There are many factors to consider when choosing the right enclosure for housing sensitive electronics equipment, as John Wilkins, Marketing Manager at Rittal; a company with broad ranging enclosure expertise discusses
We are all aware of the constant changes affecting our lives, a large proportion of which are due to the continual development of new, faster, smaller and more powerful electronic solutions. Electronics development in general has been mirrored by the instrumentation market in its’ adoption of technology, with the obvious result that equipment has shrunk significantly, reduced power demand, increased portability and reliability, consequently giving greater functionality in less volume.
Instrumentation comes in a plethora of forms and thus enclosures to house instruments need to be just as varied.
The range of enclosures stretches from weatherproof outdoor cabinets with various internal fittings to suit the equipment and application, through custom and proprietary desktop and portable cases, to relatively simple plastic and metal boxes, frequently customised to fit the application.
The application will certainly have an affect on the product selection and relevance, as will the environment in which it is to be used. Casing for equipment used to monitor water quality in close proximity to a river, will be vastly different to the handheld thermal imaging unit used to locate hotspots in a variety of processes and situations.
Both enclosures will hold printed circuit boards, have an energy source, some means of access for the information collected to be read either immediately at source or remotely and to protect against the ingress of water and other ‘contaminants’. The enclosures will, however, be very different in size, shape, construction and materials, yet perform similar jobs.
Coupled with the application, the environment in which the system is to operate should be taken into account. Whether static or mobile, the enclosure may need to withstand shock, vibration, moisture and/or dust ingress.
Parking sensitive electronics beside a busy railway line or road requires particular care as external damage may be likely, or may be prone to vandalism and graffiti, apart from being subjected to changes in external temperature along with wind, rain ice and snow.
In many applications the need to consider the ergonomics of the user and EMC will almost certainly be an issue. Considerations such as these will help to narrow the field from the wide range of alternatives available in each enclosure style.
One major misconception, which should be addressed here is the interpretation of IP ratings. These provide an indication of the performance of an enclosure to prevent dust and water from entering, under varying conditions, and over a limited time period.
It is advisable to use an enclosure specifically designed for outdoor use in these circumstances rather than just ‘the highest IP rating’, as the seals, which will withstand a limited exposure to a hose, may not be designed to withstand freezing in winter, or days of non-stop rain.
The solar gain effect can be greatly reduced by using a double-skinned design, thus saving on cooling bills in the long term. Just to confuse those who still want to select the highest IP rating for outdoor use, enclosure manufacturer Rittal has a range of IP69K enclosures specifically designed for high pressure wash-down applications, such as in operating theatres, food production areas and on vehicles (such as refuse collection trucks) where externally mounted control boxes are washed down at the end of each shift. As these were originally designed for vehicle use, they are normally suitable for outdoor applications.
There is also a need to consider the power requirements. If the unit is portable, it will need space for either batteries, or mains conversion, or both.
Less space will be needed if mains conversion takes place externally. If not portable, how will the power be supplied and distributed? Does the PSU need to be plug-in for easy exchange? Or even N+1 redundant to ensure continuity of supply following a unit failure?
Consideration needs to be given to how the system will receive and send data and in turn, is the same means available for response and control? Is there an ‘industry standard’ cabling structure involved? Can wireless or infrared be used to keep the unit remote from what it is controlling, or are fibre optic links present?
Copper connections will require different space and handling, both up to and inside the enclosure and wireless/infrared options may need additional circuitry (with accompanying space), as well as suitable sites for antennae or target windows.
Cooling provides us with more potential enclosure problems. If we need to keep dirt, moisture and EMC out, how do we get cooling air both in and out of the enclosure? As processing power and system power increases, so does the need to remove the heat generated. Even the batteries in small, portable, units will contribute to the heat generation and could be determined as ‘too hot to handle’ under certain circumstances.
Accessibility and service
Accessibility and service or exchange are important issues over the lifetime of the instrumentation, as even a simple box becomes ‘unfriendly’ when it takes a disproportionate amount of time to replace a battery. Having to remove a dozen screws to access the battery compartment may prevent unauthorised access, but what about the effect on the user who is in a hurry? Box and system design needs to allow access where necessary and to restrict it elsewhere.
In a 482.6mm (19”) environment, the cabinet may include a lockable door, while inside the subracks have easily exchanged ‘Hot-Swap’ circuit boards, power supplies and fan systems. These are partly enabled by utilising the subrack rear for Input/ Output cabling, to leave the front clear for service exchange.
High reliability systems
Reliability depends not only on the quality of the components and the design, but also whether the equipment is maintained within its design parameters, particularly temperature.
Properly cooled systems generally increase the MTBF (Mean Time Between Failures) of critical components. Inadequate dust filters become congested quickly, preventing proper airflow from cooling the system.
Proper consideration of the environment the electronics will normally operate under will ensure mechanical, EMC, dust and liquid protection is provided, to reduce the risk of external factors damaging the electronics inside.
Future upgrades and how they will be achieved may also need to be considered at the outset of the project, both from an accessibility and space perspective. Will customers expect to be able to ‘add-on’ extras as they become available without having to replace the complete model, or is the system designed to be modular and a simple replacement or addition of one part will facilitate expected future expansion?
The foregoing outlines some, but not all of the conditions, which need consideration when choosing an enclosure. Due to the range of options, as well as the need to ensure the product selected is capable of providing a long-term cost effective solution, it makes sense to involve a company with the relevant competence and widest range available.
Rittal
