Patent Publication Number: US-7711439-B2

Title: Microcontroller methods of improving reliability in DC brushless motors and cooling fans

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to cooling fans. More particularly, the present invention relates to intelligent cooling fans for use in electronic systems and for designing cooling solutions for electronic systems. 
     2. Discussion of the Related Art 
     In electronic systems, such as computer systems, cooling fans play an important role in maintaining their operational capabilities. The inability to remove excessive heat from electronic systems may lead to permanent damage of the system. Because of the complexity of existing electronic systems, cooling fans having added functionalities other than just providing cooling air, such as the ability to control the speed of a fan, the ability to monitor a tachometer pulse on a fan to determine instantaneous fan speed, and the ability to detect if a fan has failed or is slower than its preset speed, are required. Although these functionalities exist in some cooling fans today, there is no standard design or protocol that is available to control cooling fans produced by different manufacturers. Moreover, in order to implement these cooling fans within a system, specialized printed circuit assemblies (PCAs), also called controller cards, are required to be designed so as to provide signals that a fan can understand and also to receive and provide signals to the system in a form that is interpretable by the electronics of the system. 
     If one desires additional functionality, such as the ability for the fans to compensate for other failed fans by increasing in speed, the ability for fans to notify external hardware that there is a problem, or the ability for fans to increase speed in response to increased system temperatures, a specialized PCA or controller card is also required. The PCA or controller card is designed and built to be capable of detecting a fan failure, notifying the system that a fan has failed, and adjusting the speeds of the other fans in the system. The design and manufacture of PCAs and controller cards involve a great deal of engineering time and resources, which ultimately add to the cost of the overall system utilizing the cooling fan(s). 
     Designing cooling solutions for new systems is also a time-consuming process for the thermal design engineer. Typically, the PCA or controller card is required to be designed and built for controlling the fan speed and other functionality, such as failure detection and alarm settings. Often times, the design and construction of multiple control cards are required so as to test them in real world applications to obtain the right combination of fans, fan speeds, alarm settings, etc. The multiple iterations of installing sample fans in a system, determining the adequate fan speeds and power required, and testing the fans in the system, for example, are costly and inefficient. 
     Another concern involving conventional cooling fans, and in particular, direct current (DC) brushless cooling fans, is that they change speeds depending on the applied input voltage. As the input voltage is increased, the fans speed up and use more power. When input voltage is decreased, the fans decrease in speed and provide less cooling. Many typical applications have a voltage range that may vary between 24 to 74 volts. Accordingly, a system designer is charged with maintaining a constant cooling during these wide voltage swings. Accordingly, a voltage regulating power supply is usually installed in a system to keep the voltage to the fans constant. However, having to install a voltage regulating power supply adds additional complexity and cost to the overall system as well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cooling fan solution according to an embodiment of the present invention; 
         FIG. 2  illustrates an electronic system implementing a plurality of cooling fans according to an embodiment of the present invention; 
         FIGS. 3A and 3B  illustrate a schematic circuit diagram for a cooling fan according to an embodiment of the present invention; 
         FIG. 4A  illustrates voltage and current waveforms according to the prior art; 
         FIG. 4B  illustrates a voltage waveform and a current waveform according to an embodiment of the present invention; 
         FIG. 4C  illustrates a flow chart diagram of a logic path for a microcontroller to maintain a speed of a cooling fan according to an embodiment of the present invention; 
         FIG. 5  illustrates a sample screen of a fan controller user interface according to an embodiment of the present invention; 
         FIG. 6  illustrates a sample screen of advanced functions of a fan controller user interface according to an embodiment of the present invention; 
         FIG. 7  illustrates a flow chart diagram of a logic path for a cooling fan according to an embodiment of the present invention; 
         FIG. 8  illustrates a flow chart diagram of determining cooling solution specifications for an electronic system using a cooling fan according to an embodiment of the present invention; 
         FIG. 9  illustrates a method of emulating an analog current limit function according to an embodiment of the present invention; 
         FIG. 10  illustrates a cooling fan including the analog current emulation function according to an embodiment of the present invention; 
         FIG. 11  illustrates a method of predicting a life of a cooling fan utilizing a weighting factor according to an embodiment of the present invention; 
         FIG. 12  illustrates a flowchart for analyzing operating points of interest or measurement points in a cooling fan according to an embodiment of the present invention; 
         FIG. 13  illustrates a method of measuring points of interest in a cooling fan in order to keep a cooling fan from failing according to an embodiment of the present invention; and 
         FIGS. 14A and 14B  illustrate operating points of interest for an exemplary cooling fan according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a cooling fan solution according to an embodiment of the present invention. The cooling fan  100  includes a fan module  110 , which has a fan  112  (including fan blades) and a motor  114  rotatably coupled to the fan  112  to drive the fan  112 . A microcontroller  120 , such as an 18-pin PIC16C717 microcontroller device manufactured by Microchip Technology, Inc., is in direct communication with the fan module  110 , and specifically, the motor  114 . Any suitable microcontroller or processor may be utilized, though. The microcontroller  120  is preferably fixed internally within the cooling fan  100 . 
     A bus interface, such as the Inter-IC (I2C) (“I2C-Bus Specification”, Version 2.1, January 2000, from Philips Semiconductors) bus interface  130  is in communication with the microcontroller  120 . The bus interface  130  facilitates transfer of data to and from the microcontroller  120 . The bus interface  130  may be interconnected by bus lines  132 , such as I2C bus lines, to a system  140 . The I2C bus lines  132  has two lines: a data (SDA) line and a clock (SCL) line. Inter-IC (I2C) may be accessed serially so that each individual device utilizing the I2C protocol has a specific identification (ID), but may all be connected to the same communication line(s) or bus(es) (i.e., it may be connected as a parallel bus). Inter-IC (I2C) is a useful protocol because it is familiar to thermal design engineers who utilize cooling fans in their system designs, and a fair number of digital logic devices utilize the I2C protocol. However, any other bus interface systems and protocols may also be utilized. For example, the Controller-Area Network (CAN) protocol (Controller-Area Network (CAN) Specification, version 2.0, 1991, Robert Bosch GmbH, Stuttgart, Germany), utilized in the automotive industry, may also be utilized with the bus interface  130  according to an embodiment of the present invention. 
     Besides the ability for a fan customer or thermal design engineer to control the fan speed, monitor a tachometer pulse on the fan to determine instantaneous fan speed, and detect if the fan has failed or is slower than a preset speed, additional functionality, such as the ability to electronically read the part number of a cooling fan  100 , the ability to electronically determine the fan manufacturer, and the ability to electronically read the manufacturing date, is particularly desirable. Because of the concern that various fan manufacturers may have different methods of controlling fan speed, or providing alarm or tachometer signals, being able to easily obtain cooling fan  100  information such as the part number, the fan manufacturer, and the manufacturing date quickly aids in the design and repair of a cooling solution. 
     According to an embodiment of the present invention, the microcontroller  120  is programmed with program code that enables the microcontroller  120  to read byte communications provided by a system or device  140  that utilizes, for example, the I2C protocol. In a particular embodiment of the present invention, the microcontroller  120  includes a program memory into which the program code is stored. The PIC16C717 microcontroller, for example, is capable of handling 14-bit words and has a capacity of 2 kilobytes. The program or instruction code is programmed only once into the microcontroller  120  at the factory, and it is not re-programmable or re-writeable by an end user or cooling fan customer. The PIC16C717 microcontroller, for example, also includes a small data memory, or “scratch pad memory”, having a capacity of 256 bytes available to the microcontroller  120  to conduct its operations. The data memory of the microcontroller  120  is volatile and does not store any programming or instructions, but rather it is only a working memory. 
     The program code (such as code written in the “C” programming language) in the microcontroller  120  may include the cooling fan&#39;s  100  part number, manufacturer, and date of manufacture so that when the microcontroller  120  receives a command, e.g., from the host system/device  140 , to output such data to a system or device  140  connected thereto, the microcontroller  120  may readily output the requested data. Useful data other than the cooling fan&#39;s  100  part number, manufacturer, and date of manufacture, such as the current (Amps) draw of the fan, may be included as well. The microcontroller  120  may communicate data regarding the cooling fan  100  in, for example, the I2C protocol. By providing a cooling fan  100  that is capable of directly communicating with a system or device  140  utilizing a common protocol, such as the I2C protocol, PCAs or controller cards are not required at all to control or communicate with the cooling fan  100 . 
       FIG. 2  illustrates an electronic system implementing a plurality of cooling fans according to an embodiment of the present invention. A plurality of cooling fans  242 ,  244 ,  246 ,  248  are provided within the electronic system  200 . Each of the plurality of cooling fans  242 ,  244 ,  246 ,  248  are electrically connected to a connector module  230 , which is a line splitter for a power source  210  and a user system/device  140 . According to an embodiment of the present invention, the electronic system  200  utilizes the I2C protocol, and the user system/device  140  has communication lines according to the I2C protocol, a data line  222  and a clock line  224  connected to the connector module  230 . The connector module  230  in turn splits the data line  222  and the clock line  224  to each one of the plurality of cooling fans  242 ,  244 ,  246 ,  248 . Similarly, the power source lines, power line  212  and power return line  214 , from the power source  210  are connected to the connector module  230 , which in turn splits the power line  212  and the power return line  214  to each one of the plurality of cooling fans  242 ,  244 ,  246 ,  248 . 
     Specific addresses required in all I2C devices may be set externally (by connecting address lines high for a “1”, or low for a “0”), or internally during production. The data line  222  and the clock line  224  for each one of the plurality of cooling fans  242 ,  244 ,  246 ,  248  and the user system/device  140  may be connected to each other, or to an internal bus, which enables the user system/device  140 , for example, to change the fan speeds of any one of the plurality of cooling fans  242 ,  244 ,  246 ,  248 , to detect the fan speeds of any one the plurality of cooling fans  242 ,  244 ,  246 ,  248 , to read the part number of any one the plurality of cooling fans  242 ,  244 ,  246 ,  248 , etc. 
     According to another embodiment of the present invention, the microcontroller  120  may be programmed with a program code to enable each cooling fan  100  to detect failures of other cooling fans  242 ,  244 ,  246 ,  248  to notify a user system/device  140  that a fan has failed, or to adjust the speeds of the other fans in the system to compensate. In the prior art, a specialized PCA or controller card was required to be designed and built to provide these functionalities for an electronic system  200  utilizing cooling fans  242 ,  244 ,  246 ,  248 . Accordingly, the microcontroller  120  may be programmed with program code so that each cooling fan  242 ,  244 ,  246 ,  248  has the ability to detect and compensate for other failed fans by increasing its fan speed, to notify external hardware  140  that there is a problem, or to increase its fan speed in response to increased system temperatures. By having each of the plurality of cooling fans  242 ,  244 ,  246 ,  248  in communication with each other, added redundancy and functionality may be provided to the overall system  200 . 
     In one particular embodiment, the cooling fans  242 ,  244 ,  246 ,  248  are connected to each other by their communication lines  132  (see  FIG. 1 ), which may be facilitated by a connection to a shared bus. If one of the cooling fans  242 ,  244 ,  246 ,  248  fails, then the failure is detected by the other cooling fans  242 ,  244 ,  246 ,  248 . Upon this failure detection, the other cooling fans  242 ,  244 ,  246 ,  248  may be programmed to increase the fan speed to compensate for the decreased airflow due to the failure of one of the cooling fans  242 ,  244 ,  246 ,  248 . In a further embodiment, temperature sensors may be implemented utilizing the I2C protocol and connected to the plurality of cooling fans  242 ,  244 ,  246 ,  248  so that each of the cooling fans  242 ,  244 ,  246 ,  248  may communicate directly with the temperature sensors (or through the host system/device  140  if the temperature sensors are not directly connected to the cooling fans  242 ,  244 ,  246 ,  248 ). Therefore, the plurality of cooling fans  242 ,  244 ,  246 ,  248  may be further programmed to increase fan speeds if an increase in temperature is detected by the temperature sensors, or decrease the fan speed if the temperature drops. In other words, the cooling fans  242 ,  244 ,  246 ,  248  may also be aware of the temperatures detected by the temperature sensors installed within the system and act accordingly. By connecting the cooling fans  242 ,  244 ,  246 ,  248  to each other and placing them into a “multi-master” mode, each cooling fan  242 ,  244 ,  246 ,  248  is in communication with each other and the redundant and failure recovery operations discussed above may be implemented. 
     By implementing a microcontroller  120  and a bus interface  130  utilizing a standard protocol, such as the I2C protocol, engineers are freed from designing and building a PCA or controller card, the resulting system is not burdened with the additional cost of the controller card, and the cooling fan  100  may be directly added to the existing bus of the customer or design engineer hardware. The cooling fans  242 ,  244 ,  246 ,  248  (see  FIG. 2 ) may be connected to each other, or to a commonly connected printed circuit board (PCB), to greatly simplify cooling solution design and construction. Moreover, the savings of not requiring a specialized PCA or controller card are significant, as they may run three times the cost of the cooling fan itself. In one particular embodiment, the cooling fans  242 ,  244 ,  246 ,  248  may be compatible with, for example, the IBM Specification 18P3640 (October 2001) Type 5 fans. 
     According to yet another embodiment of the present invention, a cooling fan  100  (see  FIG. 1 ) is provided that is capable of operating at a constant speed even with changing/varying input voltage and/or motor load. As mentioned above, the majority of conventional DC brushless cooling fans change speeds with applied input voltage. As the input voltage is increased, the fans speed up and use more power. When input voltage is decreased, the fans decrease in speed and provide less cooling. Many existing applications have a voltage range that can vary from 24 to 74 volts. The design engineer is charged with maintaining a constant cooling for the system during these wide voltage swings. Typically, the design engineer installs a voltage regulating power supply in the system to keep the voltage to the fans constant. However, providing a voltage regulating power supply adds more complexity and increases the cost to the overall system. 
       FIGS. 3A and 3B  illustrate a schematic circuit diagram for a cooling fan according to an embodiment of the present invention. In an embodiment according to the present invention, the microcontroller  120  has program code having instructions to detect the speed of the cooling fan  100  in real time and maintain that speed, regardless of changes in the input voltage. Referring to  FIG. 3A , line E 1   312  is the voltage (in) line, while line E 2   314  is the voltage return (ground). In a preferred embodiment of the present invention, lines  322  and  324  are Inter-IC (I2C) lines: line  322  being the data line and line  324  being the clock line for communication utilizing the I2C protocol. Typically, in cooling fan applications, the input voltage may be 12 volts, 24 volts, or 48 volts. Diodes D 1  and D 2   332  provide for reverse polarity protection within the system. Zenor diode D 5   334  provides a drop in power and regulates the voltage to, for example, 12 volts. A 5V regulator  342  is included to provide regulated 5 volts to the microcontroller  120  and the speed sensor  116  (e.g., the Hall sensor). The Hall sensor  116  provides a digital signal to the microcontroller  120  based on the positions of the stator  380  of the fan motor  114  utilizing the Hall effect, which occurs when the charge carriers moving through a material experience a deflection because of an applied magnetic field. This deflection results in a measurable potential difference across the side of the material which is transverse to the magnetic field and the current direction. According to one embodiment, the Hall sensor  116  provides a 50% duty cycle signal, that is, two pulses for each revolution/cycle of the fan. Based on the signals provided by the Hall sensor  116 , the microcontroller  120  is capable of determining the speed of the cooling fan  100  and making any adjustments necessary to maintain a constant fan speed. 
     Referring to  FIG. 3B , the microcontroller  120  is connected to two metal-oxide semiconductor field effect transistor (MOSFET) drivers  350 ,  360 . Through the MOSFET drivers  350 ,  360 , the microcontroller  120  controls the duty cycle (on time vs. off time) of the voltage provided to the fan motor  114 , and more specifically, to the MOSFETs  372 ,  374 ,  376 ,  378  and across the stator  380 . According to an embodiment of the present invention, the drains of MOSFETs  372 ,  376  are coupled to the variable input voltage (from line E 1   312 ). The gate of MOSFET  372  is coupled to the high (H 0 ) line ( 7 ) of MOSFET driver  350 . The gate of MOSFET  376  is also coupled to the high (H 0 ) line ( 7 ) of MOSFET driver  360 . The logic on pin  2 , input from the microcontroller  120 , of each MOSFET driver  350 ,  360  are controlled by different lines, lines D and E, respectively. The state of pin  2  is the same as the H 0  pin of each MOSFET driver  350 ,  360 , and the microcontroller  120  alternates these signals so that MOSFETs  372 ,  376  are not in the “high” state at the same time. 
     The sources of MOSFETs  372 ,  376  are each coupled to a node to which the drains of each of MOSFETs  374 ,  378  are respectively coupled, and to which the stator  380  is coupled. The gate of MOSFET  374  is coupled to the low output (L 0 ) line ( 5 ) of MOSFET driver  350 . The gate of MOSFET  378  is also coupled to the low output (L 0 ) line ( 5 ) of MOSFET driver  360 . The sources of each of MOSFETs  374 ,  378  are coupled to a reference voltage or ground  338 . In the configuration illustrated in  FIG. 3B , MOSFETs  372 ,  378  are “on” at the same time while MOSFETs  374 ,  376  are “off”, and alternatively, when MOSFETs  374 ,  376  are “on”, MOSFETs  372 ,  378  are “off”. 
     Accordingly, when an increasing speed is detected via the Hall sensor  116 , the microcontroller  120  reduces the stator duty cycle to maintain the same energy transfer to the motor windings. The shifts in duty cycle are implemented in program code embedded within the microcontroller  120 . Resistor  336  provides a locked rotor detection signal for the microcontroller  120 . The microcontroller  120  detects the current flowing through the windings by monitoring the voltage representation of the current that appears on resistor  336 . If this voltage exceeds a set threshold set internal to the microcontroller  120 , then the output pulses are terminated and a locked rotor condition is perceived. The capacitors C 1  and C 2   338  provide for voltage ripple filtering and as additional protection to limit high switching currents from causing noise in the user&#39;s system. 
       FIG. 4A  illustrates voltage and current waveforms according to the prior art. For example, the nominal voltage for a cooling fan is 48 Vdc. If the voltage is increased to 60 Vdc, for example, the fan has a physical tendency to increase in speed as a reaction to more voltage and energy being switched by the MOSFETs  372 ,  374 ,  376 ,  378  (see  FIG. 3B ). The top waveform set  410  represents the voltage across a stator  380  with waveform  414  representing 48 volts and waveform  412  representing 60 volts. The bottom waveform set  420  represents the current through the stator  380  with waveform  424  representing a 48 volt input and waveform  422  representing a 60 volt input. Accordingly, without taking any additional measures, the increased voltage and current causes additional energy to be transferred to the coils, which results in a faster spinning fan. 
     Rather that utilizing a voltage regulating power supply as in the prior art, according to an embodiment of the present invention, the microcontroller  120  of the cooling fan  100  monitors the speed sensor  116 , such as a Hall sensor, to detect an increasing speed. Alternatively, the back electromagnetic field (EMF) generated by an increase in speed of the cooling fan  100  may be monitored to detect the increase in speed as well. To compensate for the increasing speed, the microcontroller  120  has program code having instructions to reduce the stator duty cycle (i.e., the on-time vs. the off-time) to maintain the same energy transfer to the motor  114  when an increase in speed is detected. Preferably, the fan speed is controlled utilizing Pulse Width Modulation (PWM), i.e., driving the fan motor  114  using short pulses (the pulses vary in duration to change the speed of the motor—the longer the pulses, the faster the motor turns, and vice versa). 
       FIG. 4B  illustrates a voltage waveform and a current waveform according to an embodiment of the present invention. The top waveform  430  represents a reduced stator duty cycle (on-time vs. off-time) of the voltage (e.g., 60 Vdc) as compared to waveform  412  in  FIG. 3A . The bottom waveform  440  represents a reduced stator duty cycle of the current as compared to waveform  424  in  FIG. 3A . Accordingly, while the voltage and current has increased, the “time-on” of each has been decreased to maintain the same energy transfer to the motor  114 , and thereby regulate the fan speed. In one embodiment of the present invention, shifts in the stator duty cycle based on the various voltage levels are preprogrammed in the program code embedded within the microcontroller  120 . 
       FIG. 4C  illustrates a flow chart diagram of a logic path for a microcontroller to maintain a speed of a cooling fan according to an embodiment of the present invention. A reference constant is provided  401  (programmed into the microcontroller  120 ) corresponding to the constant speed at which the cooling fan  100  is to be maintained. The microcontroller  120  enters a main routine  402  for its normal operation. The program code embedded within the microcontroller  120  determines whether a speed sensor interrupt, such as a Hall sensor interrupt signal, was generated  403 . If such an interrupt was not generated, then the operation flows back to block  402 . If an interrupt was generated, then a timer value lapsed since the occurrence of the last interrupt signal is captured  404 . It is determined  405  whether the timer value is greater or less than the reference constant, which represents the desired fan speed. If the timer value is less than the reference constant, then the duty cycle (such as the PWM duty cycle) is decremented  406  by one clock, the timer is reset  407  for a new comparison, and operation flows back to block  402 . If the timer value is greater than the reference constant, then the duty cycle (such as the PWM duty cycle) is incremented  408  by one, the timer is reset  409  for a new comparison, and operation flows back to block  402 . If the timer value is equal to the reference constant, then the operation flows back to block  402 . 
     By utilizing the cooling fan  100  according to an embodiment of the present invention, the thermal design engineer does not need to design and build a specialized power supply or other additional circuitry in a PCA, controller card, or in the fan tray in order to compensate for the negative effects on cooling due to swings of the system voltage. Moreover, specialized power supplies can easily cost three times that of the fan itself. The cooling fan  100  according to an embodiment of the present invention provides a constant fan speed regardless of the input voltage, and design time and costs are significantly reduced. 
       FIG. 5  illustrates a sample screen of a fan controller user interface according to an embodiment of the present invention. The fan controller user interface  500  is preferably a software program executing on a computer system, such as a desktop personal computer (PC) or a laptop computer. The desktop PC or laptop computer may be connected to a network and accessed remotely via, for example, the Internet using Internet Protocol (IP). The fan controller user interface software  500  enables a thermal design engineer to quickly create a cooling solution for a specific application. A typical application of the fan controller user interface software  500  is for designing a cooling solution for a new cabinet/housing for an electronic system. 
     When designing a cooling solution for a new cabinet/housing, the design engineer does not know: (1) how much airflow is needed; (2) what types of alarms are required; (3) what functions are necessary on the controller card circuitry; and (4) how the system should behave with increasing system temperature. By utilizing the fan controller user interface software  500  according to an embodiment of the present invention, the design engineer may quickly install cooling fans  100  according to embodiments of the present invention and connect these fans to a computer system (e.g., a desktop PC or a laptop computer) executing the fan controller user interface software  500  to determine the cooling solution specifications for a particular cabinet/housing. 
     The cooling fan(s)  100  are connected to a power source and then to the computer system executing the fan controller user interface software  500 . The cooling fan(s)  100  may be connected to a fan/computer adapter, which converts the communications protocol utilized by the cooling fan(s)  100 , such as the I2C protocol, to one recognizable by the computer system, such as the Universal Serial Bus (USB) protocol. The fan/computer adapter then plugs into, for example, the USB port on the computer system so that the computer system is in communication with the cooling fan(s)  100 . 
     After assembling the cooling fan(s)  100  into a system cabinet/housing, the design engineer starts the fan controller user interface software  500 . As illustrated in the main screen  500  of  FIG. 5 , the design engineer may change the speed of any cooling fan  510 ,  520 ,  530 ,  540  connected, set basic alarms, monitor the temperature sensor(s) connected, and constantly refresh the data of all of the cooling fan(s)  510 ,  520 ,  530 ,  540  (part number, speed, alarm status, etc.). In one embodiment, the temperature sensor(s)  122  may be incorporated inside the microcontroller  120 . The fan controller user interface software  500  emulates the program code resident in a microcontroller  120  to control the behavior of each cooling fan  510 ,  520 ,  530 ,  540 . In other words, the fan controller user interface software  500  is adapted to allow a user to control and operate all of the functions of each cooling fan  510 ,  520 ,  530 ,  540 . Therefore, all of the functions of each cooling fan  510 ,  520 ,  530 ,  540  are available to the thermal design engineer for design troubleshooting and prototyping. 
     The main screen shot  500  of  FIG. 5  shows basic information for four cooling fans  510 ,  520 ,  530 ,  540 , including their part numbers, fan identifications, fan speed, and status (e.g., active, stop, etc.). Basic information for two temperature sensors is also provided, including their sensor identifications, part numbers, and the temperatures detected. Other information may also be provided to the user on the screen. There is provided a fan control entry window  570  that allows a basic speed of the fans  510 ,  520 ,  530 ,  540  to be set, as well as a basic alarm, for example, to be actuated when the fan speed, revolutions per minute (RPM), drops below a certain level. A message box  580  may also be provided to inform the user of events that occur during the use of the fan controller user interface software  500 . The fan speeds of a plurality of cooling fans within a system may be set slightly different from each other so as to test for and eliminate any beat frequencies that may occur, which may cause unwanted noise. 
       FIG. 6  illustrates a sample screen of advanced functions of a fan controller user interface according to an embodiment of the present invention. In the advanced function screen  610  illustrated in  FIG. 6 , “what if” conditional scenarios may be set and tested. For example, a scenario may be configured to design an appropriate response to when one of the cooling fans  510 ,  520 ,  530 ,  540  fails. The advanced function screen  610  allows a design engineer to easily conduct such a scenario and program and test for an appropriate response. For example, the following logic condition may be set and tested:
         If FAN A speed is slower than 1500 RPM then set FAN B to 3500 RPM and TRIP ALARM 1.       
     The fan controller user interface software  500  may be configured so that the commands are in a straightforward sentence-like structure, allowing the user to manipulate the terms from a menu for the bold-underlined terms above to vary a condition. The above example illustrates a sample condition when one cooling fan (Fan A) that is failing is rotating slower than 1500 RPM, a second cooling fan (Fan B) is adjusted to increase in speed (to 3500 RPM) to provide added cooling to the system, and then alarm 1 is tripped, which may be preconfigured to alert the user that there is a problem in the system (or even more specifically, that Fan A is failing). A number of other conditional scenarios may configured using the fan controller user interface software  500  according to an embodiment of the present invention. Moreover, conditional scenarios involving temperature sensors may also be established using a similar methodology. Therefore, the thermal design engineer is able to set and test a variety of different conditions and program the appropriate behavior for each fan  510 ,  520 ,  530 ,  540  to respond accordingly to each condition. 
       FIG. 7  illustrates a flow chart diagram of a logic path for a cooling fan according to an embodiment of the present invention.  FIG. 7  illustrates a failure detect process from the perspective of Fan A in a system having four fans, Fans A-D. According to an embodiment of the present invention, each of the Fans A-D have a parallel connection to an Inter-IC (I2C) bus. Initially, Fan A sends  710  a status request to Fan B. It is determined whether a response is received  720  by Fan A from Fan B within a predetermined period of time, e.g., 2 seconds. If a response is received, it is determined whether a failure mode response was received  730 . If a failure mode response is not received, Fan A waits for a predetermined period of time, e.g., 5 seconds, then repeats  740  the above iteration with Fan C. If no response is received by Fan A from Fan B within the predetermined period of time (e.g., 2 seconds), or if a failure mode response is received by Fan A from Fan B, then the assumption is that Fan B has failed (or is failing) and Fan A proceeds to increase  750  its fan speed based on the cooling solution specifications/operating parameters and programming determined using the fan controller user interface software  500 , a failure notification regarding Fan B&#39;s failure is transmitted  760  by Fan A, and Fan A waits for a predetermined period of time, e.g., 5 seconds, then repeats  740  the above iteration with Fan C. Once the iteration with Fan C is completed, the iteration is also performed with respect to Fan D. 
       FIG. 8  illustrates a flow chart diagram of determining cooling solution specifications for an electronic system using a cooling fan according to an embodiment of the present invention. At least one cooling fan is installed  810  within a housing. Operating parameters are set  820  for the at least one cooling fan. Operation of the at least one cooling fan within the housing is conducted  830  based on the operating parameters set. The operating parameters of the at least one cooling fan are captured  840  if the operating parameters result in adequate cooling within the housing by the at least one cooling fan. 
     Once the user has made the appropriate configurations for the behavior for each fan  510 ,  520 ,  530 ,  540  and is satisfied with the functionality of the fans  510 ,  520 ,  530 ,  540  installed in the cabinet/housing, the user may “freeze” the design and store the cooling solution specifications or operating parameters determined (e.g., each fan&#39;s RPM settings, alarms, conditions, temperature conditions, conditional behaviors (e.g., to compensate for a fan failure, temperature increase), etc., for that particular cabinet/housing). The cooling solution specifications may be forwarded to a cooling fan manufacturer, and specific cooling fans adhering to the customized cooling solution specifications may be manufactured, including the appropriate programming desired by the engineer set forth during the testing with the fan controller user interface software  500 , and provided to the design engineer, knowing already that the cooling solution utilizing cooling fans with these characteristics and programming logic have already been tested and proven. 
     By utilizing the fan controller user interface software  500  according to an embodiment of the present invention, the thermal design engineer saves a significant amount of time in the design cycle by eliminating the need to design and build a specialized PCA or controller card for controlling the speeds and alarm settings of the cooling fan(s)  510 ,  520 ,  530 ,  540 , and eliminating the iteration of asking for a fan sample, trying the fan out in the system, asking for a second higher-powered fan sample, trying the fan out in the system, etc., to determine a suitable cooling solution for a cabinet/housing. The thermal design engineer is able to balance airflow, noise, redundancy, and temperature response utilizing the fan controller user interface software  500  without having to go through an iterative process. 
       FIG. 9  illustrates a method of emulating an analog current limit function according to an embodiment of the present invention. In cooling fans, a small resistor may be added in series with a current of the motor to monitor the current of the motor. While effective, this approach has three drawbacks. First, the physical size of the resistor may be large, which can cause a problem fitting the resistor into a limited size of a typical fan motor hub. Second, this physically large resistor is much more expensive than standard resistors, which increases the motor cost. Third, the power dissipated by the large resistor reduces the overall motor efficiency. 
     In an embodiment of the invention, microcontroller software or program code may mimic this function. A lookup table may be created  900  that identifies a number of duty cycle measurements and corresponding fan speeds for the duty cycle measurements. In an alternative embodiment of the invention, a lookup table could include a number of DC voltage levels and corresponding fan speeds. For example, the lookup table may include an entry that 2.5 volts DC represents 2000 revolutions per minute. In an alternative embodiment of the invention, the lookup table could include a resistance received or sensed at the microcontroller and corresponding fan speeds. For example, the lookup table may include an entry that that 10,000 Ohms represents 2000 revolutions per minute. In this case, the microcontroller provides a current through the resistance and generates a DC voltage. This table may be created in a non-volatile memory. For example, the table may include the following entries. Still in regard to step  900 , illustratively, the DC_array (Duty Cycle) table column illustrated below includes 101 entries which correspond to the 101 entries in the speed array table column. 
     
       
         
           
               
             
               
                   
               
             
            
               
                 DC_array[101] = {0, 10, 20, 31, 41, 51, 61, 72, 82, 92, 102, 113, 123, 133, 143, 154, 164, 174, 
               
               
                 184, 195, 205, 215, 225, 236, 246, 256, 266, 276, 287, 297, 307, 317, 328, 338, 348, 358, 369, 379, 389, 
               
               
                 399, 410, 420, 430, 440, 451, 461, 471, 481, 492, 502, 512, 522, 532, 543, 553, 563, 573, 584, 594, 604, 
               
               
                 614, 625, 635, 645, 655, 666, 676, 686, 696, 707, 717, 727, 737, 748, 758, 768, 778, 788, 799, 809, 819, 
               
               
                 829, 840, 850, 860, 870, 881, 891, 901, 911, 922, 932, 942, 952, 963, 973, 983, 993, 1004, 1014, 1024}; 
               
               
                 Speed_array[101] = {7500, 7177, 6881, 6608, 6356, 6122, 5906, 5703, 5515, 5338, 5172, 5017, 
               
               
                 4870, 4732, 4601, 4478, 4360, 4249, 4144, 4043, 3947, 3856, 3769, 3686, 3606, 3529, 3456, 3386, 3319, 
               
               
                 3254, 3191, 3132, 3074, 3018, 2964, 2913, 2863, 2814, 2768, 2722, 2679, 2636, 2595, 2555, 2517, 2479, 
               
               
                 2443, 2408, 2373, 2340, 2308, 2276, 2246, 2216, 2187, 2158, 2131, 2104, 2078, 2052, 2027, 2003, 1979, 
               
               
                 1956, 1933, 1911, 1889, 1868, 1847, 1827, 1807, 1788, 1769, 1750, 1732, 1714, 16, 1680, 1663, 1647, 
               
               
                 1630, 1615, 1599, 1584, 1569, 1554, 1540, 1526, 1512, 1499, 1485, 1472, 1459, 1446, 1434, 1420, 1410, 
               
               
                 1398, 1386, 1375, 1364}; 
               
               
                   
               
            
           
         
       
     
     In the table illustrated above, the DC_array value may represent a duty cycle of a pulse width modulated signal that is transmitted to the cooling fan. In an embodiment of the invention, the pulse width modulated signal&#39;s duty cycle can be integrated utilizing a series resistor and a parallel capacitor and turned into a DC voltage. In an embodiment of the invention, the DC voltage is input into a microcontroller analog to digital converter and converted into a digital value. In an embodiment of the invention, the DC voltage is input into an analog-to-digital converter external to the microcontroller and converted to a digital value. In the embodiment illustrated above, the digital value, i.e., the DC_array value, may be between 1 and 1024, which may be represented by 10 bits. 
     A Speed_array value is the speed target associated with or corresponding to the DC_array value. Illustratively, the maximum speed in the table or the array of speed_array values may be 7500 revolutions per minute (RPM). According to the table above, this corresponds to a zero voltage (digital value of 0) reading on the analog-digital (AD) pin of the microcontroller  1020 . According to the table above, the minimum speed of the speed_array is 1364 RPM, which corresponds to a 5 volt reading on the AD pin of the microcontroller  1020  (digital value of 1024). In the embodiment illustrated above, the A/D converter in the microcontroller is a 10 bit value. 
       FIG. 10  illustrates a cooling fan including the analog current emulation function according to an embodiment of the present invention. The non-volatile memory  1042  may be physically located in the microcontroller  1020 . Alternatively, the non-volatile memory  1042  may be physically located in the cooling fan  1000 . 
     The microcontroller  1020  may measure  905  a duty cycle of a signal that is sent to drive the fan. As discussed above, this may be a pulse width modulated fan signal which is input into a A/D pin on the microcontroller  1020 . 
     The microcontroller  1020  may receive  910  a speed measurement from the speed sensor  1026 . The speed sensor  1026  may be a hall sensor or a back emf sensor. The speed sensor  1026  may magnetically sense the speed of the fan and may transmit a digital or analog signal to the microcontroller  1020 . 
     The microcontroller  1020  may retrieve  915  a corresponding fan speed from the lookup table based on measured duty cycle in step  905  (or based on the duty cycle measured in step  905 ). In other words, the microcontroller  1020  may include software or program code to utilize the measured or captured duty cycle and to retrieve, from the non-volatile memory  1042 , the corresponding or expected fan speed. As illustrated above, the microcontroller  1020  captures or measures the DC_array value and retrieves the corresponding or expected speed array value from the lookup table. Illustratively, the microcontroller  1020  may capture a duty cycle or DC_array value of 82 and then retrieve the corresponding or expected speed_array value (speed value) of 5515. 
     The microcontroller  1020  may compare  920  the corresponding fan speed to the fan speed received from speed sensor  1026 . In other words, the microcontroller  1020  is determining if the actual fan speed corresponds to what the desired or expected fan speed should be. 
     If the measured fan speed is less than a predetermined fraction of the corresponding or expected fan speed, this indicates that something is not operating properly, (i.e., is the current to motor  1014  is too high). In response to the measured fan speed being less than the predetermined fraction, the microcontroller  1020  may then reduce  925  the duty cycle of the driving signal to the motor  1014 . In an embodiment of the present invention, if the measured fan speeds is less than ⅔ of the corresponding or expected fan speed, then the microcontroller  1020  may reduce  925  the duty cycle of the driving signal. The microcontroller  1020  may also request that readings at measurement points in the cooling fan be captured and recorded in order to determine the cause of the why the current to the motor is too high. 
     Illustratively, a normal fan motor is designed to run at 10,000 RPMs. Due to a malfunction or an impediment in the cooling fan  1000 , the revolutions per minute may be reduced to 6,000 RPM even thought the current that is being provided to the cooling fan is enough current to normally run the normal fan motor at 10,000 RPMs. The 6,000 RPM may be measured by the speed sensor  1026 . Because the computer system  1040  or customer was transmitting a pulse width modulation signal instructing the motor  1014  and fan  1012  to be turned at 10,000 rpm, comparison between the measured fan speed and the corresponding or expected fan speed results in the measured fan speed being less than a predetermined fraction, in this case less than ⅔. Illustratively, the microcontroller  1020  may reduce the duty cycle of the driving signal in a corresponding ratio, e.g., ⅔ of the customer or computer transmitted duty cycle. The reduction of the duty cycle reduces the current draw of the motor  1014  to prevent the motor  1014  from drawing in to much current and damaging components within the motor. 
     In an embodiment of the invention, the microcontroller  1020  may periodically attempt to test if the malfunction has been resolved, e.g., the obstruction to the fan  1012  has been removed. The microcontroller  1020  may attempt to slightly increase the duty cycle by a predetermined number of RPMs, e.g., increase a duty cycle of the driving signal by a value corresponding to 100 RPMs. After the duty cycle has been increased, the speed sensor measures or captures the speed of the motor  1014 . If the speed of the motor  1014  does not increase, the microcontroller  1020  reduces the duty cycle by the predetermined number of RPMs and waits again for a predetermined time. Illustratively, the predetermined time may be 100 milliseconds. If the speed of the motor increases by the expected predetermined number of RPMs, e.g., 100 RPMs, the microcontroller  1020  increases the duty cycle to the increase the motor speed to the normal operating speed, e.g., 10,000 RPMs. 
     In a second embodiment of the invention, the normal operating speed of the motor/cooling fan may be a speed such as 10,000 RPMs. The speed sensor may measure that the motor speed has been reduced to 6000 RPMs. The microcontroller  1020  may shut down the driving signal to the motor  1014 , i.e., the motor is shut off completely. The microcontroller  1020  waits a predetermined amount of time, e.g, 3 seconds, and transmits a driving signal to restart the cooling fan  1000 . The driving signal includes a duty cycle which causes the motor to begin operating at 10,000 RPMs. There is a time it takes the motor  1014  to increase its operating speed to the 10,000 RPM operating speed. After this time, if the motor does not rotate at 10,000 RPMs, as measured by the speed sensor  1026 , the driving signal to the motor is not transmitted, e.g., shut off. This process continues until the malfunction is corrected, e.g., the obstruction is cleared. Once the malfunction is corrected, the motor  1014  operates at full speed. 
       FIG. 11  illustrates a method of predicting a life of a cooling fan utilizing a weighting factor according to an embodiment of the present invention. During operation of the cooling fan, a temperature may be monitored  1100  utilizing a temperature sensor  1044 , e.g., a temperature measurement may be captured. In an embodiment of the invention, a temperature sensor  1044  may be internal to a microcontroller  1020 . In an embodiment of the invention, the temperature sensor may be external to the microcontroller  1020 . Under certain operating conditions, the temperature may be monitored on a continuous basis. Under other operating conditions, the temperature may be monitored on a periodic basis, such as every 15 minutes, during the time the computer system  1040  or electronic device is powered on. 
     The monitored or measured temperature may be analyzed to determine  1105  if the measured temperature is within a predefined temperature window or range, e.g., +/−5 degrees of the pre-defined temperature. Depending on the operating environment of the cooling fan  1000 , the window temperature or range may be +/−5 degrees, +/−1 degree, +/−15 degrees or +/−10 degrees. For example, a computer located in an outside environment, such as an airport hanger or an automobile repair shop, may be subject to more extreme temperature changes, and thus the range of temperatures may be larger than the range of temperatures a computer system in an office is subjected to. 
     If the measured temperature is within the predefined temperature window, a total revolution count or a total number of revolutions (Revtotal) may be incremented  1135  by a set revolution value. Illustratively, the set revolution value may be 1 revolution. Illustratively, the set revolution value may be 1000 revolutions, 10,000 revolutions, or 50,000 revolutions. Under certain operating conditions, the set revolution value may be based on a number of actual revolutions that occur in a temperature monitoring period. For example, if the temperature is monitored every fifteen minutes and the actual number of revolutions that normally occur in fifteen minutes is 150,000 revolutions, then the set revolution value may be 150,000 revolutions. 
     After the set number of revolutions is added to the total revolution count or total number of revolutions (Revtotal), Revtotal is compared  1140  to the recommended revolution life (e.g., Revlife) of the cooling fan or a milestone revolution target of the cooling fan. For example, if the set number of revolutions is 15K, Revtotal was 2,000,000 revolutions, and Revlife is 2,000,200 revolutions, then the recommended life of the cooling fan has been exceeded because the total number revolutions is now 2,015,000 which is greater the recommended revolution life of 2,000,200 revolutions. The milestone revolution targets may be values that are points in number of revolutions during the life of a cooling fan  100  that a manufacturer or system integrator deem as important. For example, this may be 100K less than the recommended revolution life value or 50%, 70%, or 90% of the recommended revolution life value. Under these operating conditions, once a cooling fan  1000  reaches the defined revolution milestone, specific actions may occur. 
     If the total revolution count or total number of revolutions, (Revtotal), is greater than the recommended life or milestone target, then a message is generated  1145 . Under certain operating conditions the message is transmitted to the computer system. Under other operating conditions, the message is stored in a non-volatile memory in the cooling fan  1000 . Illustratively, when a message is transmitted, if Revtotal is greater than the recommended life of the cooling fan, then a message may be generated and transmitted to the computer system  1040  indicating that the cooling fan  1000  is past its recommended life and should be replaced immediately. In an embodiment of the invention, this may also result in a shutdown operation being initiated for the cooling fan  1000 . 
     If Revtotal is greater than one of the revolution milestone targets, then a message may be generated identifying that a cooling fan  1000  has, for example, passed 70% of its life or is 100,000 revolutions away from the recommended life revolution number and that a new cooling fan  1000  should be ordered or procured in order to minimize downtime or degradation of the computer system. Any milestone target may be utilized including a milestone target that is 70% of the recommended revolution life of the cooling fan  1000 . Under certain operating conditions, the generate message may be stored in a non-volatile memory for later analysis or under other operating conditions may be transferred to an external system (or computing device). 
     Under certain operating conditions, a milestone revolution target may be established at 70% and 90% of the recommended revolution life. The system may be set to generate messages once the total number of revolutions (total revolution count) of the cooling fan reaches 70% of the recommended revolution life of the fan, 90% of the recommended revolution life of the fan, and at the recommended revolution life of the fan. At 70%, the message may be a message indicating that the cooling fan is approaching the end of its life. At 90%, the message may be a little more urgent, and may instruct the system operator to be prepared for the cooling fan  1000  to fail. At the recommended revolution life of the cooling fan, the system  1040  may receive a message that the cooling fan  1000  has exceeded its life and should be replaced immediately. 
     If the total revolution count or total number of revolutions is not greater than the recommended revolution life or one of the milestone revolution targets, then the monitoring of the temperature, e.g., step  1100  continues to occur. 
       FIG. 11  also illustrates operating conditions if the temperature is outside the normal operating range. In an embodiment of invention, if the temperature is not within a predefined window or range, then a weighting factor may be changed  1110 . The weighting factor is a factor that is multiplied by a number of revolutions in order to compensate for the increase in temperature. In other words, a fan running at 30 degree Celsius temperature with 100,000 revolutions experiences the same wear and tear as a fan running at 45 degree Celsius temperature with 80,000 revolutions, and the weighting factor compensates for this. A higher temperature leads to a fan not operating in as efficient a matter as one operating at a lower temperature. 
     An example weighting factor table and associated temperature table is listed below. In this embodiment of the invention, the standard operating temperature of the cooling fan is 25 degrees Celsius. The table illustrates the increase in weighting factor as the temperature increases in the cooling fan. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Temperature 
                 Weighting Factor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 25° C. 
                 1 
               
               
                   
                 35° C. 
                 1.5 
               
               
                   
                 45° C. 
                 2.7 
               
               
                   
                 55° C. 
                 4.3 
               
               
                   
                 65° C. 
                 6.4 
               
               
                   
                 70° C. 
                 10 
               
               
                   
                   
               
            
           
         
       
     
     In this embodiment of the invention, the set number of revolutions is multiplied  1115  by the temperature based weighting factor to compensate for the higher or lower operating temperature. As discussed above, the set number of revolutions may represent the number of revolutions that occur during a monitoring period. For example, if the weighting factor is 1.25 and the set number of revolutions is 1,000, then the weighted revolution total is 1,250 revolutions. Illustratively, if the temperature is 55° C., the weighting factor is 4.3 and the weighted revolution total is 4,300. 
     The weighted revolution total is added  1125  to the total number of revolutions (Revtotal) to create a temperature adjusted total number of revolutions. For example, if the total number of revolutions is 1,000,000 and the weighted revolution total is 500,000 (equal to the weighting factor of 5×100,000 revolutions), then the new total number of revolutions is 1,500,000 even though the actual number of total fan revolutions is only 1,100,000. 
     The new total number of revolutions, e.g., the temperature adjusted number of revolutions, is compared  1140  to the recommended life number revolutions of the cooling fan or milestone revolution targets. If the temperature adjusted number of revolutions is greater than one of the milestone revolution targets and/or the recommended life number of revolutions of the cooling fan  1000 , then a message is generated  1145  by the computer system indicating that the milestone revolution target or recommended life number of revolutions has been passed. If the temperature adjusted number of revolutions is less than the milestone target or the recommended life revolution of the cooling fan, then the temperature of the cooling fan is monitored again (step  1100 ) after a designated monitoring period. 
     Under certain operating conditions, the weighting factor is not calculated until after the temperature adjust number of revolutions is compared to the recommended life revolution or milestone target revolutions of the cooling fan. This is illustrated by reference numeral  1130  of  FIG. 11 . In this example, the weighted factor utilized for multiplying the revolution count is not the most recently measured temperature; instead it is the previously measured temperature. This may be utilized in situations where the weighting factor is to reflect a past temperature value of the cooling fan since the past temperature may have lead to degredation of the operation of the cooling fan  1000 . In this embodiment of the invention, the weighting factor is not changed according to the monitored temperature immediately after it is determined whether the monitored temperature is in a predefined window, as it was in step  1110 . 
     The table below illustrates three increments of the flowchart of  FIG. 11 . Each monitoring period, e.g., 30 minutes, is represented by 10,000 revolutions (10K revolutions occur each 30 minutes). The temperature for the first rotation is 25 degrees, which is the standard operating temperature. Thus, the temperature is within the first predefined temperature window. Since the total revolution count was zero, the total revolution count is now equal to 10,000. The recommended revolution life of the cooling fan is 1,000,000 revolutions, so no message is generated. During a succeeding monitoring period, the temperature of the fan is measured to be 35 degrees. The temperature is no longer within the predefined window because the predefined window is +5 degrees outside the range, if the range was +/−5 degrees. The weighting factor table is consulted and a factor of 1.5 is retrieved for 35 degrees. The set number of revolutions, e.g., 10K, is multiplied by the weighting factor to create a weighted number of revolutions of 15K. The 15K revolutions is added to the previous total revolutions which results in a new total number of revolutions of 25K. Again, the new total number of revolutions is lower than the recommended life revolutions and no message is generated. 
     During a succeeding monitoring period, the temperature of the fan is measured to be 45 degrees. Because this temperature is outside of the predefined temperature range, a weighting factor table is consulted and a factor of 2.7 is retrieved for 45 degrees. The set number of revolutions is multiplied by the weighting factor to create a weighted number of revolutions of 27K. The weighted number of revolutions is added to the new total number of revolutions, e.g., 25K, and the new total number of revolutions is 42K. This is also not greater than the recommended life revolutions of the fan so no message is generated. It is important to note that although only 30K actual revolutions of the cooling fan have occurred, a temperature adjusted 42K revolutions is recorded for the cooling fan to more accurately reflect when the cooling fan may fail. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                 Tem- 
                   
                 Weighted 
                 New Total 
               
               
                   
                 Actual # of 
                 per- 
                 Weighting 
                 Number of 
                 Number of 
               
               
                 Increment 
                 revolutions 
                 ature 
                 Factor 
                 Revolutions 
                 Revolutions 
               
               
                   
               
             
            
               
                 1 
                 10,000 
                 25 
                 1.0 
                 10,000 
                 10,000 
               
               
                 2 
                 10,000 
                 35 
                 1.5 
                 15,000 
                 25,000 
               
               
                 3 
                 10,000 
                 45 
                 2.7 
                 27,000 
                 42,000 
               
               
                   
                 30,000 
                   
                   
                   
                 42,000 
               
               
                   
               
            
           
         
       
     
       FIG. 12  illustrates a flowchart for analyzing operating points of interest or measurement points in a cooling fan according to an embodiment of the present invention.  FIGS. 14A and 14B  illustrate operating points of interest for an exemplary cooling fan according to an embodiment of the present invention. The table below identifies the operating points of interest for the cooling fan. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Reference Numeral/Identification 
                   
               
               
                   
                 Numeral 
                 Measurement Of 
               
               
                   
                   
               
             
            
               
                   
                 I 
                 Fan current 
               
               
                   
                 II 
                 Fan input voltage 
               
               
                   
                 III 
                 Microcontroller temperature 
               
               
                   
                   
                 measurement 
               
               
                   
                 322 (IV) 
                 Speed control input 
               
               
                   
                 324 (V) 
                 Tachometer alarm status 
               
               
                   
                 VI 
                 Microcontroller input voltage 
               
               
                   
                 VII 
                 MOSFET Input Voltage 
               
               
                   
                   
               
            
           
         
       
     
     Referring to  FIG. 12 , operating points of interest (or measurement points) are monitored  1200  in the cooling fan  1000 . In an embodiment of the invention, a microcontroller  1020 , may receive inputs corresponding to the operating points of interest. For the analog inputs, the analog inputs may be received at the microcontroller  1020  by dividing down the analog signals to safe levels for the microcontroller by utilizing high resistance value resistors in a resistor divider circuit. In an embodiment of the invention, the analog signal is received by the microcontroller  1020  and converted to a digital signal by an Analog/Digital converter (ADC) inside the microcontroller  1020 . The monitoring may occur on a periodic basis. Illustratively, the monitoring may occur every 1 microsecond, every second, or every 30 seconds. 
     The readings at the operating points of interest or measurement points may be captured and then stored  1205  in a memory in the cooling fan. As illustrated in  FIG. 10 , the memory  1042  may be a non-volatile memory such as a flash memory or an EEPROM. In an embodiment of the invention, the non-volatile memory  1042  may be internal to the microcontroller  1020 . In an embodiment of the invention, the non-volatile memory  1044  may be external to the microcontroller but still located inside the cooling fan  1000 . 
     In an embodiment of the invention, the captured readings at the operating points (measurement points) of interest may be transmitted  1210  to a receiver that is external to the cooling fan  1000 . As illustrated in  FIG. 10 , the microcontroller  1020  in the cooling fan  1000  may transmit the measurements at the operating points of interest through the interface  1030  to a computer system  1040  utilizing a known communication protocol. 
     In an embodiment of the invention, the captured readings at the operating points of interest or measurement points may remain in the non-volatile memory  1042  of the cooling fan  1000  for a time period. The non-volatile memory  1042  may be large enough to accommodate a set number of readings of the operating points of interest or measurement points. For example, if seven measurements are taken in each measurement period, e.g., the seven measurements listed in the table above, the non-volatile memory  1042  may be large enough to store 20 repetitions of these seven measurements. Under other operating conditions, the non-volatile memory  1042  may record the readings at the operating points of interest or the measurement points for the last hour of the cooling fan operation. By storing a number of sets of captured measurements for each of the measurement points, the non-volatile memory  1042  may be utilized as a device that can be looked at to determine the cause of failure in the cooling fan  1000 , e.g., like a black box in an airplane. 
     In an embodiment of the invention, the captured readings at the operating points of interest may be read or retrieved  1210  from the non-volatile memory on a periodic basis. In an embodiment of the invention, the captured readings at the measurements points may be transmitted to an external device or a computer system. The captured readings at the operating points or measurement points may be read each time the measurements are stored in the non-volatile memory  1042  or the measurements may be read at a specified timeframe, e.g., such as every 30 minutes. The measurements may be read utilizing the communication protocol of the system  1040  and by utilizing the interface  1030 . The measurements may also be read by creating a separate input on the cooling fan which an external device may utilize to read or retrieve the captured readings. The external device may communicate with the cooling fan  1000  utilizing serial communications. 
     The captured readings at the operating points of interest/measurement points are analyzed  1215  to assist in determining a cause of the failure of a cooling fan. Illustratively, if the cooling fan  1000  fails, the stored, transmitted, or read readings are analyzed to identify what may have caused the failure. Illustratively, the operating points of interest may include the fan current, the fan input voltage, a speed reading measurement and a MOSFET gate voltage. If the fan input voltage was outside a normal level, e.g., +45 percent of normal voltage, the data may indicate that the input voltage caused the failure of the cooling fan, and that the device that provides the fan input voltage may be malfunctioning. 
     In an embodiment of the invention, an operator of the system  1040  may view the measurements at the operating points of interest, either after the measurements are transmitted from the cooling fan or retrieved from the cooling fan. In this embodiment of the invention, the computer system may automatically analyze the measurements at the operating points of interest and may generate error messages or messages identifying the probable cause of the failure of the cooling fan. 
       FIG. 13  illustrates a method of measuring points of interest in a cooling fan in order to keep a cooling fan from failing according to an embodiment of the present invention. As discussed above in regard to  FIG. 12 , points of interest are monitored  1300 , such as cooling fan input voltage, cooling fan current, microcontroller input voltage, etc. The method prevents cooling fans from failing if unacceptable measurements are received from the operating points of interest. 
     In an embodiment of the present invention, the captured readings at the point of interests or measurement points may be transmitted  1310  to a non-volatile RAM or a volatile RAM for storage. For example, the input current measurement and the microcontroller input voltage may be transmitted to a non-volatile RAM for storage. 
     The cooling fan  1000  may store predetermined thresholds for measurements at the cooling fan points of interest in a non-volatile RAM  1024 . The non-volatile RAM  1024  may be located internal to the microcontroller  1020  or external to the microcontroller  1020 . The captured readings at the points of interest or measurement points are compared  1320  to the predetermined thresholds to determine if the captured readings exceed or are less than the predetermined thresholds. For example, the input voltage to the microcontroller may have a lower threshold of 4.6 volts and an upper threshold of 5.6 volts. If the measured input voltage for the cooling fan is 5.9 volts, then the measured input voltage exceeds the predetermined threshold. 
     If the captured readings at a cooling fan point of interest or measurement point is above one of the predetermine thresholds, then a shutdown operation or a modification operation may be initiated  1330  for the cooling fan. The shutdown operation may shutdown operation of the cooling fan by disabling the outputs of the microcontroller. The modification operation of the cooling fan may result in the increasing or the decreasing of a duty cycle of a driving signal transmitted to the motor  1014  from the microcontroller  1020 . 
     Illustratively, 1) the input voltage to the cooling fan, 2) the fan speed, 3) the MOSFET driving voltage, and 4) the input voltage to the microcontroller may be monitored. Under certain operating conditions, the fan speed may be determined to be greater than the fan speed predetermined threshold, e.g., the fan is rotating too fast. A modification operation may be initiated via the microcontroller  1020  to reduce the duty cycle of the driving signal to the motor  1014 . Under certain operating conditions, the input voltage to the microcontroller  1020  may be too high and may be higher than the microcontroller input voltage predetermined threshold. Because a high microcontroller input voltage may cause damage to the microcontroller  1020 , a shutdown operation may be initiated to shutdown operation of the cooling fan  1000 . 
     If the captured readings at one of the points of interest or measurement points is above a predetermined threshold, than an error message or message may be transmitted  1340  to the computer system that the error condition has occurred, that a modification operation was initiated, or that the cooling fan  1000  was shut down. In some cases, this information may be transmitted to a log file. Under other operating conditions, the error message or message may appear as a dialog box in the graphical user interface of the currently executing application. 
     The method described in  FIGS. 9 and 13  may be incorporated together. In other words, in step  920  of  FIG. 9 , a corresponding fan speed for a reading (duty cycle value, DC voltage, resistance) may be compare to a fan speed received from the speed sensor. In addition to reducing the duty cycle (or other value) of a driving signal if the measured fan speed is less than a predetermined fraction of the corresponding fan speed, an error message may be generated identifying that the fan is not operating correctly. Under certain operating conditions, this error message may be stored in a memory in the cooling fan. Under other operating conditions, this error message may be transmitted to a computer system coupled to the cooling fan. 
     While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.