Bürklin Elektronik Quarterly # 04/2021 Englisch

HAMMOND ELECTRONICS
TOP TIPS WHEN SPECIFYING
SMALL ELECTRONIC ENCLOSURES
Your new project has been designed, prototyped, debugged, tested, tweaked, tested again and finally
signed off for production. In the ideal world, the enclosure would have been selected far earlier in the
process, but the first question after design finalisation is normally, “what size box do I need?”
1. SIZE
How big is the PCB? Is it to be mounted
horizontally or vertically? Many
plastic enclosures have slots in the
sides for direct vertical mounting
and mounting bosses in the top and
base for horizontal mounting. Extruded
aluminium enclosures will often
have slots in the sides for horizontal
PCB mounting. How much space
does there need to be on the faces
for indicators, switches, connectors,
cable entries and similar components?
What height is required for
board-mounted components or
multiple horizontal boards?
2. INSTALLED ENVIRONMENT
Will the product be used inside or
outside? Will the ingress of dust and
water be something to be considered
– see Point 4 below. Are there likely
to be contaminants present – oils,
chemicals and so on. Is impact resistance
a consideration? If so, metal
enclosures are better than plastic
ones. Are particularly high or low
temperature expected?
3. MATERIAL
For small enclosures, the choice is
mainly between ABS or polycarbonate
plastic, aluminium and GRP.
For outside installation, polycarbonate
or GRP are the default choices
for UV stability. Fire resistance is a
consideration; the relevant standard
is UL94, which specifies a vertical
or horizontal burn. The more stringent
test is the vertical burn test;
material will be classified as V0, V1
or V2 where V0 is the highest performance.
Aluminium enclosures are either
die-cast or extruded. Both are robust
and give good impact resistance,
they do not corrode and are electrically
conductive and are easily machined.
With a suitable gasket fitted
between the lid and the base, sealing
to IP68 can be easily achieved.
4. EMC
Plastic enclosures have one specific
weakness: they offer no EMC attenuation.
If EMC is a potential problem,
internal coatings in a variety of
materials can be applied to a plastic
enclosure to give different degrees
of attenuation.
Metal enclosures, providing that
there is electrical continuity between
the top, base and removable panels,
will provide an attenuation level suitable
for the majority of commercial
applications.
5. ENVIRONMENTAL SEALING
The relevant international standard
is EN 60529, which defines ratings
written as IPxx, where the first digit
defines the protection against solid
objects and the second the protection
against water ingress.
Typically, IP54 enclosures are suitable
for general purpose use; for
installation in environments where
dust and water are likely to be present,
IP66, 67 or 68 would be specified.
The highest rating is IP69K,
which gives protection against steam
cleaning at high pressure.
SOLID OBJECT PROTECTION CLASSES
First Scope of protection
Figure
0 No protection.
1 Protection against solid objects > 50mm.
2 Protection against solid objects > 12.5mm.
3 Protection against solid objects > 2.5mm.
4 Protection against solid objects > 1.0mm.
5 Protection against dust ingress in harmful quantities.
6 Dust tight.
PROTECTION CLASSES FOR WATER PROTECTION
Second Scope of protection
Figure
0 No protection.
1 Protected against vertically falling drops of water.
2 Protection against falling water drops up to 15° from the vertical.
3 Protected against direct water sprays from up to 60° from the vertical.
4 Protected against splashing water from any direction.
5 Protection against low pressure 6.3mm jets of water from any angle.
6 Protection against powerful 12.5mm water jets from any angle.
7 Protection against temporary immersion in water up to 1 metre deep.
8 Protection against continuous immersion in water greater than
1 metre in depth.
9K Protection against high-pressure, high-temperature jet sprays,
wash-downs or steam-cleaning procedures.
For example: IP68 is totally dust tight and suitable for continuous immersion in water
greater than 1 metre in depth.
6. APPEARANCE/STYLING
Plastic enclosures offer a choice of
opaque and translucent material in
a variety of colours, they can also be
moulded in a transparent material;
styled lids have recesses for membrane
keypads and displays. Aluminium
enclosures can be painted or
anodised in different colours.
7. DISTRIBUTOR TECHNICAL
SUPPORT
Distributors keep extensive stocks
of standard enclosures on the shelf,
and they are now joining manufacturers
in providing technical support to
their customers at the design stage
to help specify the most appropriate
enclosure.
8. DOWNLOADABLE DRAWINGS
Typical downloadable resources include
dimensioned drawings in PDF
and CAD formats to assist with design
and modification requirements,
technical details and key product
attributes.
9. SUMMARY
At first glance a small enclosure
may seem to be a simple box, but in
reality, it is the result of a great deal
of design effort that has created a
feature-rich housing suitable for use
in a wide variety of environments.
From: RUSSELL IRVINE
28 Bürklin Quarterly
www.buerklin.com
29