April 17, 2023
DIECAST ENCLOSURES ARE NOT IMMUNE TO RFI/EMI
Diecast aluminium enclosures are much better at dealing with radio frequency interference (RFI) and electromagnetic interference (EMI) than their plastic counterparts. Aluminium enclosures can provide some degree of inherent RFI/EMI shielding due to the conductive properties of the metal.
But RFI/EMI can still affect the equipment. The shielding effectiveness of a metal enclosure depends on various factors such as the:
- thickness of the metal
- frequency range
- design of the enclosure.
In some cases, the shielding effectiveness may not be sufficient to prevent RFI/EMI from entering or exiting the enclosure. Enclosures may have openings where RFI/EMI can leak in or out. These can include gaps around cable entry points.
Even small gaps can allow RFI/EMI into or out of the enclosure. Ingress protection seals can be a known vulnerability when it comes to this. Furthermore, metallic fasteners, hinges, or other mechanical connections can create attenuation weak points. So additional measures such as RFI/EMI shielding coatings or gaskets may be necessary to achieve the required level of attenuation.
HOW RFI/EMI SHIELDING WORKS
RFI/EMI shielding is based on the principle of the Faraday Cage: if a conductive material is placed around an area of space, electric fields present can be cancelled out – and any magnetic fields will be redirected around the material.
When an external electromagnetic field (EMF) encounters a Faraday cage, it induces an opposite charge on the surface of the conductive material. This creates an electric field that cancels out the external field inside the enclosure, effectively blocking the penetration/emissions. The cage also reflects any electromagnetic waves that strike its surface, preventing them from passing through the material.
Electronic components within the enclosure can be designed with filters or other suppression devices to reduce the amount of RFI/EMI generated or received. Also, the enclosure must be earthed properly to prevent the build-up of electrical charges that can also be a problem.
ISSUES WITH SHIELDING GASKETS
RF gaskets are manufactured from a fine latticework of wires. They create secure but delicate contact between opening parts, and thus ensure the Faraday Cage is achieved. However, these gaskets can be fiddly, prone to breaking – and they are not particularly cost-effective (especially if you keep having to replace them).
This can be an issue at the best of times – but none more so than when an enclosure needs to be opened regularly for inspection and maintenance. This repeated opening and closing of the enclosure lid can significantly shorten the life of an RF gasket and create the risk of RFI/EMI entering or leaving the enclosure.
ROLEC have devised a much better method of shielding.
ENCLOSURES WITH BUILT-IN EMC SHIELDING
ROLEC’s conFORM and conTROL industrial diecast electronic enclosures don’t need RF gaskets because they have RFI/EMI shielding built in as standard. The enclosures have a ‘tooth and rail’ system which ensures continuous contact between base and lid. This creates the Faraday Cage necessary to protect electronics from RFI/EMI.
Each model has unpainted teeth pre-cast into the bottom section and an uncoated contact rail inside the lid. The teeth bite into the lid rail when the enclosure is screwed shut. This proven system provides metal-to-metal contact – ensuring the dependable conductivity needed for a high degree of shielding. And it does so without compromising the ingress protection offered by the seal in the lid, thanks to the separate contact and sealing levels. It’s a simpler and more effective alternative to using gaskets.
Let’s examine these two diecast enclosure models in more detail.
conFORM IP 66/IP 67 EMC-SHIELDED ENCLOSURES
Tough, ergonomic conFORM is a ‘go anywhere’ diecast aluminium enclosure for industrial applications where EMC protection is critical. Its high shielding from radiation interference has been tested by the University of Hanover.
These diecast enclosures are perfect for a wide range of industrial electronics; they can be fitted to walls, machines and bulkheads. And importantly, they are available in sizes compatible with other standard enclosures on the market – making it easy to exchange and upgrade from your existing housings.
The screw channels are outside the interior – maximising the amount of space available for electronic components. Inside, there are threaded screw bosses for the installation of PCBs, mounting plates and terminal rails.
The enclosures are powder coated in pebble grey (RAL 7032) as standard but other colours are available on request. Accessories for conFORM include external mounting brackets, lid holders, lid hinges, an installation kit, corrosion-proof coating, mounting plates and a supporting rail for series terminals. Cable glands are also available.
conTROL IP 66/IP 67 EMC-SHIELDED ENCLOSURES
Rugged conTROL diecast enclosures feature the same tooth and rail system as conFORM – again ensuring EMC protection without all the cost and hassle associated with fragile gaskets. And again, there are separate levels for sealing and contact.
What sets conTROL apart from conFORM is the deeply recessed lid which provides excellent protection for buttons and other controls in challenging industrial environments. Inside the enclosure, you’ll find threaded bosses for installing PCBs, mounting plates and terminal rails.
These diecast enclosures are available in four sizes, again all powder coated in pebble grey (RAL 7032). And again, custom colours are available on request. Accessories include external mounting brackets, lid holders, hinges, an installation kit, corrosion-proof coating, mounting plates, supporting rail and cable glands.
AT-A-GLANCE COMPARISON GUIDE
- Which of ROLEC’s EMC-shielded enclosures are available in the most sizes? ConFORM (14 sizes vs conTROL’s four sizes).
- Which enclosure offers the largest size? ConFORM (268 x 168 x 60 mm).
- Which enclosure offers the smallest size? ConFORM (79 x 84 x 67 mm).
- Which offers greater lid recess protection for buttons/controls? conTROL.
SPECIFY CUSTOMISED ENCLOSURES WITH BUILT-IN EMC SHIELDING
ROLEC enclosures can be specified fully customised – so they can go straight to your production line ready for the installation of electronic components. ROLEC’s services include machining, engraving, custom colours (powder coating or wet painting), display windows, membrane keypads and photo-quality printing of legends, logos and graphics.