Depending on the application, choosing the right cabinet might be a challenge. Outside the traditional 19”data communications and telecommunications market, cabinets may be exposed to extreme heat, high dust/contaminants, clean room/laboratories, Radio-Frequency/Electromagnetic interference (RFI/EMI) and high shock and vibration requirements. To help choose a specific 19” electronics cabinet solution this article introduces seven essential design considerations.
ONE – Design Standards
Depending on your requirements different design standards can apply. Those are defined and developed by standards committees, government agencies, and regulators. Standards result from technical agreements related to design specifications and requirements that need to be fulfilled by a product or service. Some key design standards associated with electronics cabinets include the following:
IEC - International Electrotechnical Commission (IEC) develops International standards for all electrical, electronic and related technologies. Adoption is voluntary, although they are often referenced in national laws or regulations worldwide. IEC 60297 (Mechanical structures for electronic equipment - Dimensions of mechanical structures of the 482,6 mm (19 in) series) standard provides crucial information for designing 19” cabinets – IEC 60297; IEC 60297-3-100 (19 inch Standard); IEC 60917-2-2 (25 mm metric Standard); ETS 300 119-2/-3 (European Telecommunication Standard)
RoHS Compliance - Restriction of Hazardous Substances. (RoHS), originated in the European Union and restricts the use of six hazardous materials found in electrical and electronic products.
MIL-S-901D is a special military test requirement designed for shipboard applications. Based on the type of equipment – essential or non-essential to the safety and combat-readiness of the ship – qualification testing is performed on a specified machine placed on a barge floating in a pond where explosive charges are detonated at various distances and depths in the pond to impart shock upon the equipment.
TWO – Cabinet Dimensions
19” cabinets provide a standardized frame or enclosure for mounting various types of electronics equipment. Each piece of equipment is typically 19 inches (482.6 mm) wide, including edges or mounting ears, which allow for mounting to the rack frame. Cabinet height is defined in “Units” (U), each unit equals an industry standard of 1.75 inches (44.45 mm). Rack-mountable equipment is usually designed to occupy a specified number of U. Cabinet depths may vary in accordance with diverse applications, typical depths range 600-1200mm. Detailed guidance regarding mechanical structure standards for 19-inch electronics may be referenced in IEC 60297-3-100.
THREE – Weight Load Capacity
The amount of weight loaded into a cabinet can vary widely, so it’s important to take a look at this factor to determine the right type of cabinet for a given application. Whether it is several banks of batteries for uninterruptible power supplies, or an array of hard drives, proprietary equipment or other heavy components, underestimation of weight loading requirements is a very common frustration for engineers. It is especially difficult because some tests may be conducted to ensure optimal results, such as mounting the heaviest equipment at the bottom of the cabinet, but it may not correspond to the layout for the final application. Working with heavy loads can also present other issues. Depending on the application, some cabinet designs may require dynamic protection, which in turn, necessitates a more robust design depending on the load.
FOUR – Thermal Management and Cooling
Thermal management is an important design consideration for any electrical or electronics enclosure. Thermal overload can be a common reason for operating failures in electronic devices, and the risk increases for equipment mounted into cabinets as power density of today’s electronics increases, and more heat is generated. Heat dissipation calculations are measured in ?T (Delta T), which is defined as the temperature difference between the intake air and exhaust air, or the amount of heat that is carried away by the stream of air exiting the heat load. A greater temperature difference signifies more heat being removed.
Cabinets designed for universal applications require broad thermal management compatibility and often need to meet more stringent performance demands than standard communications cabinets. There are numerous thermal management and cooling options that may be deployed in cabinets - from high perforation—which is referred to as a passive option—to fan trays, heat exchangers and air conditioners—which are considered active options.
Additional information regarding heat management design standards and recommendations are defined in IEC 61587-1.
FIVE – Shock & Vibration Protection
There are two main dynamic requirements – seismic and shock/vibration (S/V) tests. It is worth pointing out that S/V and seismic tests are very different and have very well-defined processes on loading cabinets with weight. Retesting with exact equipment is needed to ensure that the final solution offers the same S/V or seismic protection as desired. The test may not be needed if the equipment is below the threshold of the official test.
Shock and Vibration - This test is a go-to test for equipment that will be used in mobile applications and simulates a typical environment in a train car, vehicle or next to vibration-generating equipment such as a punch press or other piece of industrial equipment. Minimization of weight and S/V-optimized designs offer long-term benefits to users, especially in transportation applications.
Seismic - Seismic activity is a very complicated, but well-studied phenomenon. Testing equipment and processes are well-defined and well-known with multiple labs capable of doing tests. The test consists of placing a fully loaded, standard cabinet on a platform that can move in any direction and simulate the earth’s movements during a seismic event. Certain deformation and movement of the cabinet can lead to test failure.
SIX – Electromagnetic Compatibility (EMC)
Electromagnetic interference (EMI) has been a growing concern with equipment manufacturers. As equipment becomes faster and proliferates into all types of manufacturing and production environments the issue of EMI has become more prevalent. Environments that were once considered EMI-free are becoming more and more susceptible to interference due to an increase in automation equipment and electronics emissions. Visual inspection alone of cabinet gaskets does not suffice to ensure adequate EMI protection. Proper tests and results are needed to ensure that a cabinet design meets those requirements. Gasket integration to provide a Faraday effect is not a simple matter – competing with requirements such as cabinet cooling and perforations for air flow. The latter demands an understanding of the entire system, not just individual components, and necessitates a number of accessories that may seem redundant but solve very specific problems. Additional design requirements and recommendations can be referenced in IEC 61587-3.
SEVEN – Environmental & Safety
IEC 60529 provides guidance for classifying the ingress protection rating (IP Codes) of enclosures. IP deals with dust and water protection. Equipment that has better protection against dust/objects and water will have higher ratings. IP ratings have two numbers - one shows dust/object protection and the other shows water protection.
There are some industries where the requirement might be higher than in others - transportation, military and food and beverage industries are just a few that might have high requirements for IP rating due to the nature of the intended applications as compared to other industries. It is beneficial to partner with a supplier that has a solid understanding of the various requirements, has built various types of IP cabinets and can show test reports.