Thermal Metrology
30
Thermal and Mechanical Design Guidelines
For active heatsinks, it is important to avoid taking measurement in the dead flow
zone that usually develops above the fan hub and hub spokes. Measurements should
be taken at four different locations uniformly placed at the center of the annulus
formed by the fan hub and the fan housing to evaluate the uniformity of the air
temperature at the fan inlet. The thermocouples should be placed approximately
3 mm to 8 mm [0.1 to 0.3 in] above the fan hub vertically and halfway between the
fan hub and the fan housing horizontally as shown in the ATX heatsink in Figure
(avoiding the hub spokes). Using an open bench to characterize an active heatsink can
be useful, and usually ensures more uniform temperatures at the fan inlet. However,
additional tests that include a solid barrier above the test motherboard surface can
help evaluate the potential impact of the chassis. This barrier is typically clear
Plexiglas*, extending at least 100 mm [4 in] in all directions beyond the edge of the
thermal solution. Typical distance from the motherboard to the barrier is
81 mm [3.2 in]. For even more realistic airflow, the motherboard should be populated
with significant elements like memory cards, graphic card, and chipset heatsink. If a
barrier is used, the thermocouple can be taped directly to the barrier with a clear tape
at the horizontal location as previously described, half way between the fan hub and
the fan housing. If a variable speed fan is used, it may be useful to add a
thermocouple taped to the barrier above the location of the temperature sensor used
by the fan to check its speed setting against air temperature. When measuring T
A
in a
chassis with a live motherboard, add-in cards, and other system components, it is
likely that the T
A
measurements will reveal a highly non-uniform temperature
distribution across the inlet fan section.
For passive heatsinks, thermocouples should be placed approximately 13 mm to
25 mm [0.5 to 1.0 in] away from processor and heatsink as shown in Figure
3-3. The
thermocouples should be placed approximately 51 mm [2.0 in] above the baseboard.
This placement guideline is meant to minimize the effect of localized hot spots from
baseboard components.
Note:
Testing an active heatsink with a variable speed fan can be done in a thermal chamber
to capture the worst-case thermal environment scenarios. Otherwise, when doing a
bench top test at room temperature, the fan regulation prevents the heatsink from
operating at its maximum capability. To characterize the heatsink capability in the
worst-case environment in these conditions, it is then necessary to disable the fan
regulation and power the fan directly, based on guidance from the fan supplier.
Содержание Celeron Dual-Core E1000 Series
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Страница 26: ...Processor Thermal Mechanical Information 26 Thermal and Mechanical Design Guidelines...
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Страница 86: ...Heatsink Clip Load Metrology 86 Thermal and Mechanical Design Guidelines...
Страница 88: ...Thermal Interface Management 88 Thermal and Mechanical Design Guidelines...
Страница 120: ...Legacy Fan Speed Control 120 Thermal and Mechanical Design Guidelines...
Страница 124: ...Balanced Technology Extended BTX System Thermal Considerations 124 Thermal and Mechanical Design Guidelines...
Страница 126: ...Fan Performance for Reference Design 126 Thermal and Mechanical Design Guidelines...
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Страница 139: ...Mechanical Drawings Thermal and Mechanical Design Guidelines 139 Figure 7 57 Reference Fastener Sheet 1...
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