Technique for sensing altitude from fan speed
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.
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 INVENTIONThe 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 INVENTIONAs 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.
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 INVENTIONA 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.
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
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
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
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.
Claims
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.
Type: Application
Filed: Jul 25, 2003
Publication Date: Jan 27, 2005
Inventors: Andrew Delano (Fort Collins, CO), Robert Smith (Loveland, CO)
Application Number: 10/627,496