HOW TO SPECIFY SHIELDED ENCLOSURES TO MANAGE ELECTROMAGNETIC INTERFERENCE

CAUSES OF ELECTROMAGNETIC INTERFERENCE

Electromagnetic interference (EMI) and radio-frequency interference (RFI) can degrade the performance of a circuit or even stop it from functioning. In the case of a data path, the effects can range from an increased error rate to a complete loss of data.

EMI can be caused by electronics such as ignition systems, mobile phone networks, power lines and devices that generate changing electrical currents and voltages. It can also be the result of natural sources such as lightning, solar flares, coronal mass ejections, and the Northern and Southern Lights.

The closer an electronic device is to an EMI source, the more susceptible it is to interference. Devices placed near large motors or radio antennas are more likely to be affected. Equipment that lacks adequate electromagnetic shielding can be more vulnerable to EMI.

Many devices emit signals at multiple frequencies. Interference can occur if these frequencies overlap with those used by other devices. This is particularly relevant in communication systems where multiple signals may be transmitted simultaneously.

WHY INDUSTRIAL WORKPLACES ARE MORE PRONE TO EMI AND RFI

Factories and other industrial buildings tend to have more EMI issues because of the prevalence of heavy machinery, switching devices, variable frequency drives, power lines and high-frequency communications equipment.

This is often exacerbated by the lack of isolation. Various different types of equipment can be grouped close together, increasing the risk of EMI. Furthermore, industrial buildings are often based on large metal structures: the beams, girders and metal walls can reflect and amplify electromagnetic waves.

WAYS TO PREVENT EMI

Effective ways to reduce EMI include proper earthing, filters and maintaining separation between different cables. Increasing the distance between the source of the interference and sensitive equipment can reduce the impact of EMI/RFI. This is often considered in the layout and physical placement of equipment within an environment.

Using twisted pair wiring and designing electronic circuits and layouts to minimise interference (by separating high-frequency components from sensitive areas) can also prevent many potential EMI/RFI issues. But it is wise to specify EMC shielding if EMI and/or RFI are likely to be an issue. EMC shielding is based on the principle of the Faraday Cage…

HOW THE FARADAY CAGE STOPS EMI/RFI

A Faraday Cage is an enclosure used to block electromagnetic fields. It is named after the English scientist Michael Faraday, who invented it in 1836. The cage works by redistributing an electrical charge over a conductor, neutralising the effects of external electric fields.

A Faraday Cage can be made from a continuous covering of conductive material (or mesh) such as copper, aluminium or steel. The key is that the material must conduct electricity. When an external electric field hits the Faraday Cage, the free electrons within the conductive material cancel the field’s effect inside the enclosure. Essentially, the external electric field causes these electrons to redistribute themselves in such a way that the internal field is nullified.

For radio frequencies, the Faraday Cage operates by absorbing and reflecting the radio waves. The mesh or solid shell of the cage reflects incoming or outgoing electromagnetic radiation, stopping  it from passing through. The holes in a mesh cage must be significantly smaller than the wavelength of the radio waves they are meant to block. This is why the size of the mesh or gaps in the enclosure is crucial.

EMC SHIELDING OF PLASTIC ENCLOSURES

Plastic is non-conductive so it does not provide any natural protection against electromagnetic fields. OKW plastic enclosures can be protected with EMC shielding, which is available on request as a custom service.

OKW carries out all EMC shielding in-house to ensure optimum quality and speed of delivery. Plastic parts are vapour-plated with 99.98% pure aluminium. We apply this coating in a high vacuum to achieve a cleaner, more consistent layer of aluminium.

The absence of air and other gases produces a more even coating – minimising the presence of any contaminants or air molecules that could interfere with the deposition process. The result is a superior coating that also looks better.

Granted, the coating is inside the enclosure – and will therefore not be seen – but if a job is worth doing, it’s worth doing well. Generally, the coating is 2.5 µm thick. But other coating thicknesses are available on request.

Find out more about EMC shielding >>

EMC CONDUCTIVE SEALS TO BLOCK EMI/RFI

The seal that sits between two sections of an enclosure can be an EMI/RFI weak point. It can prevent the complete electrical continuity that is needed to create a Faraday Cage. This can be a real issue in industrial settings because enclosures need IP-rated seals to prevent the ingress of dust and/or water. And as you’ve already read, industrial locations can be an EMI/RFI hotspot.

OKW can supply conductive seals from ø 1.5 mm to 3 mm on request. As a custom assembly service, we can also fit the seals to the enclosures. You’ll thank us for this because EMC gaskets must be fitted carefully.

OKW plastic enclosures frequently requested with EMC shielding include…

SHELL-TYPE CASES: INSTRUMENT ENCLOSURES WITH SHIELDING STRIPS

SHELL-TYPE CASES are classic OKW universal instrument enclosures that provide excellent EMC shielding with custom vapour-plating – and with aluminium contact strips (accessory) that sit between the top and base shells.

These contact strips provide the extra electrical continuity needed to create the Faraday Cage effect. They are available for all four plan sizes of this enclosure, from 85 (45 x 85 mm) to 190 (138 x 190 mm).

SHELL-TYPE CASES are available in three different types: V (open front for a panel), O (open front and rear for panels) and G (closed front and rear). Types V and G can be specified with a battery compartment (2/4 x AA, 1/2 x 9 V). Tongue and groove construction add strength. Inside there are screw pillars for installing PCBs – along with guide ridges for the vertical mounting of PCBs or partitions.

These ABS (UL 94 HB) enclosures are off-white (RAL 9002) as standard. Front/rear panels (accessory) can be specified in either aluminium or infrared-transparent red PMMA. Accessories also include IP 65 sealing kits (Type G without battery compartment), a belt/pocket clip, wall mounting brackets, wall suspension elements, battery clips, a tilt foot bar, battery spacer, a plug-in contact (9 V), ring eyelets and anti-slide feet.

View the SHELL-TYPE CASES range >>

SOLID-BOX TOUGH ENCLOSURES FOR INDUSTRIAL ELECTRONICS

SOLID-BOX – OKW’s newest industrial electronic enclosure – has IK 08 impact protection, IP 66 and IP 67 ingress protection. It’s ideal for wall-mount and desktop electronics in harsh environments. And mounting points on the rear of size 145 and 175 match the hole patterns of VESA MIS-D 75/100.

Separate channels for the mounting screws and lid screws enable ‘lid closed’ installation, protecting the seal and electronics. Flush-fitting trims conceal the corrosion-resistant fixing screws (which are Torx as standard to deter tampering).

SOLID-BOX is moulded from flame-retardant PC+ABS (UL 94 V-0) in anthracite (RAL 7016) or light grey (RAL 7035). There are three sizes from 135 x 115 x 50 mm to 225 x 175 x 70 mm. Accessories include hinges and case feet.

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ROBUST-BOX UNIVERSAL IP 66 ENCLOSURES

With a name like ROBUST-BOX, this enclosure was always going to be known for its strength – but it’s much more than simply a tough housing. Some simple but smart design features make it highly versatile too.

Both case shells have a recessed operating area and pre-moulded threads so you can combine two tops, two bases or one of each to create the size you need. This helps to ensure that ROBUST-BOX is perfect for desktop, wall-mount, DIN rail and also handheld electronics.

These light grey housings can be specified either as complete enclosures or in parts. They are available in ABS (and approved as a terminal mounting case) or in PC with high heat resistance. Both plastics are rated UL 94 HB.

Choose from five widths: 80 mm (length 80-240 mm), 120 mm (length 120-240 mm), 160 mm (length 160-240 mm), 200 mm (length 300 mm) and width 240 mm (length 360 mm).

Accessories include colour-coded cover strips to conceal the fixings. These red (RAL 3020), yellow (RAL 1023), green (RAL 6024) and blue (RAL 5017) strips are an alternative to the standard light grey. There are also DIN rail fastening elements, wall mounting brackets, hinges, PCB supports, case feet, pressure equalisation elements, cable grommets, security kits and a security plug.

View the ROBUST-BOX range >>

ADVANCED SMART-BOX IP 66 PLASTIC ENCLOSURES

These contoured wall-mount and desktop enclosures for industrial electronics feature lid closed installation and covered fixings. But this time the covers are hinged and attached permanently to the lid. Two plastic straps hold the recessed lid in place when it’s open.

The fixing screws are A2 stainless steel so they have a high resistance against corrosion, even where aggressive substances are concerned. On the underside there is plenty of space for labels. Inside, there are fastening pillars for PCBs and DIN rails.

SMART-BOX is moulded from UV-stable ASA+PC (UL 94 V-0). It can be specified in eight sizes from 120 x 90 x 50 mm to 280 x 170 x 60 mm. All are rated IP 66 except the largest which is IP 65. Accessories include case feet, pressure equalisation elements, cable grommets, a security set and security plug.

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DATEC-CONTROL HANDHELD ENCLOSURES FOR LARGE DISPLAYS

DATEC-CONTROL (IP 65) is one of our more specialised handheld housings – designed specifically for standard-sized LCDs and graphics display modules. These well-balanced ergonomic enclosures sit comfortably in the hand, with lots of space for a display and a membrane keypad.

This model is typically specified for applications including mobile data collection/transfer, measurement/control, Industry 4.0, Smart Factory and medical/wellness technology. Battery options include 2/3/4/5 x AA and 9 V with mounting for PCMCIA memory card holders. Plug-in battery packs (sizes M, L) make changing cells easy.

DATEC-CONTROL is moulded from off-white or black ABS (UL 94 HB) as standard. There are four sizes from 200 x 58/94 x 39.5 mm to 266 x 90/144 x 60 mm. Accessories include docking stations, wall suspension elements, display windows, sealing kits, battery compartments, battery clips, a battery spacer, contacts, a plug-in contact (9 V), soft-touch case protectors, a ring eyelet and a strain relief cable clamp.

View the DATEC-CONTROL range >>

DATEC-MOBIL-BOX (IP 65) HANDHELD PLASTIC ENCLOSURES

DATEC-MOBIL-BOX is a high-performance handheld enclosure for standard LCD modules. Acrylic windows (accessory) protect the display and ensure a high level of protection from dust or water ingress.

These ABS (UL 94 HB) enclosures are great for mobile data recording and transfer, measurement and control, stock and sales logging – especially in challenging indoor and outdoor environments.

Seven different versions are available to house display modules including LCD Type 2" LC glass, LCD Type 2 x 16 (compact or standard), LCD Type 4 x 16, LCD Type 2 x 20 miniature, LCD Types 4 x 20 (or no display at all). The standard colours are off-white or black.

Accessories include display windows, wall suspension elements, battery compartments, battery clips, a plug-in contact (9 V), tilt foot bars, sealing kits, anti-slide feet, a ring eyelet and a case protector (size L).

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SPECIFY CUSTOMISED ENCLOSURES WITH EMC SHIELDING

All OKW wired enclosures can be specified fully customised – ready for the installation of your PCBs and other components. We carry out all the work in-house to ensure consistently high quality throughout the process. Customisation services include EMC shielding, machining, lacquering, printing, laser marking, decor foils, special materials and installation/assembly of accessories.

View our full range of customising services >>

GET EXPERT TECHNICAL ADVICE

Phone or email our expert team for specialist advice on EMC-shielded enclosures for your electronics. Request a sample of your preferred standard enclosure.