Abstract:
A method and apparatus is disclosed for detecting the ineffectiveness or failure of a fan that is used to cool an electronic device. The method and apparatus use temperatures measured before and after the fan is energized to determine if the temperature trend is affected by the operation of the fan. If the trend is not substantially affected by the operation of the fan, it is determined that the fan is not operating effectively and the user may be notified.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to the field of cooling electronic equipment using a fan, and more particularly is directed to a new system for detecting when the cooling fan of an electronic device is not operating properly. 
   BACKGROUND OF THE INVENTION 
   During operation, electronic devices typically generate heat. Often, this heat is not only unwanted, but may lead to premature failure of the electronic device. Many electronic devices utilize heat sinks, fans (or a combination of the two) or other cooling systems in order to cool the device and reduce the possibility of a premature failure. Unfortunately for many electronic devices, the cooling system, or fan, itself is one of the components that is most prone to failure because it involves a moving device that utilizes, for example, bearings that sometimes freeze in place or fan blades that may collect so much dust that they can no longer turn. Furthermore, even when the cooling system is electrically and mechanically operational, other issues may prevent cooling effectiveness, including blockage of air passages. An example of such an electronic device is a personal computer. The personal computer has several components that produce so much heat that, without active cooling, the temperatures of these components would reach a point where either the device fails, or an internal mechanism shuts down the device until the temperature falls into a suitable operational range for the component. 
   In many applications, the electronic device is at least partially enclosed in a cabinet, chassis, case, or the like. As the electronic device operates, heat is produced by the components of the device and the temperature of the air within the enclosure also increases as a result of the heat generated by the components. With current technology, when the temperature reaches a certain point, actions are taken to actively cool the system. These actions may include activating a fan located near the heat producing component(s) to produce air movement over the component or activating a fan that will force an exchange of air between the outside of the enclosure and the inside of the enclosure. Since the air outside the enclosure is generally cooler than the air inside the enclosure, the net result should be a reduction in the temperature of the air within the enclosure. Unfortunately, as noted above, these fans sometimes fail. The failure of a fan may or may not cause the system to reach a temperature where it automatically shuts down. If the fan failure does cause the system to shut down, the user may be faced with a random failure and a potential loss of data, such as data entered subsequent to the most recent “save” command. If it does not cause the system to shut down, the internal temperature may still cause secondary failures of components. For example, if the system has a hard disk drive, which typically does not generate a significant amount of heat, continued operation of the hard disk drive at high temperatures may cause an early end-of-life for the disk drive motor or the electronics associated with the disk drive. 
   Thus, there is a need to detect if, after the fan speed has been increased, the fan is actually performing its intended cooling function. A tachometer may have been employed to determine if the fan was operating, but is really only an accurate way to tell if the shaft of the fan is turning, but not if the blades of the fan are turning. However, if the fan blades are slipping on the fan shaft, then the fan isn&#39;t effectively moving air, even though the shaft is turning and the tachometer may indicate that the fan is operating properly. Additionally, the tachometer and the associated circuitry used to measure fan shaft speed add cost to the electronic device. Therefore, a system for making sure the fan is actually having the desired cooling effect, and notifying the user when it isn&#39;t having the desired cooling effect, is needed. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to a system and method for detecting the relative cooling effectiveness of a fan in order to detect a failure of the cooling fan. 
   In one aspect of the present invention, a fan is disposed in such a way that it pulls air into, or exhausts air out of, an enclosure that houses, for example, an electronic circuit. When the temperature within the enclosure reaches a predetermined value, circuitry within the electronic circuit activates or energizes the fan. A measurement of the increase of temperature is made both before the fan is energized and after the fan is energized. If, after the fan has been energized, the temperature continues to increase at substantially the same rate or trajectory as before the fan is energized, it is determined that the fan is not operating in an effective manner. In some embodiments of the present invention, notification of the fan failure is made. This notification may take the forms of, for example, a message on a display, an indicator being illuminated, or perhaps writing a value to the Desktop Management Interface or other log file so that an administrative entity may see that the fan is not working effectively. 
   In another aspect of the present invention, a fan is disposed in such a way that it moves air across a heat sink which is thermally coupled to a heat producing component such as, for example, a processor. When the temperature of the heat producing component reaches a predetermined value, circuitry within the electronic circuit energizes the fan. A measurement of the increase of temperature is made before the fan is energized and after the fan is energized. If, after the fan has been energized, the temperature continues to increase at substantially the same rate or trajectory as before the fan was energized, it is determined that the fan is not operating in an effective manner. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description serve to explain the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which: 
       FIG. 1  is a schematic block diagram of an illustrative system implementing the present invention. 
       FIG. 2  is a schematic flow chart of the present invention. 
       FIG. 3  is a schematic graph of one temperature scenario in which fan operation affects the rate of temperature rise in the electronic component. 
       FIG. 4  is a schematic graph of another temperature scenario in which fan operation does not effectively affect the rate of temperature rise in the electronic component. 
       FIG. 5  is a schematic side view of an electronic device according to the present invention and particularly showing an illustrative relationship between the enclosure and the various components of the electronic device. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
   Referring generally now to  FIG. 1 , an illustrative electronic system according to the present invention is shown. The system shown is an example of an electronic device  100  having at least one heat producing electronic component  160 , and possibly a heat sink  140  for cooling the component  160 , which in this example comprises a processor, but could also comprise another type of component. A thermal sensor  170  may be located internal to the heat producing electronic component  160 , mounted near the electronic component, thermally coupled to the electronic component, or thermally attached to the heat sink  140 . The heat sink  140  may be coupled to the heat producing electronic component  160  so that heat from the component  160  may be conducted away from the component and transferred to the surrounding air. A fan  130  may be positioned relative to the heat sink  140  such that an air flow  150  produced by the fan  130  contacts the heat sink  140 . Optionally, and not necessarily alternatively, the fan  130  may be positioned on the enclosure so that the fan  130  produces a more generalized or indirect air flow. The enclosure may include various air passages, holes, leaks, cracks, or the like to allow air to enter and to exit the enclosure. 
   A thermal management control circuit  110  monitors the temperature of the heat producing electronic component  160 , possibly taking measurements at periodic intervals such as, for example, every 5 seconds (although other relatively shorter or longer periods may be employed). Each temperature measurement may be stored, for example, in a histogram- 1   180 . The histogram- 1   180  may maintain a history of more than one prior n temperature measurements. When the measured temperature exceeds a maximum cooling threshold  115  temperature, the thermal management control circuit  110  may initiate fan operation through a fan speed control  120 . The fan speed control  120  provides power to the fan  130 , which may be positioned or located so as to blow air  150  over the heat sink  140 , though in other embodiments, the fan  130  may exchange outside air with air inside an enclosure in order to cool more than one component of the system. Methods of controlling fan speed are well known in the art and it is believed that virtually any method of fan speed control may be used. For example, the voltage to the fan may be varied, or the pulse width of the power being applied to the fan may be modulated. Methods of determining when to start a fan are well known in the art. There may be several temperature thresholds at which the fan speed is increased incrementally. There may be a degree of hysterisis in the system such that the fan remains at a speed level until the detected temperature falls below the threshold at which operation of the fan was started. This mode of operation would reduce the likelihood of the fan turning on, then after a short period (e.g., a few seconds) turning off, and then, after another short period, turning on again. 
   Once the fan is started, the thermal management control circuit  110  monitors the temperature of the heat producing component  160 , possibly taking measurements at the same periodic intervals as was done before operation of the fan was started. Each measurement is stored in histogram- 1   180  maintaining n post-fan operation temperature measurements. Once n post-fan operation temperature measurements are available, the temperature trajectory of the rate of change of the temperature in the histogram- 1   180  is compared to the temperature trajectory of histogram- 2   185 . If there is little or insignificant difference in the trajectory of both histograms, then the temperature has continued to rise at about the same rate, or in the same trajectory, even though the fan has been started and is operating. Therefore, it may be determined from the lack of change in the histograms that the operation of the fan  130  is not having an observable effect on the temperature of the component  160 . In that case, there is a high probability that the fan is not operating, or not operating effectively, and may be disconnected, stuck, slipping, or otherwise is defective in some way. At this time, the user may be warned about the high probability that the fan has failed, or is not effectively cooling, perhaps by energizing an indicator such as an LED  190  (which is preferably a red LED) or by displaying a message on a display  194 , or by writing a value to desktop management interface (DMI) table  192 . The thermal management control circuit  110  may be comprised of analog and digital logic, or it may be a combination of logic and software. The histogram- 180  and the histogram- 2   185  may be stored in memory registers, possibly as two arrays of temperatures. The organization of these histograms may be such that after n measurements are stored, upon reading a new measurement, the oldest measurement is deleted from the beginning of the array, the remaining measurements are moved down in the array and the new measurement is added to the end of the array. Various storage formats can be used such as storing the absolute temperature measurement in binary form or storing the difference between one temperature measurement and the next in digital form. 
   Referring now to  FIG. 2 , a flow chart  200  of the present invention is shown. A temperature is measured and added to the first histogram, histogram- 1   180  (step  210 ). The temperature is compared to the threshold  115  (step  220 ) to determine if the temperature is getting too high and if cooling is needed. If the temperature does not exceed the threshold, a delay (step  215 ) may be made, and then the temperature is measure again and added to the histogram (step  210 ). If the temperature exceeds the threshold, operation of the fan is initiated or the fan operation speed is increased (step  230 ). Thus, this speed increase may be from off (zero revolutions per minute) to on (something more than zero revolutions per minute), or may simply be an increase of fan speed from a relatively slower speed to a relatively faster speed. In general, the more cooling that is needed, the faster the speed of the fan, but some fans may only have one or two operational speeds. Once operation of the fan is started, another delay (step  235 ) is taken to allow cooling to start. The delay of step  245  may be similar to or the same as the delay of step  215 . Next, another temperature measurement is made (step  240 ) and added to the second histogram, histogram- 2   185 . It is then determined if a sufficient number of measurements have been made and stored in histogram- 2  (step  250 ). In one of the simplest embodiments of the present invention, only one measurement would be stored in each of histogram- 1  and histogram- 2 . If there are not a sufficient number of measurements in histogram- 2 , then steps  235  and  240  may be repeated until there are a sufficient number of measurements, at which time histogram- 1  is compared to histogram- 2  in step  260 . If only one measurement is stored in each of histogram- 1  and histogram- 2  (n=1), then the two may be numerically compared (step  270 ) and, if the measurement in histogram- 2  is higher than the measurement in histogram- 1 , perhaps with the addition of an offset quantity, then a significant rate of change will not be detected (step  270 ) and a fan failure will be detected (step  280 ). If more than one measurement is stored in each histogram, then each histogram may be smoothed to eliminate outlying measurements and then compared (step  270 ) to determine if increasing the fan speed had any effect on the rate of temperature increase. If there was a significant rate change, then it is believed that the fan is operational and the flow is done. If there was not a significant rate of change detected, the temperature may have continued to increase at the same rate and slope, and a fan failure may be indicated (step  280 ). The failure may be declared by turning on a visual indicator, such as the LED  190 , displaying a message on the display  194 , sending a message to an administrator of computers on a network, and/or making an entry into a Log File, perhaps an entry in a Desktop Management Interface (DMI) table ( 192 ). 
   Referring now to  FIG. 3 , a graph  300  of temperatures (versus time) of the present invention is shown. In this example, each histogram of the histogram- 1   340  and the histogram- 2   350  are configured to store four temperature measurements, e.g., n=4, The temperature plot line  310  is determined by smoothing the four individual temperature measurements t 0 , t 1 , t 2 , and t 3  that were taken before the fan was energized. The temperature plot line  360  is determined by smoothing the four individual temperature measurements t 4 , t 5 , t 6 , and t 7  that were taken after the fan was energized. In this example, the threshold  320  is at a temperature of 21° C. Since temperature measurement t 3  is 21.1° C. and is greater than the threshold  320  temperature measurement, the fan is started or its speed is increased at the time of plot point  330 . In this example, since the plot line  360  is sufficiently lower in either slope or value than the plot line  310 , it may be assumed that the operation of the fan that began at the time of plot point  330  had an effect on the rate of temperature rise; and therefore the fan may be assumed to be operational. 
   Referring now to  FIG. 4 , another graph  400  of temperatures of the present invention is shown. In this example, each histogram of the histogram- 1   440  and the histogram- 2   450  are configured to store four temperature measurements, e.g., n=4. Temperature plot line  410  is determined by smoothing the four individual temperature measurements t 0 , t 1 , t 2 , and t 3  that were taken before the fan was energized. Temperature plot line  460  is determined by smoothing the four individual temperature measurements t 4 , t 5 , t 6 , and t 7  that were taken after the fan was energized. In this example, the threshold  420  is at a temperature of 21° C. Since the temperature measurement t 3  is 21.1° C. and is greater than the temperature threshold  420 , the fan is started or its speed is increased at the time of plot point  430 . In this example, since the plot line  460  is substantially similar to either slope or value of the plot line  410 , it is assumed that the operation of the fan that began at the time of plot point  430  had little or no effect on the rate of temperature rise, and therefore the fan may be tissumed to not be effectively cooling, either because the fan has not started, or has not increased in speed, or is slipping, and it is likely that the fan is malfunctioning. 
   Referring now to  FIG. 5 , a view of an electronic device  500  of the present invention is shown. The electronic device may be a computer or any other device cooled by a fan. In  FIG. 5 , an enclosure  510  houses electronic components mounted upon a printed circuit board  530  or other component support. Also housed in the enclosure  510  is a fan  520 . The fan  520  is configured to move air between the inside of the enclosure  510  and the outside of the enclosure  510 . The fan  510  forces air to flow into or out of an opening  525  in the enclosure  510 . If the fan  520  blows air out of the chassis  510 , it is known as an exhaust fan and in that case, cooler air from the outside might enter through spaces or openings in the enclosure  510  such as the opening  560 . If the fan  520  blows air into the enclosure  510 , then it brings cooler air in and the warmer air escapes through spaces or openings in the enclosure  510  such as the opening  560 . In this example, a heat producing component  540  is mounted on the printed circuit board  530 . Located in proximity to the heat producing component  540  is a temperature sensor  550 . Also in this example, circuitry to monitor the temperature sensed by the temperature sensor  550  and the control fan  520  is also contained on the printed circuit board  530  and connected to the fan  520  by the cable  570 . Although one printed circuit board is shown in this example, the present invention is not limited to having any number of printed circuit boards. The electronic device may not have any printed circuit boards and components may be mounted together in other ways or may be mounted on a board and connected to each other with wires. Although, in this example, the temperature sensor  550  is shown touching the component  540 , many other configurations are possible without veering from the present invention. In another example, a temperature sensor may be integrated into the component  540 . A large variety of processors or CPUs have an integrated temperature sensor used to measure the temperature on the actual die. The temperature sensor may also be located at a distance from the component  540 , and may even be located relatively remote from the printed circuit board  530 , so as to measure the temperature of the air within the enclosure  510 . This is shown by the temperature sensor  545  which is mounted within the chassis  510  to sense the ambient temperature within the chassis and is connected to the printed circuit board  510  by a cable  546 . 
   It is believed that the system and method of the present invention and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely exemplary and explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.