Art and Science Call the Shots For Cutting-Edge Enclosure Designs

April 6, 2000
Modular enclosures used to be limited to a few functional black boxes, but now they come in any color and size, often customized for appearance and special functions at standard prices.

Mike Murphy
Industrial Product Manager
Rittal Corp.
Springfield, Ohio


Electronic enclosures are no longer just black boxes, simply intended to house components and pushbutton panels. They come in all colors and finishes and balance ergonomics with aesthetics. These features make them more attractive for communications equipment and easier to use for many HMI applications including multimedia tourist terminals, ATMs, ticket machines, and outdoor enclosures.

A major benefit of the TS8 enclosure symmetry is its identical hole pattern for both width and depth. The two-level mounting concept offers the most amount of space, separate cable routing space, and numerous options for climate controls. At the inner and outer levels, system chassis with mounting flanges can be installed at the same height, width, and depth.

Food and beverage industries require equipment enclosures that can be kept hygienically clean, corrosion free, and waterproof. Most often this demands stainless-steel enclosures.

Offshore drilling platforms often see extreme conditions where explosionproof, stainless-steel enclosures are needed. Certain types of enclosures are specifically certified for these environments, such as these Series Ex, and correspond to the new harmonized European standards.

Pharmaceutical environments see wide-ranging temperatures and pressures, aggressive chemicals, and mechanical stresses that can place extraordinary demands on housing and enclosure reliability. Like in the food and beverage industries, often only rust-free stainless steel can be used.

Electronics enclosures for variable-speed drives often need special EMI shielded panels, doors, and gaskets, as well as substantial grounding lugs for common returns and bus bars for power distribution. Not long ago, these options had to be designed and custom made by the user, but now they are standard catalog items.

The symmetry of the TS8 top enclosure system allows the frame to be directly connected (called baying or suiting) easily and quickly on all four sides as well as the top. In addition, the rear panel may be replaced with a door and the fixing components of the side panel exchanged for hinges, allowing all-around access to the enclosure.

Pendant arm systems and operator enclosures combine ergonomics with aesthetics. Strength, weight, height, width, and accessibility to controls and monitors are crucial considerations for machine operators on the factory floor.

Zone classification refers to areas where environmental or operating conditions can generate a hazardous amount of explosive atmosphere. For example, this could be a mixture of combustible gases, vapor, or dust mixed in air where a reaction automatically propagates after ignition.

Ex enclosures are specifically intended to operate under the Zone classification for hazardous areas. The enclosures and terminal boxes come in both stainless steel and plastic to meet the requirements for Exe and Exi protection categories.

Relatively simple pendant enclosures offer reliable, effective, and flexible operator panels at low cost.

Enclosures come in carbon steel for many industrial applications, often customized to fit limited space or unusual shapes on the factory floor. The automotive industry, for example, requires smooth painted carbon steel with a custom color specified by the user such as gray on the outside and white or orange on the inside. They are also supplied with flange trough collars and special cutouts or features for cable entrances and thermal management, finishes, and door seals or gaskets depending on the specific environment.

As many engineers and systems integrators know, slipping equipment enclosures neatly and easily into new or existing manufacturing lines can be an exacting science. First, enclosures provide a foundation or a structure for mounting various electrical and mechanical components, modules, and subassemblies. But they also protect components from the environment and keep operators out of harms way while allowing safe and easy access. And although many users and installers wish for standardized sizes and specifications to fit various industries, each one periodically goes through changes that require different styles, sizes, materials, and finishes. This means that enclosure makers must remain flexible and quick to fill standard as well as custom enclosure orders.

Secondly, in certain applications, looks are just as important as function — thus the art factor. For example, enclosures installed in food and beverage plants are often seen by customers or the public during plant tours. In the pharmaceutical, food, and beverage industries, the same issues are critical; these enclosures must be easy to clean and remain sanitary under all operating conditions. Moreover, large computer installations that are neat and clean with well-planned cable runs are not only attractive, but are easier and less expensive to install and maintain and significantly reduce electrical noise pollution. To meet such diverse demands in these industries and many others, enclosure suppliers must provide engineers with more and more options for their specific applications.

Although electronic components continue to shrink with each succeeding generation, more of them seem to be needed in every new control system design which, in turn, demands more enclosures and more valuable floor space. Says Tom Reilly, manager of automation engineering with Glatt Air Techniques, Ramsey, N.J., "One of our major challenges is finding an enclosure that contains the largest mounting space with the smallest footprint. Wasted space is not allowed." Glatt manufactures fluid bed dryers and coaters for pharmaceutical and food/beverage companies. It often designs equipment that fits tight spaces but must hold increasingly more gear as the processing line grows.

One way that enclosure manufacturers can help this situation is by designing frames that interconnect on any side, often called "baying or suiting." A bank of enclosures can then be easily expanded in any direction to make best use of the available space without changing the appearance of the system or compromising the operation. This is also a vital consideration when upgrading an older enclosure design. New enclosure systems should be backward compatible so that new additions blend in smoothly with older equipment.

"The real estate factor is crucial," adds Beat Küttel, vice president of engineering for Canrig Drilling Technology Ltd., Magnolia, Tex. "As a manufacturer of top drives — advanced drilling tools used in the exploration of gas and oil — we find our installations on the deck of drilling rigs. Many times, space is already at a premium, and we frequently adapt new installations to existing control systems." Reilly and Küttel both need enclosures that are modular and can be expanded into future projects.

Modularity is also important to Loren Combs, Application Engineer with Klockner-Moeller Corp., Concord, Calif., a semiconductor-equipment maker. But custom modifications still hold first priority. According to Combs, every job is as different as an enclosure's configuration. Combs requires enclosure manufacturers to be flexible throughout the entire design process. This can entail providing 3D drawings, on-the-spot technical support, as well as customized options such as special holes, sizes, and installed equipment.

Drives and motor controls is another industry that requires agile enclosure vendors. For example, Andre Icso, president, Circonix Inc., a systems integrator in Mawah, N.J., says, "As we design our system, we focus on coordinating drives lines that split into functional sections. We build bays for the feed roll, the coater, dryers, and the winders/unwinders as well as for other functional sections. Equipment must be easy to install in the enclosures and connections between them should be quick and simple, whether done here or in another location: Modularity is key."

Other factors important to Circonix includes aesthetics, equipment that's available anywhere in the world, and EMC compatibility. Enclosures must ensure EMI shielding and proper grounding because variable-speed drives can generate electrical noise and inhibit the system's EMC compatibility. And as an international supplier of drive systems, Circonix requires enclosures that are compliant with international standards.

Materials and finishes requirements span a wide spectrum and depend mostly on a specific industry. For pharmaceutical systems, a highly polished stainless steel, such as a number-eight brush finish, is the preferred option for human-machine interfaces including pendant arms and free-standing PC style enclosures. This finish eliminates crevices that could collect dirt and helps keep the surfaces clean.

The oil-refining industry also uses stainless steel in harsh, rugged environments, but with a brushed finish to hide certain types of blemishes such as fingerprints. Also, many of the systems contain high-pressure lines (up to 3,000 psi) and a leak in any one of them can become a serious hazard for the entire control system. A common practice of offshore refineries — but not necessarily a standard — is to use a combination of stainless steel for outside enclosures and fiberglass inside. Both fiberglass and stainless steel stand up well to the ocean's aggressive salt spray.

Carbon-steel, stainless-steel, or fiberglass enclosures are often installed in hazardous environments, but they require special consideration to meet safety standards. Several options are available to designers in the U.S. to meet these requirements such as purging or pressurizing (and monitoring) the enclosures to prevent contaminates from entering and affecting the internal electronics. Another solution uses enclosures that are specifically designed and certified for these locations such as those coated with certain materials to eliminate static charges. These enclosures meet the NEC Class 1, Division 2 requirements, and European Zone 1 and 2 designations.

The drives and controls industry also tends to prefer custom-configured carbon steel enclosures throughout a system, including pendant arms and operator consoles. Drives generate EMI at various frequencies and energy levels. They require special installation and shielding techniques to protect the control electronics inside as well as the environment outside the enclosure from such radiated electrical interference. The means to do this are numerous, including grounding, built-in bonding clips, zinc mounting panels, or employing fully shielded enclosures. All these methods effectively channel common return currents and suppress radiated electrical noise.

The semiconductor industry, in comparison, focuses on sterility and compact installations where the floor space in a clean room is at a cost premium. Carbon-steel and stainless-steel enclosures with smooth and nontextured surfaces are critical for eliminating contamination accumulations. In addition, much of this equipment requires 200 to 300 A to distribute through an enclosure, yet keep a small footprint. Common busbars help meet the goal by eliminating the relatively large bend radii typical of large circular conductors.

In addition to the materials and finishes that protect enclosures, these factors also play into enclosure esthetics and ergonomics, the art factors. Ergonomics in particular is often cited as an important consideration in selecting enclosure designs.

Many engineers stated that their installations are often additions to existing systems or portions of systems that are being combined — worldwide. The enclosure's stylized packaging that complements the entire system is essential to the image of the final package. Designing ergonomics into human-machine interfaces is also paramount to these engineers. "From an ergonomics standpoint, being able to maneuver around and adjust the height for workers are crucial factors," says Reilly. "Our HMI products are used by people of so many different sizes that this element is considered at the start of the design."

Küttel also finds the ergonomic requirements of outdoor operator stations important. These units often need options such as lights, switches, joysticks, and flat screens. "Because operators most often stand and watch more than one station at a time, locating the joysticks, setting the pitch of the consoles, and working with a flexible design is critical to selecting control panels," says Küttel.

Finally, regardless of the industry, engineers expect their enclosure vendors to provide more than just a box. They are looking for a complete package that does not take long to design and populate or cost too much, both for their company and their customers. Vendors that offer design support, CAD-dimensional information, and 3D engineering capabilities help these engineers meet initial project goals sooner. And companies that can deliver complete packages with heating and cooling controls, power-distribution components, subracks, and accessories let engineers buy a complete system from one source.

Modular enclosures with welded-frame construction are equally as strong and rigid as welded-panel enclosures and have many more advantages. For example, modular enclosures called TS8 are adaptable, strong, symmetrical, contain fewer parts, and are relatively inexpensive. They can be easily modified on the factory floor to accommodate rewiring or other upgrades without using a metal cutting torch, laser, or welder. Both inside and outside panels can be quickly removed, replaced, modified, and rearranged. And when they can be expanded in all directions as system needs grow, incremental costs for these enclosures tend to decrease.

Another advantage deals with conservation of space and adaptability. The TS8 frame, for example, is a space miser with its 16-fold, twin pillar profile. It provides high-load capacity and two panel-mounting levels. All sides may be outer-level mounted, inner-level mounted, or any combination. Enclosure symmetry allows doors to be installed on any or all sides as the system requires. In addition, mounting plates may be populated outside the cabinet and easily set into position and secured using special nylon molded slides.

A current trend hinges on a greater acceptance of the IEC's Zone 0, 1, and 2 classifications for hazardous areas. Although many engineers are designing products to meet the NEC's Class 1, Division 2 designation, the movement seems to be more toward adopting the IEC practices. In 1999, NEC Article 505 fully adopted IEC's three-Zone classification system. This let vendors use IEC Increased Safety (Exe) and Intrinsically Safe (Exi) practices within the Class 1, Division 2 environments. Traditionally, these enclosures had been handled by purging techniques. The newly adopted Zone classification reduces the overall cost of the installation, yet maintains the required safety in those hazardous areas.



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