FEAT
ATURETURE
ENCLOSURES
CONSIDERATIONS WHEN SPECIFYING HAND-HELD PLASTIC ENCLOSURES By Russell Irvine, Hammond Electronics
of sealing, a compressible gasket will also be used at the interface. T he relevant international standard is IEC 60529. Ty pically, enclosures rated at IP 54 are suitable for general purpose use; for installation in environments where dust and water are likely to be present, IP66, 67 or 68 would normally be specified. For completeness, t he highest rating under IEC 60529 is IP69K, which gives protection against steam cleaning at high pressure. Obviously, this extreme rating is unlikely to feature high on t he list of requirements for a hand-held enclosure.
EMC A
hand-held enclosure is just a hand- held enclosure – or is there in fact a lot more t o it than that? As with most things, a small plastic enclosure designed to fit in the hand is ostensibly a simple product. However, the more one looks into it, t he more opt ions become apparent when considering which particular design to specify.
SIZE
The primary requirement is t hat the enclosure is large enough to contain the PCB, which despite suggest ions from multiple enclosure manufacturers, will invariably be finalised before any at tent ion is paid to the enclosure into which it will be housed. Obviously, for hand-held equipment, there is t he further constraint that the finished product must be of an appropriate size and dimensions to be comfortable in use.
ST TYLING AND APPEARANC E
T he most subjective of crit eria. Plast ic enclosures offer a choice of opaque and t ranslucent material in a variet y of colours and shapes. They can also be moulded in a transparent material; st yled lids with recesses for membrane keypads and displays are also commonly found. For hand-held devices, ergonomically styling for comfort in use adds another
variable; some designs will also feature soft over-moulds t o reduce strain when using the equipment for extended periods of time.
POWER
Many enclosure designs are available with or without an integral battery compartment. A dedicated battery area is typically designed to accept either 2 x AA or a single PP3 9 Volt battery, and both types of connectors will normally be supplied. If an external power source is used, then an end panel fitted with a cord protector and a strain relief bracket can be specified. The new Hammond 1552 family is an ideal example of this option.
END P END PANELS
Hand-held enclosures will usually be available with one or two end removable end panels. Having decided how many panels are needed, again, inevitably,
SA there are further choices. Plastic or metal, or if the unit is to be used as a remote controller or a bar code reader, then IR transparent plastic panels are available.
ENVIRONMENTA ENVIRONMENT TAL PROTECTION
Sealing against the ingress of dust and water typically relies on a tongue and groove construction bet ween the mating halves of the enclosure; for higher levels
Plastic enclosures offer a choice of opaque and translucent material in a variety of colours and shapes
Plastic enclosures have one specific weakness: by virtue of the intrinsic properties of the material itself, plastic, unlike metal, offers no EMC attenuation. If EM radiation emitt ed by the housed electronics or their susceptibility to external fields is a potent ial problem, the lack of screening could be an issue. Internal coatings in a variet y of mat erials can be applied to t he inner surfaces of a plastic enclosure to give different degrees of attenuation dependent on the project requirements. By offering different materials in a range of thicknesses, the most cost-effective and t echnically competent solution can be provided.
ACCESSORIES
Many designs will have dedicated accessories such as belt clips, which enable the equipment to be conveniently placed out of the way when not
immediately required. Other accessories are a wall mounted holder t hat allows the unit to be st ored in a convenient location when not in use, a particular benefit if the equipment is used as a machine controller or scanner used in a specific location.
www.hammondmfg.com T: + 44 (0) 1256 812 812
Hammond Manufacturing
www.hammondmfg.com
Electronic enclosures. Plastic, extruded & die-cast. In-house mod services: • machining • printing • drilling • custom colours
01256 812812 • sales@ a o d e
ectronics.co.uk ha o d g com
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