Cooling fan control system

1. An apparatus comprising:

a memory configured to store a predefined function; and

a processor configured to:

calculate a target temperature value for a desired temperature at a first position based on the predefined function and a measured temperature value at a second position;

calculate a difference value between a measured temperature value at the first position and the target temperature value for the first position;

generate a fan speed control signal based on the calculated difference value; and provide the control signal to a fan responsive to the control signal to maintain the measured temperature value at the first position to be within a predetermined tolerance of the target temperature value.

2. The apparatus of claim 1 , wherein the predefined function is a look-up table or an equation, the measured temperature value at the second position is an input of the predefined function, and the target temperature value for the first position is an output of the predefined function.

3. The apparatus of claim 1 , further comprising a first temperature sensor electrically connected to the processor, the first temperature sensor configured to generate the measured temperature value at the first position; and

a second temperature sensor electrically connected to the processor, the second temperature sensor configured to generate the measured temperature value at the second position.

4. The apparatus of claim 1 , wherein the first position is proximate to a heat generating electrical component supported by an electrical hardware system, and

wherein the second position is proximate to an air inlet of the electrical hardware system.

5. The apparatus of claim 4 , wherein the electrical hardware system comprises a network communications switch or a power supply.

6. The apparatus of claim 1 , wherein the fan speed control signal generated by the processor is configured to increase the speed of a fan electrically connected to the processor in response to the difference value being greater than a first tolerance value stored in the memory, and

wherein the fan speed control signal generated by the processor is configured to decrease the speed of the fan electrically connected to the processor in response to the difference value being less than a second tolerance value stored in the memory.

7. The apparatus of claim 6 , wherein the processor is configured to calculate a minimum fan speed based on a minimum fan speed function stored in the memory and the measured temperature value at the second position, and

wherein the fan speed control signal generated by the processor is configured to decrease the speed of the fan if the decreased fan speed is greater than the minimum fan speed.

8. The apparatus of claim 6 , wherein the processor is configured to wait a first time period before generating the fan speed control signal configured to increase the speed of the fan in response to the difference value being greater than the first tolerance value and less than or equal to a first predefined difference value stored in the memory, and

wherein the processor is configured to wait a second time period before generating the fan speed control signal configured to decrease the speed of the fan in response to the difference value being less than the second tolerance value and greater than or equal to a second predefined difference value stored in the memory.

9. The apparatus of claim 1 , wherein the predefined function is a first predefined function, the difference value is a first difference value, and the memory is configured to store a second predefined function, and

wherein the processor is further configured to:

calculate a target temperature value for a third position based on the second predefined function and the measured temperature value at the second position;

calculate a second difference value, the second difference value being between a measured temperature value at the third position and the target temperature value for the third position; and

generate a fan speed control signal based on the greater of the first difference value and the second difference value.

10. A method comprising:

determining a first temperature value, the first temperature value being measured at a first position within an electrical hardware system;

determining a second temperature value, the second temperature value being determined at a second position within the electrical hardware system;

calculating, with a processor, a target first temperature value for a desired temperature at the first position as a function of the determined second temperature value;

calculating a difference value between the determined first temperature value and the calculated target first temperature value;

generating a control signal for a fan coupled with the electrical hardware system as a function of the calculated difference value and controlling a fan responsive to the control signal to maintain the determined temperature value at the first position within a predetermined tolerance of the target first temperature value.

11. The method of claim 10 , wherein determining the first temperature value comprises generating the first temperature value using a first temperature sensor, and

wherein determining the second temperature value comprises generating the second temperature value using a second temperature sensor.

12. The method of claim 10 , wherein the control signal comprises a pulse width modulated signal, and

wherein the widths of pulses in a train of on-off pulses forming the control signal determines a level of power applied to the fan.

13. The method of claim 12 , wherein generating the control signal comprises increasing the widths of pulses in the pulse width modulated signal if the difference value is greater than a first tolerance value, and

wherein generating the control signal comprises decreasing the widths of pulses in the pulse width modulated signal if the difference value is less than a second tolerance value.

14. The method of claim 10 , wherein calculating the target first temperature value comprises the processor using a fan curve look-up table or inputting the determined second temperature value into a predefined fan curve equation.

15. The method of claim 10 , wherein the difference value is a first difference value, the control signal is a first control signal, and the fan is a first fan, the method further comprising:

determining a third temperature value, the third temperature value being determined at a third position within the electrical hardware system;

determining a fourth temperature value, the fourth temperature value being determined at a fourth position within the electrical hardware system;

calculating a target third temperature value as a function of the determined fourth temperature value;

calculating a second difference value, the second difference value being a difference value between the determined third temperature value and the calculated target third temperature value; and

generating a second control signal to control a speed of a second fan of the electrical hardware system as a function of the second difference value.

16. The method of claim 10 , wherein determining the second temperature value comprises determining a minimum value between a measured temperature value proximate to an air inlet of the electrical hardware system and a measured temperature value proximate to an air outlet of the electrical hardware system, and

wherein the second temperature value is the minimum value, and the second position is proximate to the air inlet or the air outlet of the electrical hardware system.

17. The method of claim 10 , further comprising determining an operating parameter value for the electrical hardware system; and

adjusting the target first temperature value if the determined operating parameter value is above a predefined operating parameter value.

18. A non-transitory tangible storage media encoded with logic, the logic executable by a processor to:

calculate a target temperature value for a desired temperature at a first position as a function of temperature data for a second position;

calculate a difference value between measured temperature data for the first position and the target temperature value for the first position;

generate a control signal based on the difference value and controlling a fan responsive to the control signal to maintain the temperature data for the first position within a predetermined tolerance of the target temperature value for the first position.

19. The non-transitory tangible storage media of claim 18 , further comprising logic executable by the processor to:

receive the first temperature data from a first temperature sensor in or on an electrical hardware system; and

receive the second temperature data from a second temperature sensor in or on the electrical hardware system.

20. The non-transitory tangible storage media of claim 18 , further comprising logic executable by the processor to calculate the target temperature value for the first position using a look up table or an equation.

21. The non-transitory tangible storage media of claim 18 , wherein the control signal is generated to increase a speed of a fan if the difference value is greater than a first tolerance value, and

wherein the control signal is generated to decrease the speed of the fan if the difference value is less than a second tolerance value.