FEATURE CASES & ENCLOSURES Simplify Ex and unmanned applications with


Martin Hess, Intertec Instrumentation, explains how an ‘inside-out’ enclosure design approach can help reduce the presence of human operators in remote or hostile conditions

lectronics advances are making process control and instrumentation systems

much more intelligent, robust and reliable. For many operators and processing plants, the goal is to exploit these advances to dramatically lower the need for human operator presence, ideally to the point where unmanned operations become the norm. Such solutions are highly desirable, particularly where applications are remote and/or in hostile conditions - such as deserts, arctic areas, offshore, pipelines etc. They are also widely applicable in more conventional processing plants, especially in applications related to safety in hazardous areas. What are enclosure manufacturers doing to support such ambitions for the future of process automation? One development that shows promise is a concept called the ‘peri’ shelter for housing field-based instrumentation and control equipment. Peri shelters employ several techniques to help engineers design and implement field- based equipment for processing plants that help to reduce the presence of human operators, and actively avoid problems that are the common causes of faults and shutdowns - such as overheating and corrosion.

SHELTER TECHNIQUES Peri shelters employ three main configuration and technology principles to support higher levels of automation and reliability: Isolating interior electronics: configuring field

enclosures with features such as I/O connections and HMI access available externally means that sensitive electronics equipment such as PLCs, RTUs and instruments can remain completely sealed and protected against local corrosive and hazardous atmospheres. ‘Inside-out’ layouts: outdoor peri shelters can

be configured so that all system components required for site installation, start-up and normal daily operation are accessible via the building exterior (Figure 1). Failsafe cooling: most trips or shutdowns

of electronics equipment are usually a consequence of overheating. Peri shelters can be equipped with extremely reliable and failsafe cooling based on combinations of passive (unpowered) and active elements. These attributes, applied singly or in

combination by Intertec Instrumentation, can greatly simplify the creation of more efficient, safer and reliable field-based instrumentation and control applications.


Figure 1: A peri shelter featuring an 'inside out' layout with HMI, I/O panels

INSIDE-OUT LAYOUT For example, the ‘inside-out’ design approach can dramatically reduce shelter sizes, and greatly simplify construction and installation, compared with more conventional plant buildings such as ‘remote instrument enclosures’ or ‘satellite instrument houses’. Among many design problems and costs that this approach can avoid are a need to make buildings blast proof and fire- resistant (because personnel might be inside), major reductions in size by eliminating desks, control panels, door opening spaces, aisles/walkways/escape routes etc, and much simpler internal atmospheric control requirements. This also greatly simplifies construction if the cabinet or shelter is intended for a hazardous area, as it avoids the need for costly features such as airlock entry, redundant fire and gas systems, gas warning systems, etc. Inside-out layout principles also mean that the

cabinet or shelter can be assembled and fitted out in optimal factory-grade conditions. At this point, the interior may be sealed. All installation and commissioning work can then take place without disturbing this seal - protecting sensitive instruments and electronics against the corrosive atmospheres found in oil, gas, chemical and other processing plants. Additionally, because there are no people inside the shelter, the interior atmosphere does not need to have some degree of moisture - further protecting the electronics from the problems of condensation. One additional innovation for this application

area is ultra-reliable cooling. Cooling is often required for outdoor equipment cabinets and shelters. With peri shelters, this can be achieved by using combinations of active and passive

cooling technology. Passive cooling of field equipment enclosures using heat exchangers (a tank of water or other fluid stores the coolness of the night and uses it to lower enclosure interior temperatures during the day) is an influential weapon in the battle to protect electronics installed in hot and harsh environments. The temperature inside a passively-cooled enclosure cannot be lower than the night temperature, so there is a need for a comparable low night temperature in applications. However, by making the passive cooling system ‘hybrid’, with the addition of one or more active (electrically powered) cooling elements, Intertec has made it possible to create semi-passive shelters that can be used in almost all climates - even equatorial regions. If an active cooling element should fail for any reason - such as a power cut - the passive cooling system retains enough capacity to keep the shelter cool for days, giving maintenance staff plenty of time to visit. The inclusion of an active cooling element

allows both parts of cooling components to be reduced in scale - and cost - as the systems can be scaled so that the active element only needs to come on to handle occasional extremes of duty cycle, or on the hottest days of the year.

APPLICATION EXAMPLES The peri shelter shown in Figure 1 was designed to accommodate new field-based PLC, safety electronics and instrumentation systems needed for an upgrade to a refinery’s burner systems. In this application, exterior panel-mounting enclosures provide access to electrical connection and I/O termination points. The PLC is fitted with a touchscreen HMI panel on an external wall,


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