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A Comparison of CNS 13438: 1997 and CISPR 22: 1993Grace Lin In January 1997, the Taiwan Ministry of Economic Affairs began regulating EMC for commodity electronic products. Chinese National Standard (CNS) 13438: 1997, "Limits and Methods of Measurement of Radio Disturbance Characteristics of Information Technology Equipment," includes 15 articles to be implemented on a staggered schedule. Most of the articles pertain to specific product types, but at least one will specifically address the enforcement of EMC susceptibility. CNS 13438 is similar to CISPR 22: 1993 (Amendments 1 and 2), but some differences may affect achieving EMC approval of a product before it can be marketed in Taiwan (Republic of China). This article examines the scope of CNS 13438 and its deviations from the CISPR standards.1,2 Table I provides a side-by-side comparison of the two standards by topic and section. Table II shows a timetable for implementation of CNS 13438. Copiers were the first product type required to meet the new EMC standard before being placed on the Taiwan market. The next group of controlled products that required EMC approval included TVs, VCRs, fax machines, and information-technology equipment (ITE). ITE equipment is the largest electrical and electronic commodity type on the market in Taiwan. CNS 13438 also provides the inspection standard for this equipment.
Measurement Distance For ITE, CNS 13438 and CISPR 22 both specify limits at a distance of 10 m for Class A and for Class B equipment. Test data taken from a 3-m site are not acceptable to the Bureau of Standards, Metrology, and Inspection (BSMI, formerly BCIQ), the government agency that enforces EMC regulations. This limitation was set because electromagnetic radiation disturbance is not linear. Research by a Taiwan technical committee determined that the theoretical equation L2 = L1 (d1/d2) in CISPR 22, Section 11.4a, is not practical. BSMI accepts measurement data at a closer distance only when a particular test-point measurement is at a high ambient noise level.3 CISPR 22, however, is more liberal. Based on clause 10.2.1, Class B equipment can be measured at 3 m using a 20-dB/decade scaling factor (10 m is still used as the reference distance). Class A equipment should be tested at 10 m, but for ambient interference at a specific portion of the spectrum, a closer distance can be used with the 20-dB/decade scaling. The 10-m test-site requirement is not stated in the CNS 13438 standard itself. It can be found, however, in Section II of the "EMC Designated Laboratories Test Category Main Facilities" regulation on BSMI's Web site. A test site can be either an open-area test site or an anechoic chamber. Laboratories that have only a 3-m test site to perform EMC testing per CNS 13438 will not receive BSMI accreditation. A manufacturer exporting ITE products to Taiwan must be sure the laboratory testing its products has a 10-m test site and that its products are tested within that 10-m site. Other Differences The two standards differ in a number of other areas that can also affect the approval and marketability of electronic products in Taiwan. These differences include the product categories, warning labels, disturbance power, and sales restrictions, as well as the format of the two standards documents. Class B ITE Equipment. The following category has been added to the list of Class B ITE equipment in CNS 13438 under Section 4.1: "Equipment which is for the purpose of display, street sale, and mail order that does not require installation knowledge." In other words, equipment used for demonstration, retail sales, and mail order that require no technical expertise for installation are covered under this section. This requirement is based on the fact that consumers are increasingly purchasing electronic goods through mail-order resources rather than from retail stores. Adding this category to the list ensures that products ordered through the mail conform to EMC requirements. Class A Warning Label. The Chinese language version of CNS 13438: 1997, which is the reference standard whenever a dispute arises, requires Class A ITE products to carry a warning label both in the instructions and on the products themselves. It should be noted that this requirement (for products to bear the warning label) is omitted in the English (translated) version of CNS 13438. The purpose of this requirement is to warn end-users of potential EMI from a device during use. The label also distinguishes compliant products from noncompliant ones. Disturbance Power. Sections 7 and 12 of CISPR 22 provide the disturbance power requirements that are currently under consideration. Because CNS does not permit the use of the phrase "under consideration," Sections 7 and 12 of CISPR 22 do not apply to the corresponding sections of CNS 13438. Whenever CISPR 22 implements the disturbance requirements, CNS 13438 will likely follow soon thereafter. Banning of Sales. Sales restrictions are not addressed in the scope of CNS 13438. Section 8.2.4 of CISPR 22 is not contained in CNS 13438. Reference Section Format. CNS uses a different numbering system than CISPR. The CNS standard refers to a section numbering format, whereas CISPR refers to a section, clause, and subclause format (see Items 7–10 in Table I). Conclusion Measurement distance, the number of ITE categories, warning label requirements, and sales restrictions are the most important differences for test laboratories and product manufacturers to address. In addition, the latest version of CISPR 22: 1997 has added requirements for telecommunication ports. CNS 13438 requirements for telecommunication ports are currently under development. Effective August 1, 1999, under a mutual recognition arrangement (MRA) between Taiwan and the United States, products that meet EMC requirements in the United States will not be required to be retested under the CNS 13438 requirement. Manufacturers or their agencies, however, will be required to apply for BSMI approval before exporting products to Taiwan. A detailed time line for implementation of the CNS standard, as well as a list of the regulations and related information, can be found at http://www.bsmi.gov.tw. It is important to note that China (People's Republic of China) will also begin to regulate EMC requirements soon. Effective January 1, 2000, six product categories will be required to meet EMC requirements before entering the Chinese market; however, the regulations and standards governing these requirements in China are not yet known. Acknowledgments The author wishes to thank Michael J. Alvarado and Roland Gubisch, PhD, of Intertek Testing Services NA Inc. for their full support of this article and Han-Chang Hsieh of BSMI for reviewing this article. References 1. "Limits and Methods of Measurement of Radio
Disturbance Characteristics of Information Technology
Equipment," Chinese and English versions, CNS
13438: 1997, Chinese National Standards, Taipei,
Taiwan. Grace Lin is a senior project engineer in Telcom Stream, a specially assigned group in Intertek Testing Services (ITS; Norcross, GA) that focuses on the telecommunications industry. She holds a BS in electronic engineering from National Taiwan Marine University and an MS in electrical engineering from Syracuse University, Syracuse, NY. She has worked in the EMC field since 1984 and has been employed by ITS for more than six years. Her e-mail address is glin@itsqs.com
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