Innovation, demand, and falling prices have resulted in high quality large format commercial-off-the-shelf (COTS) LCD displays moving from the living room to high availability, mission critical applications.
The human cognitive ability to perceive and process data from several heterogeneous outputs and react correctly to the information is greatly enhanced with the proper representation of graphical data. Large format displays allow for the consolidation of multiple heterogeneous displays, fonts, dials, gauges, numbers, into a single homogeneous representation of situational awareness.
Mission critical systems such as industrial control rooms, shipboard control, building monitoring and mass notification have benefited from the display of intuitive information on large screen displays.
For example, for many years, firemen first to arrive on scene have been met with screeching fire alarms, indicator lights on a fire panel and “as built” drawings locked in a cabinet with a special key. Today they could now be greeted by a large format LCD with a 3D view of the building, smoke flow diagrams, and other information to help them understand the situation and make better decisions faster. Occupants leaving a building can also benefit from graphical mass notification information which can be tailored for the situation.
Ship systems comprised of different steam gauges and manual operations such as sticking tanks and closing valves can now be automated with their instruments consolidated on a single screen or redundant large screens, showing graphically status of fuel, water, and ballast, improving productivity and decreasing workload.
Similarities exist on industrial control systems where several CRTs or smaller LCDs are being replaced by a large LCD with clever graphics designed for human factors and perception.
The challenge of these applications is the proper integration of the COTS LCD technology to meet requirements of availability, reliability, and intended use.
Large LCD panels are coming out of the factory with brilliant colors and near perfect viewing angles using ASV (Advanced Super View) and IPS (In Plane Switching) innovations driven by consumer TV requirements. The challenge is ruggedizing a display to preserve as much of this as possible, this while shielding against objects, liquids, sunlight and EMI. These surface choices may adversely affect the optics of the panel, which can be reduced through bonding techniques to eliminate air gaps.
Degree of Environmental Protection
Depending on its intended use, mission critical displays may be required to operate in an environment subject to dust, sand, fog, chemicals, falling or spraying liquids (broken pipes, sprinklers, etc). Protection of the LCD panel involves designing an outer enclosure capable of keeping dust and liquids out while keeping the display operating in its proper temperature range.
Commercial electronics and LCD displays typically operate at temperatures above freezing and below 70°C (known as the clearing temperature). At temperatures greater than the specified clearing temperature, liquid crystal can go from the nematic state to an isotropic state where the display “clears” or turns black. As discussed previously, protection from environmental hazards can adversely affect the ability of the enclosure to transfer heat out of the display. For instance, a large LCD drawing 80 Watts within a sealed enclosure could have a thermal resistance of 0.6°C/Watt resulting in an internal rise of 48°C. Added to a 23°C room temperature, the display is running at its high extreme of 71°C before the ambient environment rises above room temperature.
In addition to isotropic display clearing, long-term reliability is adversely affected by running panels at or near the clearing temperature. Depending on the application, enclosures can be de signed to circulate air through filtered and louvered vents. This can prevent dust and water ingress while providing a cooling mechanism capable of keeping the panel within specified operating temperatures.
The transition of display backlights from CCFL to LED has also helped reduce the amount of energy in a panel, which has been a great benefit to thermal management. Displays that are used in direct sunlight, however, have to deal with solar gain which can add as much as 1000W /m2 to the problem on a sunny, cloudless day at high noon. The amount absorbed depends on the enclosure’s material and color, but typically blocking IR films or a laminar flow of air over the display are used to prevent the display from “blacking out”. In sub freezing environments, such as outdoor, or non temperature controlled areas, supplemental heaters may be required to prevent slow response of the LCDs due to low temperature.
Shock and Vibration
The deployment of large screen LCDs in control rooms, ships, industrial areas, or public venues requires consideration of tampering, vibration, and shock. It is important to understand the nature of the vibration or shock in magnitude and frequency to which the screen may be subjected. Sources can be motors, conveyors, engines, propeller blades or even seismic events. In many industries, there are published standards, which represent shock and vibration experienced by the display in both transit and operation. Some of the component considerations when designing a display requiring ruggedization are listed in Table 3.
Touch, gesture, and motion sensing has added an additional dimension to displays used for mission critical applications, allowing the user to interact with the graphical display of data without the use of a standard keyboard and mouse. The most popular method is the touch screen but there is an emergence of new touchless technologies using cameras and intelligent vision, which should be viable for use in the future.
There are several touchscreen technologies available, each having its own set of strengths and weaknesses. It is important to understand the end use and user to choose the best solutions. For instance, using an infrared touch screen in an outdoor location at night can attract insects which can actually cause false touches if they land on the screen and break the IR light beam. Other touch screen technologies such as capacitive are sensitive to metal enclosures making them difficult choices for very rugged applications. Some of the more popular technologies and their strengths and weaknesses are listed in Table 4.
Reliability and Maintainability
Since by definition, mission critical, high availability displays may have to operate 24 X 7 for up to several years, consideration should be given to ways of extending useful life. The primary method is selection of power and backlighting components which operate comfortably within the environmental conditions expected. Further advantage is gained by 100% brightness if possible, as well as automatically shutting off backlights when not in use. The very nature of a mission critical or life safety display usually precludes the use of PC power saving options. However, techniques such as the proximity sensing of a viewer to turn on a display, or reduced brightness during dark conditions may extend the life of the backlight and power system. In addition, sensing light output and using it to dynamically adjust display brightness over the life of the display can extend the life of the display.
Parts within a large screen display are considered to have a large Mean Time Between Failures (MTBF) usually measured in tens of thousands of hours or higher. The first reaction is to divide this number by 8760 hours per year and feel assured your 24X7 display will last that many years before it fails. However the MTBF is just a probability of failure and is calculated during the “useful life” of a part, typically at room temperature. As a part starts to wear out, or gets used at high temperature, its reliability can decrease rapidly. Solid-state components such as ICs are thought of as lasting virtually forever, but within an LCD there are several components that, when routinely maintained or changed out, will keep the reliability at its maximum. The use of intelligent health monitoring such as temperature, brightness, fan speed or air flow to trigger maintenance events will increase overall reliability and availability.
Leveraging the performance and value of large format commercial off the shelf (COTS) displays requires careful attention and understanding of the environment and operation by the end user. Using this information to develop specific design requirements, engineering a design that meet these requirements, and finally developing test steps that validate the product meets these requirements will ensure a successful large format COTS display implementation.