U.S. patent application number 13/570907 was filed with the patent office on 2013-02-14 for controlling air movers based on acoustic signature.
This patent application is currently assigned to QUALCOMM Incorporated. The applicant listed for this patent is Farshid Aryanfar, Donald R. Mullen. Invention is credited to Farshid Aryanfar, Donald R. Mullen.
Application Number | 20130037620 13/570907 |
Document ID | / |
Family ID | 47676907 |
Filed Date | 2013-02-14 |
United States Patent
Application |
20130037620 |
Kind Code |
A1 |
Aryanfar; Farshid ; et
al. |
February 14, 2013 |
CONTROLLING AIR MOVERS BASED ON ACOUSTIC SIGNATURE
Abstract
In a system that employs multiple air movers (e.g., fans) within
an enclosure, the air movers are controlled in an attempt to
optimize cooling efficiency of the system. In some aspects, current
cooling efficiency is indicated based on one or more
characteristics of an acoustic signature in the enclosure. In
particular, a reduction in cooling efficiency may be indicated by
spreading of an acoustic peak of the acoustic signature.
Accordingly, improved cooling efficiency may be achieved by
controlling the air movers in a manner that reduces spreading of
such an acoustic peak.
Inventors: |
Aryanfar; Farshid; (Allen,
TX) ; Mullen; Donald R.; (Mountain View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Aryanfar; Farshid
Mullen; Donald R. |
Allen
Mountain View |
TX
CA |
US
US |
|
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
47676907 |
Appl. No.: |
13/570907 |
Filed: |
August 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61522696 |
Aug 12, 2011 |
|
|
|
Current U.S.
Class: |
236/49.3 ;
454/256 |
Current CPC
Class: |
G06F 1/206 20130101;
F24F 2130/40 20180101; G06F 1/20 20130101 |
Class at
Publication: |
236/49.3 ;
454/256 |
International
Class: |
F24F 11/04 20060101
F24F011/04; F24F 7/007 20060101 F24F007/007 |
Claims
1. A control apparatus for controlling a plurality of fans in an
enclosure, comprising: a receiver circuit to receive signals
representative of an acoustic signature due to interaction of the
fans in the enclosure; and a control circuit to generate control
signals based on the received signals, wherein the control signals
control the fans to reduce spreading of at least one acoustic peak
of the acoustic signature.
2. The apparatus of claim 1, wherein the received signals are
generated by at least one acoustic transducer in the enclosure.
3. The apparatus of claim 2, wherein: the receiver circuit receives
a series of other signals generated by the at least one acoustic
transducer over time; the other signals are representative of other
acoustic signatures due to other interactions of the fans; and the
control circuit adjusts at least one of the control signals based
on the received other signals.
4. The apparatus of claim 3, wherein the other signals are received
continuously.
5. The apparatus of claim 1, wherein the received signals are
generated by at least one microphone in the enclosure.
6. The apparatus of claim 1, wherein the received signals are
generated by at least one pressure transducer in the enclosure.
7. The apparatus of claim 1, wherein: the generation of the control
signals comprises generating frequency spectrum information based
on the received signals; and the frequency spectrum information
represents the acoustic signature.
8. The apparatus of claim 7, wherein the at least one acoustic peak
of the acoustic signature comprises a peak of the frequency
spectrum information, and wherein the generation of the control
signals comprises: identifying a spread of the peak of the
frequency spectrum information; and adjusting at least one of the
control signals to reduce the spread of the peak of the frequency
spectrum information.
9. The apparatus of claim 1, wherein: the fans induce air flows in
the enclosure; rotational speeds of the fans are modulated due to
interaction of the air flows with the fans, thereby causing the
spreading; and the control signals change the rotational speeds of
the fans to reduce the modulation.
10. The apparatus of claim 1, wherein: the fans induce air flows in
the enclosure; rotational speeds of the fans are modulated due to
interaction of the air flows with the fans, thereby causing the
spreading; and the control signals change at least one relative
phase between at least two of the fans to reduce the
modulation.
11. The apparatus of claim 1, further comprising a second receiver
circuit to receive other signals indicative of temperature in the
enclosure, wherein the generation of the control signals is further
based on the received other signals.
12. The apparatus of claim 1, further comprising a second receiver
circuit to receive other signals indicative of rotational speeds of
the fans, wherein the generation of the control signals is further
based on the received other signals.
13. The apparatus of claim 12, wherein the generation of the
control signals limits the rotational speeds of the fans to be
within at least one defined range of rotational speeds.
14. The apparatus of claim 1, further comprising a second receiver
circuit to receive other signals relating to operation of the fans,
wherein the generation of the control signals is further based on
the received other signals.
15. The apparatus of claim 14, wherein the other signals relating
to the operation of the fans comprise at least one of the group
consisting of: signals indicative of power supplied to the fans,
signals indicative of current supplied to the fans, and signals
indicative of voltage supplied to the fans.
16. The apparatus of claim 1, wherein the acoustic signature
comprises fan blade passing noise.
17. The apparatus of claim 1, wherein the acoustic signature
comprises noise resulting from interactions of air flows induced by
the fans.
18. The apparatus of claim 1, wherein the enclosure comprises a
housing for a computing system.
19. The apparatus of claim 1, wherein the enclosure comprises: a
housing for the fans, a housing for a personal computer, or a
housing for a computer server.
20. The apparatus of claim 1, wherein the control circuit employs
an optimization algorithm that uses information derived from the
received signals to maintain the spreading within a defined target
value.
21. The apparatus of claim 1, wherein the apparatus comprises an
integrated circuit.
22. A method for controlling a plurality of fans in an enclosure,
comprising: receiving signals representative of an acoustic
signature due to interaction of the fans in the enclosure; and
generating control signals based on the received signals, wherein
the control signals control the fans to reduce spreading of at
least one acoustic peak of the acoustic signature.
23. The method of claim 22, wherein the received signals are
generated by at least one acoustic transducer in the enclosure.
24. The method of claim 23, further comprising: receiving a series
of other signals generated by the at least one acoustic transducer
over time, wherein the other signals are representative of other
acoustic signatures due to other interactions of the fans; and
adjusting at least one of the control signals based on the received
other signals.
25. The method of claim 24, wherein the other signals are received
continuously.
26. The method of claim 22, wherein the received signals are
generated by at least one microphone in the enclosure.
27. The method of claim 22, wherein the received signals are
generated by at least one pressure transducer in the enclosure.
28. The method of claim 22, wherein: the generation of the control
signals comprises generating frequency spectrum information based
on the received signals; and the frequency spectrum information
represents the acoustic signature.
29. The method of claim 28, wherein the at least one acoustic peak
of the acoustic signature comprises a peak of the frequency
spectrum information, and wherein the generation of the control
signals comprises: identifying a spread of the peak of the
frequency spectrum information; and adjusting at least one of the
control signals to reduce the spread of the peak of the frequency
spectrum information.
30. The method of claim 22, wherein: the fans induce air flows in
the enclosure; rotational speeds of the fans are modulated due to
interaction of the air flows with the fans, thereby causing the
spreading; and the control signals change the rotational speeds of
the fans to reduce the modulation.
31. The method of claim 22, wherein: the fans induce air flows in
the enclosure; rotational speeds of the fans are modulated due to
interaction of the air flows with the fans, thereby causing the
spreading; and the control signals change at least one relative
phase between at least two of the fans to reduce the
modulation.
32. The method of claim 22, further comprising receiving other
signals indicative of temperature in the enclosure, wherein the
generation of the control signals is further based on the received
other signals.
33. The method of claim 22, further comprising receiving other
signals indicative of rotational speeds of the fans, wherein the
generation of the control signals is further based on the received
other signals.
34. The method of claim 33, wherein the generation of the control
signals limits the rotational speeds of the fans to be within at
least one defined range of rotational speeds.
35. The method of claim 22, further comprising receiving other
signals relating to operation of the fans, wherein the generation
of the control signals is further based on the received other
signals.
36. The method of claim 35, wherein the other signals relating to
the operation of the fans comprise at least one of the group
consisting of: signals indicative of power supplied to the fans,
signals indicative of current supplied to the fans, and signals
indicative of voltage supplied to the fans.
37. The method of claim 22, wherein the acoustic signature
comprises fan blade passing noise.
38. The method of claim 22, wherein the acoustic signature
comprises noise resulting from interactions of air flows induced by
the fans.
39. The method of claim 22, wherein the enclosure comprises a
housing for a computing system.
40. The method of claim 22, wherein the enclosure comprises: a
housing for the fans, a housing for a personal computer, or a
housing for a computer server.
41. The method of claim 22, wherein the generation of the control
signals comprises employing an optimization algorithm that uses
information derived from the received signals to maintain the
spreading within a defined target value.
42. A control apparatus for controlling a plurality of fans in an
enclosure, comprising: means for receiving signals representative
of an acoustic signature due to interaction of the fans in the
enclosure; and means for generating control signals based on the
received signals, wherein the control signals control the fans to
reduce spreading of at least one acoustic peak of the acoustic
signature.
43. A control system for a plurality of fans in an enclosure,
comprising: at least one transducer to generate signals
representative of an acoustic signature due to interaction of the
fans in the enclosure; a receiver circuit to receive the signals
from the at least one transducer; and a control circuit to generate
control signals based on the received signals, wherein the control
signals control the fans to reduce spreading of at least one
acoustic peak of the acoustic signature.
44. A computer-program product for controlling a plurality of fans
in an enclosure, comprising: computer-readable medium comprising
code for causing a computer to: receive signals representative of
an acoustic signature due to interaction of the fans in the
enclosure; and generate control signals based on the received
signals, wherein the control signals control the fans to reduce
spreading of at least one acoustic peak of the acoustic signature.
Description
CLAIM OF PRIORITY
[0001] This application claims the benefit of and priority to
commonly owned U.S. Provisional Patent Application No. 61/522,696,
filed Aug. 12, 2011, the disclosure of which is hereby incorporated
by reference herein.
BACKGROUND
[0002] Some computing systems enclosures employ multiple air movers
(e.g., fans) to provide air flow cooling for the system. For
example, a typical personal computer includes a power supply fan,
one or more processor fans, and an exhaust fan. As another example,
a server system typically includes one or more fans for each rack
of the server system.
[0003] In such systems, the control setting for a given fan is
commonly selected based on a temperature measurement associated
with that fan. For example, the operating speed of a fan associated
with a processor is generally controlled based on the temperature
at that processor. As another example, the operating speed of an
exhaust fan is generally controlled based on air temperature
readings within the enclosure or, in some cases, on inlet ambient
air temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Sample features, aspects and advantages of the disclosure
are described in the detailed description and appended claims that
follow and the accompanying drawings, wherein:
[0005] FIG. 1 is a simplified diagram of an embodiment of a system
including an apparatus for controlling fans in accordance with the
teachings herein;
[0006] FIG. 2 is a flowchart of an embodiment of operations for
controlling fans in accordance with the teachings herein;
[0007] FIG. 3 is a simplified diagram that illustrates sample fan
interactions and an embodiment of an apparatus for controlling fans
in accordance with the teachings herein;
[0008] FIGS. 4A and 4B are simplified graphs illustrating a
theoretical example of an effect that fan interaction has on an
acoustic signature;
[0009] FIG. 5 is a flowchart of an embodiment of operations for
reducing spreading of an acoustic peak of a frequency spectrum in
accordance with the teachings herein;
[0010] FIG. 6 is a flowchart of an embodiment of operations for
controlling fans based on signals from multiple transducers in
accordance with the teachings herein;
[0011] FIG. 7 is a simplified block diagram of an embodiment of a
system employing an optimization algorithm for controlling fans in
accordance with the teachings herein;
[0012] FIG. 8 is a simplified diagram of an embodiment of a system
including a housing for multiple fans; and
[0013] FIG. 9 is a simplified diagram of an embodiment of a server
system including multiple fans.
[0014] In accordance with common practice, the various features
illustrated in the drawings are typically not drawn to scale.
Accordingly, the dimensions of the various features are arbitrarily
expanded or reduced for clarity in some cases. In addition, the
drawings are typically simplified for clarity. Thus, the drawings
will generally not depict all of the components of a given
apparatus or method. Finally, like reference numerals are used to
denote like features throughout the specification and figures.
DETAILED DESCRIPTION
[0015] The disclosure relates in some aspects to controlling
multiple air movers in a manner that improves cooling efficiency of
a system. In general, cooling efficiency tends to be higher when
there are minimal interactions between the air movers since the air
movers support a more balanced air flow in this case. For example,
a more balanced air flow will occur when air flows from different
air movers are substantially in phase and, hence, constructive. In
contrast, cooling efficiency tends to be lower when undesirable
interactions between the air movers result in less balanced air
flow in the system. For example, unbalanced air flow will occur
when air flows from different air movers are out of phase and,
hence, destructive. In some embodiments, these different conditions
are identified by using one or more transducers to acquire spectral
information associated with air flow in an enclosure. Here, a more
narrowband acoustic spectrum is expected when there is minimal
interaction between the air movers, while a wider acoustic spectrum
is expected when there is more air mover interaction. Thus, cooling
efficiency may be improved in such a system by controlling the air
movers in a manner that results in a narrower acoustic spectrum.
For purposes of illustration, several embodiments are described
below in the context of a fan control system. It should be
appreciated, however, that the teachings herein may be applicable
to other types of air movers as well.
[0016] FIG. 1 illustrates an embodiment of a control circuit 102
for controlling several fans 104 in an enclosure 106. In a typical
implementation, the enclosure 106 comprises a housing for a
computing system as discussed in more detail below. The control
circuit 102 receives transducer signals 108 from one or more
transducers 110 and processes these signals to generate control
signals 112 that control the fans 104.
[0017] The transducer signals 108 are representative of acoustic
signatures in the enclosure 106. For example, in some embodiments,
each transducer 106 comprises a microphone that detects sound such
as fan noise within the enclosure 106. The signals generated by the
microphone are thus representative of one or more characteristics
of the sound in the enclosure 106. Such a characteristic may
comprise a frequency spectrum, an amplitude spectrum, or some other
acoustic-related quality.
[0018] Different fan operating conditions will result in different
acoustic signatures in the enclosure 106. In particular, the
acoustic signature generally changes when the loading on a fan
changes (e.g., when there is a change in the rotational speed
and/or air flow of one or more of the fans 104). For example, a
frequency spectrum associated with noise from a given fan will
generally have a peak corresponding to the blade passing frequency
of the fan and smaller peaks corresponding to harmonics of the
blade passing frequency. As the rotational speed of the fan
changes, a corresponding shift occurs in the blade passing
frequency which results in a shift in the locations of the peaks in
the frequency spectrum.
[0019] In accordance with the teachings herein, the control circuit
102 controls the fans 104 to reduce spreading of at least one
acoustic peak of an acoustic signature represented by the
transducer signals 108. For example, air flow generated by a first
fan 104 will interact with (e.g., affect the loading on) a second
fan 104 under certain conditions. This fan interaction is
undesirable in cases where it causes the fans to work against one
another rather than with one another to move air through the
system. However, such an undesirable fan interaction may be
evidenced by spreading of one or more acoustic peaks in an acoustic
signature generated under these conditions. Such spreading is
caused, for example, by modulation of the loading on a given fan as
a result of the fan interaction. In such a case, as the rotational
speed and/or air flow of the fan shifts over time (e.g., within a
certain range) due to the loading modulation, the acoustic peaks of
the corresponding frequency spectrum will spread by a corresponding
amount.
[0020] Accordingly, the control circuit 102 generates the control
signals 112 in a manner that tends to reduce this spreading. For
example, by controlling one or more of the frequency, voltage, or
phase of the control signals, the operating point (e.g., rotational
speed and/or phase) of one or more of the fans 104 is adjusted to
reduce the undesirable fan interactions. By subsequently analyzing
the peak spread of a later acquired acoustic signature, the control
circuit 102 can determine whether the adjustment of the control
signals did in fact reduce the fan interactions. Through the use of
this scheme, the control circuit 102 controls the fans 104 so that
they more effectively work together to move air through the system.
Thus, cooling efficiency in the system may be improved since the
fans 104 may use less power to provide the desired level of
cooling. In addition, fan-related noise in the system may be
reduced in some cases due to more efficient fan operation.
[0021] Advantageously, the fan control scheme of FIG. 1 can
dynamically adapt to changes that affect air flow in the system
over time. For example, optimum air flow in a system is generally a
function of one or more factors including fan speed, physical
orientation of the fans, the design of the system enclosure, air
filters, screens, or fan impeller/housing design. In the event
there is a change in any of these factors that adversely affects
the aerodynamics in the enclosure 106, this change is automatically
detected (e.g., by detecting spreading of an acoustic peak) and
then compensated for by adjusting fan control signals as taught
herein. For example, in a system that includes general purpose and
graphics processors, the loading on different processor fans will
be different and will change over time due to changes in the
temperatures of the processors. Since the fan control scheme of
FIG. 1 is able to detect and respond to these types of changes,
this fan control scheme may provide better cooling efficiency as
compared to a system where the fan control settings are fixed for a
specific system configuration, system impedance, and speed
range.
[0022] Furthermore, the fan control scheme of FIG. 1 provides a
relatively straightforward way of accounting for the complex system
enclosure impedance, air flow impedance, and air flow interaction
that result from the use of multiple fans. Accordingly, the fan
control scheme of FIG. 1 may provide better cooling efficiency as
compared to a system where each fan is independently
controlled.
[0023] The control circuit 102 optionally generates the control
signals 112 based on signals 118 received from one or more
transducers 120. As discussed in more detail below, in some
implementations, the control signals are generated based on one or
more of: inlet ambient air temperature, temperature in the
enclosure, rotational speed of one or more of the fans 104, power
supplied to one or more of the fans 104, current supplied to one or
more of the fans 104, or voltage supplied to one or more of the
fans 104. Accordingly, each transducer 120 will be of a suitable
type to provide the desired information. In an implementation that
employs more than one transducer 120, two or more of the
transducers 120 may be of the same type or different types.
[0024] The components of FIG. 1 may be implemented in various ways
in different embodiments. For example, the control circuit 102 may
be implemented in an integrated circuit (e.g., an application
specific integrated circuit (ASIC)) configured to provide the
desired functionality, a processor (e.g., a digital signal
processor (DSP) or general purpose processor) that executes code to
provide the desired functionality, a state machine, analog
circuitry, some other suitable circuitry, or some combination of
the above. The processing of the received signals 108 to provide
the control signals 112 may thus be performed in the digital domain
(e.g., a DSP configured to perform a fast Fourier transform (FFT)
function) and/or in the analog domain (e.g., an analog circuit
configured to perform an FFT function).
[0025] In the example of FIG. 1, the transducer signals 108 are
received via a receiver circuit 114 and passed to the control
circuit 102, and the signals 118 are received via a receiver
circuit 122 and passed to the control circuit 102. The circuitry
used here depends on the technology employed in a given
implementation. In an implementation where a transducer 110 or 120
outputs analog signals, a receiver circuit 114 or 122 includes, for
example, a buffer, discrete transistors, an amplifier (e.g., an OP
amp), or other suitable circuitry for receiving analog signals. In
an implementation where a transducer 110 or 120 outputs digital
signals, a receiver circuit 114 or 122 includes, for example, a
digital buffer, discrete transistors, a latch, or other suitable
circuitry for receiving digital signals. Here, it should be
appreciated that each receiver circuit 114 or 122 will include
separate receiver components that are coupled to dedicated
transducer signal paths (e.g., discrete wires or printed circuit
board (PCB) traces) in cases where the receiver circuit 114 or 122
is coupled to multiple transducers 110 or 120.
[0026] Also in the example of FIG. 1, a driver circuit 116 drives
the control signals 112 based on signals output by the control
circuit 102. The circuitry used for the driver circuit 116 depends
on the technology employed in a given implementation. In an
implementation where the control circuit 102 outputs digital
signals, the driver circuit 116 includes, for example, a digital
buffer, discrete transistors, a latch, or other suitable circuitry
for receiving digital signals. In an implementation where the
control circuit 102 outputs analog signals, the driver circuit 116
includes, for example, a buffer, discrete transistors, an amplifier
(e.g., an OP amp), or other suitable circuitry for receiving analog
signals.
[0027] The driver circuit 116 also includes circuitry for
outputting the control signals in an appropriate format for
controlling the fans 104. For example, a DC fan is typically
controlled by a pulse width modulation (PWM) signal. Hence, the
driver circuit 116 will be configured to output an appropriate PWM
signal in this case. Conversely, an AC fan is typically controlled
by a variable frequency AC signal. Thus, the driver circuit 116
(e.g., employing a variable frequency inverter) will be configured
to output an appropriate variable frequency signal in this case. It
should be appreciated that the driver circuit 116 typically
includes separate driver components that are coupled to dedicated
signal paths so that each of the fans 104 is controlled in an
independent manner.
[0028] In some implementations, one or more of the circuits 114,
116, or 122 are configured to convert signals from one domain to
another. For example, in some cases, a receiver circuit 114 or 122
includes analog-to-digital conversion circuitry to convert analog
signals from a transducer 110 or 120 to digital signals used by the
control circuit 102. In addition, in some cases, the driver circuit
116 includes digital-to-analog conversion circuitry to convert
digital signals from the control circuit 102 to analog signals that
drive the fans 104.
[0029] The control circuit 102, the receiver circuit 114, the
driver circuit 116, and the receiver circuit 122 may be implemented
separately or within a common apparatus. For example, in various
embodiments, these circuits may be implemented within a single
integrated circuit, implemented on a single PCB, or implemented as
discrete components.
[0030] In some implementations, each transducer 110 comprises an
acoustic transducer (e.g., a microphone) that is capable of
detecting mechanical waves in air or other similar medium. In other
implementations, each transducer 110 comprises or is based on a
static or dynamic pressure transducer.
[0031] A transducer 120 will take different forms depending on the
physical property being measured. In an implementation where the
signals 118 are representative of temperature, a transducer 120
comprises a temperature sensor or some other type of transducer
that is capable of generating signals from which
temperature-related information may be derived. In an
implementation where the signals 118 are representative of
rotational speed of one or more of the fans 104, a transducer 120
comprises a Hall sensor or some other type of transducer that is
capable of generating signals from which fan rotation information
may be derived. In an implementation where the signals 118 are
representative of power, current, or voltage supplied to one or
more of the fans 104, a transducer 120 comprises a power sensor, a
current sensor, a voltage sensor, or some other type of transducer
that is capable of generating signals from which this information
may be derived. In an implementation where the signals 118 are
representative of mechanical vibration, a transducer 120 generates
signals from which mechanical vibration-related information may be
derived.
[0032] To reduce the complexity of FIG. 1, the fans 104, the
transducer(s) 110, and the transducer(s) 120 are each represented
by a single box. In practice, the fans 104 are located at different
locations (e.g., adjacent different processors, exhaust vents,
inlet vents, etc.) to provide air flow at designated locations
within the enclosure 106. Similarly, in an implementation that uses
multiple transducers 110, these transducers are typically located
at different locations to acquire acoustic information from
different places within the enclosure 106. Also, in an
implementation that uses multiple transducers 120, these
transducers are typically located at different locations to acquire
information from different places within the enclosure 106.
[0033] In general, a control circuit will include or have access to
one or more memory storage components for storing one or more of:
data, parameters, executable code, or some other type of
information that is used in conjunction with fan control
operations. For example, in FIG. 1, the control circuit 102
includes a memory device 124.
[0034] FIG. 2 describes a sample embodiment of high-level
operations for controlling fans in accordance with the teachings
herein. This flowchart describes operations that are typically
performed on a repeated basis (e.g., periodically or continually)
in an attempt to maintain optimum air flow within an enclosure
under dynamic operating conditions. It should be appreciated,
however, that these operations also could be employed on a static
basis to provide long-term fan control settings. The operations of
FIG. 2 (or any other operations discussed herein) may be performed
by the components of FIG. 1 or by other suitable components. Also,
one or more of the operations described herein may not be employed
in a given implementation.
[0035] As represented by block 202, at some point in time, signals
representative of an acoustic signature due to interaction of fans
in an enclosure are received. In a typical implementation, these
received signals were generated by one or more acoustic transducers
(e.g., a microphone), each of which is located within the enclosure
or in the vicinity of the enclosure (e.g., adjacent an inlet vent
or an outlet vent).
[0036] As discussed above, the received signals will be analog or
digital signals depending on the particular transducer
implementation. In some cases, analog signals from a transducer are
sampled (e.g., on a periodic or continual basis) by a receiver
circuit and provided to a digital control circuit. In some cases,
analog signals from a transducer are provided on a continual basis
to an analog control circuit via an analog receiver circuit. In
some cases, digital signals from a transducer simply forwarded to a
digital control circuit via a digital receiver circuit.
[0037] As represented by block 204, control signals are generated
(e.g., adjusted) based on the signals received at block 202. In
particular, the control signals are generated in a manner that
controls the fans to reduce the spreading of at least one acoustic
peak of the acoustic signature. For example, upon analyzing the
received signals, it may be determined that spreading of an
acoustic peak has increased relative to spreading identified by a
prior analysis or it may be determined that the spreading of an
acoustic peak exceeds a defined spreading value (e.g., a designated
maximum, a designated range, or some other type of target value).
In such a case, the control signal for one or more of the fans is
adjusted (e.g., by changing the frequency and/or phase of the
signal) in a manner that is expected to decrease undesirable fan
interaction and, hence, decrease the spreading of the acoustic
peak. A more detailed example of the operations of block 204 is
described below in conjunction with FIG. 5.
[0038] As represented by block 206, the fans are driven using the
generated control signals. Typically, different control signals are
used to control different fans. In some implementations, however, a
single control signal is used to control a subset of the fans.
[0039] The manner in which a control signal is controlled to change
the speed of a fan depends of the type of fans being used. For
example, in some implementations, a DC fan is driven via a PWM
signal. Here, the speed of the DC fan is controlled by changing the
width of the pulse output by a driver circuit. As another example,
in some implementations, an AC fan is driven via a variable
frequency AC signal. In this case, the speed of the AC fan is
controlled by changing the frequency (at a motor-specific
volts/hertz ratio) of the AC signal output by a driver circuit
(e.g., based on a control signal from a control circuit).
[0040] The relative phase of two or more fans is controlled, for
example, by temporarily (e.g., instantaneously) changing the speed
of one or more of the fans. Thus, for PWM-based DC fans, the
relative phase of the fans is changed by temporarily adjusting the
pulse width for at least one of the fans. For AC fans, the relative
phase of the fans is changed by temporarily adjusting the frequency
of the AC signal for at least one of the fans.
[0041] The arrow from block 206 to block 202 indicates that the
operations of FIG. 2 are typically repeated to dynamically adjust
the control signals over time. Thus, a series of other signals
(e.g., in the form of a continuous signal) representative of other
acoustic signatures due to other interactions of the fans are
received over time (block 202) and at least one of the control
signals is adjusted over time based on the received other signals
(block 204). In this way, optimum cooling within the enclosure may
be achieved even under dynamic fan loading conditions due to, for
example, changes in processor workload.
[0042] As described in more detail below in conjunction with FIG.
7, in some implementations, the fan control signals are repeatedly
adjusted based on an optimization algorithm. For example, such an
algorithm may employ a brute force scheme, a lookup table-based
scheme, a least mean square-based scheme, or some other suitable
scheme that attempts to keep the spreading to a minimum.
[0043] FIG. 3 illustrates, in a simplified manner, sample fan
interactions that affect spreading of acoustic peaks of an acoustic
signature. In this example, an enclosure 302 for a computing system
is shown as housing a PCB 304, (e.g., including processors, memory
devices, and other integrated circuits, not shown), and fans 306,
308, 310, and 312. To reduce the complexity of FIG. 3, other
components such as power supplies, hard drives, interface circuits,
and so on, that may be housed within the enclosure 302 are not
shown.
[0044] The fans 306, 308, 310, and 312 are installed at designated
locations within the enclosure 302 to provide certain cooling
functions. The fan 306 is positioned adjacent an inlet duct (not
shown) to draw outside air into the enclosure 302. The fan 308 is
positioned adjacent an outlet duct (not shown) to exhaust air from
the enclosure 302. The fans 310 and 312 are positioned over
respective integrated circuits (e.g., processors, not shown)
mounted on the PCB 304 to draw heat away from these integrated
circuits.
[0045] The dashed arrows in FIG. 3 illustrate simplified air flows
that are induced by the operation of the fans 306, 308, 310, and
312. As represented, for example, by the dashed arrows 314, 316,
318, and 320, the air flows induced by different fans interact with
one another in different ways throughout the enclosure 302. In
particular, the air flows will work with one another or against one
another at various locations in the enclosure 302 depending on the
current frequency and phase of the fans.
[0046] Moreover, as represented in a simplified manner by the
dashed arrows 322, 324, and 326, these air flow interactions affect
the operations of the fans under certain conditions. Specifically,
the loading (i.e. static pressure vs. volume air flow) on a given
fan, and hence the rotational speed of the fan, continually changes
as a result of the air flow interactions. For example, an
instantaneous merging of air flows in the same direction (in phase)
will result in an instantaneous change of a combination of air flow
and static pressure. If this air flow is directed toward an inlet
or outlet of a fan (e.g., the fan 308), the loading on the fan will
change and result in an instantaneous change (increase or decrease)
in the fan speed. As another example, an instantaneous merging of
air flows in opposite directions (out of phase) will result in an
instantaneous change in air flow (e.g., a null in some case). For
example, if this occurs near an inlet or an outlet of a fan (e.g.,
the fan 308), the loading on the fan could change and result in an
instantaneous change in the fan speed.
[0047] Such fan interaction may be particularly prevalent in
enclosures for computing systems which tend to be relatively small
(e.g., much smaller than a building), yet have relatively stringent
air flow requirements. For example, enclosures for computer
graphics cards, personal computers, computer servers, and the like
will typically each have several fans that move relatively large
amounts of air to ensure that the electronic components in the
enclosures are protected from overheating.
[0048] Once the air flow interactions within the enclosure 302
achieve a steady state, the loading on a given fan in the enclosure
302 may be modulated by these air flow interactions. That is, due
to the complex nature of the air flow interactions, the loading on
the fan will change within a given range in a repetitive manner
over time. Hence, a modulation of the rotational speed of the fan
is induced by the interaction of the air flows with the fan.
[0049] The modulation of a given fan results in a corresponding
modulation of the blade passing frequency of the fan. The blade
passing frequency is defined as the number of times a fan blade
passes a fan support (e.g., fan strut) in a given period of time
(e.g., one minute). Thus, the blade passing frequency is calculated
based on the current rotational speed of the fan, the number of fan
blades, and the number of fan supports (typically three or four).
As described in more detail below at FIG. 4, a portion of the noise
spectrum generated by a fan corresponds to the blade passing
frequency and harmonics of the blade passing frequency. In some
aspects, this is due to the mechanical action of the fan blades
impacting the air and the moving air in turn hitting the fan
supports.
[0050] In the example of FIG. 3, modulation of the fans 306, 308,
310, and 312 is detected by a microphone 328 that is coupled to a
fan controller 330 (e.g., comprising receiver, control, and driver
circuits embodied in an integrated circuit). As represented in a
simplified manner by the curved dashed lines 332, 334, 336, and 338
in FIG. 3, each of the fans 306, 308, 310, and 312 generates noise
that is detectable by the microphone 328. As discussed above, the
noise from a given fan includes components corresponding to the
blade passing frequency of that fan. Moreover, under certain
conditions, these blade passing frequency components will be
modulated due to the interactions of the fans 306, 308, 310, and
312 as discussed herein.
[0051] Hence, the fan controller 330 can use received signals from
the microphone 328 to detect spreading of these frequency
components that result from an increase in fan modulation caused by
interactions between two or more of the fans 306, 308, 310, and
312. The fan controller 330 then changes the rotational speed
and/or phase of one or more of the fans 306, 308, 310, and 312 to
reduce this modulation and thereby potentially improve the cooling
efficiency of the system.
[0052] FIGS. 4A and 4B depict an example of how such fan modulation
affects the acoustic signature associated with the fan. A waveform
402 in FIG. 4A illustrates, in a simplified manner, an example of
an acoustic signature associated with a fan that is operating
without interactions with other fans. For example, the waveform 402
could correspond to the acoustic signature when the fan is
operating in free space for a given static pressure and airflow. In
contrast, a waveform 404 in FIG. 4B illustrates a simplified
example of an acoustic signature associated with fan operation when
there are undesirable interactions with at least one other fan in
an enclosure.
[0053] The waveform 402 includes several peaks associated with the
blade passing frequency of the fan. The leftmost and highest peak
406 corresponds to the fundamental blade passing frequency of the
fan. The other major peaks correspond to harmonics of the blade
passing frequency. Of note, in the absence of fan interaction, the
peaks of the waveform are relatively "tonal" in nature. That is,
each of the peaks (including peak 406) is associated with a
relatively narrow frequency range.
[0054] In contrast, the peaks of the waveform 404 exhibit spreading
due to modulation of the fan caused by the interactions between the
fans in the enclosure. That is, as mentioned above, the fan
interactions cause each peak associated with the blade passing
frequency to shift slightly over time. As noted above, this
frequency shifting will tend to stay within a small frequency range
once the system achieves a steady state. Hence, the acoustic
signature exhibits spreading of each acoustic peak as shown in the
waveform 404 when there are undesirable interactions between the
fans in the enclosure. For example, a relatively wide peak spread
408 is associated with the fundamental blade passing frequency in
this case.
[0055] The peak spread may be defined in various ways. In some
implementations, the peak spread is defined as the range of
frequencies associated with specified dB points of a peak. For
example, the specified dB points may correspond to the points on
each side of the peak that are the specified number of dB (e.g., 3
dB) down in magnitude from the maximum magnitude of the peak. In
the example of FIG. 4, this magnitude is expressed in terms of
acoustic power. Sound pressure or sound pressure level (SPL) are
alternative measures of this magnitude.
[0056] Based on the teachings herein, it should be understood that
other mechanisms may be employed for optimizing cooling based on
acoustic information from a fan enclosure. For example, in addition
to noise components such as fan blade passing noise (e.g., caused
by fan blades impacting the air), an acoustic signature (e.g.,
collected over a defined period of time) also may include noise
that results from interactions of air flows generated by the fans.
Accordingly, any changes (e.g., spreading) that occur relating to
this noise may be monitored to determine whether and/or how to
adjust the control signals for the fans.
[0057] With the above in mind, sample operations for adjusting fan
control signals will be described in more detail with reference to
the flowcharts of FIGS. 5 and 6. FIG. 5 illustrates an example of
operations for identifying peak spread and adjusting control
signals accordingly. FIG. 6 illustrates an example of operations
for adjusting control signals based on signals received from
different types of transducers.
[0058] Referring initially to FIG. 5, as represented by block 502,
signals are received from one or more transducers. As discussed
above in conjunction with block 202 of FIG. 2, these signals are
representative of an acoustic signature in an enclosure. In an
implementation where the control processing is implemented in the
digital domain, the operations of block 502 involve, for example,
sampling signals received from one or more microphones to generate
a data set that includes data representative of the acoustic
signature.
[0059] As represented by block 504, frequency spectrum information
is generated based on the received signals. For example, the
control processing may employ an FFT algorithm that operates on the
received signals (e.g., a digital data set or analog signals) to
extract frequency components of those signals. Accordingly, a
frequency spectrum representative of the acoustic signature is
obtained.
[0060] As represented by block 506, the spread of at least one peak
of the frequency spectrum is identified. Here, the peaks indicated
by the frequency spectrum information correspond to the acoustic
peaks of the acoustic signature discussed above. In some
implementations, identifying a peak spread from the frequency
spectrum information involves determining the frequency range
associated with the 3 dB points for the fundamental blade passing
frequency and/or some other specified frequency (e.g., a harmonic
of the blade passing frequency). Other techniques for determining a
peak spread may be employed in other cases.
[0061] As represented by block 508, a determination is made as to
whether the peak spread identified at block 506 needs to be
reduced. In some implementations, this involves comparing the
current peak spread value with a prior peak spread value (e.g.,
identified and stored during the last iteration of the algorithm).
If the peak spread has increased, a decision may be made to reduce
the peak spread.
[0062] In some implementations, the determination of block 508
involves comparing the current peak spread value with a target peak
spread. If the peak spread is not within (e.g., less than or equal
to) the target peak spread, a decision may be made to reduce the
peak spread. Such a target value is determined, for example, based
on simulations and/or empirical testing. The resulting value is
then stored in a memory device that is accessible by the control
processing (e.g., the memory device 124 in the control circuit 102
of FIG. 1).
[0063] As represented by block 510, based on the determination of
block 508, at least one of the fan control signals is adjusted to
reduce the peak spread, if applicable. A determination regarding
which control signals are to be adjusted and how those control
signals are to be adjusted may be made in various ways.
[0064] In some implementations, this determination is based on
simulations and/or empirical testing. For example, it may be
determined by such testing that adjusting the relative frequency
and/or phase of certain fans in the enclosure tends to reduce
spreading. As another example, it may be determined that different
fans should be adjusted under different conditions (e.g., different
loading conditions, different temperature conditions, and so
on).
[0065] In some implementations, an iterative process is used to
determine how to adjust the fan control signals. For example, upon
determining that a peak spread is to be reduced, the control signal
for one or more fans is adjusted in a defined manner (e.g., to
increase fan frequency). The operations of blocks 502-508 are then
repeated to determine whether this adjustment resulted in an
increase or a decrease in the peak spread. If the peak spread
decreased, the fan control signals are adjusted in the same manner
as the immediately prior adjustment. If the peak spread increased,
the fan control signals are adjusted in the opposite manner as the
immediately prior adjustment, or are adjusted in some other manner.
In an iterative process, the determination as to which control
signals are to be changed and how those signals are to be changed
(e.g., under certain conditions) may be specified, for example, by
random selection, simulations, or empirical testing.
[0066] The arrow from block 510 to block 502 indicates that the
operations of FIG. 5 are typically repeated to dynamically adjust
the control signals over time. Thus, the peak spread is repeatedly
checked over time to determine whether at least one of the control
signals is to be adjusted.
[0067] As mentioned above, the teachings herein may be employed in
embodiments that use different types of transducers (e.g., not just
acoustic transducers). Referring now to FIG. 6, as represented by
blocks 602 and 604, signals are received from different types of
transducers in this scenario. For example, the signals received at
block 602 correspond to acoustic-based signals (e.g., corresponding
to block 502 of FIG. 5), while the signals received at block 604
are received from one or more transducers that provide information
regarding other operating conditions in the enclosure.
[0068] In a typical implementation, temperature information is
received via a temperature transducer (e.g., a temperature sensor)
that provides signals indicative of temperature at a certain
location in the enclosure. This temperature information is used,
for example, to ensure that each of the fans is operating at a
sufficient speed to achieve the desired cooling at the location of
the temperature transducer (e.g., at a processor).
[0069] In some implementations, fan speed information is received
from at least one transducer that detects the rotational speed of a
fan and generates signals that are indicative of this rotational
speed. In some cases, this type of transducer consists of a fan
speed sensor such as a Hall sensor that is built into the fan. In
other cases, a fan speed sensor is located external to a fan. The
fan speed information is used, for example, to identify the fans
being modulated (e.g., as indicated by repetitive changes in the
fan speed) and to detect the extent of this modulation. Thus, this
information is used in some cases to determine which control
signals are to be adjusted and how these control signals are to be
adjusted.
[0070] In some implementations, fan power-related information is
received from at least one transducer that detects one or more of
power, current, or voltage being supplied to a fan and that
generates signals indicative of each detected parameter. In a
typical case, this type of transducer consists of a power, current,
or voltage sensor that is placed in-line with the fan control
signals. The fan information is used, for example, to identify the
fans being modulated (e.g., as indicated by minute changes in the
fan loading, current draw, or applied voltage) and to detect the
extent of this modulation. Thus, this information can be used to
determine which control signals are to be adjusted and how these
control signals are to be adjusted.
[0071] As represented by block 606 of FIG. 6, at least one of the
fan control signals is adjusted based on the signals received at
blocks 602 and 604. For example, in some cases, the signals
received at block 602 are processed as described above at FIG. 5 to
make an initial determination regarding whether and how to adjust
the control signals. In addition, such an algorithm may take into
account the signals received at block 604 to further verify or
quantify peak spreading.
[0072] As represented by block 608, in some cases, the adjustment
of a control signal is limited based on one or more factors. For
example, the fan speed of one or more fans will typically be
limited to be within a defined rotational speed range depending on
the temperature that is required at specified locations in the
enclosure (e.g., at a processor or at an interior space). Thus, in
some implementations, one or more of the frequency, phase, or some
other parameter of the control signals is selected to meet a
defined temperature profile. This limiting of the control signal
adjustment is based, for example, on received temperature signals
and, optionally, received fan speed signals.
[0073] The arrow from block 608 to block 602 indicates that the
operations of FIG. 6 are typically repeated to dynamically adjust
the control signals over time. For example, each time around the
loop, one or more of the control signals may be adjusted according
to an optimization algorithm (and optionally one or more control
parameters).
[0074] FIG. 7 illustrates an example of a system 700 that employs
an optimization algorithm to control spreading (e.g., to maintain
spreading within a defined target value). In a typical
implementation, a control circuit employs an optimization algorithm
whereby information derived from transducer signals received over
time is used to adjust the fan control signals over time, as
needed. This optimization algorithm may be embodied, at least in
part, in executable code that is executed by a processing system,
in a state machine, or in some other suitable manner.
[0075] In the embodiment of FIG. 7, transducer signals received
from one or more transducers (not shown) are subjected to
analog-to-digital conversion 702 to generate transducer data 704.
The transducer data 704 is subjected to signal processing 706 that
generates an indication of the current spreading 708. For example,
in some embodiments, the signal processing 706 employs an FFT
algorithm that operates on the transducer data 704 to extract
frequency spectrum information, identify a peak spread from the
frequency spectrum information, and generate a numerical spreading
value corresponding to the peak spread.
[0076] An optimization algorithm 710 generates fan speed control
and fan phase control data based, at least in part, on the
indication of the current spreading 708. To this end, the
optimization algorithm may store one or more fan control and
spreading values 712 in a memory device (not shown). The type of
values stored and the manner in which these values are used depends
on the type of optimization algorithm being used.
[0077] In some embodiments, the optimization algorithm 710 employs
a brute force scheme to minimize spreading. For example, the
value(s) used for the last adjustment made to the fan speed control
and fan phase control values may be stored along with at least one
prior spreading value that was used to determine the adjustment.
The optimization algorithm 710 may then compare the indication of
current spreading 708 (e.g., a new spreading value) to the stored
prior spreading value(s) to determine whether the last adjustment
resulted in a decrease or an increase in spreading. The
optimization algorithm 710 then generates at least one new
adjustment value based on this determination (e.g., it continues
adjusting the control values in the same manner if spreading
decreased, or it adjusts the control values in a different manner
if spreading increased). Similar techniques may be employed in
other types of optimization schemes (e.g., a scheme that employs a
least mean square-based algorithm).
[0078] In some embodiments, the optimization algorithm 710 employs
a lookup table or other similar information. This information may
specify, for example, the control value(s) to be used for a given
current spreading value. For example, a predefined mapping between
fan control and spreading values 714 may be predetermined (e.g.,
based on simulations and/or empirical testing) and stored in a
memory device (not shown). Upon determining the current spreading
value (e.g., the indication of current spreading 708), the
optimization algorithm 710 uses this spreading value to lookup the
new fan control value(s) to be used based on the mapping. It should
be appreciated that other information (e.g., the current fan
control value(s)) is taken into account here in some
embodiments.
[0079] As additional transducer signals are received over time, the
optimization algorithm 710 determines whether the speed control and
phase control values need to be adjusted. For example, if the
indication of current spreading 708 calculated based on the latest
transducer signals indicates that the spreading is within a target
value, the optimization algorithm 710 may maintain the speed
control and phase control values at their current levels.
Conversely, if the indication of current spreading 708 calculated
based on the latest transducer signals indicates that the spreading
is not within a target value, the optimization algorithm 710 may
adjust the speed control and phase control values in a manner that
is expected to reduce the spreading (e.g., as discussed
herein).
[0080] As mentioned above, the teachings herein may be employed in
various types of computing systems. FIGS. 8 and 9 illustrate two
additional examples of how a fan control system as taught herein
may be deployed in a computing system.
[0081] In FIG. 8, an enclosure 802 for a circuit 804 (e.g., a
graphics card) houses several fans 806 and 808. In addition, a fan
controller 810 (e.g., comprising receiver, control, and driver
circuitry) and a microphone 812 are deployed within the enclosure
802 for proving fan control as taught herein. It should be
appreciated that the functionality of the fan controller 810 and/or
the microphone 812 is incorporated into the circuit 804 in some
implementations.
[0082] In the example of FIG. 8, the circuit 804 connects to a PCB
814 (e.g., a motherboard). The PCB 814 is typically installed
within an enclosure that has one or more fans (not shown). Thus, in
some cases, the fan control circuitry for the enclosure 802
cooperates with fan control circuitry for the larger PCB enclosure
to control all of the fans in the combined system in a manner
consistent with the teachings herein. In implementations that
employ multiple enclosures such as the enclosure 802, the fan
control circuitry for each enclosure may cooperate with one another
(and, optionally, with fan control circuitry for the PCB 814) to
control all of the fans in the combined system in a manner
consistent with the teachings herein. In some implementations, a
single controller is employed (e.g., on the PCB 814 or in the
enclosure 802) whereby that controller receives signals from all of
the transducers in the system (e.g., including the microphone 812)
and generates control signals for all of the fans in the system
(e.g., including the fans 806 and 808).
[0083] In FIG. 9 (e.g., a top view of a server rack for server
cards), an enclosure 902 houses several circuit cards 904A-904G and
several fans 906A-906G. A fan controller 908 (e.g., comprising
receiver, control, and driver circuitry) and several microphones
(represented by the microphones 910A and 910B) are deployed within
the enclosure 902 for proving fan control as taught herein. The
functionality of the fan controller 908 and/or the microphones 910
may be incorporated into one or more of the circuit cards 904 in
some implementations.
[0084] It should be appreciated that various modifications may be
incorporated into the disclosed embodiments based on the teachings
herein. For example, different algorithms may be employed in other
embodiments to adjust the operation of a fan based on received
acoustic-related information. Also, different types of transducers
and/or different combinations of transducers other than those
specifically shown may be employed in other embodiments.
[0085] A computing system as taught herein may be used in a variety
of applications. For example, such a computing system may comprise
or be incorporated into a portable device, a computer graphics
card, a videogame console, a printer, a personal computer, a
computer server, a processing system (e.g., a CPU device), or some
other apparatus that employs multiple fans.
[0086] It also should be appreciated that the various structures
and functions described herein may be implemented in various ways
and using a variety of apparatuses. For example, an apparatus
(e.g., a device) including functionality as described herein may be
implemented by various hardware components such a processor, a
controller, a state machine, logic, or some combination of one or
more of these components. In some aspects, an apparatus or any
component of an apparatus may be configured to provide
functionality as taught herein by, for example, manufacturing
(e.g., fabricating) the apparatus or component so that it will
provide the functionality, by programming the apparatus or
component so that it will provide the functionality, or through the
use of some other suitable means.
[0087] In some embodiments, code including instructions (e.g.,
software, firmware, middleware, etc.) may be executed on one or
more processing devices to implement one or more of the described
functions or components. The code and associated components (e.g.,
data structures and other components by the code or to execute the
code) may be stored in an appropriate data memory that is readable
by a processing device (e.g., commonly referred to as a
computer-readable medium).
[0088] The recited order of the blocks in the processes disclosed
herein should generally be considered to be an example of a
suitable approach. Thus, operations associated with such blocks may
be rearranged in some cases while remaining within the scope of the
disclosure. Similarly, the accompanying method claims present
operations in a sample order, and are not necessarily limited to
the specific order presented.
[0089] The components and functions described herein may be
connected or coupled in various ways. The manner in which this is
done may depend, in part, on whether and how the components are
separated from the other components. In some embodiments some of
the connections or couplings represented by the lead lines in the
drawings may be in an integrated circuit, on a circuit board, in a
cable, implemented as discrete wires, or implemented in some other
way.
[0090] The signals discussed herein may take various forms. For
example, in some embodiments a signal may comprise electrical
signals transmitted over a wire, light pulses transmitted through
an optical medium such as an optical fiber or air, or RF waves
transmitted through a medium such as air, etc. In addition, a
plurality of signals may be collectively referred to as a signal
herein. The signals discussed above also may take the form of data.
For example, in some embodiments an application program may send a
signal to another application program. Such a signal may be stored
in a data memory.
[0091] Also, it should be understood that any reference to an
element herein using a designation such as "first," "second," and
so forth does not generally limit the quantity or order of those
elements. Rather, these designations may be used herein as a
convenient method of distinguishing between two or more elements or
instances of an element. Thus, a reference to first and second
elements does not mean that only two elements may be employed there
or that the first element must precede the second element in some
manner. Also, unless stated otherwise a set of elements may
comprise one or more elements. In addition, terminology of the form
"at least one of A, B, or C" or "one or more of A, B, or C" or "at
least one of the group consisting of A, B, and C" used in the
description or the claims means "A or B or C or any combination of
these elements."
[0092] It should be appreciated that specific structural and
functional details disclosed herein are merely representative and
do not limit the scope of the disclosure. For example, based on the
teachings herein one skilled in the art should appreciate that the
various structural and functional details disclosed herein may be
incorporated in an embodiment independently of any other structural
or functional details. Thus, an apparatus may be implemented or a
method practiced using any number of the structural or functional
details set forth in any disclosed embodiment(s). Also, an
apparatus may be implemented or a method practiced using other
structural or functional details in addition to or other than the
structural or functional details set forth in any disclosed
embodiment(s).
[0093] In view of the above, it will be understood that various
modifications may be made to the illustrated embodiments and other
embodiments as taught herein, without departing from the scope
thereof. Accordingly, the teachings herein are not limited to the
particular embodiments or arrangements disclosed, but are rather
intended to cover any changes, adaptations or modifications which
are within the scope of the appended claims.
* * * * *