Apart from the style, image, price, service, quality and reputation of the organisation, this report shows what needs to be taken into consideration when selecting an enclosure. Design engineers should choose the enclosure first and then select the electronic and mechanical components to suit the enclosure.
The Material
The two main choices are between plastic (ABS, Polycarbonate, Polyester) enclosures and metal (aluminium, stainless steel) enclosures. Plastics are normally light weight, have flexibility in design, higher functionality, better insulation and radio frequency permeability. Metals have greater mechanical strengths, better resistance against ultraviolet (UV) radiation, a wide temperature range as well as EMC characteristics. Chemical resistance may also be required but this will depend on the type of material and coating used.
Plastics are used in electronic applications and metals are used in industrial applications.
Environmental Considerations
From airborne debris, temperature and UV rays, environmental elements can have a significant impact on how an enclosure will perform over many years of operation. For example, a fiberglass enclosure exposed to direct sunlight for several years will likely experience fiber-bloom and a mild steel enclosure will rust in wet or corrosive environments. Stainless steel may also rust if sprayed with salt. To prevent these problems, customers must take into consideration whether the enclosure will be located indoors or outdoors (a pressure compensation gland may be required for outdoor applications), the weather, UV and harsh chemical sprays. Customers should also evaluate if the enclosure will be located in a highly active environment, such as heavy industrial equipment or an electronic device where the enclosure is frequently used. Different materials offer varying degrees of impact resistance, and both plastic and metal enclosures are available with options to provide easy access to the enclosed components.
Electromagnetic Compatibility (EMC)
Electromagnetic compatibility (EMC) refers to a characteristic which is normally required. It aims to ensure that equipment items or systems will not interfere with each other as a result of undesirable electrical or electromagnetic influences. Plastic enclosures often have low EMC characteristics where as metal enclosures has high EMC characteristics.
This means that a metal enclosure should be used when electromagnetic compatibility is very important. Although enclosure manufacturers may offer processes to optimise the EMC characteristic of a plastic enclosure to the level of a metal enclosure.
The Ingress Protection
Many applications require electrical and electronic equipment to work safely and reliably for many years under difficult environmental conditions. The ingress protection classification DIN EN 60529 supports protection against accidental contact and foreign bodies as well as protection against water. The IP categories specify the extent to which the surface of the enclosure is closed and is protected from dust and water. The letters IP (ingress protection) is followed by a two-digit number.
The first digit indicates the level of protection against accidental contact and foreign bodies:
|
Digit |
Protection against accidental contact |
Protection against foreign bodies |
|
0 |
No protection |
No protection |
|
1 |
Protection against large-area bodies Ø 50 mm |
Large foreign bodies (Ø 50 mm and higher) |
|
2 |
Finger protection (Ø 12 mm) |
Medium-sized foreign bodies (Ø 12.5 mm and higher, up to 80 mm in length) |
|
3 |
Tools and wires (Ø 2.5 mm and higher) |
Small foreign bodies (Ø 2.5 mm and higher) |
|
4 |
Tools and wires (Ø 1 mm and higher) |
Granular foreign bodies (Ø 1 mm and higher) |
|
5 (K) |
Wire protection (same as IP 4) dust-protected |
Dust deposits |
|
6 (K) |
Wire protection (same as IP 4) dust-proof |
No entry of dust |
The second digit indicates the level of protection against water:
|
Digit |
Protection against water |
|
0 |
No protection |
|
1 |
Protection against water dripping vertically |
|
2 |
Protection against water dripping vertically when the enclosure is inclined at an angle of up to 15° |
|
3 |
Protection against water spraying onto the enclosure onto the enclosure at up to 60° on both sides of the vertical |
|
4 |
Protection against splash water from all sides |
|
4k |
Protection against splash water from all sides at increased pressure, applies only to road vehicles |
|
5 |
Protection against water jets (nozzle) from any direction |
|
6 |
Protection against powerful water jets (flooding) |
|
6K |
Protection against powerful water jets at increased pressure (flooding), applies only to road vehicles |
|
7 |
Protection against temporary immersion – Immersion depth: 1 meter, test time 30 minutes |
|
8 |
Protection against constant immersion – agreed between manufacturer and customer |
|
9K |
Protection against water during high-pressure/steam jet cleaning, applies only to road vehicles |
Dimensions
The internal and external dimension of an enclosure is extremely important when developing a new piece of equipment. In many cases the printed circuit board is chosen first and this makes it difficult for the design engineer to source the best enclosure solution.
Modification of Standard Enclosures
There are many ways of designing enclosures to meet customers’ individual requirements. The enclosure manufacturer may support modification with added value services that include milling, drilling, cutting and sawing. They may also provide a service to fit membrane keypads, front membranes or displays on the enclosure as well as a complete solution. There are various enclosure accessories such as decor seals and decorative stripes that can also make a considerable difference to the design and look of a standard enclosure.
If the customer wants the enclosure to have colours of the company’s corporate image, then a water transfer process can be applied or the enclosure can also be lacquered.
Ease of Assembly
An important point to consider when selecting an enclosure is how easy it will be to fit the components. A complicated design and construction may make it difficult to assemble electronic and mechanical components in the enclosure.
This problem can be avoided by using enclosures with a snap lock or quick-release fastening. Some enclosure manufacturers may also provide a fitting and assembly service and support the customer with a system solution including testing. The customer will provide the printed circuit board including components and the enclosure manufacture will produce the final product.
