Chassis and Enclosures

A Special Look at Chassis and Enclosures: When a Box Becomes a System

Today’s embedded systems are moving into ever more challenging applications and environments. They must often resolve conflicting demands of modularity, ruggedness, cooling and more. Developers are rising to these challenges with ever more innovative answers.


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It is perhaps common to think of electronic enclosures and chassis as a given or maybe as a side issue in most systems. Of course, we all know that is not the case—not even for the seemingly endless rows of racks that populate modern data centers. And it is even more definitely not the case in terms of embedded systems—especially mobile systems.

Embedded systems, by their very name must fit very high compute and I/O power into ever smaller spaces. It’s no surprise that such requirements pose challenges for power, heat and space that must be dealt with not only for the needed functionality, but also for reliability. Ruggedization has become a specific design criterion. Not only must many systems be built to withstand extremes of shock and vibrations, but many must also protect their components from hostile surrounding conditions like harmful chemicals or extreme weather. And these rugged designs must still be able to dissipate the heat to the same component requirements as those used in comfortable air-conditioned settings.

We present here a look at some of today’s most innovative enclosures. Some are offered from their vendors as standard products designed to accommodate certain widely known requirements. Still almost all can be modified and customized by their vendors to meet the specific requirements of users. Some enclosures presented here are from vendors who specialize in offering standard and custom enclosure designs for customers. Others are presented with the systems they contain because the manufacturer saw fit to mention and/or emphasize the nature of the chassis or enclosure as an important aspect of the system design. We can see from these examples several trends or characteristics aimed at the wide range of embedded applications. Among these are flexibility and modularity as well as innovative approaches to ruggedization and cooling.

Configurability and Modularity at Center Stage

For example, a modular system assembled from standard building blocks, the TecSYS from Verotec is user-configurable around the default options if required (Figure 1). Typically, TecSYS is housed in the field-proven Diplomat desktop enclosure, available in 3U and 6U heights, full and half widths and a variety of depths; other variants support 19 inch rack mounting. Thermal management, power supply configuration and backplane size and architecture are selected from Verotec’s standard product portfolio, ensuring short lead times and platforms configured exactly to the requirements of the application. TecSYS is suitable for use in both the development and production environments.

Figure 1
The TechSYS from Verotech

The TecSYS platform can be very easily configured for any standard bus structures such as VPX, VMEbus, VME64x and cPCI, with boards mounted either horizontally or vertically as required.

A typical platform is configured for VPX. The system is housed in a 10.5 inch half-width 6U, 12.7 inch (322mm) deep Diplomat enclosure, which is configured with a 2U plenum chamber at the bottom, a 3U KM6-RF subrack in the middle and a 1U air exhaust chamber at the top. The heart of the system is a 5-Slot 3U full mesh X4 PCI Express VITA 46.4 backplane, which also provides VITA 46.10 RTM capability, an important consideration for I/O, which is easily accessed through a removable rear panel; the top cover is also readily removable for improved access. The backplane provides System Management and JTAG Interfaces; it gives fat pipe communications between all five slots and provides an interface with one of the most widely used architectures, PCI Express. Pluggable PSUs with two independent converters operating in parallel provide 30A at 5V and 40A at 3.3V simultaneously.

Getting the most in terms of efficiency and functionality in the ATCA world is aided by a chassis design that offers a number of options. A redundant shelf manager integrated with the switch fabric saves two slots that are usually dedicated switch fabric slots in the ATCA chassis from Pixus Technologies (Figure 2) for an ATCA system platform compliant to PICMG 3.0 Rev.2.0. The two extra slots can then be utilized as standard payload slots, allowing more boards/performance in significantly less space.  The PXS0640 can optionally be configured for full HA redundancy across all FRUs, including power modules, cooling units, shelf managers/telco alarm, and switches.  If AC power is not required, a 5U chassis option is available.

Figure 2
The Pixus PSX0640

The 40GBASE-KR4, 6-slot backplane supports dual star fabric, with an option for a full mesh, and an option for a replicated mesh on node slots so that the combined switch/shelf manager allows a full 6 node slots. Full redundancy is supported with dual shelf manager, dual cooling units, dual switches and dual power modules. A 4 x 1100W AC supply (N+1), 2 x 50 Amp DC PEM allows AC and DC to run at same time for swapping modules. There is a front power entry module, front and rear ESD jack. Redundant FRU information devices and a telco alarm are also included.The PXS0640 is RoHS compliant.

The PXS0610 6U shelf combines the shelf management slots with the Hub providing 50% more payload slots on the same form factor. The HASS integrates a VT003 shelf manager from Vadatech and a 40GbE/10GbE switch and a GbE switch on the same module. This allows saving of two slots in the system for the payload vs. having dedicated switches in the system. With two VT003s in the system there is full redundancy and failover both on the switch side as well as on the shelf manager side. The VT003 can also run as a protocol analyzer to monitor, inject, capture and validate I2C traffic on the Intelligent Platform Management Bus (IPMB). A Graphical User Interface (GUI) validates and displays the IPMI packets or schedules IPMI messages for injection into the Shelf. The GUI application communicates with the VT003 through the Ethernet port. The VT003 is fully hot-swappable to minimize service down time.

The industry is telling us there is a specific need for small, compact construction style cases that are also robust, with ease of assembly and convenient mounting options for the electronics inside. The cases should also be high quality, offer EMI protection, and have an attractive look.  Looking beyond the 19-inch industry standard to also include smaller form factors, the Interscale M case from Pentair (Figure 3) offers flexibility, competitive delivery, and a very competitive price point. Along with customized printing, available optional cutouts for specific  I/O requirements and a wide range of standard sizes the Interscale M is making a strong push to fit and exceed these industry needs.

Figure 3
The Pentair Interscale M case

Additional performance features include a case designed to meet IP 30, consisting of just four parts that can be easily assembled and disassembled with two screws!  A total of 21 case sizes are available direct from stock. EMI protection is achieved by the interlocking case walls and offers 20 dB at up to 2 GHz. A wide range of standard accessories, e.g. flexible board mounting configurations, various case feet options, a range of fans and internal PCB mounting options allow the Interscale M user to integrate electronics quickly, simply and affordably.  Further services are also available such as final assembly of the chassis, including accessories and heat simulation using FLOWTHERM or a wind-tunnel test.

Modular components equate to high availability and shortened time to market, which can be especially critical in the PC/104 and 3.5-inch SBC market. A new embedded enclosure design with highly configurable modularity from ADL Embedded Solutions makes it possible to expand or reduce a system without replacing the entire enclosure (Figure 4) ailability starting point for meeting your specifications. Once integrated, the ADLMES-8200 lends itself to extending the life of existing products by allowing the enclosure to be modified with minimal impact, translating into lower development and sustaining costs, and shorter development cycles.

Figure 4
The ADLMES-8200 from ADL Embedded Solutions

 Also addressing critical cooling issues for compact systems, the ADLMES-8200 has a thermally conductive base, ribbed sidewalls and finned top that provide radiative and conductive cooling paths for superior thermal management to the outside of the enclosure. The ADLMES front I/O plate can be quick-turned and built to custom specifications to support most types of I/O connectors. If additional I/O connectors are required, the MES backplate can also be customized in a minimal configuration.

The ADLMES-8200 can be further customized for high IP requirements by replacing the front I/O plate and bezel with a custom milled faceplate that supports the pre-specified high IP connectors. Supported by ADL Embedded Solutions’ Team of SolidWorks design and modeling engineers, customizations are handled expertly and efficiently.

Air cooling can be important in most situations and in many, such as office environments, it must minimize noise. VadaTech, a manufacturer of embedded boards and complete application-ready platforms, has released a new 6U MicroTCA embedded computing system platform with quiet fan trays designed to operate at under 55dBA, suitable for office use.   

The VT898 is a 6-slot cube chassis that is 10.5 inches tall by 10 inches wide by 10.5 inches deep (Figure 5).   The “Whisper” chassis features redundant cooling in a push/pull front-to-rear airflow configuration.  The elegant design includes a spring-loaded handle that is flush to the top of the chassis when I’m not in use and glide strips for smooth PSU and fan tray extraction. 

Figure 5
The VT898 from Vadatech

The 6U Cube chassis platform includes a 40GbE-capable backplane, a 1000W AC power supply, Telco Alarm, and a JTAG Switch Module.  The backplane has routing for FCLK, and TCLK A-D. VadaTech offers MicroTCA and other form factor chassis platforms in various styles including Cubes, Vertical Shelves, Horizontal Shelves, and Rugged ATRs.

Combining Requirements for Versatility

Considerations for configurability, ruggedness and cooling come together in a low cost data-grade MicroTCA chassis that is suitable for a wide range of embedded applications including industrial and defense applications that do not require all of the functionality of a fully compliant MicroTCA system. Enhanced ruggedization options are available for defense applications. The PXS0108 from Pixus Technologies (Figure 6) leverages over 20 years of superior cooling, backplane, and packaging innovation with proven Kaparel and Rittal technologies.

Figure 6
The Pixus PXS0108

The PXS0108 has an active backplane that alleviates the need for expensive power modules (PMs). The backplane provides a power manager for each slot that controls and limits the management and payload power to the maximum allowed 8 Amps per slot. On power-up, payload power is delayed to allow the MCH(s) to fully come online. The AMCs are then sequentially enabled allowing for a smooth power up sequence. The PXS0108 has configuration options that allow redundant power supplies, backplane topologies and FRU information de-vices.

Features include the MicroTCA System Platform based on the PICMG MicroTCA.0 R1.0 specification. The unit is 19 inches x 1U x 9 inches deep and is RoHS compliant. Redundant or non-redundant backplane configurations are available and AMCs are hot swappable. In redundant configuration, MCH fail-over support and MCHs are hot swappable. A superior cooling configuration for airflow uses a push-pull, side-to-side configuration that removes the need for expensive Cooling Units (CUs). An active backplane removes the need for expensive Power Modules (PMs).

The PXS0108 has nine fixed fans. Eight provide for a push-pull configuration in the module area and one provides cooling in the power supply area. Airflow is from right to left.

The fans are fixed and are not managed and therefore constantly operate a full speed.

There is no air inlet filter on the PXS0108. Pixus Technologies can modify this product to meet specific customer requirements without NRE (minimum order placement is required).

Achieving ruggedness can also pose a challenge to weight and cooling issues, especially when size is also critical. In addition, when heat and cooling are critical, it can be an advantage to have the power supplies tailored to and supplied with the enclosure. In the case of the Crystal Group, this has led to an innovative choice of materials.  Their new new, rugged 2U Server features a chassis constructed from light-weight carbon fiber and strain-hardened aircraft aluminum, and designed for use in harsh environments like those found in military, oil & gas, mining and other industrial applications. The RS2516PS18 (Figure 7) provides high data storage capability in a compact 2U design. The unit measures 18 inches in depth and weighs 25 lbs. dependent on content. The server is constructed with carbon fiber and aluminum materials for light weight and high data density applications. The unit can be configured for 24 by 9mm SSD’s or 16 hot swappable 2.5 inch 15mm drives. The RS2516PS18 contains rear I/O for power and SAS connections and can be mounted on Jonathan rails or Delrin glides.

Figure 7
The RS2516PS18 from the Crystal Group

The RS2516PS18 is designed to be advantageous to customers looking to put large amounts of storage in a compact lightweight form factor. It is able to be configured with 24 hot swappable SATA/SAS disks while still maintaining the shock/vibe levels that customers are accustomed to, as well as retaining the same thermal profile of -40°C to +55°C without any degradation in computational performance.

The RS2516PS18 is an air cooled unit with six high speed, high volume, and low noise fans. The unit’s power conscious performance comes from a 460W AC power supply or a 425W 18-36VDC supply. The rugged storage device is available with optional humidity and EMI kits and is covered by a 5 plus year warranty backed by superior customer support and service. Independent test labs certify Crystal Group’s RS2516PS18 Rugged 2U Server meets requirements for MIL-STD-810, MIL-S-901, MIL-STD-461, and FCC Class A certification.

And Now Bullet Proofing

A number of chassis that may also find use in military—especially UAV—applications have in addition to what we think of as “ruggedness” also the need to be bullet proof. All the while they must contain the electronics and dissipate the heat.

Dawn VME provides a family—of 3U Open VPX products called CUBE to provide for the needs of the UAV market is available in 1 through 6 slots (Figure 8). Each chassis is shipped complete with backplane, power system and is I/O ready for the addition of boards. Backplane topology and I/O to panel connectors may be mapped into the system at time of order by using Dawn’s patented and performance “Eye-tested” Fabric Mapping Module Technology. The CUBE chassis provides a bullet proof sealed environment for application and boards to run in. Each design is thermally modeled using the latest in 3D modeling and thermal analysis CAD software. Dawn can model a planned configuration and determine exact thermal performance before placing order.

Figure 8
The CUBE enclosure from Dawn VME

Dawn’s 3U form factor conduction cooled chassis for cold plate deployment is designed for all rugged environments: Airborne, Land and Sea. Conduction-cooled base coupled, via short and efficient path, provides for optimum cooling. Maximum power dissipation depends on cold plate. A RuSH enhanced 3U conduction cooled power supply monitors system-critical performance parameters including voltage, current, and temperature. Power supply startup is under firmware control and may be factory modified to operate with startup-sensitive boards. The RuSH monitor is interfaced into the OpenVPX IPMB (I2C) management plane, providing communication link up with system cards.

The rigid front panel interface eliminates wiring challenges and backplane overlays enable PMC/XMC to I/O customization with I/O mappable between backplane and rigid I/O board using Dawn’s patented FMM modules.

Liquid Cooling Meets Rugged

A liquid cooled High Performance Embedded Computer (HPEC) server is designed for maximum performance in rugged environments. Safe, reliable liquid cooling enables the Dynatem BoldHPC with greater performance—1000 times more effective than air-cooling—and consumes less energy than fans. The design is extremely energy efficient with greater than 3.15 Gflops per watt (Figure 9).

Figure 9
The Dynatem BoldHPC

The BoldHPC is a 19-inch rack mount computer offering one or two chassis offers optional configurations including double blades, single blade with PSU, and single blade with PCIe expansion for I/O boards and mass storage. The introduction of the BoldHPC brings supercomputing power to applications never previously possible. The design is extremely energy efficient and liquid cooling is reliable for high performance in difficult environments.

The BoldHPC is based on the ACPU-20 blade which includes 1 or 2 Intel E5 v2 processors with up to 12 cores each, and up to two NVIDIA  Kepler  GPUs or two Intel Phi coprocessors can be populated per blade. The BoldHPC 50-10 is rugged and reliable without any moving parts, making it suitable for intelligent surveillance and reconnaissance, heavy computational loads, simulation, signal processing, data concentrators and other rugged HPC applications.

The Chassis as System

There comes a point where the technical capabilities built into a chassis to support the range of capabilities that may be built into it take on the characteristics of a system design in themselves. This appears to be the cased with an 18-slot chassis that features a high-bandwidth, all-hybrid backplane to meet a wide range of high-performance test and measurement application needs. The hybrid connector type in every peripheral slot of the NI PXIe-1085 from National Instruments (Figure 10) enables the most flexibility in terms of instrumentation module placement. It also incorporates all the features of the latest PXI specification including support for both PXI and PXI Express modules with a built-in 10 MHz reference clock, PXI trigger bus, and PXI star trigger for PXI modules and a built-in 100 MHz reference clock, SYNC100, and PXI differential star trigger for PXI Express modules.

Figure 1
The TechSYS from Verotech

Figure 10
The National Instruments NI PXIe-1085

This chassis enables higher-bandwidth systems and provides the flexibility needed to work with both hybrid-compatible PXI and PXI Express modules. There are a total of 16 PXI hybrid-compatible slots and one PXI Express system timing slot that can accept either a PXI Express system timing module or PXI Express module. The PXI Express system slot offers one x16 and one x8 PCI Express Gen 3 link to two switches. Each switch provides a x8 PCI Express link to eight or nine peripheral slots.

The NI PXIe-1085 chassis integrates three PWM system fans to provide forced-air cooling that meets the increased cooling demands of PXI Express and CompactPCI. The NI PXIe-1085 incorporates the power supply components into a modular unit that can be replaced quickly, resulting in a mean time to repair (MTTR) of less than five minutes.Additionally, the three cooling fans are hot-swappable and easily replaceable with access to the rear of the chassis. The chassis also monitors power supply health/voltages, air intake temperature, and fan health/speed. It also provides any failure feedback to the user via status LEDs located on the front bezel of the chassis. 

This chassis includes IN/OUT SMA connectors for the 10 MHz reference clock on the front of the chassis. When the backplane detects a 10 MHz signal on the IN connector, it phase locks PXI_CLK10,  PXIe_CLK100, and PXIe_SYNC100 to the external clock. The OUT connector provides a buffered, non-TTL version of the 10 MHz reference clock.

The NI PXIe-1085 chassis is configured with NI Measurement & Automation Explorer (MAX). With this software configuration tool, you can easily configure NI PXIe-1085 systems without time-consuming manual installation of initialization files. MAX creates the pxisys.ini file that defines the layout and parameters of your PXI system including chassis, controller, and plug-in modules.

So we can definitely say that for modern embedded systems, chassis and enclosures are far from a side issue and can often take on the character of systems in their own right. The task for developers of such enclosures is to battle often conflicting demands for configurability, cooling, size, weight, connector placement, power supplies and ruggedness. That is definitely a set of challenges that demands a systems approach.

ADL Embedded Solutions
San Diego, CA

Crystal Group
Hiawatha, IA
(319) 378-1636

Dawn VME Products
Fremont, CA
(510) 657-4444

Mission Viejo, CA

National Instruments
Austin, TX
(512) 683-0100

Minneapolis, MN
(763) 545-1730

Pixus Technologies
Waterloo, Ontario
(519) 885 5775

Henderson, NV
(702) 896-3337 

Derry, NH
(603) 821-9921