Local Ambient Temperature Measurement Guidelines - Intel Q9450 - Core 2 Quad Quad-Core Processor Design Manual

3.3 Local Ambient Temperature Measurement
Guidelines
The local ambient temperature T
the processor. For a passive heatsink, T
temperature; for an actively cooled heatsink, it is the temperature of inlet air to the
active cooling fan.
It is worthwhile to determine the local ambient temperature in the chassis around the
processor to understand the effect it may have on the case temperature.
T is best measured by averaging temperature measurements at multiple locations in
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the heatsink inlet airflow. This method helps reduce error and eliminate minor spatial
variations in temperature. The following guidelines are meant to enable accurate
determination of the localized air temperature around the processor during system
thermal testing.
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 Figure 5 (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
motherboard, add-in cards, and other system components, it is likely that the T
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 6. 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.
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is the temperature of the ambient air surrounding
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is defined as the heatsink approach air
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Thermal and Mechanical Design Guidelines
Thermal Metrology
in a chassis with a live
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