Conformity Magazine - September 2007 - (Page 28)

Round robin testing was performed on a total of 15 sample EUTs at three lab locations. The complete details of the round robin are beyond the scope of this article, but the net result of this study was that reducing the high frequency content of the test generator alone does not significantly improve the reproducibility of ESD test results. Overall, the variation in pass/fail data with the modified test generators was no better than it is when using the unmodified generators. Because of these findings, the IEC removed the changes to the discharge current specification in the subsequent second CD [4]. The data simply did not justify changing this element of the test generator. Proposed Changes to the Standard So, where does this leave the revision to the standard? The second CD includes several proposed changes that are expected to improve the overall effectiveness and reproducibility of the test. These proposals include the following items: 1. The specification of the test generator focuses on the generator’s output, and not so much on specific values of the storage capacitor and discharge resistor. The simplified model is still based on typical values of 150 pF and 330 Ω, but these are listed as typical values, not rigid requirements. This change is a reflection of reality. The discharge current specifications cannot be met by strict adherence to a simple 150 pF/330 Ω model. The nominal values of rise time, peak current and current at 30 nS and 60 nS are not changed. A mathematical formula for calculating the discharge current has been added. This formula will be useful in modeling the effects of ESD in electronic equipment. It also will allow accurate calculation of the discharge current at any point in time along the curve. • The metrology of the system used for calibrating the test generator is improved. A new current target with improved frequency response is specified. The target’s insertion loss must be flat to within ± 0.5 dB up to 1 GHz and within ± 1.2 dB between 1 and 4 GHz. • The analog bandwidth of the oscilloscope is increase to a minimum of 2 GHz. • A method of verifying the performance of the calibration measurement system is introduced. • Specific details of the physical setup for calibration, including treatment of the generator’s ground strap, are given. Experience has shown that the routing of this strap can have a significant influence on the calibration measurements. Hence, attention to this seemingly minor detail is crucial to reliable calibration. • The calibration procedure is listed in detail. These enhancements are intended to give a more complete, accurate and consistent picture of the test generator’s performance. For example, any high frequency content on the discharge current will be more evident. 2. The text of the standard has been improved to clarify that the material used for coupling planes is to meet the same requirements as material for the ground reference plane (GRP), but they do not have to use the exact same material. The GRP could be made of copper and the coupling planes from aluminum, for example. This clarification was added in direct response to inquiries from test labs that use the standard. The minimum size of the horizontal coupling plane is maintained at 1.6 by 0.8 m, but a larger plane can be used to accommodate EUTs that will not fit onto this size plane. 3. Figure 2: Simplified model of the ESD test generator 28 Conformity September 2007

Table of Contents Feed for the Digital Edition of Conformity Magazine - September 2007

Contents Editor’s Note FCC Extends Disability Access Requirements to VOIP Commission Fines Importer $3 Million Over Non-Compliant TVs FCC Gets Tough on Retailers Over Analog TV Tuner Labeling Analog Cellular Service Sunset Date Reaffirmed Commission Adopts Recommendations of Katrina Panel Free-Space Antenna Factors Through the Use of Time-Domain Signal Processing Editorial Correction ESD Open Forum An Update on Revisions to IEC 61000-4-2, the Basic Standard on ESD Practical Advice for Meeting the DFS Testing Requirements of the FCC The EMC Impact of Embedded Software ESD Design Buyer's Guide Tate Renominated to the FCC EPA Releases Report on U.S. Electronic Waste Additional Standards For The EU’s Toy Directive Medical Device Manufacturer Enters Consent Order Updated Guidance Document on Laser Products Issued FDA Offers Advice on Defective Heating Pads CPSC Issues China Product Safety Program Report Other CPSC Actions In The News IEC Standards Update Product Reviews Product News UL Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - September 2007

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