U.S. patent application number 12/107140 was filed with the patent office on 2008-12-18 for intelligent air moving apparatus.
Invention is credited to John P. Franz, David F. Heinrich, Stephen A. Kay, Thomas D. Rhodes, Wade D. Vinson.
Application Number | 20080310967 12/107140 |
Document ID | / |
Family ID | 40132514 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080310967 |
Kind Code |
A1 |
Franz; John P. ; et
al. |
December 18, 2008 |
INTELLIGENT AIR MOVING APPARATUS
Abstract
An intelligent air moving apparatus for cooling an electronics
enclosure includes a motor for driving a fan at a variable
rotational speed and a microcontroller for controlling the
rotational speed of the motor. The microcontroller includes a speed
sensor for sensing the rotational speed such that when the sensed
rotational speed deviates below a target speed, the microcontroller
detects a locked rotor condition.
Inventors: |
Franz; John P.; (Houston,
TX) ; Vinson; Wade D.; (Magnolia, TX) ;
Rhodes; Thomas D.; (The Woodlands, TX) ; Heinrich;
David F.; (Tomball, TX) ; Kay; Stephen A.;
(Tomball, TX) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD, INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
40132514 |
Appl. No.: |
12/107140 |
Filed: |
April 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60943679 |
Jun 13, 2007 |
|
|
|
Current U.S.
Class: |
417/32 ; 318/434;
318/455; 318/461; 318/471; 340/648; 388/809; 417/44.11 |
Current CPC
Class: |
F05D 2270/335 20130101;
Y02B 30/70 20130101; F04D 27/004 20130101; F04D 27/008 20130101;
G06F 1/20 20130101; H05K 7/20209 20130101 |
Class at
Publication: |
417/32 ; 388/809;
318/434; 318/461; 318/471; 417/44.11; 340/648; 318/455 |
International
Class: |
F04B 49/06 20060101
F04B049/06; H02P 7/285 20060101 H02P007/285; H02H 7/093 20060101
H02H007/093; G08B 21/18 20060101 G08B021/18 |
Claims
1. An intelligent air moving apparatus for cooling an electronics
enclosure, the apparatus comprising: a motor for driving a fan at a
variable rotational speed; a microcontroller for controlling the
rotational speed of the motor, the microcontroller comprising a
speed sensor for sensing the rotational speed; wherein when the
sensed rotational speed falls below a target speed by at least a
threshold amount, the microcontroller detects a locked rotor
condition and initiates a sequence to shut down and restart the
motor.
2. The air moving apparatus of claim 1, wherein the speed sensor
senses back electromotive force from the motor.
3. The air moving apparatus of claim 1, the microcontroller further
comprising a voltage sensor, the motor having one or more phases,
wherein when the voltage sensor senses a drop in voltage indicative
of removal of power from the motor, the microcontroller
simultaneously energizes all motor phases to stop the motor from
rotating.
4. The air moving apparatus of claim 1, the microcontroller further
comprising a memory for storing data including speed avoidance
zones, wherein when the target speed is within one of the speed
avoidance zones, the microcontroller controls the motor speed to be
slightly outside said speed avoidance zone.
5. The air moving apparatus of claim 1, further comprising an
interface for electronically communicating between the
microcontroller and an infrastructure controller external to the
air moving apparatus, wherein when the interface indicates a loss
of communication, the microcontroller maintains the rotational
speed at a default speed.
6. The air moving apparatus of claim 1, the microcontroller further
comprising memory for storing static data and an interface for
electronically communicating between the microcontroller and an
infrastructure controller external to the air moving apparatus,
wherein the microcontroller communicates the static data to the
infrastructure controller via the interface.
7. The air moving apparatus of claim 1, the microcontroller further
comprising memory for storing dynamic data and an interface for
electronically communicating between the microcontroller and an
infrastructure controller external to the air moving apparatus,
wherein the microcontroller communicates the dynamic data to the
infrastructure controller via the interface.
8. The air moving apparatus of claim 1, further comprising an
overcurrent protector for shutting down and restarting the motor
upon the detection of a high current condition.
9. The air moving apparatus of claim 1, further comprising an
interface having redundant communication channels for
electronically communicating between the microcontroller and an
infrastructure controller external to the air moving apparatus, the
infrastructure controller being adapted to switch between channels
when one of the channels fails.
10. The air moving apparatus of claim 1, further comprising at
least one light emitting diode in electronic communication with the
microcontroller to indicate at least one status condition of the
apparatus.
11. The air moving apparatus of claim 1, wherein the
microcontroller further provides a failure alert when a locked
rotor condition is detected.
12. The air moving apparatus of claim 1, wherein the
microcontroller further provides an alert indicating that
inspection of the fan is needed after a predetermined number of
shut down and restart sequences.
13. The air moving apparatus of claim 1, wherein the
microcontroller further measures power to the motor, and wherein
the microcontroller provides a pre-failure alert when a deviation
is detected from an expected relationship between the motor
rotational speed and the motor power.
14. The air moving apparatus of claim 1, further comprising a
temperature sensor for measuring motor temperature, wherein the
microcontroller provides a pre-failure alert when the motor
temperature deviates from an expected normal operating
temperature.
15. The air moving apparatus of claim 1, further comprising a
temperature sensor for measuring fan air inlet temperature, wherein
the microcontroller controls the motor rotational speed based on
the fan inlet temperature.
16. A system for cooling an electronics enclosure, comprising: a
plurality of fan modules, each fan module comprising: a motor for
driving a fan at a variable rotational speed; a microcontroller for
controlling the rotational speed of the motor; an interface for
electronically communicating between the microcontroller and an
infrastructure controller external to the fan module, the
infrastructure controller providing a target speed to the
microcontroller; and a memory for storing data including speed
avoidance zones; wherein when the target speed falls within one of
the speed avoidance zones, the microcontroller controls the motor
speed to be slightly outside said speed avoidance zone.
17. The system of claim 16, the microcontroller comprising a speed
sensor for detecting the rotational speed, wherein when the
rotational speed sensed by the speed sensor falls below a target
speed by at least a threshold amount, the microcontroller detects a
locked rotor condition and initiates a sequence to shut down and
restart the motor.
18. The system of claim 16, the microcontroller comprising a
voltage sensor, wherein when the voltage sensor senses a drop in
voltage indicative of removal of power from the motor, the
microcontroller simultaneously energizes all one or more motor
phases to stop the motor from rotating.
19. The system of claim 16, wherein when the interface indicates a
loss of communication with the infrastructure controller, the
microcontroller maintains the rotational speed at a default
speed.
20. The system of claim 16, the fan module further comprising a
crystal oscillator to ensure an accurate time base for motor speed
measurements.
21. A method of cooling an electronics enclosure comprising:
providing at least one fan module comprising a multi-phase motor
for driving a fan at a variable rotational speed and a
microcontroller for controlling the rotational speed of the motor;
sensing the rotational speed; and detecting a locked rotor event
when the sensed rotational speed falls below a target speed by at
least a threshold amount.
22. The method of claim 21, further comprising: controlling the
rotational speed to be outside one or more speed avoidance zones
defined by natural frequencies of the fan module.
23. The method of claim 21, further comprising: when more than one
fan module is provided, starting the fans sequentially instead of
simultaneously to avoid power surges.
24. The method of claim 21, further comprising: providing a
communications interface adapted to receive a target speed signal;
and maintaining the rotational speed at a default speed when the
communications interface detects a loss of the target speed signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. Provisional
Application No. 60/943,679, filed Jun. 13, 2007, entitled
"Intelligent High Performance Air Mover."
BACKGROUND
[0002] Fans powered by electric motors are commonly used to cool
computer servers and other electronic equipment within an
electronics enclosure. Existing electronics enclosure cooling fans
have limited intelligence and provide little or no communication to
an infrastructure controller capable of monitoring the electronics
systems the fans are designed to cool. Therefore, existing fans
lack the ability to be optimized for thermal performance, noise,
power consumption, reliability, maintenance and warranty costs, and
other relevant parameters.
[0003] In typical computing systems, including computer servers,
multiple fans are required to maintain sufficient airflow to cool
the electronics equipment within the enclosure. Further, the
multiple fans must be able to operate effectively and harmoniously
in conjunction with each other. Therefore, limited intelligence
fans require substantial amounts of computational overhead to
ensure the fans are operating to provide adequate cooling, and to
detect fan failures before the electronics equipment overheats.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The accompanying drawings illustrate embodiments of an
intelligent air moving apparatus as described herein.
[0005] In the drawings:
[0006] FIG. 1 shows a schematic view of a fan module interconnected
to an infrastructure controller.
[0007] FIG. 2 shows an electronics enclosure having a plurality of
fan modules mounted thereto for providing cooling.
DETAILED DESCRIPTION
[0008] There is shown in FIG. 1 an air moving apparatus 100
comprising a fan module 10 interconnected to an infrastructure
controller 50. The infrastructure controller 50 is further
interconnected to an electronics enclosure 60 to monitor various
operational parameters including temperature of the electronics
enclosure 60. The fan module 10 comprises a fan 12, a
microcontroller 20, and an interface 40. The fan 12 has a motor 14
adapted to drive a fan blade 16 at a variable rotational speed, as
commanded by the microcontroller 20, to accommodate the cooling
needs of the electronics enclosure 60. The microcontroller 20
controls the speed of the motor 16 and includes a speed sensor 30
to sense the motor rotational speed and to provide a feedback
signal of the actual motor speed. The microcontroller can
additionally include other sensors, such as a voltage sensor 34,
and a current sensor 36. In an embodiment, the microcontroller 20
receives instructions from the infrastructure controller 50 and
sends fan status information to the infrastructure controller 50
via the interface 40.
[0009] The microcontroller 20 can be a microprocessor.
Alternatively, the microcontroller functions can be performed by
solid state components or other circuitry. An exemplary
microcontroller is commonly known as a Programmable Interface
Controller or Programmable Intelligent Computer ("PIC"), an
inexpensive chip-based programmable microcontroller. The term "PIC"
is used interchangeably with the term "microcontroller" in this
application. The microcontroller 20 includes a memory 28 for
storing data.
[0010] The microcontroller 20 includes features to allow the fan
module 10 to assess its own status. The microcontroller 20 further
is adapted to communicate information regarding operation of the
fan module 10 to the infrastructure controller 50 to facilitate
efficient and quiet cooling provided by the fan 12 to the
electronics equipment 60. The microcontroller 20 can reduce power
consumption and noise generation by the fan module 10, and can
increase reliability of the fan 12, optimizing the fan 12 to
operate at a level adequate to ensure adequate cooling of the
electronics equipment 60 rather than having to operate at a margin
of safety above such a level.
[0011] Precise Speed Control.
[0012] In order to optimize fan module performance, the
microcontroller 20 includes a feedback control loop and a speed
control algorithm for precisely regulating the rotational speed of
the motor 14. In one embodiment, a DC motor is used and motor speed
is controlled by pulse-width modulation (PWM). The speed is
controlled to a target speed that can be a preprogrammed speed, a
speed setpoint received from the infrastructure controller 50, or a
default speed at which the fan motor 14 operates in the event of a
communication failure between the infrastructure controller 50 and
the fan module 10. The default speed can be the most recent target
speed received from the infrastructure controller 50 or a preset
default speed stored in the memory 28 of the microcontroller 20.
The control loop detects the actual rotational speed of the motor
14 as measured or sensed by the speed sensor 30 and the algorithm
compares the actual speed to the target speed. The motor rotational
speed can be measured periodically over various time spans
depending on the accuracy of control required. When the measured
speed of the motor 14 deviates from the target speed by at least a
preset tolerance, the algorithm adjusts the control signal to the
motor 14 to cause the actual motor speed to approach the target
speed. Accurate speed control is used to improve power usage and
reliability by causing a fan motor 14 to operate only as fast as
necessary to achieve the required cooling.
[0013] Speed control can also be accomplished by using a thermal
sensor (not shown) measuring fan inlet air temperature changes that
may be caused by changes to the ambient conditions of the room or
loading of the electronic equipment in the enclosure. A target
speed can be set based on the fan inlet temperature detected by the
thermal sensor. In one example, if the ambient temperature becomes
too high (e.g., the room air conditioning fails), the fan can
accelerate to a higher speed as required. In another example, if an
electrical short causes a visual thermal event (i.e., a fire), the
fan can shut down and allow the event to extinguish itself (since
most materials in the electronics enclosure are rated to stop
burning) rather than aggravating the fire by providing additional
air.
[0014] In one embodiment, an external crystal oscillator is used to
ensure an accurate time base for motor speed measurements. The
speed control algorithm can contain optimizations to handle large
changes in motor speed settings by attempting to estimate the
correct PWM setting for a given motor speed, thereby achieving the
target speed faster by making fewer incremental steps. Optimization
of the speed control algorithm is particularly useful in the event
that the motor speed or target speed changes by a large amount in a
short period of time.
[0015] Avoidance of Natural and Beat Frequencies.
[0016] Providing precise speed control of the motor 14 enables the
fan module 10 to avoid natural vibration frequencies. All devices
with rotating components, including the fan 12 and fan module 10,
have natural vibration frequencies at certain speeds, and often
these speeds fall within the range of normal operation. If the
device is operated at such speeds, the natural vibration
frequencies can cause not only vibrations but also acoustic noise.
These natural vibration frequencies can be readily determined,
either by theoretical or empirical methods, and correlated with
motor speeds, based at least in part on the characteristics of the
motor 14, the fan blade 16, and the fan module 10. In an
embodiment, speed avoidance data is stored in tables in the memory
28 of the microcontroller 20. The data tables (generally expressed
in RPM) establish speed avoidance zones within a predetermined band
around each of the natural vibration frequencies. The speed
avoidance zone data can be stored in the microcontroller 20 or can
be communicated to the microcontroller 20 from the infrastructure
controller 50. The microcontroller 20 does not permit the fan 12 to
operate within any of the speed avoidance zones. Instead, when
cooling requirements call for a speed within a speed avoidance
zone, the microcontroller 20 sends the fan motor 14 a speed
setpoint that is slightly above or below the prohibited zone, in
order to maintain sufficient cooling flow while minimizing power
used by the motor 14. The speed setpoint can be outside the
avoidance zone by a percentage of the target speed or by a fixed
number of RPM, depending on the characteristics of the fan. In one
embodiment, the microcontroller 20 controls the fan motor 14 to
operate at a speed approximately 100 RPM above or below the speed
avoidance zone.
[0017] A system 100 may comprise two or more fan modules 10
operating in conjunction to cool an electronics enclosure 60, as
shown in FIG. 2. Whenever two similarly sized fans 12 operate
nearby each other at similar speeds, there is a potential for beat
frequencies to occur. As an extension of the speed avoidance
tables, additional speed avoidance zones can be created to avoid
such beat frequencies. As with the individual speed avoidance
zones, when a target speed is provided to a microcontroller 20 to
operate a fan 12 in one of the beat frequency speed avoidance
zones, the microcontroller 20 automatically adjusts the rotational
speed of the fan 12 to be slightly above the prohibited range in
order to prevent unwanted tone resonance and beat frequencies while
still achieving at least the minimum speed required to provide
proper cooling.
[0018] Locked Rotor Protection.
[0019] In one embodiment, the fan motor 14 is a conventional DC
motor having a stator and a rotor, wherein the fan blade 16 spins
along with the rotor while the stator remains stationary with
respect to the remainder of the fan 12. If the rotor locks up, the
fan blade 16 will not spin and the fan 12 will not be able to
deliver cooling. Additionally, a locked rotor can damage the fan
12. There are at least four possible types of locked rotor events
that prevent the fan 12 from rotating when it is instructed to
rotate by the microcontroller 20: lock-up at startup, lock-up while
running at constant speed, lock-up during speed changes, and
partial lock-up that creates a drag but does not completely stop
the fan blade from spinning. Typically, these events occur when the
fan blade 16 is blocked from running due to loose cables or other
objects obstructing the fan 12 in one way or another, or due to
debris or wear in the bearings of the motor 14.
[0020] Some fans in the industry use Hall effect sensors (which
sense proper commutation of the motor) to detect situations when a
fan is commanded to run but the fan blade or impeller is not
spinning as it should. However, in an embodiment in which the fan
module 10 is packaged into a very small volume, there is
insufficient space for Hall effect sensors. In other embodiments,
it may be cost-prohibitive to use Hall effect sensors. Therefore,
in order to detect a locked rotor event, the microcontroller 20
employs a speed sensor 30 capable of detecting back electromotive
force voltage (back EMF) and correlating the back EMF with fan
speed. When the back EMF sensor 30 detects a locked rotor event
based on back EMF, a failure alert is generated by the
microcontroller 20 and a motor restart sequence is initiated. In an
embodiment, the microcontroller 20 is a PIC and this functionality
is accomplished by code on the PIC, combined with hardware
circuitry. In another embodiment, the microcontroller 20 uses
hardware circuitry alone.
[0021] Back EMF voltages are tabulated or stored in the memory 28
of the microcontroller 20 for known operating conditions when the
fan 12 is operating normally, so they can be compared with voltages
measured at various actual operating conditions to detect whether
the actual operating conditions have deviated by at least a
threshold amount outside normal ranges. The threshold amount can be
specified as a percentage of the target speed or as a fixed number
of RPM. If such a deviation is detected by the speed sensor 30, a
comparator in the microcontroller 20 triggers a restart of the
motor 14. Alternatively, the microcontroller 20 can sample the back
EMF voltages detected by the speed sensor 30 and code can be used
to determine whether the voltage value is normal or abnormal. If
abnormal, the microcontroller 20 can instruct the motor 14 to shut
down and restart.
[0022] In one embodiment, the time to detect a locked rotor
condition is dependent upon the target speed of the fan 12, ranging
from about 1 second at a high target speed to about 6 seconds at a
low target speed. During a shut down and restart, the fan 12 is
turned off for about 7 seconds and takes an additional 3-4 seconds
to restart. To prevent overheating of the motor 14, the number of
restart cycles can be limited, and an alert created when the limit
is reached to indicate that the fan 12 needs inspection and/or
replacement.
[0023] Speed Brake.
[0024] Rotating devices such as cooling fans can be dangerous to
maintenance or repair personnel. In particular, high performance
cooling fans such as the fan 12 can operate at speeds of 18,000 RPM
or higher. Therefore, the fan 12 is provided with an electronic
speed brake to stop the fan blade 16 from rotating within about one
second after when power is removed from the motor 14 or the module
10 is removed, thereby significantly reducing the chance that a
service person, tool, or other object will contact rotating fan
blades during servicing and/or removal of the fan 12 and/or the fan
module 10. The electronic speed brake functions as follows. After
power is removed from the motor 14, the voltage sensor 34 senses or
detects a corresponding voltage drop indicative of the removal of
power. When a predetermined threshold drop in voltage is reached,
the microcontroller 20 simultaneously energizes all motor phases,
causing the sequenced commutation to stop substantially immediately
and thus substantially immediately stopping the fan blades from
rotating.
[0025] Autonomous Operation.
[0026] In one embodiment, the fan module 10 operates autonomously
and has intelligence keep the fan 12 running to cool the system
even when the microcontroller 20 does not receive a target speed
signal from the infrastructure controller 50. Once the fan 12 has
been instructed to operate at a rotational speed or RPM setpoint,
the fan module 10, through the microcontroller 20 or PIC, is
capable of controlling and monitoring its own performance.
Therefore, the fan module 10 will maintain the speed of the fan 12
at a target speed. The target speed can be provided by the
infrastructure controller 50 or can be stored in the memory 28 of
the microcontroller 20.
[0027] If the fan 12 is unable to reach or maintain the target
speed, the microcontroller 20 communicates an alert signal to the
infrastructure controller 50. By having this intelligence built
into the fan module 10 as opposed to being centralized in the
infrastructure controller 50, the fan 12 can operate to cool the
electronics enclosure 60 if the infrastructure controller 50 is not
operating or if the fan module 10 loses communication with the
infrastructure controller 50. Also, because some electronics
enclosures 60 have ten or more cooling fan modules 10, intelligence
built into the fan module 10 reduces the computational loading on
the infrastructure controller 50.
[0028] Sequenced and Gradual Startup.
[0029] In a system 100 including multiple fan modules 10, starting
two or more fans 12 simultaneously at a desired setpoint speed
could result in undesirable power surges. To avoid such power
surges, the microcontroller 20 can implement various strategies. In
one embodiment, the fans 12 can be started up sequentially. In
another embodiment, the fans 12 can be started up at a relatively
low speed and then gradually ramped up to the setpoint speed. In
yet another embodiment, the fans 12 can be started up sequentially
at a relatively low speed and then each fan gradually ramped up to
the setpoint speed.
[0030] Fan Failure Indicator.
[0031] The fan module 10 can include at least one colored light
emitting diode (LED) to indicate status conditions of the fan 12.
In an embodiment, a green LED 22 and an amber LED 24 are connected
to the microcontroller 20. When the fan module 10 is off, i.e., no
power is being delivered to the fan 12 and the microcontroller 20
has not been instructed to operate the fan 12, neither LED 22, 24
is illuminated. When power is on and the fan 12 is operating
normally, i.e., within a preset range of a target speed, the green
LED 22 is illuminated. The present range can be bounded by a
percentage of the target speed or by a number of RPM above and/or
below the target speed, and can be provided by the infrastructure
controller 50 or stored in the memory 28 of the microcontroller 20.
When the fan 12 fails to operate, the amber LED 24 is illuminated.
Circuitry is included to keep the LED 24 illuminated amber in the
event of loss of programming to the microcontroller 20 or corrupted
microcontroller memory 28 to help distinguish and diagnose this
failure scenario. When an error condition is present that does not
prevent the fan 12 from operating, the amber LED 24 blinks. Error
conditions can include, but are not limited to, the fan module 10
being installed in an incorrect location, a loss of communication
from the infrastructure controller 50 to the fan module 10 (i.e.,
to the microcontroller 20), and receipt of an override signal.
Blinking the amber LED 24 to indicate such conditions helps to
diagnose problems prior to an indication from the infrastructure
controller 50 of a more serious condition, such as insufficient
cooling being provided to the electronics enclosure 60.
[0032] Because the microcontroller 20 has the ability to measure
both speed of the motor 14 and power drawn by the motor 14, a
pre-failure alert can be provided when the microcontroller 20
detects a deviation from the expected relationship between fan
speed and power. Such a deviation could be due to bearing wear,
debris build-up at the fan inlet, or other conditions requiring
attention. Similarly, one or more temperature sensors can be used
on the motor 14 to detect deviations from expected normal operating
temperatures that can be indicative of impending motor failure.
[0033] Interactive Communication.
[0034] In one embodiment, the interface 40 is a bi-directional
interface through which the fan module 10 can exchange
communications with the infrastructure controller 50 via a primary
communication link 70. Through the interface 40, the
microcontroller 20 communicates operational and other information
to enable optimization of fan performance or diagnosis of problems
within the fan module 10 in the event of an error condition or
failure. The infrastructure controller 50 can instruct the
microcontroller 20 to operate the fan 12 at a target rotational
speed. Further, the infrastructure controller 50 can read status
parameters of the fan 12, as collected by the microcontroller 20
through its various sensors, such as the motor speed and the
voltage and current being supplied to the motor 14. The
infrastructure controller 50 can also read static and dynamic data
stored in the memory 28 of the microcontroller 20. Static data can
include identifying information such as spare part numbers, serial
numbers, and date of manufacture, as well as operational
information such as power-on speed and override PWM setting.
Dynamic data can include information such as total hours of motor
operation, total revolutions of motor operation, and logged
failures or error events (e.g., locked rotor restarts). The
infrastructure controller 50 can update the stored data to affect
operation of the fan 12, for example to update the speed zone
avoidance data and overall speed range settings.
[0035] Power Circuit and Overcurrent Protector.
[0036] The microcontroller 20 includes a power sensing circuit 38
to measure the power being consumed by the fan 12, thereby enabling
the infrastructure controller 50 to monitor and effectively
allocate power to the various fan modules 10. The power circuit 38
computes power based on measurements from the voltage sensor 34 and
the current sensor 36, and reports dynamic power consumption to the
infrastructure controller 50, which tracks power allocation. In
addition the power circuit 38 can be used to monitor for impending
failures due to bearing wear in the fan motor 14, i.e., to provide
a pre-failure notification when the motor 14 is drawing more power
than it should for a specified rotational speed.
[0037] Conventional power circuits use a "one time" fuse that blows
if a threshold current is exceeded. When such a fuse blows, any
equipment powered through that fuse ceases to function until the
fuse is replaced. In the disclosed embodiment, the power sensing
circuit 38 monitors power levels. If the power circuit 38
determines that current being drawn by the fan module 10 is too
close to a predetermined shutdown threshold, an overcurrent
protector 39 shuts off power while preventing damage to itself. The
microcontroller 20 is then able to reset and restart the fan 12,
avoiding the need for hardware repair resulting from a high current
condition.
[0038] Redundant Communication Channels.
[0039] In one embodiment, the interface 40 in the fan module 10
uses a bus architecture to provide a communication link 70 to the
infrastructure controller 50. In particular, an I2C bus may be
used. If the communication link 70 is broken, an alternate signal
path 75 is provided from the interface 40 to the infrastructure
controller 50. Thus, in the event that the infrastructure
controller 50 and interface 40 cannot communicate with one another,
the infrastructure controller 50 automatically switches over to the
alternate signal path and causes the microcontroller 20 to perform
a self diagnostic recovery reset, which in most cases will restore
the bus communication link 70 from the infrastructure controller 50
to the interface 40.
[0040] As shown in the embodiment illustrated in FIG. 2, a system
100 comprising three fan modules 10 is provided. Any number of fan
modules 10 can be provided in a system 100. Because each fan module
10 has an independent microcontroller 20, the fans 12 can be
individually controlled to allow fine cooling control and to avoid
large current surges caused by changing power states on all fans 12
simultaneously. An infrastructure controller 50 provides control
signals to each fan module 10. The fan modules 10 are supplied with
48 VDC and the speed of each fan motor 14 is controlled by a
pulse-width modulated (PWM) 5 VDC signal operating at 20 kHz. The
speed sensor 30 in each fan module 10 produces a tachometer signal
which is used by the microcontroller 20 to determine rotational
speed, and cooling capacity can be inferred from the tachometer
signal based on the speed versus airflow characteristics of the fan
blade 16. In an embodiment, the tachometer signal is produced as an
open collector square wave signal four times per revolution of the
fan motor 14. If no control signal is received by a particular fan
module 10, that module 10 instructs the fan 12 to spin at a default
speed. The default speed can be stored in the memory 28 of the
microcontroller 20 or can be the most recent target speed provided
by the infrastructure controller 50. Each microcontroller 20
generates a fault signal if any one of a number of "error"
conditions occurs, and the fault signal is communicated to the
infrastructure controller 50 through an interface 40 in the fan
module 10.
[0041] When installed, each fan module 10 drives a presence signal
low, so that if the fan module 10 loses connection with the
infrastructure controller 50, the presence signal will go high and
the infrastructure controller will be alerted. Each fan module 10
preferably carries in the memory 28 of the microcontroller 20 a
unique identifying information (e.g., model and serial numbers) to
facilitate tracking of individual fan modules 10. Each fan module
memory 28 also records operating characteristics of the fan 12 and
stores pre-failure warranty information.
* * * * *