(Click here to view article in digital edition)
Until five to ten years ago, many remote I/O application projects in processing plants were calling for sophisticated small plant buildings to protect the equipment – commonly called satellite instrument houses or remote instrument enclosures (an approach still used today of course).
Such plant buildings are typically air conditioned, and often designed to support human access as well as equipment installation – which can then necessitate complex additional features such as blast- and fire-resistance.
However, by specifying more rugged dust- and water-proof enclosures to protect remote control equipment located deep inside the processing area, engineers are increasingly able to realise more versatile control architectures. With the growing use of software configured I/O solutions, this is allowing control equipment enclosures to be assembled and sealed in the factory for instance – an efficient and cost effective process – so that enclosures do not need to be opened and exposed to dangerous local conditions at the site during installation and operation.
The use of GRP (glassfibre reinforced polyester) enclosure construction materials is particularly suited to this application. One reason is that control and instrumentation equipment sited very close to the process will often be exposed to corrosive media and atmospheres. The special GRP material used in Intertec’s enclosures is highly stable and virtually immune to the effects of salt and most common petrochemicals and airborne pollutants for example.
The ability of GRP enclosures to be supplied with embedded insulation (two layers of GRP sheet with embedded insulation inside) is another major virtue. Insulation is now commonly required because modern remote I/O applications use sensitive electronic devices, with lifetimes and reliabilities that are drastically reduced by overheating. Efficient insulation helps protect against temperature extremes. This is one reason why the simple steel cabinets widely used today for cabling-related field junction boxes are not adequate for the more sophisticated remote I/O applications now starting to be deployed. Because of the electronic devices used, some form of cooling may also be required. If power is available at site, this can be in the form of conventional fan cooling. However, the temperature stability of highly insulated GRP boxes also makes it possible to efficiently exploit passive cooling techniques – which require no electricity and have no moving parts. A tank of water plus a heat exchanger can utilise the coolness of the night to moderate interior temperature during the day. Passive cooling is widely used in hot countries, and often for larger outdoor shelters (the shelter in Figure 1 is passively cooled). However, if electricity is available, passive cooling can be boosted by the addition of a small active cooler, and this approach allows the cooling technique to be used in a much broader range of climates.
Novel enclosure configuration techniques are also aiding moves towards more highly distributed control schemes. One of the most versatile is the ability to build field cabinets or shelters employing ‘inside-out’ layout techniques that are able to seal sensitive electronics inside the enclosure, yet allow plant operators to access elements such as electrical connection and I/O termination points via panel-mounting enclosures on the exterior. If there is also a need to access or program equipment inside the shelters then similarly, touchscreen HMI panels sited on an external wall can be fitted and protected by an inspection door. In this way, sensitive electronic equipment such as PLCs can be effectively sealed inside protected and conditioned enclosure spaces for their operating lifetimes. Such approaches can be particularly beneficial if the application environment is hazardous. In hazardous areas maintenance can be prohibitively expensive as the enclosure may not be opened while in operation, potentially necessitating partial or full process shutdowns for routine maintenance.
The images show examples of Intertec GRP enclosures providing environmental protection for remote control equipment positioned at the point of use. The shelter in Figure 1 houses a real-time PLC controller sited in a hazardous area of a refinery. The interior control system was assembled at the factory and sealed before shipment. External panel-mounting enclosures and a touchscreen HMI panel with inspection door allow plant operators to access all elements required for installation and daily operation without entering the shelter. The door is there purely for access during shutdowns or special circumstances. This approach eliminates costly and time consuming work that would have been involved if a more conventional plant building designed for human access had been chosen.
Figure 2 shows a shelter design for housing electronic and hydraulic equipment used to operate lock gates on a Dutch shipping canal. The hydraulic and electronic elements are located in separate compartments. For many of the locks on this canal, the controller is actuated by a remote operator who monitors activity via video. Because the canal has considerable leisure value, the shelters are also decorated with slats.
As many advanced remote I/O applications will require cooling, and will – by their nature – be compact and small, Intertec has developed passive cooling systems for smaller-scale cabinets and enclosures. Figure 3 shows two examples: the cabinet has a passive cooling system with a heat exchanger that doubles as a sunshade. The performance of the passive cooler is boosted by a small active element – in this case a water cooler (fitted to the side). The second image shows a small panel-mounting enclosure, with a sunshade and a passive cooling heat exchanger in the form of corrugated flexible tubing. Intertec believes that passively cooled enclosures like this are practical for enclosure sizes down to around 40 litres in volume. For more information, visit www.intertec.info
About the author:
Thijs Overgoor is General Manager of Intertec Instrumentation’s support centre in The Netherlands.
Print this page | E-mail this page
Discover the future of engineering today
Download a copy of our digital magazine