How to Work Effectively With Your EMC Test Lab

The formidable task of meeting product compliance requirements can become very difficult if you select the wrong test laboratory or if you don’t prepare sufficiently for certification testing. This can be particularly true in the case of electromagnetic compatibility (EMC) testing.

For instance, some companies spend needless time and money on redundant testing, using multiple labs rather than one-stop shopping at a full-service lab using harmonized procedures. Others use labs that do not provide design and debug support. This forces companies to take their products out of the labs when they fail, fix or redesign them, and then resubmit them for retesting—a potentially long and costly process.

Even though a product has been designed for EMC, other important items must be considered to make the testing process as economical and expedient as possible. Here are some suggestions to help simplify the certification effort.

Choice of Test Facilities

Choose a lab that performs all of the test protocols required. The lab also must be accredited by the proper authorities in accordance with industry and agency requirements, including any necessary foreign accreditations or recognitions. For instance, FCC Part 15 testing performed at labs accredited by the American Association for Laboratory Accreditation or the National Voluntary Laboratory Accreditation Program can serve as a basis for Declarations of Conformity and eliminate further FCC testing.

The lab chosen should be able to determine which tests to perform. Since some EMC test standards allow selection of applicable test methods, considerable money can be saved by testing only to the necessary methods.

The lab should be willing to perform quick-look or pre-scan testing at an economical fixed rate. This can identify EMC problems early in the product development cycle.

The lab also should troubleshoot the design if compliance problems are encountered during testing. The engineers should support debugging and assist with shielding, filtering, bonding and grounding techniques, and associated materials, if required.

A visit to the lab can be an important discriminator because it allows you to familiarize yourself with the lab’s capabilities, facilities, equipment, and personnel. Note the lab’s convenience relative to lodging and transportation so that future trips will be as efficient as possible.

Preparation for Testing

If a new design is to be tested, the cognizant design engineer must be at the test site or on-call. Not only will this ensure that the test article will be operated properly, but unexpected issues also can be addressed much faster and easier with a decision-maker on-site. It would be even better to have an EMC design engineer available from either the manufacturer or the test laboratory.

Be sure all documentation required by the lab is available before testing. This package should include:

Product description with dimensions and application information.

Schematics.

Assembly drawings.

Technical manuals.

Unit label.

Brand/model name information (for multiple listings).

If there are regulatory-agency documentation requirements and fees, account for them in terms of scheduling and budgeting. Also, determine who will be responsible for any agency submittals.

Preparation for immunity testing can be particularly important. Ideally, the test program should be designed to flag error conditions and stress levels.

Have two test specimens available, one to serve as backup in case of functional failures. A complete set of test support equipment, including software, also should be available. It must be capable of fully exercising the specimen in a typical-use mode or generating agency-specified operating conditions, such as the ANSI/FCC H pattern used for exercising video display units.

Provide sufficient cable lengths to connect support equipment to the test specimen in the lab. Some labs require cables of 50 to 100 feet to run between the open-area sites and the facility that houses test-article support equipment.

Carefully package the test article for shipment, and specifically mark it to the attention of the cognizant lab person. On-time delivery is very important because independent labs have specific time frames set aside for each test job, and missing a window can impact the schedule significantly.

During Testing

While at the laboratory, there are several items to keep in mind over the course of the test program. One of the most important is to work closely with the laboratory personnel to familiarize them with the operation and other aspects of the test article.

Flexibility and patience are required because schedules may have to be altered to accommodate unforeseen test failures. Various test programs could interfere with one another, so each program must permit some give and take. Allow a little extra time for these events.

The on-site representative also should be prepared for possible periods of inactivity while tests are in process. This is a good opportunity to work on other projects, so be sure the lab provides customer offices and related support.

A little time spent on lab selection and test preparation will go a long way toward making your EMC certification effort as quick and economical as possible.

About the Authors

Dave Dougherty is director of program development for the Eastern Test Operations at Wyle Laboratories. He has been involved with business development and customer service activities for more than 25 years.

Mike Harris is senior staff engineer for compliance testing and engineering at Wyle’s Eastern Test Operations. He has been involved with the design, development, and conformity assessment of electronic products for more than 25 years. Previously, he managed a global compliance facility for Hayes Microcomputer Products.

Wyle Laboratories, Eastern Test Operations, P.O. Box 077777, Huntsville, AL 35807, (205) 837-4411, www.wylelabs.com.

INTRO ART

Copyright 1998 Nelson Publishing Inc.

May 1998