EMI@EMC²
EMC Corp.'s EMI engineers test computer storage systems in a lab designed to handle a 5000-lb beast.
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 8/1/2004
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Read the August 2004 features: Find reflections in glass For more information on EMC test, visit www.tmworld.com/emc. |
"Prior to constructing the EMI lab, we were at the mercy of third-party lab schedules," said Cliff Stark, senior manager of compliance engineering. "We would schedule a test for an eight-hour shift at a lab, then spend three hours setting up the EUT. When the shift ended, we had to remove the equipment and set it up again on another day to complete our testing."
The company had other test issues, too. For example, a large storage system may contain nearly 600 hard drives, weigh about 5000 lbs, and consume 10,000 W of electricity. Given those hefty stats, Stark and his team couldn't use most outside EMI labs.
Built in 1999 at a cost of $4 million, EMC2's EMI test lab houses the first 10-m semianechoic chamber built in New England (Figure 1). Five NARTE-certified (www.narte.org) engineers and technicians now work in the lab.
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Figure 1. A storage system under-goes RF immunity and emissions tests in the 10-m chamber. Courtesy of EMC Corp. |
Compliance engineers Ken Klimasewski and Dan Marino (Figure 2) use the chamber to test new products for radiated and conducted emissions. They also test for surge and other AC mains immunities as well as ESD immunity. In addition, the compliance team works with design engineers early in a product's design cycle to identify potential EMI issues.Bridge the gap
Because the lab must accommodate large, heavy EUTs, it has some unusual characteristics. Most EMI chambers have a pivoting door lined on the inside with absorbing cones. Usually, the bottom of the door is a few inches off the floor, and a strip of chamber wall runs between the door opening and the floor. A person enters the chamber by stepping over the strip, but moving heavy racks into and out of the chamber is nearly impossible.
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Figure 2. EMI engineers Ken Klimasewski (left) and Dan Marino use a small horn antenna and EMI receiver to locate teh source of radiated emissions. Courtesy of EMC Corp. |
Behind the white tiles on the chamber walls reside the usual absorbing cones. Behind the cones, 74,000 ferrite tiles absorb RF emissions produced by a product under test.
Among the chamber's other unusual features are overhead lights that are embedded in the ceiling tiles to prevent reflecting signals. A fiber-optic camera, also embedded in the ceiling, lets engineers view the EUT from outside the chamber. While inside the chamber, engineers can talk to people in the control room through an intercom in the walls.
The lab needs enough electric power to provide the 10,000 W needed for some storage systems. "We built the lab with is own 75-kVA motor generator to provide clean, sufficient, three-phase power at 50 Hz," noted EMI engineer Boris Shusterman. Power cables for the storage racks and antenna mast, plus signal cables from spectrum analyzers, amplifiers, and signal generators in the control room, enter the chamber from under the floor's ground planes.
Engineers use software to control the test equipment and switch among three antennas during an EMI scan. "The three antennas let us automatically measure emissions at frequencies up to 7 GHz for compliance to EMI standards," said Shusterman. "We test at frequencies beyond 7 GHz, but we run those tests manually."
Because of automation, EMC2's EMI engineers can perform a standard 30-MHz-to-1000-MHz scan in about 2.5 hrs. The best part is that they don't have to break down a test setup just because a shift ends.
