AV Technology - October 2008 - (Page 29)

Ground loops occur because no two points in a grounding system are ever at exactly the same voltage. the mesh grounding technique. It is a network of copper or aluminum wires or straps typically arranged in a 2x2-foot grid and supports a raised floor of removable tiles. The tiles are usually slightly conductive to help control static electricity build-up. Power and signal cabling is routed under the floor and the space sometimes serves as a conduit for air conditioning as well. This kind of SRG has been used for over 30 years in data processing centers and was effectively standardized in 1983 when the U.S. Government published FIPS PUB 94, “Guideline for Electrical Power for Automatic Data Processing Installations.” At that point in time, “high-speed” computers used 20 MHz clock frequencies. To make matters worse, most data interfaces were unbalanced (RS-232, parallel ports, or backplane) and notoriously susceptible to ground voltage differences. The noise problems were real and the SRG was an important part of an effective solution. But today computers run at least 100 times faster and use balanced data interfaces (Ethernet, RS-485, etc.) that are much less susceptible. Increasingly, data centers are now being constructed on slab floors where it would be difficult if not impossible to install an SRG under the floor. So far, data centers installed without SRGs have experienced no adverse effects on the operation of the IT equipment, leading some technical experts to questions the need for SRGs. Yet, in spite of evidence that mesh grounding is increasingly unnecessary, it is still often specified today — presumably to eliminate problems with so-called “sensitive” equipment. Modern AV systems, and the equipment itself, have evolved over the years into hybrid mixture of “low-frequency” analog and “high-frequency” digital. As the frequency of digital signals has rapidly increased, grounding methods like the SRG have become essentially obsolete. Saavy manufacturers are now making high-frequency noise control an issue of internal equipment design rather than system grounding. Bill Whitlock is president of Jensen Transformers, Inc., and a leading authority on matters relating to power systems, grounding, and signal integrity. He can be reached at whitlock@jensen-transformers.com. http://crwww.com http://crwww.com

Table of Contents Feed for the Digital Edition of AV Technology - October 2008

AV Technology - October 2008 Contents Precedent Corporate: Residential AV Does Not Equal Commercial AV Government: Funding Problems? Education: DIY ISP.EDU, Part Two The Cost of Bandwidth Star Grounding Wars Understanding IoIP How to Equip a Smart Classroom Two Rooms With A View From Primitive to Professional Product Review:�Visionary Solutions AVN 420 Encoder Product Spotlight: Document Cameras New Products Ad Index AV MO: Using Infrared Microphones

AV Technology - October 2008

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