Rugged displays do more than meets the eyeStory
May 16, 2009
Today's rugged display monitors must be able to do more than just produce pretty pictures; they must also meet harsh environment and EMC requirements, and potentially integrate with an entire embedded computing subsystem or touch screen.
Rugged display monitors are an essential part of every military system having a man in the loop. With applications ranging from command and control, combat systems, sensor/image displays, ground stations, shelters, training systems, all types of armored vehicles, and many more, these displays are the key decision-making interfaces between man and machine. Available in a multitude of resolutions and sizes, flat-panel Liquid Crystal Display (LCD) is the most popular choice due to its small space envelope, low power consumption, and enduring ability to be tailored to customers' specific environmental requirements. While primarily based on commercial LCD glass panels, a typical rugged display subsystem is often reengineered to meet a project's wide temperature range operation, readability, shock, vibration, and Electro-Magnetic Compatibility (EMC) requirements in addition to the potential integration of a touch screen or complete embedded computing subsystem.
Flat-panel display options
Flat-panel displays have completely displaced the bulky and power-hungry Cathode Ray Tube (CRT) in all but a few legacy military applications. LCD panels use a variety of associated technologies and offer excellent viewing characteristics as well as a wide operational temperature range when compared to LCDs available a few years ago. Color plasma displays commonly used in large screen, high-definition television have excellent picture quality and color spectrum but cannot meet the required temperature range, ruggedization levels, or low power dissipation of rugged LCD displays.
Flat-panel LCDs are an example of a commercial technology market segment still displaying healthy growth, receiving significant development investment, and continuing to evolve very rapidly in performance and affordability. Because the scope of application for rugged displays is diverse and the technology evolution fast, customers look for rugged displays that meet their project-specific needs rather than selecting a particular technology up front. As a result, most rugged display subsystems incorporate some customization to precisely match them to the application. Variables include contrast ratio, video standard, size, shape, weight, mounting fixtures, power supply, temperature range, shock and/or vibration tolerance, or EMC. However, most of these individual specification items will be based on existing and proven technology offering fast turnaround and low risk to the user.
Unlike a household television that is operated and viewed in a very narrowly controlled environment, a rugged display might be required to operate in the open and must be readable in daylight or direct sunlight, requiring a much greater contrast ratio. In the case of LCDs, this is provided by cold cathode fluorescent backlighting with a wide dynamic range to provide the brightness required. For extended temperature range operation, the display must be heated at low temperatures to maintain its response times. Both the heating and lighting contribute to power dissipation, but improved efficiency and intelligent, selective control can be used to reduce a display subsystem's overall power dissipation to typically less than 30 W.
An LCD panel, being only a few millimeters thick, has little structural rigidity of its own. Additionally, the display cells might even distort under certain vibration conditions. To overcome this, the panel is bonded to a layer of toughened glass; this assembly can then be mechanically isolated within a chassis for additional protection. The layer of glass offers a base for the deposition of many types of coatings to improve the display's optical qualities. This glass will also incorporate an electrically conductive layer for EMC control. Touch screens are also a popular addition to rugged displays, being more intuitive and easier to use with the military gloved hand than most typical keyboards.
Typical within a general purpose, PC-compatible range of rugged displays is the Sentinel from GE Fanuc Intelligent Platforms (Figure 1). Available in a range of sizes from 15" to 21", this type of rugged display subsystem is ideal for use in many naval applications, ground-based vehicles and shelters, and a variety of training environments.
Rugged LCD displays are excellent examples of how the military has profited from a strong commercial market. Just as LCD technology will continue its rapid evolution, so will the technologies required to ruggedize it.
To learn more, e-mail Duncan Young at [email protected]
Figure 1: Typical within a general purpose, PC-compatible range of rugged displays is the Sentinel from GE Fanuc Intelligent Platforms.