Compliance Testing: New Standards in Store for Using TEM Cells

Heyno Garbe

After years of playing second fiddle to large anechoic chambers and open-area test sites (OATS), TEM cells are finally getting a chance at playing first chair. If CISPR approves proposed amendments to CISPR 16-1 and CISPR 16-2, IEC 6100-4-3, emission measurements of small objects (without cables and wires leaving the test volume) will be acceptable as long as the correlation to an OATS is shown.

An amendment to IEC 61000-4-20, "Electromagnetic Compatibility (EMC)—Part 4-20: Testing and Measurement Techniques—Emission and Immunity Testing in Transverse Electromagnetic (TEM) Waveguides," will also allow this correlation. Amendments are being proposed to CISPR 16-1 and 16-2, as well as to Annex A of IEC 61000-4-20, according to Heyno Garbe, convenor of the joint task force CISPR/A and SC 77B on TEM waveguides. IEC 61000-4-20 will contain general information on the new test procedures. Normative annexes will address emissions, susceptibility, and transient testing. The test procedures would cover all types of TEM waveguides, including classical TEM cells, GTEM cells, and symmetrical cells.

This fall, SC 77B will vote on an amendment to Annex 1 of IEC 61000-4-3, "Radiated, Radio-Frequency, Electromagnetic Field Immunity Test." "The annex will be informative," says Garbe. Voting on the amendment to CISPR 16-1 and 16-2 will likely take place this summer. "On the next general assembly of CISPR, which will be in the first two weeks of June in St. Petersburg, Russia, the proposed amendments will be discussed. I hope that CISPR will distribute them as CDV [committee draft for vote]," Garbe says. For the amendments to IEC 61000-4-20, SC 77B is responsible for the changes to the main section of the standard and to Annex B (susceptibility), and CISPR/A will vote on changes to Annex A (emissions). A joint task force will discuss a second committee draft of IEC 61000-4-20 at the IEEE EMC Symposium in Washington, DC, in August.

According to Garbe, SC 77B has established test procedures for using TEM cells as an independent source for susceptibility tests. However, CISPR/A, which is responsible for emissions testing, will likely still require correlation of TEM cell measurements to an OATS. Under IEC 61000-4-3, TEM cells can be used for compliance testing, but the committee still must determine which test procedure will be required for compliance testing. "This could be a TEM cell, a reverberating chamber, or an OATS," says Garbe. "It is possible that the committee may allow only one procedure or all of them."

Diethard Hansen

The gains being made are significant, according to Diethard Hansen, president of Euro EMC Service (Berikon, Switzerland) and inventor of GTEM and EUROTEM cells. "The big difference between a TEM cell and an OATS is that in a TEM cell, it's the way you position the cables, which is extremely critical for good correlation. It's usually smaller than an ordinary turntable, sometimes limiting cable layout. These devices, however, offer advantages that other alternatives do not." For example, he says, symmetrical cells make cables electromagnetically invisible when positioned exactly on the longitudinal line of symmetry. One of the biggest concerns, he says, has been that many people believe that TEM cells don't provide ideal wave propagation, but he notes that this assumption is not true for well-designed cells. TEM cells have already been widely accepted for immunity testing, just not for emissions testing despite the existing reciprocity, he says. Unlike fully absorber-lined chambers, it is not likely, he says, that TEM cells will soon have stand-alone limits for free-space measurements.

"It is important to note that emissions tested in a TEM device can be correlated very well to an open-area test site. Some people in the EMC community are reluctant to accept the physics, but for the marketplace, it's mainly an economical question. There is no sense using a large, expensive anechoic chamber to test a little telephone handset," Hansen says.

Currently, all measurements must be correlated to an OATS, which Hansen says is a very difficult and specialized procedure. "For ideal measurements, you should have total radiated power in free space. The ground plane on an OATS was introduced because in open areas, measurements deviated tremendously due to different ground reflections such as wet or dry soil. We needed something to refer to. An anechoic chamber is just a dome above an OATS, and TEM cells are basically compact chambers that function is a similar way," he says.

Emission correlation, Hansen says, should generally be done to free space. "This interpretation makes much more sense in terms of physics and may take several more years before it is widely accepted," he says. More information on this topic is available at http://www.euro-emc-service.de.

ANSI Given Green Light to Accredit "Mini FCCs"

A precedent-setting arrangement announced June 2 by FCC, ANSI, and NIST is expected to make certifying new telecommunications equipment to federal and foreign compliance requirements faster and more cost-effective. Under the arrangement, NIST recognizes ANSI as a qualified accrediting agency of product certifiers, or rather, TCBs (telecommunications certification bodies), which are designed to relieve the burden of approvals on FCC by approving radio transmitters, telephone handsets, and other radio frequency and telephone terminal equipment that test compliant with FCC regulatory standards.

Beginning June 5, the 13 TCBs currently accredited by ANSI for such approvals will be able to compete for the roughly 6000 product approval applications that FCC receives annually. FCC will continue offering equipment approval during what is currently an undefined transition period, according to William Hurst, vice president of Communication Certification Laboratory (Salt Lake City) and interim chair of a council that works with TCBs to address critical issues. "The duration of the transition phase," says Hurst, "has to be determined through rule making, and this is the responsibility of the Common Carrier Bureau for telephone equipment connected under Part 68 and of FCC's Office of Engineering and Technology for radio equipment."

The goal is to "move resources to enforcement," says Hurst, citing FCC's plan to focus more on market surveillance through random product testing.

ANSI's recognition as a TCB accrediting body comes on the heels of a two-day, on-site assessment of the organization's program by NIST. ANSI staff were audited as they evaluated the competency of two certification bodies and the bodies' compliance with established international standards and NVCASE (National Voluntary Conformity Assessment Evaluation) procedures. Results of the assessment and the audits were presented to an evaluation panel comprised of NIST and FCC experts, which voted unanimously on May 26 to approve ANSI as an accrediting agency. The organization's recognition by NIST is valid through May 2002, and it can be renewed after formal NIST review.

Designating ANSI-accredited certifiers as TCBs "privatizes the technical portion of regulatory activity—the portion that is most resource-intensive," says John Donaldson, ANSI vice president for conformity assessment. "Creating the equivalent of mini FCCs with well-defined scopes of responsibility should make the system more efficient and more responsive," says Donaldson.

Still unresolved for TCBs, however, is the issue of SAR measurement. "Until the matter is resolved," says Hurst, "FCC has to publish procedures, which, for the time being, are a limitation on TCBs."

The 13 ANSI-accredited TCBs are as follows: American TCB Inc. (McLean, VA); BABT Product Service Inc. (Santa Clara, CA); CKC Certification Services (Mariposa, CA); Communication Certification Laboratory (Salt Lake City, UT); Compliance Certification Services (Sunnyvale, CA); Curtis-Straus LLC (Littleton, MA); Elite Electronic Engineering Inc. (Downers Grove, IL); Intertek Testing Services (Cortland, NY); MET Laboratories Inc. (Baltimore, MD); PCTEST Engineering Laboratory Inc. (Columbia, MD); Timco Engineering Inc. (Newberry, FL); TUV Rheinland of North America Inc. (Newton, CT); and Underwriters Laboratories Inc. (Northbrook, IL).

For a list of the types of equipment each TCB has been designated to approve, visit the Commission on the Web at http://www.fcc.gov/Bureaus/Engineering_Technology/
Public_Notices/2000/da001223.txt. For information on ANSI and NIST, go to http://web.ansi.org and http://www.ta.nist.gov, respectively.

CE Names New Board Member

New Compliance Engineering advisory board member Martin J. Alexander, BSc, MIEE, C.Eng, is probably best known for designing and developing National Physical Laboratory's (NPL) facility for the calibration of dipole antennas in the frequency range of 30 MHz to 1 GHz. Developing the facility for calibration of dipole antennas broke new ground by achieving uncertainties as low as ±0.1 dB for the gain of omnidirectional VHF and UHF antennas. In December 1999 he and two colleagues were awarded a prestigious finalist prize by IEE for this work and for their contribution to the practice of measurement.

Alexander has also done extensive research developing methods for evaluating 3-m anechoic chambers (see his article on page 46).

As a member of CISPR/A, he participates in the development of antenna calibration methods and uncertainty calculations in EMC measurements. He also participates in the evaluation of GTEM cells for calibration. In his own work, he is codeveloping with Tokin Corp. an accurate electro-optic field transfer standard to transfer the low uncertainties of field strength using the calculable standard dipole into TEM and GTEM cells.

Alexander, who is principal research scientist for NPL (Teddington, UK), is also investigating methods for reducing the cost of fully anechoic rooms (FARs) by introducing partial absorber lining. He is actively promoting the use of FARs for full-compliance EMC testing and is a key contributor to the CENELEC preliminary standard prEN 50147-3. He is also promoting the adoption of this method in CISPR. Since 1988, Alexander has been employed at NPL where he is now head of the RF free-field section of the Centre for Electromagnetic and Time Metrology. He received a degree in physics from Exeter University (Exeter, UK) in 1971. From 1971 to 1974, he taught physics and math. In 1974, he left teaching to join the antenna division of the GEC-Marconi Research Centre, designing transmission line components and antennas in the frequency range of 800 MHz to 15 GHz.

ETSI and TIA Launch Partnership Project

The European Telecommunications Standards Institute (ETSI) and the Telecommunications Industry Association (TIA) announced at a conference for the public-safety community that they have launched a new partnership project to address standardization needs in North America and Europe.

The Public Safety Partnership Project (PSPP) will develop the public-safety mobile-broadband specifications and their capabilities, which will support the public-safety community's technology needs for the wireless transport and distribution of rate-intensive data, digital video, and digital voice for both service-specific and general applications. The PSPP will primarily address air-interface data rates beyond current standards. For more information go to http://www.etsi.org.

TETRA Standard Nears Completion

Drafting of the TETRA (TErrestrial Trunked RAdio) standard Release 1 will be virtually completed by the end of 2000, and developments for a new release will begin as soon as possible, according to the European Telecommunications Standard Institute (ETSI).

TETRA, which uses digital private mobile radio (PMR) and public access mobile radio (PAMR) technology, is designed to meet the needs of such applications as shared systems for public and national safety, emergency and security services, public access systems for use by professional commercial users, and private systems run by major organizations, like public transport operators. (See "TETRA the Noise Source: Preventing Interference" on page 36 for an in-depth look at how TETRA will affect existing communications devices.)

"The TETRA standard has now reached maturity with almost 95% of TETRA Release 1 finalized. However, like GSM [global system for mobile communication], TETRA will continue to evolve, and a significant effort is now going into the planning of the next generation of TETRA. This will maintain the unique characteristics of TETRA, including fast call setup and group-style communication, while adding new multimedia services and increasing data rates to ensure its compatibility with existing technologies," says Brian Oliver, chairman of ETSI Project TETRA.

TETRA uses time division multiple access (TDMA) technology with four user channels on one radio carrier and 25-kHz spacing between carriers. The unique features of TETRA include comprehensive group communication services and facilities, the capability for direct communication between radio terminals, and subsecond call setup time. Other services include circuit data and Internet protocol (IP) compatible packet data, frequency economy, and a wide range of security features.

ETSI Project TETRA currently involves more than 150 representatives in various technical working groups, with support from the TETRA MoU [memorandum of understanding] Association providing further expertise in specialist areas. ETSI Project TETRA has already produced 131 deliverables, according to ETSI. About 70 additional publications are planned for this year. Another 20 are planned for 2001, and an additional 5 for 2002.

The TETRA standard is now used throughout Europe and is already deployed or will be deployed soon in the Far East, the Middle East, Africa, and South America. According to ETSI, this rapid deployment in just a few years has signaled the success of TETRA, not only as a replacement technology in traditional mobile radio markets, but also as a technology suitable for new markets, such as the military.

"TETRA already has well over 50 contracts or commitments from a wide variety of user organizations. The current TETRA market value is estimated to be in excess of $2 billion, with market projections for over $10 billion by 2004," says Phil Godfrey, chairman of the TETRA MoU Association.

A workshop on TETRA for civil use is to be held at ETSI headquarters in Sophia Antipolis, France, in June. Its purpose is to highlight the civil use of TETRA in addition to the public-safety use. Future developments of TETRA standards will be discussed during the workshop.

EMC York 2000

The EMC York 2000 Conference and Exhibition will take place July 10–11, 2000, at the Exhibition Centre at the University of York, UK. Among those expected to attend the show, which is dedicated to EMC and CE-marking compliance issues, are EMC professionals, approvals managers, and design engineers.

Organized by York EMC Services Ltd., the conference will feature 45 international speakers and cover such issues as EMC standards and regulations, CE-marking directives, and radio spectrum management. Workshop sessions will include an introduction to EMC and discussions of electrical-system safety and product recall. In addition to the conference, the exhibition will feature materials, instrumentation, components, and other compliance-related products and services.

The event will also host the European COST 261 meeting, which will address the issues associated with EMC in large and distributed systems, and a chapter meeting of the IEEE EMC Society (UK), which will include a discussion of automotive EMC. Both meetings will be open to all conference registrants.

For further information, please contact Chris Marshman or Savilla Liddle of York EMC Services Ltd.; phone: +44 1904 434440; fax: +44 1904 434434; e-mail: enquiry@yorkemc.co.uk; Internet: http://www.yorkemc.co.uk.

Clarion Receives ISO/TS 16949 Certification

Automotive supplier Clarion Technologies Inc. has received certification for compliance with ISO/TS 16949, a quality standard that addresses the requirements of the automotive industries in the United States and Europe. Developed by the International Automotive Task Force (IATF), the standard is based on ISO 9001:1994, AVSQ (Italy), EAQF (France), QS-9000 (United States), and VDA 6.1 (Germany).

The new standard does not replace previous standards, but acts as an international equivalent to country-specific standards, allowing suppliers to avoid multiple registrations. The new standard also contains reassignment of supplier resources to quality improvement, including the introduction of the term product realization to address the process of designing, planning, and delivering products that meet customer requirements.

Certification of Clarion's plant in Greenville, MI, was awarded by Entela Inc. QSRD, the first of an anticipated 31 firms to be approved as ISO/TS 16949 registrars. The Greenville plant is one of six manufacturing facilities operated by Clarion Technologies in Ohio, Michigan, and South Carolina. The company intends to pursue ISO/TS 16949 certification at each of these locations, in addition to its technical design center in Jenison, MI.