Systems in Transportation
When Transportation Applications Get Rugged
Mobility and environmental extremes are critical considerations for transportation applications. Utilizing rugged products to create a tailored solution can help speed the development cycle and limit the need for compromising on application requirements.
JEFF MUNCH, ADLINK TECHNOLOGY
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Transportation solutions are most often housed outdoors or in moving vehicles, where exposure to a variety of climates dictates the need to operate in extended temperatures and to power up in any extreme. By starting with a rugged board or system that is designed for harsh environments from the ground up, application developers can knock out some of the complications inherent in transportation design. To support the extremes of shock, vibration, humidity and temperature, care is given to component selection, circuit design during rugged board development, printed circuit board (PCB) layout and materials, thermal solutions, enclosure design, and manufacturing process. Robust test methods, including Highly Accelerated Life Testing (HALT), ensure optimal product design phases in order to meet a product’s stringent requirements, such as -40° to +85°C operating temperature range, MIL-STD, shock and vibration, and long-term reliability.
Bigger Isn’t Always Better
Transportation applications typically need as much functionality as possible in the smallest form factor. Weight and size—the lighter and smaller, the better—are critical requirements because of where the hardware is located, such as suspended on a post for traffic signage or located under dashboards or in small overhead spaces for bus, train, or military vehicle applications. Unfortunately, as form factor size decreases, functionality requirements increase. Controllers are now burdened with extreme loads of information and intricate tasks. Robust power controllers are critical for mobile or remote outdoor transportation applications to support multiple data usage requirements, such as collecting video, checking the health of system devices, and sending command controls, and must also support a wide operating temperature range—on average of -20° to +70°C. And at the same time that processing power requirements are increasing, lower power consumption and thermal output is expected—all this while issues such as the current state of power supply technology can put limits on size reduction.
Distributed transportation systems that are housed outdoors must be able to handle exposure to high concentrations of dirt and moisture. Designers can look for boards with conformal coating to reduce degradation from such exposure. Conformal coating is used in small form factor manufacturing rather than potting, which is a similar process that uses a heavier material and is harder to inspect, test and repair. Though considered the highest level of environmental protection, potting encapsulates the entire PCB, which adds weight and expands dimensions of a unit. Even an extra ounce or millimeter can be critical in small form factor design, which is why conformal coating—with a single-part material that conforms to the board—is a better option (Figure 1).
Conformal coating (shown in violet) tightly seals all components while remaining repairable, and allows superior heat transfer.
A variety of conformal coating materials (such as acrylic, polyurethane, epoxy and silicone) and application methods (such as brushing, spraying and dipping) are currently used to protect against moisture, dust, chemicals and temperature extremes that can potentially damage electronics. The correct coating or application method varies depending on established standard operating conditions for an application. With transportation applications, different coatings may be selected based on a primary need for moisture resistance versus abrasion resistance versus temperature stability.
Dealing with Data
Rugged computing solutions in transportation also demand more memory space than ever before for both data storage as well as application performance. Options for storage include rotating hard disk drives (HDDs) for economy or solid-state drives (SSDs), which are truly rugged, but also come at a higher price point (cents per gigabyte for HDDs versus dollars per gigabyte for SSDs). HDDs contain spinning disks and movable read/write heads, whereas SSDs retain data in non-volatile memory chips and contain no moving parts, making them less susceptible to physical shock, altitude and vibration issues. SSDs have faster access time and lower latency than do HDDs, but SDDs cannot provide the capacity of an HDD; because of the higher cost per gigabyte, SSDs are typically no larger than 120 Gbyte, while HDDs average 500 Gbyte-1 Tbyte. Higher performing HDDs also require heavier materials than either a standard HDD or the flash memory and circuit board materials of SSDs.
Many transportation applications call for video capture, which requires solid vibration control in order to deliver quality output. Some rugged boards offer a thicker PCB fabrication to add rigidity so the board can withstand higher levels of vibration strain. The thicker PCB offers stability to the overall surface area, protecting electronic components from damage due to vibration. The thicker PCB also offers the ability to use more copper between layers for thermal considerations. Heat is a common unwanted by-product of processing power. In addition to cooling fans and large heat sinks, which may not always be possible for compact, mobile transportation designs, PCBs with adequate amounts of integrated copper facilitate heat conduction away from temperature-sensitive electronic components to prevent performance degradation (Figure 2).
Thermal flow from chips to heatsink, and secondarily through PCB copper planes.
For an in-vehicle or outdoor video/audio capture application design, the board itself needs high-performance graphics and host interface support for multiple peripherals. In addition to the integration of a video camera, features such as remote monitoring and wireless video download call for some form of connectivity. Both satellite and cellular connectivity require either an antenna or antennaed device to connect directly to the system. Ample Ethernet and serial interface ports —with at least one port supporting RS-232/422/485 for transmit and receive—are critical to accommodate function-specific peripherals.
PC/104 and Embedded Board eXpandable (EBX) are good format options for designs that can handle slightly larger Single Board Computer (SBC) form factors. Intended for data acquisition in rugged environments, the PC/104 embedded computing format has no backplane, instead allowing modules to stack together like building blocks—a more rugged design than typical bus connections in PCs. And with just 46 square inches of surface area (8” x 5.75”), EBX balances size and functionality with a bolt-down SBC format supporting rugged embedded designs with higher-performance CPUs, such as those using multicore technology for networking, digital signal processing (DSP) and graphics-heavy applications, and generous onboard I/O functions to support everything from large data exchange to video.
However, the most extendable and customizable application design method accommodates a broad range of custom and off-the-shelf needs by using modularity. Computer-On-Modules (COMs) are complete embedded computers built on a single circuit board for use in small or specialized applications requiring low power consumption or small physical size. Though they are compact (ETX/XTX at 114 x 95 mm and COM Express at 125 x 95 mm) and highly integrated, COMs can accommodate complex CPUs.
With the COM approach, all generic PC functions are readily available in an off-the-shelf core module. A custom designed carrier board complements the COM with additional functionality that is required for transportation-specific applications. The carrier board provides all the interface connectors for peripherals, such as storage, Ethernet, keyboard/mouse and display. This modularity allows the designer to upgrade the COM on the carrier board without changing any other board design features, and also allows more customization of peripherals as dictated by a specific application.
The COM Express form factor offers flexibility in the development and advancement of ultra-rugged embedded applications for transportation. By using the modular processing block, the designer creates a price and value advantage; he/she isn’t locked into a single vendor for board creation and can customize based on pricing and performance requirements. For instance, customized COM Express boards can have all components soldered on for increased reliability and can incorporate mechanical stand-offs to provide insulation from external elements. Because it is easily swapped from a carrier board and comes in one of the smallest form factors, COM Express is ideal for long-life embedded applications with a critical development cycle, as well as more progressive applications that require frequent processor upgrades without affecting other application design elements.
Case study: Outdoor Toll Plaza Application
Adlink Technology is currently working with a supplier of complete systems for toll collection—whether for manual or automatic payment—comprised of hardware and software for lane level, plaza level and host level operation. The toll plaza system is a multi-lane vehicle flow and payment enforcement system that is located throughout the Eastern U.S. and extends into Mexico. It uses elevated, outdoor camera capture and laser-scanner technology for multi-lane and single-lane environments, and depends on operation even in bad weather and with heavy vibration from constant traffic flow.
Ampro by Adlink is a line of extreme rugged embedded computers and systems that provides designers of rugged applications with a head start to development. For the toll plaza’s video capture and data transfer system, designers created a rugged solution around the Intel embedded architecture and EBX SBC form factor. The design accommodates both functionality and rugged requirements for the outdoor system with dual Ethernet, CRT and flat panel video, multiple serial and USB ports, SATA and IDE interfaces, CompactFlash socket, PCIe Mini Card socket, high-definition audio, and General Purpose Input/Output (GPIO) support for easy upgrades from older EBX board designs, as well as a PC/104-Plus expansion interface for legacy PC/104 and PC/104-Plus modules.
Key requirements for the toll plaza application are uptime and long product life. Product life expectancy and reliability are greatly affected by heat output that is generally managed by an internal fan. Because of the environment in which the application resides, effective use of a fan can be hampered by vibration or corrosion. To solve this issue, the Atom N270 processor, with a standard speed of 1.6 Gbyte, has been clocked down to 1.0 Gbyte in order to accommodate a passive cooling system.
Accommodating mobility and/or environmental requirements for transportation applications often calls for rugged, small form factor design. Rugged products consider shock, vibration, humidity and temperature needs when dealing with power, storage and data processing. Formats such as PC/104, EBX and COMs have been created specifically to address rugged, embedded system requirements—in particular, size and weight—while also handling complex CPU technology for applications that require heavy processing power. Modularity also helps designers to create customizations while taking into account cost and value requirements. The bottom line for any transportation design is to understand all application requirements and how/where existing formats and products can address those needs.
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