Conformity Magazine - October 2008 - (Page 53)

them, the key parameters are the transimpedance (voltage output for a given current) versus frequency. Power Quality Testing Equipment In the European Union, CE-marked equipment is often subjected to harmonics and flicker requirements, EN 61000-2 and 3, respectively (EN 61000-12 for high current equipment). There are also requirements for dips and interrupts. A key component for all of these tests is a programmable power source with enough power and of low distortion (the purity of the source is specified in EN 61000-3-2). For harmonics and flicker testing, this has to be coupled with data acquisition and analysis circuitry. For dip and interrupt testing, where the power voltage is varied, inrush current capability is also a relevant specification. When assessing the capabilities of a programmed power source, software function and reliability is of concern. Think of the programmable power source as a multi-kilowatt arbitrary waveform function generator. It becomes apparent that software or hardware glitches that affect the output can potentially damage the equipment under test. Upgradeability is also an important factor. The harmonics and flicker standards, in particular, have changed frequently in the past several years. A system that can be modified to meet newer standards via software or hardware updates is a significant plus. Transients Until now, we have been discussing frequency domain tests. Transients are time domain tests. The three most commonly performed transient tests for ITE and telecom equipment are: 1. 2. 3. Surge test, per EN 61000-4-5; EFT (electric fast transient burst), per EN 61000-4-4; ESD (electrostatic discharge) per EN 61000-4-2. Electrostatic Discharge (ESD) per EN 61000-4-2 is the test that simulates discharge to a product from charged personnel. This ESD test uses a very fast (less than 1 nSec rise time) pulse, but the energy is modest. The details of the waveshape are specified in the standard, and form a part of verifying instrument calibration. Indeed, in recent years, auditors have increased their requests that waveform verification of surge equipment, including ESD, be performed more often than at the typical semi-annual instrument calibration checkup. Often, daily verification is required. ESD testing can be performed with a one-shot trigger, but some programmability can make testing easier. For example, some ESD standards require a number of repetitions in each polarity at a given location on the product, and with an interpulse spacing long enough to allow the equipment under test to “settle” from the effect of the prior pulse. The test is a lot easier to administer if this counting and timing can be automated. When looking for transient generation equipment, one question is whether or not to buy combination test equipment (which performs two or even three of these tests) or separate, single purpose units. There is no definite answer. Things to consider are convenience, cost, intensity of equipment use (only one thing can be done at a given time), and software. Summing Up It takes a long shopping list to fill up an EMI/EMC lab. In this brief article, we’ve highlighted some of the things you’ll need, and discussed factors which differentiate competing products. Michael Buchholz is the laboratory manager for CurtisStraus LLC, a Bureau Veritas company, and can be reached at Michael.Buchholz@us.bureauveritas.com. Each of these tests is quite different in terms of the speed and energy of the transient waveform. The surge waveform has a 1.2/50 uSec rise/fall time, and is delivered through a low impedance. Surge generators must be able to handle the range of voltages required for the type of equipment being tested. Different coupling circuitry is required for AC and signal lines. Note that on three phase lines, the surge has to be delivered at known phase angles with relation to the incoming power. EFT waveforms are faster, but have much less energy. The waveform is much quicker (5/50 nSec), but is delivered in repetitive bursts. EFT testing is performed on the mains and on signal cables. The mains tests are delivered through a backfilter coupling device which decouples the EFT generator from the mains voltage while blocking the pulses from going down the mains supply. The EFT standard also contains detailed construction plans for a capacitive clamp, which is used for testing non-mains cables. FAST Link www.conformity.com/2270 oCtober 2008 Conformity 53 http://www.conformity.com/2270

Table of Contents Feed for the Digital Edition of Conformity Magazine - October 2008

Conformity Magazine - October 2008 Contents Editor's Note FCC Releases Annual Report on National Do-Not-Call Registry Commission Cracks Down (for the Fourth Time!) On Junk Fax Marketer FCC Releases Quarterly Reports on Consumer Inquiries and Complaints Greenpeace Ranks Electronics Manufacturers Standards List For The EU’s Energy Consumption Directive Published EU Commission Publishes Standards List for Directives on Pressure Equipment, Pressure Vessels Standards List for the EU’s Medical Devices Directive Available The IEEE Product Safety Engineering Society: The First Five Years ESD Open Forum Improving Election Security and Accuracy: The Future of Voting System Certification Conformity Assessment and Accreditation: Their Role in the Global Market Design Issues in Extreme EMC Environment Focus On... Test Equipment Buyers Guide Product News Updated Standards List for EU Directive on Active Implantable Medical Devices FDA Warns of Effects from CT Scans on Electronic Medical Devices FDA Provides Report Card on Its PMA Review Process CPSC Releases Import Safety Strategy Other CPSC Actions in the News IEC Standards Update Product Reviews UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - October 2008

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