Conformity Magazine - August 2008 - (Page 43)

or many years, the only radio frequency (RF) system in an automobile was an AM radio. AM radios were notorious for reacting to impulse noises, such as lightning and ignition firing, and RFI suppression was typically handled by concealing the ignition and generator or alternator noise using bypass capacitors and resistive ignition wires. In any event, car radios and other early automotive electronic systems were analog devices. They did not emit high levels of unintentional radiation, and were not susceptible to interference other than the aforementioned impulse noise. How the automotive electronic landscape has changed! First came compact disc (CD) players, which introduced the first digital signals within the automotive entertainment environment. Then, about 12 years ago, auto manufacturers starting equipping vehicles with navigation GPS-based systems, which added another receiver to the automobile. At the same time, digital electronics were being developed to control everything, from fuel injection and ignition to anti-skid braking. Today, consumers shopping for automobiles have a host of convenience and safety options from which to choose, including satellite radios from Sirius and XM, Bluetooth connections for handheld devices, remote keyless entry systems, adaptive cruise control systems that adjust a vehicle’s speed based on actual driving conditions, and tire pressure monitoring systems that tell you when to add air to your tires! And not far down the road (no pun intended!) are WiFi communications systems that will allow drivers to download information from the Internet, and direct short-range communication systems, which will allow vehicles to “talk” to one another and lead to the development of intelligent traffic systems. The bottom line is that, for all of these systems to work properly, they need to be able to operate together without interfering with each other. There are relatively high power transmitters, sensitive receivers, digital and analog infotainment systems, radar, control systems, and so on, all contained within a very small environment. Electromagnetic compatibility (EMC) is a must for each of these systems to function as intended. The vehicle and the electronics within it are also exposed to a vast external electromagnetic environment. Along with these conditions, the components must meet mandatory EMC requirements imposed by the auto manufacturers. F And of course, safety cannot be compromised, and is the most important EMC issue. Calculating Emissions and Susceptibility The equation for emissions from a basic circuit is: E = 1.316 AIF2/(dS) Where: E = field strength in µV/m, A = loop area in square centimeters, I = drive current in amps, F = frequency in megahertz, d = separation distance in meters, S = shielding ratio between source and point of measurement. Analyzing this equation, it is clear that frequency is the biggest culprit because emissions increase as the square of the frequency (F) increases. For current (I), emissions increase linearly, which is also true for loop area (A). The distance (d) is set by the specification, and 1.316 is a constant. Since the system designer has no control over these last two parameters, they must not be considered. The equation for susceptibility is: Vi = 2ΠAEFB/(300S) Where Vi = volts induced into the loop, A = loop area in square meters, E = field strength in volts per meter, F = SOLAR ELECTRONICS COMPANY 10866 Chandler Blvd., North Hollywood, CA 91601 (800) 952-5302 • (818) 755-1700 • Fax (818) 755-0078 See our catalog online at www.solar-emc.com Contact us at sales@solar-emc.com Innovative EMI Solutions Since 1960 The Solar Model 2654-1 Lightning Generator synthesizes electrical impulses needed for testing susceptibility to transients induced in aircraft equipment by lightning strikes. The peak voltage and current requirements of RTCA/DO-160E, Section 22 are met at Levels 1 through 3. Using available accessory probes, pulses can be applied by pin injection, cable bundle injection, and ground injection. AUGUSt 2008 Conformity 3 http://www.solar-emc.com http://www.solar-emc.com http://www.solar-emc.com

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

Conformity Magazine - August 2008 Contents Editor’s Note FCC Seeks Comment on Reauction of 700 MHz D Block Commission Cracks Down (Again!) on Junk Fax Marketer Canada Levies Fees for Public Safety Radio Spectrum FDA Issues Guidance on Medical Device Tracking Greenpeace Challenges Video Game Manufacturers The IEEE EMC Society: A Proud History of Accomplishments ESD Open Forum An Update on Changes to the Automotive ESD Standard, ISO 10605 Modeling of Radiated Electromagnetic Disturbances in Automotive Applications Design Issues in Automotive Radio Frequency Systems IEEE EMC Symposium IEEE 2008 Show Preview Exhibitors Buyer’s Guide Product News Most Eco-Friendly Companies Updated Standards List For the EU’s Pressure Equipment Directive Commission Issues Updated Standards List For Directive on Gas-Fired Appliances HHS Releases Fact Sheet on U.S. Imports from China Customs Agents Seize Holiday Lights IEEE PSES Symposium Set for October CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Product Reviews Advertisers

Conformity Magazine - August 2008

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