Flat-panel display technology offers many benefits for medical equipment, but a look inside the box that holds the display reveals a myriad of other engineering details to be considered before an image ever appears on the screen. Having decided which type of display technology to use, the medical system designer now confronts a more complicated series of choices relating to exactly how the display will be used. Designers often select a flat-panel display as the operator interface for the equipment based upon its size, power consumption, display quality, and lack of electromagnetic interference. This section introduces other considerations related to building a system around the display and some suggestions for handling them.
The Rest of the System
A fundamental decision is choosing the computing platform with which the flat-panel display will be used. Will the display function as a monitor (cathode ray tube [CRT] replacement) remoted to the host computer, or will the computer and display be an integrated unit? If used as a monitor, will the display be connected to the host's analog port, like a CRT, or will it communicate digitally? Many newer medical products have an analog RGB output for CRTs, so the application requirement has simply been to replace the CRT. Designers must also consider the distance between a flat-panel monitor and its host computer. For best performance, the maximum distance should be 150 ft.
Both platforms—flat-panel monitor and flat-panel computer—offer designers a selection of operator input devices, including keyboard, mouse, touch screen, or bar code reader. If the goal is to minimize space requirements, a touch screen is the logical choice. Depending upon the stylus to be used (finger, gloved hand, or pen input), the desired resolution, and the operating environment, designers can choose among infrared, resistive, capacitive, or guided acoustic wave technologies.
Other concerns involve where the flat-panel display system is to be used. If it is a stationary system, how will it be mounted: on the floor, on the wall, or inside another piece of equipment? If it is mobile, will it be hand-carried or mounted on a cart or other vehicle? What are the desired ergonomic features in terms of weight, viewing angle, display orientation, and brightness? Improvements in display backlighting technology have resulted in color liquid crystal displays (LCDs) that are sunlight-readable. If this is desirable, designers must consider whether the display will also have to be dimmed.
It is also important to take into account any environmentally challenging factors such as temperature extremes or vibration. Electroluminescent displays typically have a wider temperature range than LCDs, but if color is needed, solutions can be engineered that can heat or cool a color LCD for optimal performance. High-vibration environments are difficult for any computer system, but proper mounting and sealing of system components can minimize problems.
All of these operational requirements will dictate the type of box required for the system. Flat-panel display systems are available in open-frame configurations, which enable mounting it in a custom enclosure or in off-the-shelf enclosures. Enclosures range from simple vented boxes, which basically protect the electronic components, to industrially hardened, sealed boxes that can withstand moisture, dirt, and most types of abuse. It is imperative that in planning a system, designers keep in mind regulatory requirements for FDA, UL, CE, and so on. It is equally important to look toward the next generation of equipment. Designers should build upgradability into the present design.
There are additional considerations to address when designing a system that uses a display. It is important to determine how to spec, buy, test, and stock components, as well as how to decide what cost level is acceptable. It is critical to avoid long lead times and unforeseen parts obsolescence.
OEMs must also determine how to design and build special boards that a system may require, such as custom printed circuit boards for mounting connectors. Other considerations include software issues, such as the custom BIOS setup that is required by each display; compatibility among vendors; long-term availability of parts, especially the display; and repairs.
When a new product is being designed from the ground up, a single-board computer integrated with the display can control both the display and the instrument itself. If medical device designers accept this challenge, they often find themselves in the computer manufacturing business, deciding upon processors, communications protocols, memory, and other system parameters.
Another option is to have an outside source integrate the flat panel into the system. This enables the OEM to focus its design engineering resources on the medical electronics and control software. As equipment moves into the production phase, the display unit should arrive as a fully assembled and tested system, ready to integrate into the core product. A flat-panel integrator should provide applications assistance and should address display interfacing issues for any platform, as well as special display concerns, particularly enhanced brightness. An integrator should provide enclosure design assistance, including either actual manufacturing or working with the OEM to select the appropriate box supplier. In addition, assembling, testing, and supporting the entire display system, as well as providing service and repair, should be considered. An integrator should ensure long-term availability of the product, which could include inventory stocking and last-time buys.
Flat-panel displays provide medical equipment designers a variety of options. To maximize investment in this rapidly changing technology and to meet time-to-market pressures, designers must carefully consider the flat-panel options and determine the most efficient and cost-effective way to integrate the display into the final product.