical Manufacturers Association ANSI/NEMA WC 61-2005 (R2015) Page iii 2015 National Electrical
21、 Manufacturers Association CONTENTS Foreword iv Section 1 SCOPE AND REFERENCED DOCUMENTS . 1 1.1 Referenced Documents and Publications . 1 Section 2 GENERAL . 2 2.1 Precision and Bias . 2 2.2 Significance and Use . 2 Section 3 SAMPLE PREPARATION . 3 3.1 General 3 3.2 Sample Preparation . 3 3.2.1 Cir
22、cuit Verification . 8 3.2.2 DC Resistance (dcR) of the Shield 8 Section 4 TEST PROCEDURE 9 4.1 General 9 4.2 Cable Measurement 9 4.3 Calculation of Transfer Impedance 9 4.4 Verification of Dynamic Range 10 ANSI/NEMA WC 61-2005 (R2015) Page iv 2015 National Electrical Manufacturers Association Forewo
23、rd In December 1985, the NEMA Electronic Wire and Cable Technical Committee decided to evaluate transfer impedance test procedures. The goal was to establish measurements of shield effectiveness that would provide correlation among manufacturers and end-users. A series of four round-robin test progr
24、ams were performed in conjunction with technical discussions about the merits of different test procedures. This program led to the development of a NEMA Transfer Impedance Test Procedure. The test program and discussions are summarized below. First Round-Robin TestResults published in minutes of NE
25、MA Ad Hoc Task Force on Transfer Impedance Testing, April 8, 1986. Six manufacturers tested the transfer impedance of coaxial and twisted pair samples shielded with copper tubes. No specific test method was called out, but MIL-C-85485 and the terminated triaxial fixture were the only procedures used
26、. Correlation between test facilities and methods was sufficient to encourage testing of production cables rather than lab constructions. Second Round-Robin TestFinal results published in the minutes of the NEMA Electronic Wire and Cable Technical Committee Meeting, December 10, 1986. Samples of RG-
27、213 and RG-58 from one lot of one source were evaluated by eight manufacturers. Correlation was not good. In some cases, the same manufacturer got varying results on the same cable type. The frequency limitations of both the terminated triaxial and the MIL-C-85485 methods became obvious. Third Round
28、-Robin TestResults published in Conference Report of Ad Hoc Task Force on Transfer Impedance Meeting, September 28, 1987. Samples of RO-58 and RG-213 shielded with a steel tube were prepared by Belden and tested by seven manufacturers. This shielding was chosen because its transfer impedance could b
29、e calculated. Each company prepared its samples for testing per MIL-C-85485. After testing, these samples were circulated to other participants in the program. The data showed that different facilities got close results on the same samples. This implied that measurement equipment was not the signifi
30、cant source of the errors. This was no surprise because this transfer impedance measurement is an insertion lost test. The data demonstrated the theoretical upper frequency limit of the MIL-C-85485 method as described in the referenced paper by A. Martin and M. Mendenhall. That paper and additional
31、testing by the Task Force suggested that the upper frequency limit could be extended from 30 MHz to 100 MHz by testing shorter samples. The most significant source of error in the test was determined to be sample preparation. Fourth Round-Robin TestResults published in the Conference Report of Ad Ho
32、c Task Force on Transfer Impedance Meeting, March 9, 1988. Spectra-Snip built MIL-C85485 type m transfer impedance fixtures. These were submitted as a standard for measurement. Four companies tested the fixtures and the correlation up to 100 MHz was excellent. The data established that different tes
33、t facilities testing identically constructed stable devices would achieve the theoretical results. ConclusionThis procedure is an effective tool for comparing shield effectiveness. Different shields over the same core, coaxial and twisted pairs, can be quantified and ranked logically. Results are re
34、peatable. However, the method does have inherent limitations, but within its range, results can be verified with other test methods. This procedure is recommended as an efficient, effective means of evaluating cable shield performance. This Standards Publication input of users and other interested p
35、arties has been sought and evaluated. Inquiries, comments, and proposed or recommended revisions should be submitted to the concerned NEMA product subdivision by contacting the: Senior Technical Director, Operations National Electrical Manufacturers Association 1300 North 17thStreet, Suite 900 Rossl
36、yn, VA 22209 ANSI/NEMA WC 61-2005 (R2015) Page 1 2015 National Electrical Manufacturers Association Section 1 SCOPE AND REFERENCED DOCUMENTS 1.1 SCOPE This standard is intended to provide a reliable surface transfer impedance test method for coaxial cables and shielded multiconductor cables over the
37、 frequency range from DC to 100 MHz. 1.2 REFERENCED DOCUMENTS AND PUBLICATIONS International Electrotechnical Commission 3, rue de Varemb P.O. Box 131 CH - 1211 Geneva 20 Switzerland IEC 60096 Radio-Frequency Cables Navy Publishing and Printing Service Office 700 Robbins Avenue Philadelphia, PA 1911
38、1-5094 MIL-DTL-24640B Military Specification for Cable and Cord, Low Smoke, Lightweight, for Shipboard Use MIL-DTL-24643B Military Specification for Cable and Cord, Low Smoke, for Shipboard Use MIL-C-85485A Cable, Electric, Filter Line Radio Frequency Institute of Electrical and Electronics Engineer
39、s 445 Hoes Lane Piscataway, NJ 08854 EMC-26 No. 2 IEEE Transactions on Electromagnetic Compatibility Volume. A Fast, Accurate and Sensitive Method for Measuring Surface Transfer Impedance, A. R. Martin, M. Mendenhall, Pages 66-70, May 1984. ANSI/NEMA WC 61-2005 (R2015) Page 2 2015 National Electrica
40、l Manufacturers Association Section 2 GENERAL 2.1 PRECISION AND BIAS When samples are prepared and tested in accordance with this procedure, different laboratories using different (but appropriate) equipment can expect to get similar results. The differences found in the NEMA round-robin test progra
41、m which produced this procedure were generally less than 20%. Significant differences in test results were most commonly a result of problems with samples preparation. Samples shorter than m are not recommended because of difficulties with accurate sample preparation and termination errors. The 1 m
42、sample is recommended for all measurements up to 30 MHz. The m samples may be used up to 100 MHz. 2.2 SIGNIFICANCE AND USE Transfer impedance data general via this test procedure may be used by both users and manufacturers to classify relative EMI/EMC performance of different shields. Additionally,
43、EMP response may be related to transfer Impedance using the following formula: EMP response = (-185) 10 Log+)()()(222220dBfBfdffZtFWhere: Z t (f) = surface transfer impedance at frequency (f) (ohms/m) = 2.39 x 105 B = 4.12 x 107f = frequency (Hz) F = upper frequency limit 100 MHz for m length; 30 MH
44、z for 1 m length Assume that Zt is constant in the frequency range DC to 0.1 MHz. The MIL-C-85485 test procedure itself does not delineate frequency limitations or caution the tester about potential pitfalls. The method as modified by this test procedure addresses both of these issues. It formulates
45、 the relationship between sample length and maximum frequency limit. Correct sample preparation can be verified using shield DC resistance. The NEMA test procedure refines MIL-C-85485 and offers a simple, accurate, and reproducible method for cable shield evaluation. ANSI/NEMA WC 61-2005 (R2015) Pag
46、e 3 2015 National Electrical Manufacturers Association Section 3 SAMPLE PREPARATION 3.1 GENERAL Sample preparation provides the greatest opportunity for introducing error into transfer impedance measurement. By using DC resistance as a benchmark, the validity of the test can be demonstrated. Close a
47、dherence to lengths of samples and proper soldering technique will yield good samples. The amount of shield under test is critical. The distance between short circuits, whether 1.0 or .33 m, must be as accurate as possible. The specific amount of cable beyond these short circuits will not affect the
48、 measurement but should be kept as short as possible. Though MIL-C-85485 specifies Type TNC connectors, other coaxial connectors such as Type BNC or Type N may be substituted as determined by cable size. 3.2 SAMPLE PREPARATION For a 1 m sample, approximately 4 ft (1.22 m) of cable shall be used. For
49、 m sample, approximately 2 ft (0.61 m) of the cable shall be used. Sample preparation shall be as follows: Approximately 3 in. (7.6 cm) of the cable jacket shall be removed from one end of the cable (end “A“) and the shield pushed back to expose the insulated conductors. The insulation shall be removed from the conductors to within 1 in. (2.54 cm) of the pushed back shield as shown in Figure 3-1. For multi-conductor cable, all the conductors shall be connected together and these connected wires shall be referred to as “the conductor.“ The shield shal
