U.S. patent application number 10/627496 was filed with the patent office on 2005-01-27 for technique for sensing altitude from fan speed.
Invention is credited to Delano, Andrew D., Smith, Robert B..
Application Number | 20050019164 10/627496 |
Document ID | / |
Family ID | 34080657 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050019164 |
Kind Code |
A1 |
Delano, Andrew D. ; et
al. |
January 27, 2005 |
Technique for sensing altitude from fan speed
Abstract
A DC fan, or lot of DC fans is characterized at a constant
voltage to determine the variation of their rotational speed with
respect to altitude. Many such DC fans will have a substantially
linear response in speed with respect to altitude. From this
relationship, a converter is constructed to convert the rotational
speed into an altitude. The converter may be a discrete electronic
device including a look up table or capable of performing the
arithmetic algorithm representing the relationship between fan
speed and altitude. Alternatively, the converter may be
incorporated into the system to be cooled by the DC fan. For
example, it may be a software routine run by the computer that the
DC fan is used to cool.
Inventors: |
Delano, Andrew D.; (Fort
Collins, CO) ; Smith, Robert B.; (Loveland,
CO) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
34080657 |
Appl. No.: |
10/627496 |
Filed: |
July 25, 2003 |
Current U.S.
Class: |
416/61 |
Current CPC
Class: |
H05K 7/20209 20130101;
F04D 27/00 20130101; G01C 5/00 20130101 |
Class at
Publication: |
416/061 |
International
Class: |
F04D 029/00 |
Claims
What is claimed is:
1. A device, comprising: a fan including a speed output, wherein a
rotational speed of said fan is characterized with respect to
altitude; and a converter electrically coupled to said speed output
from said fan, wherein said converter receives a fan speed and
outputs an altitude.
2. The device of claim 1, wherein said converter uses an arithmetic
algorithm to calculate said altitude from said fan speed.
3. The device of claim 1, wherein said converter uses a look up
table to calculate said altitude from said fan speed.
4. The device of claim 1, wherein said fan speed is output by said
fan as a digital signal.
5. The device of claim 1, wherein said fan speed is output by said
fan as an analog signal.
6. A device, comprising: a fan, wherein a rotational speed of said
fan is characterized with respect to altitude; a fan speed
detector, outputting a fan speed; a converter, electrically coupled
with said fan speed detector, wherein said converter receives said
fan speed and outputs an altitude.
7. The device of claim 6, wherein said converter uses an arithmetic
algorithm to convert said fan speed to said altitude.
8. The device of claim 6, wherein said converter uses a look up
table to convert said fan speed to said altitude.
9. The device of claim 6, wherein said fan speed is output by said
fan speed detector as an analog signal.
10. The device of claim 6, wherein said fan speed is output by said
fan speed detector as an analog signal.
11. A method for the determination of an altitude, comprising the
steps of: a) characterizing a rotational speed of a fan with
respect to altitude; b) measuring a rotational speed of said fan;
and c) converting said rotational speed into an altitude.
12. The method of claim 11, wherein said converting step is
performed using an arithmetic algorithm.
13. The method of claim 11, wherein said converting step is
performed using a look up table.
14. The method of claim 11, wherein said measuring a rotational
speed of said fan step is performed by said fan.
15. The method of claim 11, wherein said measuring a rotational
speed of said fan step is performed by an optoelectronic
device.
16. A device, comprising: means for detecting the speed of a fan;
and means for converting said speed of said fan into an
altitude.
17. The device of claim 16, further comprising: means for
characterizing said speed of said fan with respect to altitude.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to application Ser. No.
xx/xxx,xxx entitled, "Utilizing an Altitude Sensor to Control Fan
Speed," filed on or about the same date as the present application,
and hereby incorporated herein by reference. Application Ser. No.
xx/xxx,xxx discloses and claims a technique utilizing the altitude
calculated from the fan speed in a method to set a fan speed
sufficient to allow for proper processor thermal margin.
FIELD OF THE INVENTION
[0002] The present invention relates generally to the field of
cooling technologies and more specifically to the field of cooling
technologies within a device enclosure where cooling efficiency is
related to fan speed and altitude.
BACKGROUND OF THE INVENTION
[0003] As altitude above sea level increases, atmospheric density
decreases. This decrease in atmospheric density is responsible for
a reduction in cooling capacity of a fan running at a given speed.
Since there is less air at higher altitudes, at a given fan speed
fewer air molecules will be passing over a heat-generating device,
than would be present in the identical system at a lower altitude.
This fact presents a problem for designers looking to characterize
system requirements, since a given configuration that works well at
sea level, may be sufficiently degraded in cooling capacity at
higher altitudes such that some electronic devices may no longer be
operating within their thermal design margins.
[0004] Designers have typically solved this problem by requiring
sufficient cooling of all of their systems for performance at
altitude. However, this solution is not optimum for systems
operating at sea level, since the same system could operate at a
higher frequency at sea level due to the improved air-cooling
present at sea level. System performance could be maintained at all
altitudes by requiring fans in high altitude systems to run faster,
however this requires knowledge of altitude. While it is certainly
possible to require users to input altitude information upon first
use of a system, this approach is prone to errors. There is a need
in the art for a method allowing electronic systems to detect their
operating altitude so that they may respond accordingly.
SUMMARY OF THE INVENTION
[0005] A DC fan, or lot of DC fans is characterized at a constant
voltage to determine the variation of their rotational speed with
respect to altitude. Many such DC fans will have a substantially
linear response in speed with respect to altitude. From this
relationship, a converter is constructed to convert the rotational
speed into an altitude. The converter may be a discrete electronic
device including a look up table or capable of performing the
arithmetic algorithm representing the relationship between fan
speed and altitude. Alternatively, the converter may be
incorporated into the system to be cooled by the fan, for example,
it may be a software routine run by the computer that the DC fan is
used to cool.
[0006] Other aspects and advantages of the present invention will
become apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a view of a DC fan and converter according to the
present invention.
[0008] FIG. 2 is a graph showing the relationship between fan
rotational speed and altitude in an example embodiment of the
present invention.
[0009] FIG. 3 is a graph showing the relationship between fan
rotational speed and processor thermal margin in an example
embodiment of the present invention.
[0010] FIG. 4 is a flowchart of an example embodiment of the
calculation of altitude from fan rotational speed according to the
present invention.
DETAILED DESCRIPTION
[0011] FIG. 1 is a view of a DC fan and converter according to the
present invention. In an example embodiment of the present
invention a DC fan 100 including fan blades 104, a motor 102, and
an electrical port 108 is provided to cool a heat-generating
device. The DC fan 100 may have the ability to output its
rotational speed from the fan 100 itself without any additional
devices. Alternatively a speed sensor 106, such as an
opto-electronic device that counts fan blades 104 may be used for
DC fans 100 without the ability to output their rotational speed.
The speed data from the fan 110, or the speed data from the speed
sensor 112 is then input to a converter 114 that converts the speed
data into altitude data 116. The converter 114 is programmed using
data obtained by characterizing the rotational speed of the DC fan
100 with respect to altitude. While FIG. 1 shows a discrete
converter device 114 for simplicity and clarity, other embodiments
of the present invention may include the converter function in
other electronic devices present in the overall device that is
being cooled by the DC fan 100. For example, in a computer system
cooled by the DC fan 100, the converter functionality may be built
in to the processor chip, or may operate in software under the
computer operating system. The physical location and construction
of the converter 114 is not critical to the present invention, and
the converter 114 functionality may be implemented anywhere desired
by the system engineer. A sample of DC fan characterization data is
shown in FIG. 2.
[0012] FIG. 2 is a graph showing the relationship between fan
rotational speed and altitude in an example embodiment of the
present invention. Since the atmosphere is less dense at altitude
than at sea level, a DC fan 100 supplied with a constant power
voltage will rotate at a higher rate at higher altitudes. An
example graph of this relationship between rotational speed and
altitude is shown in FIG. 2. In this example graph of a
characterization of a DC fan 100, the horizontal axis 204
represents altitude above sea level, measured in feet, and the
vertical axis 202 represents rotational fan speed, measured in
revolutions per minute (RPM). In this example embodiment, the
characterization data 200 is represented by a straight line.
Naturally, most embodiments of the present invention will take fan
speed data at a variety of atmospheric pressures related to a
variety of altitudes and then a curve will be fit to the data. This
curve may be linear in some cases, but other curves may be fit to
the characterization data within the scope of the present
invention.
[0013] Note that in this example characterization graph, at a first
data point 214, the DC fan 100 rotates at 2500 RPM (represented by
point 206 in FIG. 2), and at a second data point 216, when the DC
fan 100 is at an altitude of 2000 feet (represented by point 208 in
FIG. 2). At a higher altitude of 12,000 feet (represented by point
212 in FIG. 2), the DC fan rotates at 3000 RPM (represented by
point 210 in FIG. 2). While this sample characterization data is
linear, characterization of other DC fans 100 may result in
non-linear characterization data within the scope of the present
invention. This characterization data may be described by an
arithmetic algorithm, a look up table, or other equivalent
mechanisms or methods for calculation of an altitude when given a
fan rotational speed. The resulting characterization data is then
programmed into the converter 114 shown in FIG. 1.
[0014] FIG. 3 is a graph showing the relationship between fan
rotational speed and processor thermal margin in an example
embodiment of the present invention. As fan speed increases, the
amount of air flowing over a heat-generating device also increases.
This increased airflow results in more efficient cooling of the
heat-generating device resulting in a lower temperature of the
heat-generating device. This relationship is shown graphically in
FIG. 3. In this example graph of the relationship between the
temperature of a heat-generating device, the horizontal axis 304
represents the fan speed, measured in RPM, and the vertical axis
302 represents the temperature of the heat-generating device, shown
as thermal margin in a processor, and measured in degrees
Centigrade (degrees C.). Processor thermal margin is the
temperature difference between the current temperature of the
processor and the maximum allowed temperature. Lower actual
temperatures of the heat-generating device result in larger thermal
margins. The example thermal data 300 shown in FIG. 3 is
represented by a straight line, however other embodiments of the
present invention may result in non-linear thermal data.
[0015] Note that in this example thermal graph, at a first data
point 314, at a fan speed of 2500 RPM (represented by point 308 in
FIG. 3), the processor has a thermal margin of 1 degree C.
(represented by point 306 in FIG. 3), and at a second data point
316, at a fan speed of 3000 RPM (represented by point 312 in FIG.
3), the processor has a thermal margin of 8 degrees C. (represented
by point 310 in FIG. 3). Thus, for an increase in fan speed of 500
RPM the processor thermal margin increased by 7 degrees C., which
may be critical to processor performance in some designs.
[0016] FIG. 4 is a flowchart of an example embodiment of the
calculation of altitude from fan rotational speed according to the
present invention. In an example embodiment of the present
invention, a method of determining altitude from fan speed is begun
at a start step 400. In a preliminary step 402 a DC fan, or a group
of DC fans, is characterized to determine their response to
altitude as measured by rotational fan speed at a constant input
voltage. Note that in some embodiments of the present invention, it
may not be necessary to characterize every individual DC fan.
Process variations within a given model of fan may be sufficiently
small that characterization of a sample of fans from that given
model may be sufficient to generate characterization data usable by
all fans of that model. In a step 404, a DC fan speed of a fan is
detected. In a step 406, this fan speed is converted to an altitude
by a converter, and the method ends in a finish step 408.
[0017] The foregoing description of the present invention has been
presented for purposes of illustration and description. It is not
intended to be exhaustive or to limit the invention to the precise
form disclosed, and other modifications and variations may be
possible in light of the above teachings. The embodiments were
chosen and described in order to best explain the principles of the
invention and its practical application to thereby enable others
skilled in the art to best utilize the invention in various
embodiments and various modifications as are suited to the
particular use contemplated. It is intended that the appended
claims be construed to include other alternative embodiments of the
invention except insofar as limited by the prior art.
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