Why do EMC testing at your own facility? After all, it requires expert personnel and a financial investment that’s much too large since a product design only needs to be tested once.
Wrong. In reality, EMC products testing is an on-going process, and in-house testing is an easy and cost-effective alternative to using an approved EMC test lab. Many companies also are discovering that EMC test systems are beneficial design tools that can improve product reliability early in the development stage.
Many manufacturers think that a European Competent Body must perform EMC tests or validate any tests performed in-house by the manufacturer. This is simply not true. Manufacturers can perform the required tests themselves—after all, they are always responsible for compliance. And a simple cost analysis will show that establishing in-house EMC testing is a cost-effective solution.
Methods of Compliance
Manufacturers have a choice of three methods of compliance, only two of which require the involvement of European agencies:
Self-Certification—the preferred method for most manufacturers. The manufacturer performs the tests in accordance with the standards and files a Manufacturer’s Declaration of Compliance based on those tests. The manufacturer is responsible for ensuring compliance.
Technical Construction File—a method used when the manufacturer cannot perform tests to the standards as specified, or appropriate standards cannot be identified. Perhaps the product is too big to be tested in accordance with the standards, and some alternate EMC tests must be performed.
A European Competent Body evaluates the manufacturer’s technical construction file, usually performs some testing, and issues a report or certificate. Then the manufacturer uses that report or certificate as the basis for filing the Manufacturer’s Declaration of Compliance. Still, the manufacturer is responsible for ensuring compliance.
Type Acceptance—for intentional radiators (radio transmitters) for telecommunications. A European Notified Body, usually a government agency, is responsible for issuing Type Acceptance. The Notified Body determines if the product is in compliance with the EMC Directive and issues a certificate that the manufacturer then uses as the basis for filing the Manufacturer’s Declaration of Compliance. The manufacturer is still responsible for ensuring compliance.
Notice that with all methods the manufacturer always is the responsible party. If there is ever a problem, the manufacturer is responsible for proving compliance, and it is the manufacturer who signs the declaration.
Ongoing EMC Testing
EMC testing for compliance with the EMC Directive is an ongoing process during various stages in the life cycle of a product:
New products under development for initial compliance.
Products that have been modified or enhanced to ensure that the changes have not affected EMC performance or compliance.
Quality assurance programs to ensure that there have been no changes in the production process and no changes in EMC performance.
The New Design Tool
Since all products must comply with EMC regulations, it makes sound engineering sense to design products from the beginning to comply with the standards. If compliance is to be easy and inexpensive, it must be a requirement of the design and a part of the process, not an obstacle to be overcome at the end of the design cycle.
To achieve this design goal, the engineer needs the tools for EMC compliance, starting with a method of evaluating circuit performance for EMC early in the design cycle. Filters, protective devices, shielding, and software must be selected before the design is finalized. This cannot be done without the proper design tools—starting with simulators to test critical components and circuits.
Even the smallest change can affect the EMC performance of a product. For example, a manufacturer of television sets with a history of few field returns began experiencing a dramatic increase in failures. It was only after a costly investigation that the problem was isolated: A PCB redesign placed raw AC line voltage too close to a 5-V logic line that coupled noise and transients into sensitive logic circuitry. Using an EMC simulator as a design tool before making the change and for retesting EMC immunity performance after the change would have saved this company considerable time, money, and damage to its reputation.
The Real Costs of Compliance
The cost of using commercial test facilities to perform EMC testing often is much higher than in-house testing. In addition to providing a cost-effective alternative for many manufacturers, in-house testing gives engineers complete control of the process. To determine the cost-effectiveness of in-house testing, a cost/benefit analysis should be completed, such as the spreadsheet that accompanies this article.
The spreadsheet includes calculations for lost revenue due to shipping delays as a result of a product’s initial test failure and need for redesign and retest. The time engineers spend fixing design problems instead of designing new products results in the loss of future revenues. Upon review of the spreadsheet, the greatest cost is the loss of revenues due to product noncompliance and delay to market.
The analysis is simple and assumes complete loss of revenue due to delays associated with test cycles at commercial facilities. In the real world, products still may be shipped to customers not requiring CE Marking or other EMC tests.
To account for this, just divide the incremental annual sales volumes for current and later products by the appropriate ratio. However, after realizing these sales, the lost revenue still greatly exceeds the cost of bringing most EMC testing in-house. The loss may not be out-of-pocket, but it is lost revenue and can never be recovered.
Bringing EMC Testing In-House
Several of the tests most manufacturers must perform can be done in-house:
ESD—mandatory now.
EFT—mandatory now.
Surge—mandatory for some products now, for all products by mid 2001.
RF Immunity—mandatory for all products.
Dip and Interrupts—mandatory for all products by 2001.
AC Magnetic-Field—mandatory for products with CRTs and Hall effect sensors.
Harmonic/Flicker—mandatory for many products now, for all products in mid 2001.
Because RF emissions tests require very large anechoic chambers or open-area test sites (OATS), most manufacturers will contract commercial test facilities to perform these tests at the compliance level. But for precompliance verifications, all manufacturers will benefit from in-house testing.
The range of costs to perform precompliance tests is very wide. And like many things, the least expensive method is likely to provide the least information. However, some relatively inexpensive TEM cells do provide good correlation with an OATS. When weighed against the costs of redesign and retest cycles, these cells are very cost-effective.
Although new drafts of the RF Immunity Standards (IEC 1000-4-3, Annex D) state that small TEM cells can be used for compliant RF immunity testing, large products still must be tested in an anechoic or semianechoic chamber, which begin at over $100k. But for small products, the new TEM cells are a bargain—complete systems for well under the cost of the smallest, uninstrumented chamber.
What EMC Design Tools Do You Need?
Table 1 can help you decide which tests to bring in-house by taking into account what is needed to perform the tests, the costs, and the benefits. Only when the testing involves large chambers, such as radiated RF emissions or immunity tests, is any special training or skills necessary. Most basic EMC tests, including RF immunity and precompliance emissions tests in small chambers, can be performed by any engineer or technician with little training.
All the tests provide three benefits:
Test-house costs are eliminated for some tests and reduced for others. For those tests, such as RF emissions where it is likely you will still have to have tests done at a commercial facility, in-house precompliance testing will ensure the outcome of the compliance tests and eliminate the need for later redesign.
Time-to-market is substantially reduced because fixes can be tried and retested quickly.
Because EMC testing is an on-going process, your investment in test instruments is just that—an investment that will pay for itself sooner than you think.
Cost-Analysis Spreadsheet
Do the cost analysis for your own products, and make an informed decision about meeting your test requirements. If you would like a copy of the spreadsheet in electronic format, just e-mail [email protected] with your request. Once you have the spreadsheet, enter the requested information and the real costs, and lost revenues will be calculated for you. The spreadsheet also is available on EE’s web site at www.evaluationengineering.com.
About the Author
Michael Hopkins is director of sales and marketing for KeyTek EMC products. He has 20 years experience in EMC and currently is an active member of ESD Association WG14 for Simulators, the IEC TC77A Working Group 6, and several ANSI committees and working groups. Mr. Hopkins also is a full member of the IEEE and the IEEE EMC Society and has participated in numerous national and international seminars as author, speaker, and panelist. KeyTek, Division of Thermo Voltek, a Thermo Electron Co., One Lowell Research Center, Lowell, MA 01852, (800) 753-9835, www.thermovoltek.com.
Copyright 1998 Nelson Publishing Inc.
July 1998
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