Utilizing an altitude sensor to control fan speed
A heat-generating device is characterized to determine the relationship between the speed of a DC cooling fan, and the thermal margin of the heat-generating device. Since the speed of DC fans is substantially linear with respect to their input voltage, the speed of the fan may be adjusted within a system to provide the speed necessary for cooling needs. An altitude is input to a converter which uses the characterization of the heat-generating device to determine a fan speed necessary at that altitude to cool the heat-generating device to a temperature within its operating range. The converter then controls the voltage supplied to the DC fan to result in the needed fan speed.
This application is related to application Ser. No. ______ entitled, “Technique for Sensing Altitude from Fan Speed,” filed on or about the same date as the present application, and hereby incorporated herein by reference. Application Ser. No. ______ 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 heat-generating device is characterized to determine the relationship between the speed of a DC cooling fan, and the thermal margin of the heat-generating device. Since the speed of DC fans is substantially linear with respect to their input voltage, the speed of the fan may be adjusted within a system to provide the speed necessary for cooling needs. An altitude is input to a converter which uses the characterization of the heat-generating device to determine a fan speed necessary at that altitude to cool the heat-generating device to a temperature within its operating range. The converter then controls the voltage supplied to the DC fan to result in the needed fan speed.
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 configured to run at a variable speed; and
- a converter electrically coupled to said fan in such a way as to control a speed of said fan, wherein said converter receives an altitude and outputs a fan speed control signal calculated from said altitude to said fan.
2. The device of claim 1, wherein said converter uses an arithmetic algorithm to calculate said fan speed control signal from said altitude.
3. The device of claim 1, wherein said converter uses a look up table to calculate said fan speed control signal from said altitude.
4. The device of claim 1, wherein said fan speed is controlled by said converter using a digital signal.
5. The device of claim 1, wherein said fan speed is controlled by said converter using an analog signal.
6. A device, comprising:
- a fan configured to run at a variable speed;
- 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 an altitude and outputs a fan speed control signal calculated from said fan speed and said altitude to said fan.
7. The device of claim 6, wherein said converter uses an arithmetic algorithm to convert said fan speed and said altitude to said fan speed control signal.
8. The device of claim 6, wherein said converter uses a look up table to convert said fan speed and said altitude to said fan speed control signal.
9. The device of claim 6, wherein said fan speed control signal is output by said converter as an analog signal.
10. The device of claim 6, wherein said fan speed control signal is output by said converter as an analog signal.
11. A method for the setting of a fan speed, comprising the steps of:
- a) characterizing a thermal margin of a heat-generating device with respect to a fan speed;
- b) receiving an altitude;
- c) converting said altitude into a required fan speed; and
- d) setting a fan to said required fan speed.
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. A method for the setting of a fan speed, comprising the steps of:
- a) characterizing a thermal margin of a heat-generating device with respect to a fan speed;
- b) receiving an altitude;
- c) measuring a fan speed;
- d) converting said fan speed and said altitude into a required fan speed; and
- e) setting a fan to said required fan speed.
15. The method of claim 14, wherein said measuring a fan speed step is performed by said fan.
16. The method of claim 14, wherein said measuring a fan speed step is performed by an optoelectronic device.
17. A device, comprising:
- means for receiving an altitude; and
- means for calculating a thermal margin of a heat-generating device from said altitude; and
- means for setting a fan speed corresponding to a desired thermal margin.
18. The device of claim 16, further comprising:
- means for characterizing said thermal margin of a heat-generating device with respect to a fan speed.
Type: Application
Filed: Jul 25, 2003
Publication Date: Jan 27, 2005
Inventors: Andrew Delano (Fort Collins, CO), Robert Smith (Loveland, CO)
Application Number: 10/627,832