Mechanical design of the HP 4980 Network Advisor - protocol analyzer - Technical

Hewlett-Packard Journal, Oct, 1992 by Kenneth R. Krebs

Many of our part interfaces were designed with 2-to-3-micro-mthick aluminum coating in mind and therefore had very small clearances. The move to O.003-to-O.OO7-inch-thick zinc caused some clearances to become interferences. In some cases, this required tool modifications to make parts thinner. Fortunately, in most cases this could be accomplished by simply shaving the core-side parting line and readjusting shutoffs if necessary. In other cases, costlier tool modification requiring welding and recutting was needed. However, in one case welding was impractical and zinc had to be masked from affected areas. While shielding effectiveness was reduced, the ZAS process, coupled with other internal electrical and cabling modifications, gave us enough margin to pass the CISPR 11 specification.

The package was tested to the HP class Bi shock and vibration specification. It was tested in closed-up-for-travel, desktop (display up, keyboard down), and floor-standing configurations in both color and monochrome display versions. No unacceptable damage was sustained.

Cooling of the package is provided by an 80-mm-square tubeaxial fan with a maximum airflow of 38 ft3/min. Ambient air is drawn in at the rear of the pod, across the pod electronics, and up through the top of the pod into the bottom chassis. Once inside the mainframe, it joins air coming from the base of the front panel, goes across the power supply and the PC system printed circuit board, and exhausts through the rear panel. Our worst-case pod, dissipating approximately 50 watts, experiences an air temperature rise of only 16*C. The temperature rise in the mainframe is 12*C above the system board and 19*C above the power supply.

All of these temperatures remain well below what we can tolerate given the temperature limitations of the disk drives and the LCD. The maximum allowable ambient operating temperature of the hard disk drive and color LCD is 40*C, and that of the flexible disk drive and monochrome LCD is 45*C. The minimum allowable storage temperature of either display is -25*C. Therefore, the full HP class Bi temperature specification had to be waived in deference to these components. The monochrome LCD experiences extreme response sluggishness at very low temperatures and washes out at high temperatures (adjusting the contrast control does not help). The color LCD experiences no such performance or visual degradation at the temperature extremes.

The supersoak and condensation portions of our humidity testing were not done because the LCDs and disk drives do not allow them. The polarizers on the LCDs cannot tolerate standing water for any length of time. However, we have an optical film applied to both LCDs for anti-glare and protection from scratching and chemical contamination. The other humidity testing done on the instrument presented no problems.

While our altitude testing indicated no problems, we learned a valuable lesson regarding altitude effects. The large label that covers the ribbing on the underside of the display cover lid entraps air in the dozens of hermetically sealed pockets it forms. When an instrument built at a 6000-foot altitude (like Colorado Springs) made its way to sea level, these pockets collapsed a little causing an unacceptable dimpling effect in the label. As an interim remedy, we had to machine vents into the top of one rib in each pocket to allow the pressure to equalize. Later, 122 pins were added to the mold to provide these vents.