Reliability is probably the most difficult measure by which a product can be judged when making a purchase decision. Understanding and comparing performance features is relatively easy, but really understanding the expected reliability of a monitor takes an understanding of the factors that can affect reliable operation.
Heat is probably the single biggest enemy of any electronic device, particularly in high-resolution grayscale monitors, where the demands for high contrast force designers to drive circuitry to very high performance levels. Controlling heat buildup and ensuring proper heat dissipation is key.
An internal cooling fan is the most obvious option. However, fans have moving parts, and thus tend to have shorter lifespans than the monitors themselves. They also tend to produce audible noise. If the fan were to fail prematurely, it could force a monitor hardware failure that could otherwise have been avoided. Therefore, other methods of regulating heat are needed.
Also, monitor manufacturers need to consider the natural convection cooling process, and design their heat dissipation methods to take advantage of this effect. When evaluating monitors for future use, it's important to be aware of the heat the product generates, and whether the monitor incorporates any special circuitry for monitoring internal temperature conditions (and if the monitor automatically shuts down to prevent overheating and failures from occurring).
Another factor that can affect reliability is the monitor's ability to handle internal CRT arcs. An arc can occur within a CRT when a loose particle is dislodged, or a capacitive charge is built up inside the CRT elements. This is a normal phenomenon for any CRT device, but when an arc occurs, the dissipation of electrical energy can damage electronic components and cause monitor failure.
As a result, manufacturers must build in circuitry that suppresses arcs and protects the electronic components. Traditionally the way to "arc-protect" a monitor is to install protective devices at the cathode input near the CRT. However, these devices can reduce the bandwidth and image quality of the display. The monitor manufacturer must balance this trade-off to ensure there is adequate arc-protection and good image quality. Ensure that your monitor choice utilizes sufficient arc-protection, and ask for test results performed during the design process.
The ultimate indicator of reliable performance is proven field data from installed systems. Ask your prospective monitor supplier for the field data on their installed base. Find out how many products of this model type have been deployed, and what the average lifetime is. You should also ask for details on how failure data is evaluated and what corrective design actions have been taken to extend the life of the product. There are industry standards for calculating life expectancy and mean time between failure (MTBF), based on component choices and field performance.
With solid electronic design, it's possible to reduce annual field failure rates to as low as 2%-3% -- in sharp contrast to failure rates of nearly 60% reported in the Baltimore VA and University of Maryland study.
By expanding the scope of the purchase decision beyond image quality and price to include these often overlooked considerations, high-resolution monitor buyers can get much closer to a realistic set of performance expectations. This does not negate the need for a good quality assurance program, but it clearly makes the transition into a more proactive maintenance routine a possibility.
Further help may also be on the way. With continuing advances in electronic design and digital control circuitry, monitor manufacturers are now considering unique methods of conformance testing to validate stability. One idea being considered is hands-off conformance testing, which can automatically sense luminance levels and confirm overall video system stability, including the video card and monitor. And new advances such as flat-panel technology, are bringing a whole new set of concerns and issues surrounding stability and reliability that will need to be addressed.
If you are currently facing issues of monitor failure and instability, these ideas may seem a bit far-reaching, but they can save you a lot of trouble in the long run.
As you make your way across the exhibit floor at this year's RSNA conference, taking in the technology and thinking about what might be possible for your institution, you might want to consider the importance of high-resolution monitors in the PACS environment. With a little advance planning, you can visit monitor vendors with expanded criteria to use in your decision-making. Rather than trying to inspect quality into high-resolution monitors, you can choose an educated approach that could bring you a little closer to the perfect PACS world.
Mr. Scott is a technical marketing and product support manager at Siemens Display Technologies. He can be reached by email at [email protected].
November 20, 2000
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