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EMC Comes to the Fore
High-speed industrial systems push enclosure shielding needs
Terry Costlow -- Design News, April 5, 2004
As more high-speed electronics find their way into industrial applications, electromagnetic interference is becoming a bigger issue. Enclosure makers are adding shielding to a number of their products, helping system designers meet regulations to mitigate electromagnetic coupling.
"Over the years, we've seen an increase in demand for EMC protection, with more and more coming in industrial environments. Before, the only demand was in electronics," says Mike Herzog, industrial product manager at Rittal Corp. of Springfield, OH (http://rbi.ims.ca/3847-514).
That's driven in part by Europe's CE regulations, which have required protection since the late 1990s. Additionally, bus specifications such as Compact PCI require minimal emissions from electronic systems.
In some environments, concern goes beyond EMI leaking out of high- performance computers. In factories and other noisy environments, for instance, noise can sometimes cause spurious errors for sensitive electronics.
Some enclosure manufacturers say that EMC shielding is becoming a standard feature, while other manufacturers addressing other markets say the majority of their customers don't yet require shielding. The main reason for the latter category is the cost. "A big challenge is to do EMC cabinets at a cost the market will bear," says one industry expert, George B. Ross, a spokesman for Schroff Products of Warwick, RI (http://rbi.ims.ca/3847-515).
The pricing premium comes primarily from the expense of coating the inside of cabinet walls with nickel or other conductive materials. Gaskets and additional flanges also add to the cost of shielding.
"The biggest issue is where the door and the body come together. With higher frequencies, the waves are smaller so it's easier for them to leak out," says Abdi Jama, design engineer at Hoffman Enclosures Inc. headquartered in Anoka, MN (http://rbi.ims.ca/3847-516).
Engineers whose systems nearly meet EMC requirements can sometimes avoid the added expense by simply moving to an unshielded system with better attenuation. For example, Rittal's TS enclosure has integrated grounding clips, which dig into the base metal of the skin, providing a bit more grounding.
"That can provide about 20 dB better attenuation, which often solves the problem so companies don't need to go to shielded packages," Herzog says.
Not just shielding
Many of the shielding techniques used for high-speed office computers will work in industrial environments. But as EMC packaging moves into harsher environments, engineers may find that they need to move to different shielding techniques. "Another issue in terms of the material people choose is corrosion. That can cause degradation in performance," says Trent Jones, engineering manager at Hoffman Enclosures. The company has patented techniques that stand up to water, cutting fluid, and other corrosive materials, he adds.
While a growing number of design engineers are starting to think about EMC, enclosure makers note that their counterparts in medical applications and other fields are becoming concerned about magnetic emissions. Those who figure that the same shielding works in both areas may be in for a surprise. "Enclosures that provide excellent magnetic attenuation may not provide good electronic attenuation," says Brian Mordick, senior product manager at Hoffman.
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