EMI/RFI Test Labs Get Your Products to Market on Time

Now that the EMC compliance procedures for the European Union (EU) are in force, you may need help to hasten and ease the entry of your products into the unified market. For you, assistance is as close as the nearest independent test lab that specializes in discovering the best route through the new technical and legal issues.

But before you select a test lab to gain easier access to Europe, you must be aware of the directives and the differences between the corresponding U.S. regulations, said Jay Wilson, program development manager at Wyle Laboratories. Next, locate a reputable testing source that has a thorough understanding of the CE marking requirements. Finally, make sure the lab fully understands the labeling guidelines and documentation requirements for the compliance route chosen.

Plan ahead for unexpected and time-consuming design deficiencies, continued Mr. Wilson. Some of these problems may occur as a result of complex EU requirements such as the risk-assessment provisions for the Machinery Directive. You can avoid these delays by understanding the requirements and ensuring that the equipment design is within the EU parameters.

Although labs can offer advice, any design tip will depend on the product type, said Al Slutman, compliance engineering

manager at Siemens. Seek compliance advice early in the design cycle. It reduces the number of fixes and test cycles for a product.

To shorten the time it takes to ship your product to Europe, request that your test

lab fax or mail raw test data along with a statement that the product passed the generic tests to your European distributor, said Jack Rogers Jr. of Global Certification Laboratories. This allows you to apply for the CE Marking before receiving the formal test report, saving a substantial amount of time.

Meeting the Requirements

Most digital equipment that has problems meeting the EU requirements fails the emission test, the ESD test, or both, according to Michael Violette, president of Washington Laboratories. Failures due to radiated immunity or electrically fast transient testing are rare except for those caused by improper cable shielding, aperture leakage that allows slot radiation and lack of filtering on unshielded wires. These coupling paths allow energy to escape.

Other problem areas for conducted and radiated immunity testing are process- control equipment, instrumentation-based equipment and devices with analog inputs such as temperature and speed, added Mr. Violette. The RF energy applied in these tests bypasses input filtering and causes error voltages to corrupt reference voltage and sensor inputs.

The problem occurs when the engineer designs the circuit with low-pass filtering on the front-end of the sensor input that may cut off at hundreds of kilohertz. Above this frequency in the RF range, parasitic passband windows occur that allow the RF energy to enter the circuit. The solution is wideband filtering on these inputs.

Often, circuit-design problems occur when engineers are unaware of regulation changes. For example, many sectors of the economy that were once exempt from the Federal Communications Commission (FCC) regulations, such as household appliances, must now meet the EMC requirements, said Mr. Violette. This has been a rude awakening for many manufacturers.

The news is good, though. Products designed to comply with today’s FCC emission rules are already well on their way to meeting EU immunity standards, said Steven Roll, vice president at Inchcape Testing Services. Many of the actions that reduce emissions also improve immunity capabilities.

Because the radiated emission and immunity characteristics are interrelated, a coordinated design program is needed to meet the requirements, said Ron Brewer of Instrument Specialties. To meet these EMC specifications, three interlinked steps are essential:

· Minimize circuit speed and bandwidth.

· Reduce PCB coupling loop areas.

· Shield all problem circuits.

Minimizing circuit speed is not a popular option because today’s tendency is to increase speed even where it is not needed, such as using high-speed logic devices in low-speed circuits, observed Mr. Brewer. The slower-speed devices with lower bandwidth, however, will reduce emissions as well as help desensitize the circuit to external fields.

Also, the higher-speed devices have lower noise margins than low-speed devices. If you need greater processing capability, use low-speed parallel rather than high-speed serial, he said.

To reduce the circuit bandwidth, use low-pass suppression components such as filters, ferrite beads and bypass capacitors, continued Mr. Brewer. They significantly decrease high-frequency harmonics. But be aware that this technique also

decreases the processing capability.

The next step is to minimize PCB coupling loop areas. For double-sided boards, lay out the clock and sensitive analog loop areas first, said Mr. Brewer. Then provide segregation and isolation between the analog and digital circuits. Decoupling capacitors should be used at each active device, with their value based on switching time, demand current and self-resonant frequency (SRF). The SRF should be equal to or greater than the fifth harmonic.

You can reduce loop areas by using multilayer boards whenever possible, added Mr. Brewer. Multilayer boards also permit controlled- impedance design and allow isolated ground planes to be fabricated into the board.

Shielding is the final step in meeting the combined emission and immunity requirements, said Mr. Brewer. It is the only non-invasive suppression technique. For existing designs, shielding can frequently be used as a stand-alone solution. In new designs, shielding should be used in conjunction with, or after, circuit layout and bandwidth reduction procedures, observed Mr. Brewer.

The FCC, the EU and MRAs

Gaining access to the EU is not about technical competence, according to many U.S. labs. It really is a political issue, said Walter Poggi, president of Retlif Testing Laboratories.

Manufacturers need affordable and locally available Competent-Body and Notified- Body services to assure that their products meet the EU requirements. U.S. labs can provide the assistance because they understand the technical issues. They just need permission from the EU to fully operate within the European framework. This would enable labs to offer cost-effective and timely services to their customers.

On this side of the Atlantic new guidelines have been implemented to help manufacturers and labs speed up product movement into the United States. Effective Aug. 19, 1996, the FCC adopted changes to Part 15 that permit manufacturers and importers of personal computers and associated equipment to use a new streamlined procedure.

For more information on the Part 15 changes, see “Get to Know the New FCC Procedure for Digital Devices” in this issue. The procedure enables nearly on-the-spot authorization of products, said Don Sweeney, president of D.L.S. Electronic Systems. The process includes a Declaration of Compliance, stating the device does not cause harmful interference and that it accepts any interference including interference that may cause undesired operation.

The testing procedure remains the same as before the Part 15 changes, except that a lab accredited by the National Voluntary Laboratory Accreditation Program (NVLAP) or the American Association for Laboratory Accreditation (A2LA) must perform the tests. Also, the laboratory must be located in the United States or a country having a mutual recognition agreement (MRA) with the United States.

The FCC requires accreditation for laboratories testing in support of the Declaration of Conformity, but is not in charge of direct lab oversight, said Mr. Violette. That is the responsibility of either the National Institute of Standards and Technology (NIST) or the A2LA.

NIST establishes programs for conformity assessment of U.S. labs, including accrediting bodies such as NVLAP and A2LA, added Mr. Roll. Making NIST a regulatory agency establishes harmony with the EU governing bodies for accepting test data from U.S. labs.

The FCC will become the competent authority for EMC, while NIST, through the NVLAP, will provide the route to accreditation, said Gary Fenical of Instrument Specialties. NIST may also become a Competent Body once MRAs are fully in place.

U.S. labs want the MRAs adopted as quickly as possible because they will help level the playing field between the EU and the United States for exchange of services. The MRAs will allow testing to proceed for devices such as transmitters, medical devices and telephone products.

From the start, the EU has insisted that the United States labs meet regulations for competence of testing with approval on a par with the EU laboratories. If accepted, MRAs will allow U.S. manufacturers to test and approve products going to Europe.

The MRAs also will permit European manufacturers to test and approve products coming into the United States. The Department of Commerce estimates that 50% to 80% of testing and certification costs can be eliminated with the implementation of the MRAs, said Julius Knapp of the FCC.

But the general and administrative overhead for EMC test labs will need to expand significantly to accommodate MRAs, said Lee Pulver, President of Pulver Laboratories. The resulting test-lab organization will be much stronger and better structured.

One final note concerns the creation of a system for establishing equivalent certifying bodies, said Mr. Violette. If a single certifying body is established in the United States, a monopolistic condition is created and the effective turnaround time may not be improved over the present system.

These companies supplied information for this article:

D.L.S. Electronic Systems (847) 537-6400

EMCC Dr. Rasek (011) 49 9194 9016

Euro EMC Service (011) 49 3328 430 141

Global Certification Lab (860) 873-1451

Inchcape Testing Services (508) 689-9353

Instrument Specialties (717) 424-8510

Pulver Laboratories (408) 399-7000

Radiation Sciences (215) 256-4133

Retlif Testing Laboratories (516) 737-1500

Siemens (408) 492-3923

Tempest (703) 836-7378