EMC: RFI PROTECTION
❱❱ Modular elements gain EMC treatment from Verotec to provide protection in complex rack-mounted environments; conductive sealing gaskets and tape products, inset, provide a simple way of enhancing the RFI protective quality of enclosures
Achieving EMC closure P
Jonathan Newell looks at two ways of enclosing susceptible electronics systems to protect them from harmful RFI
utting susceptible electronic assemblies into a metal box to isolate them from harmful RFI environments is a cheap, effective and widely practiced way of
achieving EMC compliance. Yet there are many things to consider: temperature build-up, sealing of the enclosure, what to enclose, how to provide connectivity and other benefits the enclosure might bring.
SEALING GASKETS Door sealing gaskets are available that have conductive coatings to protect the contents from RFI. Some gaskets are impregnated so that conductivity is maintained throughout the cross-section while others are sheathed in a conductive coating. EMC versions of the EPDM rubber
gasket by cabinet specialist Emka have a conductive external skin to attenuate the transmission of electro-magnetic interference across a sealed junction. According to Emka, this conductive
coated gasket and tape system provides a contiguous conductive pathway to ensure EMC performance on steel enclosures and cabinets where that of the original design was insufficient or perhaps non-existant. As such, it is a useful add-on that can mitigate an existing EMC problem. Such gaskets also provide other
advantages such as gap sealing, noise reduction, vibration damping and impact cushioning of the cabinet.
BESPOKE ENCLOSURES Sometimes it isn’t enough to simply cage your electronics in a metal box. More complex electronic architectures require a more bespoke approach, particularly if the unit to be protected is already in an enclosure or is rack mounted and needs protection from other parts of the system. An example of is a mass spectrometer
controller housing. The spectrometer supplier needed to provide EMC screening while also achieving improved thermal management and mechanical protection, all while keeping costs under tight control.
The controller sits within the mass
spectrometer and is rack mounted. Solid side plates and top and bottom ventilated covers provide an 80 per cent open aperture ratio for ventilation with effective attenuation. The 6U high card cage has four different designs of EMC screened front panels and a plain EMC blanking panel. The backplane is just 1.5mm thick and
mounts as normal on the rear tiebars, extending below the card cage to give an I/O area fitted with multiple Min D connectors. A solid rear cover provides both EMC shielding and mechanical support for the backplane; an additional separate front cover protects the Min D
connectors. Conductive gaskets ensure ground continuity; the large cable aperture through the rear panel is also fitted with an additional external EMC cover once the cable is installed. Three 80mm top- mounted fans provide managed cooling. The mass spectrometer protection was
provided by specialist company Verotec as part of its KM6 subrack family of products. The KM6 family benefits from the
availability of a wide choice of EMC kits, anodised or Alochrome conductive finishes, standard plug-in modules and front panels, divider kits, ventilated and plain top and base covers, front and rear panels and thermal management products. EE
September 2018 /// Environmental Engineering /// 35
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