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.

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.