Subracks, also known as card cages, are used for the reception of printed circuit boards (PCBs) and plug-in units (PIUs) in many different industries like telecom, transportation, test and measurement, aerospace and defense. For choosing the right subrack for your application, it is essential to be familiar with the fundamental requirements and standards. Check out seven criteria on how to select a subrack.
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The size and type of electronics assemblies determine the dimensions of subracks. Also, the place of operation can lead to the need to meet certain specifications or restrictions.
Using the 19” standard
In general, we recommend the use of commercially available standardized boards that comply with the 19″ standard, as a large number of solutions are available according to these standards. Making use of off-the-shelf products saves the user development time, tooling costs, and no need to keep stock of specific components. Typical dimensions are 3 U and 6 U (height units: 1 U = 1¾ inches).
The downside of using “non-standard” components
For “non-standard” electronic components, such as non-standard printed circuit boards (PCBs), it is vital to ensure that the internal configuration of the subrack allows the inclusion of such non-standard components. If the electronics assemblies are small enough, frame type plug-in units provide compact solutions built into standardized subracks or cases. The external dimensions of the frame-type plug-in units are 19″ compatible and can accommodate both standardized and non-standardized electronic components. This allows non-standardized boards or components to be installed in a chassis or with a mounting plate in the subrack.
Trends influencing dimensions
Thanks to the ongoing miniaturization of components and the growing degree of integration, more than 70% of standardized boards are now produced in 3 U (Euroboard) format. This leads to a trend towards a reduction in the height dimensions of subracks. Another trend emerging is the increased use of active cooling of the boards with high heat dissipation losses using DC or AC blowers. To reduce the noise level during operation, intelligent blowers are becoming popular, which are controlled via system management.
Always consider the environmental conditions
The location where the system is finally installed naturally influences the dimensions of the subrack. Often the space available for installation – e.g., on ships or other vehicles or in data centers – is very limited, so the relevant specifications must be observed.
Depending on the application, certain international and/or market-specific standards and specifications apply.
Commonly used IEC standards
Current standards contain additional dimension specifications (IEC -1, IEC -2, IEC -3-101, IEC -3-102, IEC -3-103, IEC -2-1, IEC -2-2, IEC -2-X) and – at a higher level – criteria for physical integration (IEC -1, IEC -3), earthquake resistance (IEC -2), electromagnetic compatibility (IEC -3), and thermal management (IEC Ed.1). The ETS standards were defined by ETSI (the European Telecommunication Standardization Institute). ETS standards are closely related to IEC standards, particularly in respect of European telecommunications systems.
Market-specific standards
In addition to IEC standards, there are specifications for specific market segments. For example, VME from VITA (VME International Trade Association) and CompactPCI, MicroTCA, and AdvancedTCA from PICMG (PCI International Computer Manufacturing Group). Also, there are particular standards and guidelines for applications in railroad or military technology, such as welding certifications (EN ), environmental tests (EN ) for railroad systems and shock and vibration testing (MIL 901D) for the navy, etc.
Protection and Safety standards
Also, special protection and safety standards must be considered, such as (to name a few).
Other essential criteria in selecting a subrack are the physical forces acting on it and the level of electromagnetic shielding required. In measurement, instrumentation, and control systems, the requirements for shock and vibration resistance are generally not particularly high (up to 0 or 3 g). For applications ranging from traffic light control and industrial machine control to measuring systems for research or in accelerator rings, basic subracks are generally sufficient.
Often no EMC shielding is required, as this is provided, for example, by the cabinet in which the subrack is installed. If high deflection forces are expected due to the width of the unit and the heavy built-in parts, more robust designs are required.
Subracks for infrastructure applications, e.g., in passenger information or entertainment systems in railroad systems, on buses or aircraft, or as controllers for loading ramps, may in certain situations have to be shock and vibration resistant from > 5 to 25g. Loads of this kind also occur predominantly in defense systems, e.g., in controllers for target acquisition devices on ships. Applications for this particularly robust subrack include power generation for the control of wind turbines. In this case, the subrack is mounted in the nacelle of the windmill and the shock and vibration influences are similarly high. For these applications, the circuit boards mounted in the subracks are additionally secured with Card-Loks or Wedge-Loks.
The weight of the installed components is the main cause of static loads. This results in the choice of materials for the assembly system and the construction method – glued, welded or as a one-piece unit. Depending on the application, it may be necessary to fit additional reinforcements or stiffening elements. In the case of mobile use of a subrack, it is usually exposed to different dynamic loads. These different shock and vibration influences near the installation site must be taken into account, e.g., in the vicinity of rotating machines, in railway or traffic facilities, as well as on ships or aircraft. Seismic tests must be carried out prior to installation if the installation site is located in an earthquake zone.
The electromagnetic shielding requirements of electronic devices vary depending on the application and environment in which they are used. This applies not only to high-frequency factors. Shielding is designed to cover electrostatic discharge issues and includes low-frequency capacitive or inductive coupling and cable-related faults, as well as high-frequency electromagnetic interference.
Side, top, and bottom plates, as well as the rear and front panels of subracks, are therefore provided with a conductive surface (passivated, etc.) and are conductively connected to each other via contacts such as stainless steel springs or textile EMC seals.
Each position of the cable entry must also be adequately protected. Standardized EMC tests (VG Part 15) determine whether the EMC shielding measures meet the requirements of a specific application and ensure the reproducibility of this performance level.
The IEC environmental standard also defines tests for the EMC behavior of subracks. Section 3 of IEC outlines the test conditions for subracks in respect of their EMC shielding properties in the frequency range from 30 MHz to 21 GHz and the attenuation values.
The standard is mainly based on IEC and IEC . To determine which degree of shielding is required, the critical interference frequencies must be identified. These tests are usually carried out by the manufacturer of the finished equipment or outsourced to independent external test centers.
Typically, the function primarily determines the appearance of a subrack and whether or not it is installed in an electronics cabinet. If the subrack is installed in the cabinet, the emphasis is clearly on functionality. But the front panel still plays a larger role in the visual design factor. Standard blank panels are available on the market in various sizes and versions.
But only a few manufacturers today have the necessary facilities to carry out individual designs and still efficiently produce panels. Some subrack manufacturers, such as nVent, offer complete service with a broad range of front panels offering paint or multi-color (also digital) printing options. This makes it easy for the customer to design an individual front panel, e.g., adding a logo.
If you are looking for more details, kindly visit Subrack Chassis.
In addition to the basic mechanical assembly, demand for the integration of further components is increasing. At nVent, system integration includes electromechanical and electronic components such as EMC elements, cabling, switches, backplanes, power supply units, monitoring units, and cooling solutions, all in one subrack. As a result, users get a type of plug-and-play product for their 19” technology. nVent undertakes the entire project management and advises the customer from the initial specification and design, purchasing, prototype manufacture, testing, and checking right through to the actual product manufacture, including logistics and after-sales service.
With the EuropacPRO subrack nVent SCHROFF is offering a flexible subrack platform based on the 19” form factor, with a wide variety of possible configurations and modifications.
Subracks, also known as card cages or chassis, are essential components in electronic systems, providing structural support and protection for PCBs (Printed Circuit Boards) and other electronic modules. Whether you're setting up a telecommunications system, industrial control equipment, or a military application, selecting the right subrack is critical to ensuring the reliability and efficiency of your electronic setup. This ultimate buyer's guide will help you navigate through the key factors you should consider when purchasing subracks.
The first step in selecting a subrack is understanding your specific application requirements. Different industries have varying needs, such as size, weight, thermal management, and environmental protection. For example, subracks used in telecommunications might require specific shielding for electromagnetic interference (EMI), while those used in military applications need to meet ruggedization standards for harsh environments.
Key Considerations: Determine the size and number of PCBs or modules the subrack will house. Identify the operating conditions, such as temperature, humidity, and potential exposure to dust or chemicals. Lastly, ensure that the subrack meets any industry standards relevant to your application, such as IEC, IEEE, or MIL-SPEC standards.
BEK Series Subrack
Subracks come in various sizes and form factors to accommodate different types of electronic modules. The size of the subrack will determine how many modules it can hold and how much space it will take up in your system. Common sizes include 3U, 6U, and 9U, referring to the height of the subrack in rack units (1U = 1.75 inches). The depth and width should also be considered to ensure proper fit within your overall system configuration.
How to Choose: Measure the dimensions of your PCBs or electronic modules and select a subrack that provides enough space for them. Ensure that the subrack's form factor aligns with your system’s requirements, whether it's a compact 19-inch rackmount or a larger, standalone chassis. Check for compatibility with existing racks or cabinets in your setup.
The material and construction quality of the subrack play a significant role in its durability, heat dissipation, and overall performance. Subracks are typically made from materials such as aluminum, steel, or reinforced plastic. Aluminum subracks are lightweight and provide excellent thermal conductivity, making them suitable for applications where cooling is critical. Steel subracks offer higher strength and are often used in more rugged environments.
What to Look For: Choose a material that balances weight, durability, and heat dissipation based on your application needs. Pay attention to the build quality, including the precision of the machining and the quality of the surface finish. High-quality subracks should have smooth edges, accurate dimensions, and robust assembly points.
Effective thermal management is crucial in electronic systems to prevent overheating and ensure reliable operation. When choosing a subrack, consider how well it manages heat dissipation. Some subracks feature built-in ventilation slots, while others are designed to accommodate additional cooling solutions, such as fans or heat sinks.
How to Optimize: If your electronic modules generate significant heat, look for subracks with ample ventilation or provisions for active cooling. Ensure that the design allows for adequate airflow around your PCBs. For high-power applications, consider subracks with integrated thermal management solutions.
Depending on your project’s requirements, you may need subracks with specific features or the ability to expand over time. Customizable subracks allow you to add or remove components, modify the layout, and integrate specific connectors or mounting options. Some manufacturers offer modular subracks that can be easily expanded or reconfigured as your system grows.
Why It Matters: Customization ensures that your subrack meets the exact needs of your application. If you anticipate future upgrades or changes, opt for a modular subrack that allows for easy adjustments. Check with manufacturers about available customization options and whether they can provide tailored solutions for your project.
Q: What is the difference between a subrack and a standard rack?
A: A subrack is a smaller, modular structure that holds PCBs or modules within a larger rack or enclosure. Standard racks, on the other hand, are full-size enclosures that can house multiple subracks or other equipment. Subracks are typically used to organize and protect individual electronic components within a larger system.
Q: How do I ensure my subrack provides adequate EMI shielding?
A: To ensure proper EMI shielding, choose a subrack with conductive materials, such as aluminum or steel, and ensure that all seams and joints are tightly sealed. Some subracks also feature specialized coatings or gaskets to enhance EMI protection. Always verify that the subrack meets relevant EMI standards for your application.
Q: Can I install different types of modules in the same subrack?
A: Yes, many subracks are designed to accommodate different types of electronic modules, such as PCBs, power supplies, and communication modules. Ensure that the subrack offers the necessary mounting options and enough space to house all the components you need. Modular subracks can provide even greater flexibility for mixed installations.
By considering these key factors—application requirements, size, material, thermal management, and customization—you’ll be able to choose the perfect subrack for your electronic system. Proper planning and selection will lead to a more organized, reliable, and efficient setup, ensuring your system performs optimally in any environment.
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