Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
2000-06-19
2003-03-04
Le, N. (Department: 2858)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S511000, C324S537000, C318S463000
Reexamination Certificate
active
06528987
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for determining a performance characteristic of a fan, and in particular, though not limited to a method and apparatus for determining the speed of a cooling fan in an enclosure for electronic circuitry.
BACKGROUND TO THE INVENTION
Computers comprise a cabinet within which the electronic components of the computer are housed. Some of these components, for example, the central processing unit and the power supply module operate at relatively high temperatures, thus generating significant quantities of heat. One or more cooling fans are provided in such computer cabinets for circulating air and for changing air within the computer cabinet for maintaining the temperature within the cabinet within an acceptable temperature range. In order to minimise acoustic noise and power consumption such fans are only operated when the temperature exceeds an upper limit of the acceptable temperature range. More recently variable speed control techniques have been developed for operating the fans at various speeds, depending on the temperature within the computer cabinet. One of the more recent variable speed control techniques which have been developed is based on pulse width modulation of the power supply to the fan motor. Typically, a control circuit outputs a pulse width modulated signal for switching the power supply to the fan motor so that the power supply to the fan motor is pulse width modulated. The control circuit also measures the speed of the fan by monitoring a tachometer signal received from the fan motor. However, one problem with such fan control is that in general the tachometer signal from the fan motor is only available when the duty cycle of the pulse width modulated power supply to the fan motor is in the on state. Thus, the tachometer signal read over one or more duty cycles is not an accurate representation of the fan speed.
Due to the relatively high heat output of some central processing units and power supply modules, it is essential that the cooling fans should operate at a speed which is at least up to the speed at which they are set to operate, and which is determined by the mark/space ratio of the duty cycle of the pulse width modulated power supply. An under-speed in a fan can have serious consequences including failure and destruction of components within the computer cabinetry. It is therefore essential that under-speed in a fan can be accurately detected and determined.
The present invention is directed towards providing a method and apparatus for determining a value of a performance characteristic of a fan, such as for example fan speed.
SUMMARY OF THE INVENTION
According to the invention there is provided a method for determining a value of a performance characteristic of a fan driven by a motor powered by a pulse width modulated power supply in which a monitoring means associated with the fan outputs a signal indicative of the value of the performance characteristic to be monitored and the monitoring means is powered by the pulse width modulated power supply, the method comprising the steps of:
reading a predetermined portion of the signal from the monitoring means during a period of a duty cycle of the pulse width modulated power supply when the power supply during the duty cycle is in the on state for powering the fan motor,
holding the power supply in the on state during the duty cycle while the predetermined portion of the monitoring means signal is being read, and
determining the value of the performance characteristic from the read predetermined portion of the monitoring means signal.
In one embodiment of the invention the off period of the next duty cycle of the power supply to the fan motor is commenced in response to the predetermined portion of the monitoring means signal having been read, in the event that the power supply had been held in the on state longer than the normal on period of the duty cycle.
In another embodiment of the invention the performance characteristic to be determined is the fan speed, and the monitoring means outputs a pulsed signal indicative of the fan speed, and a predetermined number of sequential pulses of the pulsed signal are read, and the time period during the predetermined number of sequential pulses of the pulsed signal is determined for determining the time period of one revolution of the fan motor.
In a further embodiment of the invention the predetermined number of sequential pulses of the pulsed signal from the monitoring means which are read is at least two sequential pulses. Preferably, the predetermined number of sequential pulses of the pulsed signal from the monitoring means which are read is at least three sequential pulses.
In one embodiment of the invention the time period during the predetermined number of sequential pulses of the pulsed signal from the monitoring means which are read is determined by counting the number of clock pulses in a reference clock signal during the time period for the predetermined number of sequential pulses. Preferably, the number of clock pulses of the reference clock signal are counted from an edge of the first of the sequential pulses of the pulsed signal to a corresponding edge of the last of the sequential pulses of the predetermined number of sequential pulses for determining the time period during the predetermined number of sequential pulses of the pulsed signal from the monitoring means.
In one embodiment of the invention the pulsed signal from the monitoring means is derived by monitoring the current through the fan.
Preferably, the value of the performance characteristic determined from the signal from the monitoring means is compared with a reference value of the performance characteristic at which the fan should have been performing in response to the duty cycle of the pulse width modulated power supply for determining if the fan is operating at the reference performance characteristic value, and an alert signal is issued in the event that the determined value does not comparing favourably with the reference value of the performance characteristic. Advantageously, the alert signal is issued in the event of the determined value of the performance characteristic being less than the reference value of the performance characteristic.
In one embodiment of the invention the method according to the invention is for monitoring the fan speed of a cooling fan located in an enclosure for electronic circuitry.
Additionally, the invention provides apparatus for determining a value of a performance characteristic of a fan driven by a motor powered by a pulse width modulated power supply in which a monitoring means associated with the fan outputs a signal indicative of the value of the performance characteristic to be monitored, and the monitoring means is powered by the pulse width modulated power supply, the apparatus comprising:
a means for reading a predetermined portion of the signal from the monitoring means during a period of a duty cycle of the pulse width modulated power supply when the power supply during the duty cycle is in the on state, for powering the fan motor,
a control means for holding the power supply in the on state during the duty cycle while the predetermined portion of the monitoring means signal is being read, and
a means for determining the value of the performance characteristic from the read predetermined portion of the monitoring means signal.
In one embodiment of the invention the control means holds the power supply in the on state during the duty cycle in response to the reading means commencing to read the monitoring means signal.
In another embodiment of the invention the control means is responsive to the predetermined portion of the monitoring means signal having been read for commencing the off period of the next duty cycle of the power supply to the fan in the event that the power supply had been held in the on state for a period longer than the normal on period of the duty cycle.
In a further embodiment of the invention the performance characteristic to be d
Blake John
Hanrahan David
Yoshida Kohji
Analog Devices Inc.
Le N.
Sundaram T. R.
Wolf Greenfield & Sacks PC
LandOfFree
Method and apparatus for determining fan speed does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for determining fan speed, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for determining fan speed will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3005008