U.S. patent application number 12/655754 was filed with the patent office on 2010-05-27 for cloud water characterization system.
This patent application is currently assigned to Science Engineering Associates, Inc.. Invention is credited to Daniel B. Bouley, Lyle E. Lilie, Christopher P. Sivo.
Application Number | 20100131203 12/655754 |
Document ID | / |
Family ID | 38233590 |
Filed Date | 2010-05-27 |
United States Patent
Application |
20100131203 |
Kind Code |
A1 |
Lilie; Lyle E. ; et
al. |
May 27, 2010 |
Cloud water characterization system
Abstract
A system and method for providing a statistical measure of the
size of liquid water droplets in a cloud, as well as a system and
method for the detection and/or measurement of the presence of a
cloud, liquid water content in the cloud and ice water content in
the cloud, among other parameters.
Inventors: |
Lilie; Lyle E.; (Ashford,
CT) ; Sivo; Christopher P.; (Ellington, CT) ;
Bouley; Daniel B.; (Columbia, CT) |
Correspondence
Address: |
ARTHUR G. SCHAIER;CARMODY & TORRANCE LLP
50 LEAVENWORTH STREET, P.O. BOX 1110
WATERBURY
CT
06721
US
|
Assignee: |
Science Engineering Associates,
Inc.
|
Family ID: |
38233590 |
Appl. No.: |
12/655754 |
Filed: |
January 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11329894 |
Jan 11, 2006 |
7643941 |
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12655754 |
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Current U.S.
Class: |
702/3 |
Current CPC
Class: |
G01W 1/02 20130101 |
Class at
Publication: |
702/3 |
International
Class: |
G01W 1/00 20060101
G01W001/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This invention was partially made with U.S. Government
support under Contract No. NAS3-02162. Accordingly, the U.S.
Government may have certain rights in this invention.
Claims
1. A system for determining a measure of cloud water droplet size
based on sensor cooling by cloud water and stored sensor power
ratio and droplet size data, said system comprising: a first and
second temperature controlled co-located self heated sensors, the
cooling of said sensors being substantially independent of ice
water; a self heated compensation sensor oriented to be
substantially independent of cloud water cooling; a variable power
source coupled to each first and second sensor for keeping each
sensor at a temperature and each having a measurable output power;
a variable power source coupled to the compensation sensor for
keeping the sensor at a temperature and having a measurable output
power; and a control unit for: correcting the measured power to
each of the first and second sensors to reflect only heat loss due
to cloud water by subtracting from the measured power an adjusted
compensation sensor measured value; and forming a ratio of
corrected power of each of the first and second sensors to identify
a liquid water droplet size based on the stored power ratio and
droplet size data.
2-22. (canceled)
Description
BACKGROUND OF THE INVENTION
[0002] The present invention is generally directed to aircraft
icing sensors, and in particular, to a system and methodology for
providing among other things as set forth herein, a measure of a
water droplet size in a cloud containing liquid water, ice water or
both.
[0003] Aircraft icing is a serious safety problem for general
aviation and some commuter transport airplanes. There has been
tremendous growth in the commuter aviation industry in the last few
years. When compared to heavy transport category aircraft, these
types of aircraft generally operate at lower altitudes and
consequently spend a greater proportion of their time operating in
icing conditions.
[0004] Airframe icing severity depends on the liquid water content,
droplet size and degree of glaciation of the cloud. Liquid water
content (LWC) is normally expressed in grams/cubic meter and is a
measure of the unfrozen water content of the cloud. Droplets occur
in nature not in a single size but in a distribution of sizes. The
median volume diameter (MVD) of the droplet distribution has
historically been used as a bulk measurement of droplet spectrum
size. For example, FAA aircraft and engine certification criteria
are expressed in terms of a combination of LWC and MVD.
[0005] The droplet size plays a critical role in the way that ice
accumulates on airframe and engine surfaces. In general the larger
the MVD the more problems the accumulated ice will cause. Small
droplets tend to freeze immediately on impact whereas larger
droplets flow along the structural surfaces before freezing. If the
drops have a very large MVD, i.e. greater than 50 microns, they may
run past the anti-ice/deice systems and freeze in critical,
unprotected places on the airframe. These are the so-called
supercooled large drop (SLD) cases. SLD encounters are of
particular interest for aviation safety.
[0006] Cloud total water content (TWC) includes both unfrozen
droplets (liquid water) and frozen water in the form of ice
crystals. The degree of glaciation in the cloud can be determined
by comparing the liquid water content to the total water
content.
[0007] In general, airframe and engine icing depend primarily on
liquid water content because the unfrozen, but super-cooled
droplets, freeze upon impact whereas already frozen ice crystals
will not. However, there are some very important exceptions. In
some particular cases of temperature and airspeed, ice crystals can
melt upon impact and then refreeze. This can cause severe problems
for both airframes and engines.
[0008] In the past several years there have been a number of fatal
commuter aircraft accidents attributed to severe icing conditions
having SLD. Though SLD was thought to occur infrequently, the
significant increase in commuter aircraft traffic has raised a
concern that the chances of encountering this icing condition may
be far greater than previously thought. At the present time
aircraft ice protection systems are not required to provide
protection against SLD. Therefore a simple device that could
provide warning that SLD conditions are present would be highly
desirable.
[0009] Cylindrical and wire like sensors for measuring LWC are
known. However, the heating for such known sensors use external
windings to heat the sensor. The external windings are quite
delicate giving these sensors a very short life due to damage from
encounters with typical atmospheric concentrations of ice crystals.
Generally speaking sensors using external heater windings are
problematic because the windings create small "pockets" that trap
ice crystals causing a significant fraction of ice crystals to be
captured and evaporated. The evaporation of ice from a liquid water
sensor therefore gives false measurements or indications of liquid
water when in the presence of ice crystals.
[0010] Other prior art LWC sensors have used an internal, switched
indirectly heated, cylindrical element to collect super cooled
liquid water that freezes onto the cylinder. The cylinder is
oscillated at its natural mechanical resonant frequency
(approximately 40 kHz). As ice builds up the frequency decreases to
a preset value at which time a heating cycle is initiated to clear
the ice from the cylinder. The internal heater cycles on and off to
remove the accumulated ice. The rate of cycling provided an
indication of the amount of liquid water present.
[0011] However, it is believed that deficiencies exist in these
prior art arrangements, such as the ability to reject unwanted ice
crystals when measuring LWC. Tests have shown that the present
invention provides a better than ten times improvement over
previous LWC sensors in rejecting unwanted ice crystals, due to the
shape and surface construction of the sensors.
[0012] The development of portions of the present invention has
been carried out under a NASA Small Business Innovative Research
(SBIR) contract between the NASA Glenn Research Facility and
Science Engineering Associates, Inc. (SEA) as part of NASA's
Aviation Safety Program initiative to significantly reduce aircraft
accidents. Part of this program, is to establish the frequency of
occurrence of SLD conditions. Once this frequency of occurrence is
established, it would be expected that agencies like the Federal
Aviation Administration (FAA) could use this information to affect
changes in current aircraft icing certification regulations. This
in turn would lead to changes in the design of aircraft ice
protection systems, potentially to protect against severe icing
conditions.
[0013] Present research activities aimed at establishing this
frequency of occurrence have been limited to a handful of research
organizations using heavily instrumented research aircraft (e.g.
the NASA Glenn Research Centers' Twin Otter Icing Research Aircraft
and the NRC Convair-580 aircraft). Though effective, this approach
is limited in scope and somewhat biased because the research
flights are specifically directed into areas having the highest
probability of severe icing conditions. Therefore a more extensive
approach, such as that offered by instrumenting a large number of
commercial/military aircraft, would be of great value. The key to
this approach is the development of a small, reliable, low power
integrated icing instrument, which has not previously been
available.
[0014] It is believed that the present invention, in addition to
providing needed capabilities in a research environment, will also
help provide the needed protection against icing in private and
commercial aircraft and overcomes the deficiencies set forth above
and achieves the objectives set forth herein.
SUMMARY AND OBJECTIVES OF THE PRESENT INVENTION
[0015] It is thus an objective of the present invention to overcome
the deficiencies existing in the state of the art.
[0016] In particular, an objective of the present invention is to
provide a plurality of sensors that are each designed, calibrated,
co-located and oriented within a small common shroud, for the
calculation of cloud parameters previously only possible by using
multiple instruments on research aircraft.
[0017] Yet another objective of the present invention is to provide
a statistical measure of the size of liquid water droplets in the
cloud, commonly called the MVD (Median Volumetric Diameter).
[0018] Still another objective of the present invention is to
overcome the difficulties found in the prior art of duplicating
cloud conditions, and MVD in particular, in wind tunnel
testing.
[0019] Yet another objective of the present invention is to provide
a system and method for measurement and detection of cloud water
conditions that is lightweight and suitable for use on non-research
aircraft.
[0020] Further objectives of the present invention are to provide a
system and method for the detection and/or measurement of the
presence of a cloud, LWC, Ice Water Content (IWC), and SLD
parameters.
[0021] Still other objectives and advantages of the invention will
in part be obvious and will in part be apparent from the
specification.
[0022] The invention accordingly comprises the features of
construction, combination of elements, arrangement of parts and
sequence of steps which will be exemplified in the construction,
illustration and description hereinafter set forth, and the scope
of the invention will be indicated in the claims.
[0023] Therefore, and generally speaking, in one embodiment, the
present invention is directed to a system for determining a measure
of cloud water droplet size based on sensor cooling by cloud water
and stored sensor power ratio and droplet size data, the system
comprising a first and second temperature controlled co-located
self heated sensors, the cooling of the sensors being substantially
independent of ice water; a self heated compensation sensor
oriented to be substantially independent of cloud water cooling; a
variable power source coupled to each first and second sensor for
keeping each sensor at a temperature and each having a measurable
output power; a variable power source coupled to the compensation
sensor for keeping the sensor at a temperature and having a
measurable output power; and a control unit for correcting the
measured power to each of the first and second sensors to reflect
only heat loss due to cloud water by subtracting from the measured
power an adjusted compensation sensor measured value; and forming a
ratio of corrected power of each of the first and second sensors to
identify a liquid water droplet size based on the stored power
ratio and droplet size data.
[0024] In another embodiment, the present invention is directed to
a system for measuring water droplet size in a cloud, wherein the
system comprises a sensor head comprising a first heated sensor
having a resistance characteristic that is temperature dependent,
wherein power loss from the sensor is at least essentially not
affected by the presence of ice water in an airflow thereacross; a
second heated sensor having a second resistance characteristic that
is temperature dependent, wherein power loss from the second sensor
is at least essentially not affected by the presence of ice water
in the airflow thereacross; a heated compensation sensor being
positioned to be responsive to the airflow thereacross and having a
power loss at least essentially not affected by the presence of
liquid water or ice water in the airflow thereacross; a respective
temperature controller associated with each of the first sensor,
second sensor and compensation sensor, each of which for
maintaining the temperature of the respective sensors at respective
temperature values using its temperature dependent resistance
characteristic, wherein, for each of the first and second sensors,
the respective controller maintains the sensor at the temperature
value by adjusting a power level fed to the sensor; calculates the
total power required to maintain the sensor at the temperature
value when the sensor is exposed to an airflow comprising at least
one of liquid water and ice water; and a control unit for receiving
power levels from each of the first sensor and second sensor;
subtracting, from each total power calculation, a dry power
component determined from the power required to maintain the
compensation sensor at its temperature value in the presence of the
airflow comprising at least liquid water, thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first and second sensors at the
respective temperature values in the presence of at least liquid
water in the airflow; and for forming a ratio of the wet power
value of the first sensor to the wet power value of the second
sensor to obtain an estimated value of the measure of water droplet
size in the cloud from a predetermined calibrated relationship of
wet power ratio to water droplet sizes.
[0025] In yet another embodiment, the present invention is directed
to a system for determining liquid water content in a cloud,
wherein the system comprises a sensor head comprising a first
heated sensor having a first resistance characteristic that is
temperature dependent, wherein the first sensor is at least
essentially not affected by the presence of ice water in an airflow
thereacross; a second heated sensor having a second resistance
characteristic that is temperature dependent, wherein the second
sensor is at least essentially not affected by the presence of ice
water in the airflow thereacross; a heated compensation sensor
being positioned to be responsive to the airflow thereacross and at
least essentially not affected by the presence of liquid water or
ice water in the airflow thereacross; a respective temperature
controller associated with each of the first sensor, second sensor
and compensation sensor, each of which for maintaining the
temperature of the respective sensors at respective temperature
values using its temperature dependent resistance characteristic,
wherein, for each of the first and second sensors the respective
controller maintains the sensor at the temperature value by
adjusting a power level fed to the sensor; calculates the total
power required to maintain the sensor at the temperature value when
the sensor is exposed to an airflow comprising at least liquid
water; and a control unit for receiving power levels from each of
the first censor and second sensor; subtracting, from each total
power calculation, a dry power component determined from the power
required to maintain the compensation sensor at its temperature
value in the presence of the airflow thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first and second sensors at the
respective temperature values in the presence of at least liquid
water in the airflow; and calculating a liquid water content for
the first sensor and sensor wet power values and selecting the
higher LWC as the desired liquid water content.
[0026] In still another embodiment of the present invention, a
system is provided for determining liquid water content in a cloud,
the liquid water having a determined droplet size, wherein the
system comprises a sensor head comprising a first heated sensor
having a first resistance characteristic that is temperature
dependent, wherein the first sensor is at least essentially not
affected by the presence of ice water in an airflow thereacross; a
second heated sensor having a second resistance characteristic that
is temperature dependent, wherein the second sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a heated compensation sensor being positioned
to be responsive to the airflow thereacross and at least
essentially not affected by the presence of liquid water or ice
water in the airflow thereacross; a respective temperature
controller associated with each of the first sensor, second sensor
and compensation sensors, each of which for maintaining the
temperature of the respective sensors at respective temperature
values using its temperature dependent resistance characteristic,
wherein, for each of the first and second sensors the respective
controller maintains the sensor at the temperature value by
adjusting a power level fed to the sensor; calculates the total
power required to maintain the sensor at the temperature value when
the sensor is exposed to an airflow comprising at least liquid
water; and a control unit for receiving power levels from each of
the first sensor and second sensor and having a stored droplet size
verses liquid water content correction curve for each first and
second sensor; subtracting, from each total power calculation, a
dry power component determined from the power required to maintain
the compensation sensor at its temperature value in the presence of
the airflow thereby arriving at a wet power value attributable to
the incremental power associated with maintaining the respective
first and second sensors at the respective temperature values in
the presence of liquid water in the airflow; and calculating a
liquid water content for the first sensor and second sensor wet
power values, selects the higher of the calculated liquid water
content values, and corrects the higher of the two values using a
droplet size verses liquid water content correction curve.
[0027] In yet another embodiment, a system is provided for
determining the presence of ice water in an airflow, wherein the
system comprises a sensor head comprising a first heated sensor
having a first resistance characteristic that is temperature
dependent, wherein heat the from first sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a second heated sensor having a second
resistance characteristic that is temperature dependent, wherein
heat from the second sensor is at least essentially not affected by
the presence of ice water in the airflow thereacross; a third
heated sensor having a third resistance characteristic that is
temperature dependent, wherein heat loss from the third sensor is
affected by a presence of ice water in the airflow thereacross; a
heated compensation sensor being positioned to be responsive to the
airflow thereacross and having a heat loss least essentially not
affected by the presence of liquid water or ice water in the
airflow thereacross; a respective temperature controller associated
with each of the first sensor, second sensor, third sensor and
compensation sensors, each of which for maintaining the temperature
of the respective sensors at respective temperature values using
its temperature dependent resistance characteristic, wherein, for
each of the first, second and third sensors, the respective
controller maintains the sensor at the temperature value by
adjusting a power level fed to the sensor; calculates the total
power required to maintain the sensor at the temperature value when
the sensor is exposed to an airflow comprising at least ice water;
and a control unit for receiving power levels from each of the
first sensor and second sensor; subtracting, from each total power
calculation, a dry power component determined from the power
required to maintain the compensation sensor at its temperature
value in the presence of the airflow comprising at least ice water,
thereby arriving at a wet power value attributable to the
incremental power associated with maintaining the respective first,
second and third sensors at the respective temperature values in
the presence of at least ice water in the airflow; and calculating
a water content measurement for the first sensor, second sensor and
third sensor wet power values, selecting a higher water content
value from the first and second sensor and subtracting the higher
value from the water content value of the third sensor to indicate
a presence of ice water.
[0028] In still another embodiment, a system is provided for
warning of cloud water, the system comprising a first temperature
controlled self heated sensor, a variable power source for the
first sensor having a measurable output power responsive to changes
in cloud water; a processor for averaging the measured output power
of the power source and subtracting a substantially instantaneous
measure of the output power of the power source to determine
fluctuations around the average; and comparing the fluctuations to
a threshold indicative of the presence of cloud water.
[0029] In still further embodiments, the system for determining a
measure of cloud water droplet size based on sensor cooling by
cloud water and stored sensor power ratio and droplet size data,
may comprise means for keeping each of the first and second sensors
at a temperature and each having a measurable output power; for
keeping the compensation sensor at a temperature and having a
measurable output power; correcting the measured power to each of
the first and second sensors to reflect only heat loss due to cloud
water by subtracting from the measured power an adjusted
compensation sensor measured value; and forming a ratio of
corrected power of each of the first and second sensors to identify
a liquid water droplet size based on the stored power ratio and
droplet size data.
[0030] Similarly, in yet another embodiment, the system for
measuring water droplet size in a cloud may comprise means
associated with each of the first sensor, second sensor and
compensation sensor, for maintaining the temperature of the
respective sensors at respective temperature values using its
temperature dependent resistance characteristic, wherein, for each
of the first and second sensors, the means maintains the sensor at
the temperature value by adjusting a power level fed to the sensor
and calculates the total power required to maintain the sensor at
the temperature value when the sensor is exposed to an airflow
comprising at least one of liquid water and ice water; and means
for receiving power levels from each of the first sensor and second
sensor; subtracting, from each total power calculation, a dry power
component determined from the power required to maintain the
compensation sensor at its temperature value in the presence of the
airflow comprising at least liquid water, thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first and second sensors at the
respective temperature values in the presence of at least liquid
water in the airflow; and for forming a ratio of the wet power
value of the first sensor to the wet power value of the second
sensor to obtain an estimated value of the measure of water droplet
size in the cloud from a predetermined calibrated relationship of
wet power ratio to water droplet sizes.
[0031] Likewise, the system for determining liquid water content in
a cloud may comprise means associated with each of the first
sensor, second sensor and compensation sensor, for maintaining the
temperature of the respective sensors at respective temperature
values using its temperature dependent resistance characteristic,
wherein, for each of the first and second sensors the sensor is
maintained at the temperature value by adjusting a power level fed
to the sensor; and the total power required to maintain the sensor
at the temperature value when the sensor is exposed to an airflow
comprising at least liquid water is calculated; and means for
receiving power levels from each of the first sensor and second
sensor; subtracting, from each total power calculation, a dry power
component determined from the power required to maintain the
compensation sensor at its temperature value in the presence of the
airflow thereby arriving at a wet power value attributable to the
incremental power associated with maintaining the respective first
and second sensors at the respective temperature values in the
presence of at least liquid water in the airflow; and calculating a
liquid water content for the first sensor and sensor wet power
values and selecting the higher LWC as the desired liquid water
content.
[0032] Moreover, the system for determining liquid water content in
a cloud, the liquid water having a determined droplet size, may
comprise means associated with each of the first sensor, second
sensor and compensation sensors, each of which for maintaining the
temperature of the respective sensors at respective temperature
values using its temperature dependent resistance characteristic,
wherein, for each of the first and second sensors the means
maintains the sensor at the temperature value by adjusting a power
level fed to the sensor and calculates the total power required to
maintain the sensor at the temperature value when the sensor is
exposed to an airflow comprising at least liquid water; and means
for receiving power levels from each of the first sensor and second
sensor and having a stored droplet size verses liquid water content
correction curve for each first and second sensor; subtracting,
from each total power calculation, a dry power component determined
from the power required to maintain the compensation sensor at its
temperature value in the presence of the airflow thereby arriving
at a wet power value attributable to the incremental power
associated with maintaining the respective first and second sensors
at the respective temperature values in the presence of liquid
water in the airflow; and calculating a liquid water content for
the first sensor and second sensor wet power values, selects the
higher of the calculated liquid water content values, and corrects
the higher of the two values using a droplet size verses liquid
water content correction curve.
[0033] Still further, the system for determining the presence of
ice water in an airflow may comprise means associated with each of
the first sensor, second sensor, third sensor and compensation
sensors, each of which for maintaining the temperature of the
respective sensors at respective temperature values using its
temperature dependent resistance characteristic, wherein, for each
of the first, second and third sensors, the means maintains the
sensor at the temperature value by adjusting a power level fed to
the sensor and calculates the total power required to maintain the
sensor at the temperature value when the sensor is exposed to an
airflow comprising at least ice water; and means for receiving
power levels from each of the first sensor and second sensor;
subtracting, from each total power calculation, a dry power
component determined from the power required to maintain the
compensation sensor at its temperature value in the presence of the
airflow comprising at least ice water, thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first, second and third sensors at the
respective temperature values in the presence of at least ice water
in the airflow; and calculating a water content measurement for the
first sensor, second sensor and third sensor wet power values,
selecting a higher water content value from the first and second
sensor and subtracting the higher value from the water content
value of the third sensor to indicate a presence of ice water.
[0034] The present invention is also directed to a plurality of
methodologies. For example, in accordance with a first embodiment,
a method for determining a measure of cloud water droplet size
based on sensor cooling by cloud water and stored sensor power
ratio and droplet size data, utilizing a system comprising a first
and second temperature controlled co-located self heated sensors,
the cooling of the sensors being substantially independent of ice
water, a self heated compensation sensor oriented to be
substantially independent of cloud water cooling; a variable power
source coupled to each first and second sensor for keeping each
sensor at a temperature and each having a measurable output power;
and a variable power source coupled to the compensation sensor for
keeping the sensor at a temperature and having a measurable output
power, wherein the method comprises the steps of correcting the
measured power to each of the first and second sensors to reflect
only heat loss due to cloud water by subtracting from the measured
power an adjusted compensation sensor measured value; and forming a
ratio of corrected power of each of the first and second sensors to
identify a liquid water droplet size based on the stored power
ratio and droplet size data.
[0035] In yet another embodiment, the present invention is directed
to a method of measuring water droplet size in an airflow,
utilizing a system comprising a sensor head comprising a first
heated sensor having a resistance characteristic that is
temperature dependent, wherein power loss from the sensor is at
least essentially not affected by the presence of ice water in the
airflow thereacross; a second heated sensor having a second
resistance characteristic that is temperature dependent, wherein
power loss from the second sensor is at least essentially not
affected by the presence of ice water in the airflow thereacross; a
heated compensation sensor being positioned to be responsive to the
airflow thereacross and having a power loss at least essentially
not affected by the presence of liquid water or ice water in the
airflow thereacross, wherein the method comprises the steps of
maintaining the temperature of the respective sensors at respective
temperature values using its temperature dependent resistance
characteristic; and wherein, for each of the first and second
sensors, the method comprises the steps of maintaining the sensor
at the temperature value by adjusting a power level fed to the
sensor and calculating the total power required to maintain the
sensor at the temperature value when the sensor is exposed to an
airflow comprising at least one of liquid water and ice water;
wherein the method further comprises the steps of receiving power
levels from each of the first sensor and second sensor;
subtracting, from each total power calculation, a dry power
component determined from the power required to maintain the
compensation sensor at its temperature value in the presence of the
airflow comprising at least liquid water, thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first and second sensors at the
respective temperature values in the presence of at least liquid
water in the airflow; and forming a ratio of the wet power value of
the first sensor to the wet power value of the second sensor to
obtain an estimated value of the measure of water droplet size in
the cloud from a predetermined calibrated relationship of wet power
ratio to water droplet sizes.
[0036] In still yet another embodiment, a method is provided for
determining liquid water content in an airflow, utilizing a system
comprising a sensor head comprising a first heated sensor having a
first resistance characteristic that is temperature dependent,
wherein the first sensor is at least essentially not affected by
the presence of ice water in an airflow thereacross; a second
heated sensor having a second resistance characteristic that is
temperature dependent, wherein the second sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a heated compensation sensor being positioned
to be responsive to the airflow thereacross and at least
essentially not affected by the presence of liquid water or ice
water in the airflow thereacross; wherein the method comprises the
steps of maintaining the temperature of the respective sensors at
respective temperature values using its temperature dependent
resistance characteristic, maintaining the sensors at the
temperature value by adjusting a power level fed to the sensor;
calculating the total power required to maintain the sensor at the
temperature value when the sensor is exposed to an airflow
comprising at least liquid water; receiving power levels from each
of the first sensor and second sensor; subtracting, from each total
power calculation, a dry power component determined from the power
required to maintain the compensation sensor at its temperature
value in the presence of the airflow thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first and second sensors at the
respective temperature values in the presence of at least liquid
water in the airflow; and calculating a liquid water content for
the first sensor and sensor wet power values and selecting the
higher LWC as the desired liquid water content.
[0037] Still in another embodiment, a method is provided for
determining liquid water content in an airflow, the liquid water
having a determined droplet size, utilizing a system comprising a
sensor head comprising a first heated sensor having a first
resistance characteristic that is temperature dependent, wherein
the first sensor is at least essentially not affected by the
presence of ice water in an airflow thereacross; a second heated
sensor having a second resistance characteristic that is
temperature dependent, wherein the second sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a heated compensation sensor being positioned
to be responsive to the airflow thereacross and at least
essentially not affected by the presence of liquid water or ice
water in the airflow thereacross; wherein the method comprises the
steps of maintaining the temperature of the respective sensors at
respective temperature values using its temperature dependent
resistance characteristic and, for each of the first and second
sensors, maintaining maintains the sensor at the temperature value
by adjusting a power level fed to the sensor and calculating the
total power required to maintain the sensor at the temperature
value when the sensor is exposed to an airflow comprising at least
liquid water; wherein the method further comprises the steps of
receiving power levels from each of the first sensor and second
sensor and having a stored droplet size verses liquid water content
correction curve for each first and second sensor; subtracting,
from each total power calculation, a dry power component determined
from the power required to maintain the compensation sensor at its
temperature value in the presence of the airflow thereby arriving
at a wet power value attributable to the incremental power
associated with maintaining the respective first and second sensors
at the respective temperature values in the presence of liquid
water in the airflow; and calculating a liquid water content for
the first sensor and second sensor wet power values, selects the
higher of the calculated liquid water content values, and corrects
the higher of the two values using a droplet size verses liquid
water content correction curve.
[0038] In yet another embodiment, a method is provided for
determining the presence of ice water in an airflow, utilizing a
system comprising a sensor head comprising a first heated sensor
having a first resistance characteristic that is temperature
dependent, wherein heat the from first sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a second heated sensor having a second
resistance characteristic that is temperature dependent, wherein
heat from the second sensor is at least essentially not affected by
the presence of ice water in the airflow thereacross; a third
heated sensor having a third resistance characteristic that is
temperature dependent, wherein heat loss from the third sensor is
affected by a presence of ice water in the airflow thereacross; a
heated compensation sensor being positioned to be responsive to the
airflow thereacross and having a heat loss least essentially not
affected by the presence of liquid water or ice water in the
airflow thereacross; wherein the method comprises the steps of
maintaining the temperature of the respective sensors at respective
temperature values using its temperature dependent resistance and
wherein, for each of the first, second and third sensors,
maintaining the sensor at the temperature value by adjusting a
power level fed to the sensor and calculating the total power
required to maintain the sensor at the temperature value when the
sensor is exposed to an airflow comprising at least ice water;
wherein the method further comprises the steps of receiving power
levels from each of the first sensor and second sensor;
subtracting, from each total power calculation, a dry power
component determined from the power required to maintain the
compensation sensor at its temperature value in the presence of the
airflow comprising at least ice water, thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first, second and third sensors at the
respective temperature values in the presence of at least ice water
in the airflow; and calculating a water content measurement for the
first sensor, second sensor and third sensor wet power values,
selecting a higher water content value from the first and second
sensor and subtracting the higher value from the water content
value of the third sensor to indicate a presence of ice water.
[0039] In still another preferred embodiment of the present
invention, a method is provided for warning of cloud water using a
first temperature controlled self heated sensor and a variable
power source for the first sensor having a measurable output power
responsive to changes in cloud water, wherein the method comprises
the steps of averaging the measured output power of the power
source; subtracting a substantially instantaneous measure of the
output power of the power source to determine fluctuations around
the average; and comparing the fluctuations to a threshold
indicative of the presence of cloud water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The above set forth and other features of the invention are
made more apparent in the ensuing Description of the Preferred
Embodiments when read in conjunction with the attached Drawings,
wherein:
[0041] FIG. 1 is a view of an overall system constructed in
accordance with the present invention;
[0042] FIGS. 2A, 2B, 2C, 2D, 2E, 2F, and 2G are perspective, detail
and cross-sectional views of a sense head constructed in accordance
with the present invention;
[0043] FIGS. 3A, 3B, 3C and 3D are differing views of the various
sensors used in the present invention;
[0044] FIG. 4 is an exemplary temperature control circuit
constructed in accordance with the present invention for use in
connection with each of the sensors set forth in FIG. 3;
[0045] FIG. 5 is a block diagram of a deice temperature control
circuit constructed in accordance with the present invention;
[0046] FIG. 6 is an exemplary resistance-temperature characteristic
curve for one of the sensors of FIG. 3;
[0047] FIG. 7 relates dry power for a compensation sensor to dry
power for a medium, a thin and a scoop sensor;
[0048] FIG. 8 relates a ratio of sensor wet power to MVD value
based on wind tunnel tests;
[0049] FIG. 9 is an exemplary correction curve to correct liquid
water content measured value based on MVD data;
[0050] FIG. 10 depicts a control unit constructed in accordance
with the invention; and
[0051] FIG. 11 depicts an alternate embodiment of a control unit in
accordance with the invention.
[0052] Identical reference numerals in the figures are intended to
indicate like parts, although not every feature in every figure may
be called out with a reference numeral.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] As will be set forth in greater detail below, the present
invention, generally speaking, uses the heat loss from a medium
diameter sensor, thin diameter sensor and semi-cylindrical shaped
scoop-like sensor that are each designed, calibrated, co-located
and oriented within a small common shroud, for the calculation of
cloud parameters previously only possible by using multiple
instruments on research aircraft.
[0054] Among other things, the invention measures cloud ice water
content (IWC), liquid water content (LWC) and total cloud water
content (TWC), which is the sum of the cloud LWC and IWC, all of
which are measured in gm/m.sup.3. In addition, the present
invention provides a statistical measure of the size of liquid
water droplets in the cloud (e.g. the MVD). As used herein, the
term MVD is defined as a droplet diameter that divides the total
amount of cloud water in half; half the water volume will have
droplets with diameters larger than the MVD value and half of the
water volume will have droplet diameters smaller that the MVD
value. MVD is measured in microns.
[0055] As is will be understood by one skilled in the art, there
are a number of measures of droplet size other than MVD that are
useable with the invention. These include: Average Drop Diameter,
Median Drop Diameter, Mode Drop Diameter, Average Volume Diameter,
Mode Volume Diameter and Sauter Mean Diameter all of which can
characterize an aggregate of drops where the individual drops come
in various sizes. The particular characterization is substantially
determined by the calibration device(s)/method(s) used for the
invention. The term MVD, which is the term preferred by the FAA, is
often used herein to characterize drop size but its use is in no
way intended to limit the invention.
[0056] As is known to those skilled in the art, cloud conditions,
and MVD in particular, are very difficult to duplicate consistently
in different wind tunnels or even in a single wind tunnel. This
condition results from the nature of the hardware used to form
cloud ice and water as well as the instrumentation used to measure
the parameters of the formed cloud. The present inventors have
found, however, that the present invention provides excellent
repeatability and allows its use as a standard for comparing wind
tunnels as well as the accuracy and repeatability needed to improve
safety of flight in all aircraft.
[0057] The present invention uses the principle that the total
electrical power required to maintain a heated sensing element at a
preset constant temperature is substantially equal to the power
lost due to interaction of the sensing element with the cloud
environment. When the sensor is moving relative to moisture laden
air and heated to a temperature that will cause water in contact
with a sensor to evaporate, then the total heat loss can be
expressed as the sum of the heat loss that would occur if there was
no moisture being evaporated (dry power) and the heat lost from the
sensor due to evaporation of liquid water or ice water present (as
the case may be) on the sensor (wet power).
[0058] In addition, the invention uses the known principle that the
heat loss from a specific sensor geometry can be used in an
analysis of cloud water to differentiate between water and ice as
well as droplet sizes. The geometry of the sensor is important
since it affects its ability to "capture" and or "hold" the water
from a cloud long enough to cause evaporation.
[0059] The present inventors have also discovered in wind tunnel
tests that the use of a semi-cylindrical shaped self heated
scoop-like sensor (scoop sensor) provides improved measurement of
TWC as compared to prior art conical shaped TWC sensors. Likewise,
the present inventors have found that a large fraction of the water
present in ice crystals is lost when the ratio of the width to the
depth of a scoop sensor is one half or less. By definition a half
cylinder has a width to depth ratio of exactly one half.
[0060] Through testing, the present inventors have found that
adding additional depth in the form of straight sides, or
extensions 174, as shown in FIG. 3C, leading into the half cylinder
greatly increases the amount of water measured from ice crystals.
We have tested scoop sensors with a width to depth ratio of 0.5 to
4.0 and have found that deeper tends to be better with respect to
ice water measurement, but the extra heated surface of the deeper
ratio elements requires additional dry power, which requires larger
power supplies and their attendant disadvantages. A compromise
between power and measurement accuracy occurs for a range of depth
to width ratios from between about 1.0 to about 2.0.
[0061] The loss of water from ice crystals is due to the fact that
the ice arrives inside the scoop in solid form which cannot spread
out quickly, like a liquid droplet, until it is melted. This takes
additional time. If the ice crystal and the liquid water derived
from the ice crystal are not retained in the scoop, then the
accuracy of the measurement of the amount of ice is reduced.
[0062] In addition, the straight sides or extensions 174 on the
basic half cylinder establish circulation currents inside the scoop
that tend to keep ice and water from escaping from scoop 116. A
second purpose of the straight sides 174 is to help prevent the
loss of ice crystals by direct bouncing out of scoop 116 and back
into the air stream.
[0063] An advantage using directly heated sensors is the increased
intimacy of contact with the ice crystal in the case of the scoop
sensor which helps to impart heat to the crystal as rapidly as
possible. Likewise with the medium and thin sensors, discussed
below, the self heated configuration provides improved evaporation
efficiency for water droplets and allows smooth surface conditions
which helps discriminate against ice.
[0064] Also, as indicated above, testing has determined that there
is a better than ten (10) times improvement over prior art LWC
sensors in rejecting unwanted ice crystals due to the use of a
medium and thin sensor having a substantially smooth external
surface of less than about 2.5 .mu.m. Likewise we have found that
the response time of each of the sensors with their associated
temperature controller power supply is less than 0.01 seconds thus
allowing the identification of pockets of cloud water during
flight.
[0065] The present invention determines measures of LWC from the
wet power lost from a medium and thin sensor and MVD by using a
calibrated ratio of wet power lost from the medium sensor to wet
power lost from the thin sensor.
[0066] We have also discovered in wind tunnel tests that the
preferred sensor temperature control systems and sensors, having
low thermal mass, are responsive to short term "bursts" of ice
water or liquid water and allows early detection of cloud
water.
[0067] The present invention provides two temperature control
systems. The first system is used to maintain each sensor at a
known temperature so that the wet and dry power values discussed
above can be determined. The second system controls the average
temperature of the shroud to prevent ice build up on the sensor and
minimize errors that may occur due to undesirable heat flow paths
not related to the evaporation of water or determination of dry
power. The heated shroud provides the additional benefit of
operation even at zero airspeed.
[0068] Turning now to the figures in particular, reference is first
made to FIG. 1, which illustrates an overall view of the system of
the present invention, generally indicated at 5. System 5 comprises
a sensor head, generally indicated at 10, a temperature controller
generally indicated at 20 and a control unit generally indicated at
30.
[0069] As illustrated in FIGS. 2A-2C, sensor head 10 includes a
sensor module 110 having four sensors; a medium sensor 112, thin
sensor 114, scoop sensor 116, and compensation sensor 118. Sensor
head 10 also includes heated shroud 120, a heated strut 130 and a
mounting surface 18 for mounting the sensor head 10 to an aircraft
surface or wind tunnel (not shown). Sensor head 10 is preferably
mounted with strut 130 in a horizontal position for receiving air
stream 104.
[0070] Temperature controller 20 includes individually controlled
power sources that power each sensor located in sensor module 110
and keep each of the sensors at a predetermined temperature which
is preferably 140 degrees C. The strut 130 and shroud 120 include
individual heaters (not shown in FIG. 1) that are powered by a
single deice temperature control system 308 shown in FIG. 5 that is
also located in temperature controller 20.
[0071] The temperature of each sensor 114, 116, 112, and 118 is
determined by measurement of each sensor's electrical resistance
and holding that resistance substantially constant by varying the
amount of electrical power passed through the sensor. The shroud
and strut temperatures are controlled using a thermistor (not shown
in FIG. 1) to feed back a resistance value from which temperature
is readily calculated. The thermistor 140 is located at the
interface between the sensor module 110 and the strut, as shown in
FIG. 2F.
Sensor Details
[0072] Turning to FIGS. 2A and 2B in particular and as mentioned
above, sensor module 110 houses the four self heated sensors,
namely scoop sensor 116, medium sensor 112, thin sensor 114 and
compensation sensor 118. The scoop sensor 116, medium sensor 112,
and thin sensor 114 are oriented substantially normal to the
direction of airflow and parallel to each other. These sensors have
a projected area in the flow of air of approximately their width
times their height. The compensation sensor 118, being oriented
parallel to the airflow 104, has a projected area into the airflow
of approximately equal to its cross sectional area
[0073] Front, top (cross-sectional) and side (cross-sectional)
views of sensor head 10 are shown in FIGS. 2C-2G. Strut 130 assists
to keep sensor head 10 away from the mounting surface and fairing
134 provides a transition from the sense module 110 to strut 130.
The relative locations of the sensors 114, 116 and 112 and
compensation sensor 118 are shown in the various figures of FIGS.
2D and 2E. In the preferred embodiment, sensors 112 and 114 are
mounted forward of the scoop sensor 116, which is itself mounted
forward of compensation sensor 118. This preferred layout reduces
errors due to liquid water bouncing off scoop sensor 116 from
striking either the medium sensor 112 or thin sensor 114. Further,
having scoop sensor 116 forward of compensation sensor 118
introduces turbulence in the vicinity of compensation sensor 118,
thus improving its linearity as a function of airspeed.
[0074] Small protrusion 122 in FIG. 2E is a small nickel plated
copper pin preferably about 0.063 inch dia.times.0.150 inch high
(1.6 mm dia.times.3.81 mm high). Because the fwd mounting post for
compensation sensor 118 is preferably electrically insulated from
both the inner shroud 126 and the outer shroud 128, it is not
sufficiently deiced for all conditions by the heated shroud.
[0075] Under very cold conditions ice can build up on the leading
edge of the mounting post for compensation sensor 118 and change
the airflow around the compensation sensor 118 resulting in a poor
estimate of dry power. The purpose of protrusion 122 is to
intercept and warm stray water that passes scoop sensor 116 and
keep it from freezing onto the front mounting post of the
compensation element 118.
[0076] Compensation sensor 118 is mounted parallel to the airflow
and therefore exposed only to the cooling effects of the general
flow and not to cooling from liquid water or ice water. Because the
power required to maintain the compensation sensor 118 at a given
temperature in moisture free air is proportional to only the amount
of airflow in airstream 104, this power value is used to determine
the wet power for each sensor which is the incremental power needed
to evaporate water on the medium sensor 112, the thin sensor 114,
and the scoop sensor 116.
[0077] Because the geometries and locations of the medium sensor,
thin sensor, scoop sensor and compensation sensors are different,
correction curves relating dry power values as measured by the
compensation sensor to dry powers for the medium sensor 112, thin
sensor 114 and scoop sensor 116 is required, the preferred
embodiment being illustrated in FIG. 7.
[0078] FIGS. 3A-3C, in conjunction with Table 1, gives the
preferred mechanical and electrical parameters of thin sensor 114
(shown in FIG. 3A), medium sensor 112 (shown in FIG. 3B), scoop
sensor 116 (shown in FIG. 3C) and the compensation sensor 118
(shown in FIG. 3D).
[0079] Scoop sensor 116 is preferably substantially 1/2 of a
directly heated cylinder (split lengthwise) having flattened
extensions giving an overall width to depth ratio of about 1.0 and
an overall length of approximately 24 mm, dimensions of which are
illustrated in the FIG. 3C.
[0080] Scoop sensor 116 includes end caps 172 which are welded to
both ends of the scoop sensor 116. End caps 172 include holes for
receiving a necked down section of copper connector 166 for
soldering to a shroud mounted pin 167. Shroud pin 167 is soldered
to shroud 120 forming a ground connection for scoop sensor 116.
Medium sensor 112 receives neck down copper connector 162 and neck
down connector 168 receives thin sensor 114 to make ground
connections by soldering to shroud mounting pins 167 in a manner
similar to that described for scoop sensor 116. Copper connectors
162, 166 and 168 are preferably silver soldered to each of the
sensors. A similar arrangement (not shown) provides a ground
connection for compensation sensor 118 at 138 in FIG. 2G. Each of
connection points 167 and 138 provide substantially rigid single
ended supports for each of the sensor to accommodate thermal
expansion of the sensors 112, 114, 116 and 118.
[0081] Medium sensor 114 is preferably a cylinder so that the
majority of the power dissipated by the sensor takes place on its
surface in direct contact with any water on the sensor. The thin
sensor 114 is preferably a solid wire of stainless steel having the
preferred dimensions given in FIG. 3A.
[0082] Surface roughness may be added to the inside of scoop sensor
116 in the form of ridges, convolutions, or indentations, which
tend to increase the retention of water melted from ice crystals
and therefore give more opportunity for evaporation. Alternatively,
bonding a rough material having a high electrical resistance and
low thermal resistance, such as diamond chips or silicon carbine
chips, may be used to increase the surface roughness. Testing
indicates that a surface roughness of greater than about
approximately 2.5 .mu.m peak to peak for scoop sensor 116 and less
than approximately 2.5 .mu.m peak to peak for medium sensor 112 and
thin sensor 114 are preferred.
[0083] Alternate embodiments of the scoop sensor 116 include shapes
having open-sided rectangular, triangular, trapezoidal or
square-like cross-sections through their long axis. Alternate
embodiments of the medium sensor 112 and thin sensor 114 include
shapes having rectangular, triangular, trapezoidal or square-like
cross-sections through their long axis.
[0084] FIGS. 2A-2G illustrates other features, including certain
mounting features, of the present invention, such as the insulation
block, grounding and power source connections to each of the
sensors.
Temperature Control Systems
[0085] The preferred embodiments of the invention provide for two
basic temperature control system configurations, namely a control
system shown in FIG. 4 that preferably maintains a sensor at
140.degree. C. by controlling the voltage across the sensor, and a
control system shown in FIG. 5 that applies power to heaters 268,
264 and 266 to maintain the temperature of the shroud 120, fairing
134 and strut 130 at an average temperature of preferably
50.degree. C. The basic difference between the temperature
controllers of FIGS. 4 and 5 is that in the sensor temperature
control system shown in FIG. 4, the resistance of the heated sensor
is itself an indicator of its temperature whereas in the deice
temperature control system of FIG. 5, a thermistor provides a
feedback indication of the shroud 120, strut 130 and fairing 134
temperature.
Sensor Control System
[0086] Four preferably similar sensor control circuits and software
routines are used for each of the sensors 114, 112, 116 and 118.
The serial outputs of the control circuits are combined in a
multiplexer (not shown) and fed to control unit 30 or 3A for
further analysis.
[0087] Preferably, the basic operation of all sensor temperature
control systems are similar, so only system 208 for medium sensor
112 is described herein, with the others being similarly
constructed and the description thereof being omitted for purposes
of brevity. However, it should be understood that the sensor
temperature control systems do differ in that each includes stored
data that characterizes the particular sensor in terms of its
temperature--resistance characteristic in a manner suitable for
temperature control and the calculation of wet and dry power.
Characterization data for each sensor is given in Table 1 and
discussed further below.
TABLE-US-00001 TABLE 1 thin Medium Scoop Comp Sensor Sensor Sensor
Sensor 114 112 116 118 Sensor Dimensions Width (mm) 3.962 2.108
0.533 0.279 Length (mm) 23.622 20.447 21.590 16.764 Area (mm.sup.2)
93.590 43.102 11.507 4.684 Sensor resistance Room Temp 53.965
32.145 24.185 76.170 as function of room 85 57.435 34.370 30.160
93.510 and oil bath 100 58.345 34.865 31.815 98.270 temperatures
115 59.195 35.430 33.515 103.025 130 60.035 35.935 35.245 108.300
145 60.855 36.455 37.025 113.145 Characterization of Slope (dT/dR)
17.5783 28.6165 8.7396 3.0416 sensor resistance Offset -925.1580
-898.3378 -178.2307 -199.0406 characteristic R @ 100.degree. C.
58.3197 34.8868 31.8357 98.3183 (mohm)
[0088] As noted, sensor temperature control system 208 is explained
with regard to temperature control of a medium sensor, namely
sensor 112. Sensor control system 208 preferably maintains sensor
112 at a constant temperature by increasing or decreasing the power
level fed to medium sensor 112 in response to changes of sensor
112's measured resistance. With a fixed power level into sensor 112
and an increasing moisture level in the air flowing through sense
module 110, the temperature will tend to drop and will be indicated
by a decreasing R.sub.sensor of medium sensor 112. Conversely, as
the moisture content in airflow passing through sensor module 110
decreases, the temperature of sensor 110 will tend to increase as
indicated by an increasing R.sub.sensor. An exemplary curve showing
the relationship between sensor resistance and sensor temperature
is shown in FIG. 6. In particular, FIG. 6 gives the relationship
for sensor 112, that is preferably determined in a temperature
controlled circulating oil bath when sensor 112 is
manufactured.
[0089] The stored values that characterize a
temperature--resistance relationship of medium sensor 112, for
example, is characterized by two values, R@100 and dT/dR. The value
R@100 gives medium sensor 112 resistance in milliohms at
100.degree. C. while the value dT/dR gives the slope of the
temperature vs. resistance line in terms of degrees C. per
milliohm. Given the stored values of R@100, dT/dR and a desired
operating temperature ST.sub.set 228, processor 240 calculates a
desired resistance value indicative of the preferred ST.sub.set
which, in the preferred embodiment, is 140.degree. C. The power
necessary to maintain a desired resistance value, and therefore
temperature, is controlled by the control system set forth in FIG.
4 and described as follows.
[0090] The output from controlled DC-DC converter 214, operating as
a power amplifier, preferably ranges between substantially 0 volts
up to substantially 3 volts. A voltage across sensor 112 and
current through shunt 212, are measured and fed back to processor
240 via voltage amplifier 216 and current amplifier 218
respectively. The outputs of the voltage amplifier 216 and current
amplifier 218 are filtered by filters 252 and 254 and fed to Analog
to Digital (A/D) converters 220 and 222 where they are converted to
digital values. The digital values are preferably supplied to a
software routine represented by divider 224 and stored in processor
240 and wherein a substantially instantaneous value of sensor 112's
resistance is calculated. Likewise multiplier 236 calculates a
power value based on the fed back values of sensor 112's voltage
and current to give a value proportional to the power dissipated in
sensor 112. The output of multiplier 236 is sent to the control
unit 30 or 30A via a serial UART 244.
[0091] The output of the divider block 224, is fed to subtractor
226. In subtractor 226 a present value of sensor 112's resistance
from divider 224 is compared to ST.sub.set and the difference
(resistance error signal 230) is fed to PID (Proportional, Integral
and Derivative) controller 232. The error 230 is processed by the
digital PID control loop which continually calculates a new value
to be fed to D/A converter 234, where it is converted to an analog
value and amplified by controlled DC to DC converter 214. The
output of controlled DC to DC converter 214 is then fed to medium
sensor 112 to raise or lower the sensor 112's power level until the
average resistance error 230 is zero and sensor 112's temperature
is at the preferred value of 140 degrees Centigrade.
[0092] PID controllers are often used for closed loop control and
are known to those skilled in the art. The basic principle of
operation of the PID loop is to output the sum of three terms, P,
I, and D, which perform different specific functions. The
Proportional, or P, term multiplies the error by a constant and
feeds it directly to the sum; if the wire temperature falls below
the set point, the P term immediately calls for more power. The
Integral, or I, term integrates the error and applies it to the
output sum. In this way small errors will accumulate over a period
of time so that the average error is zero. The Derivative, or D,
term applies a rate feedback term to the output sum to keep the
system from overshooting. We have discovered that, in the preferred
embodiment of the temperature control systems for thin sensor 114,
medium sensor 112, scoop sensor 116 and compensation sensor 118 the
D term is not required.
[0093] Preferably, D/A 234 has an adjustable minimum voltage
setting that sets a minimum power level that will be delivered to
medium sensor 112 to prevent divide by zero errors in a resistance
calculation of divider 224 of FIG. 4 for example. Preferably, this
minimum power level is set low enough to not substantially heat
sensor 112 and introduce errors into a power calculation for the
determination of wet or dry power and allow for safe operation down
to zero airspeed.
Deice Temperature Control System
[0094] A deice temperature control system 308 is located in
temperature controller 20 and maintains sense module shroud 120,
strut 130 and fairing 134 at a substantially constant temperature
to control heat loss from thin sensor 112, medium sensor 114, scoop
sensor 116 and compensation sensor 118 to the shroud. In the
preferred embodiment shroud 120, strut 130 and fairing 134 are at
ground potential and form a return path for current through sensors
112, 114, 116 and compensation sensor 118 as well as for heater
sections 264 and 266. The return path connection for sensors 112,
114, 116 is through the shroud at region 135 of FIG. 2G and the
connection for compensation sensor 118 is made by stud 138 as shown
in FIG. 2G.
[0095] Deice temperature control system 308 includes deice strut
heater 268, shroud heater 252 which is preferably in the form of a
heater tape placed between inner shroud portion 126 and outer
shroud portions 128. As illustrated in FIGS. 2G and 5, shroud
heater 252 comprises fwd heater portion 264 section and aft heater
portion 266, both of which are fed by an electrical connection 262
in region 136 as shown in FIG. 2C. In the preferred embodiment, the
electrical connection forces the fwd portion 264 of heater 252 (see
2G) to have a lower resistance than aft portion 266 to provide more
heat at the forward portion of the shroud which is first cooled by
airstream 104. The lower resistance of the fwd section 264 than the
resistance of aft section 266 provides that the shroud heater 264
operates at a higher power level then aft heater 266.
[0096] Strut heater 268 and heater sections 264 and 266 are
preferably connected in parallel and fed by pulse width modulator
314 having a fixed frequency of approximately 895 hz. The
temperature of the shroud 120, fairing 134 and strut in the region
of thermistor 140 is controlled by feeding back the resistance read
at thermistor 140 and adjusting the output of pulse width modulator
314 to maintain thermistor 140 at a constant temperature of
preferably 50 degrees C.
[0097] One end of thermistor 140 is connected to fairing 135 which
is at ground potential and the other end is connected to A/D
converter 324 via amplifier 316 and RMS converter 352. A/D
converter 324 preferably includes a current source output fed to
thermistor 140 to convert the resistance of thermistor 140 into an
analog voltage. The analog voltage is converted to its digital
equivalent by A/D converter 324.
[0098] The output of A/D converter 324 is compared to a desired
Deice Temperature Set point (DTset) stored in processor 340 and a
difference from subtractor 326 is fed to PID controller 332 and
there to pulse width modulator 314. We have found that the "D" term
of the PID controller used in the Deice temperature control systems
can be useful for maintaining the shroud 120, fairing 134 and strut
130 at a correct temperature because of its greater thermal mass as
compared individual sensors 112, 114, 116 and 118.
[0099] The power supplied to heaters 268, 264 and 266 is calculated
by sensing heater voltage between sense point 262 and ground while
current through the heaters is measured by shunt 312. The
calculated power as well as the resistance of thermistor is sent to
control unit 30 or 30A and is used in the preferred embodiment as a
backup indicator of total water content and a measure of the
condition of the heaters 268, 264 and 266.
[0100] At low or zero airspeed, a minimum amount of deice power is
required. As the airspeed increases, or ambient temperature
decreases, the amount of deicing power will increase. Furthermore
during encounters with liquid water and or ice water, extra power
will be delivered by the deice control loop to compensate for the
increased cooling of the impinging water. Preferably up to 375
watts of heating power can be provided to the shroud 120, fairing
134 and strut 134 heaters.
Calculation of Water Content
[0101] The cooling of compensation sensor 118, by virtue of its
orientation, is substantially independent of both the LWC and IWC
of the air flowing in airstream 104 through sensor module 110.
Thus, the power to hold the compensation sensor 118 at a constant
temperature is substantially only a function of the airflow or dry
power.
[0102] Preferably, the dry power value to subtract from the total
power provided to each sensor 112, 114 and 116 is determined using
the curves of FIG. 7, which relate the dry power for compensation
sensor 118 to a dry power value for each of sensors 112, 114 and
116. For best performance, the curves of FIG. 7 are preferably
generated in a wind tunnel with a substantially water free airflow
104. In an alternate embodiment the curves would be generated from
thermodynamic considerations.
[0103] Water content, whether originating as ice water or liquid
water, is measured by measuring the power (wet power) to keep a
sensor at a fixed temperature while the water in contact with a
sensor is evaporated.
[0104] When a droplet of liquid water impacts any of the sensors
112, 114 or 116, two steps are necessary to evaporate the droplet.
First the droplet must be heated from its initial temperature to
its evaporative temperature, which at standard conditions requires
1 calorie/gram. Then, once at the evaporative temperature, an
additional approximately 540 cal/gram (corrected for the
evaporative pressure when known), the latent heat of evaporation,
will cause the droplet to evaporate.
[0105] Likewise it is known from theory that if the water to be
evaporated started in a glaciated state (i.e. as ice) as might be
the case of the scoop sensor 116, an additional 80 cal/gram would
be necessary to convert the ice into water. We have found however
that ignoring the 80 cal per gram factor simplifies calculations
without having a major influence on results.
[0106] As one skilled in the art knows, the temperature at which a
droplet begins to rapidly evaporate, T.sub.evap, depends on ambient
pressure and that the latent heat of vaporization depends on the
T.sub.evap and methods for determining these corrections are
therefore not further discussed for purposes of brevity.
[0107] The next step in the calculation of liquid water content
measured by sensor 112 and 114 and liquid water and or ice water
content as measured in scoop sensor 116, is to convert the power
dissipated in each of the sensors, after correction for the dry
power losses, into grams of water currently being evaporated and
then, knowing the projected area of each sensor and true airspeed,
into grams per cubic meter. These conversions are expressed in the
following equation known to those skilled in the art:
LWC ( g m 3 ) = P sense . wet ( watts ) 2.389 .times. 10 5 [ L evap
cal g + 1.0 cal g .degree. C . ( T evap - T ambient ) ] TAS m s L
sense mm W sense mm ##EQU00001##
Where:
[0108] P.sub.sense,wet=Wet Power measured by the sense element
watts L.sub.evap=Latent heat of evaporation cal/gm as corrected for
evaporative temperature T.sub.evap=Evaporative temperature in
.degree. C. as corrected for Ambient pressure T.sub.ambient=Static
Ambient temperature in .degree. C. L.sub.sense=Length of the sense
element in mm W.sub.sense=Width of the sense element in mm TAS=True
airspeed in m/s
[0109] The equation above gives the water evaporated by each of the
medium sensor 112, thin sensor 114 and scoop sensor 116.
[0110] We have confirmed in wind tunnel tests that the design and
placement of scoop sensor 116 tends to capture and evaporate liquid
water and ice water without affecting the response of the medium or
thin sensors 112 and 114. The result is that heat lost from scoop
116, after subtraction of dry power, is a measure of the TWC (the
sum of LWC and IWC) in a cloud. Likewise, and as discussed, the
powers to keep medium sensor 112 and thin sensor 114 at a constant
temperature (after subtraction of the dry power) are measures of
the LWC water in airstream 104 through the sensor module 110.
[0111] Moreover it is known that larger diameter drop sizes tend
not to stick to the thin sensor 114 long enough to evaporate while
they do tend to stick to the medium sensor 112. Likewise smaller
drops tend to pass around the medium sensor but stick to the thin
sensor. This behavior results in different measurements of LWC
using medium sensor 112 and thin sensor 114 and this difference is
useful in estimating MVD.
[0112] The calculations above are performed in Control unit 30 and
30a using power data transmitted from temperature controller 208
via UART 244 as shown in FIG. 4.
Estimation of MVD
[0113] The difference in response of the medium sensor and thin
sensor to droplet size, when expressed as a ratio of wet power of
medium sensor 112 to wet power of thin sensor 114, and calibrated
in a wind tunnel, has been found to be a repeatable discriminator
of the MVD of cloud liquid water. Calibration is accomplish by in a
wind tunnel using a calibrated source of known MVD, logging the
ratio of wet powers of the medium and thin sensor as a function of
MVD and storing the results in EPROM 424 located in Control Unit 30
and 30a and shown in FIGS. 10 and 11. FIG. 8 shows calibration
results from wind tunnel measurements for the preferred embodiment
at true airspeeds speeds of up to 100 meters per second and MVD's
up to 100 microns.
Detection and Measurement of Ice Water
[0114] Since the heat loss from the preferred medium sensor 112 and
preferred thin sensor 114 do not substantially change in the
presence of the ice water but the scoop sensor 116 does show
increased heat loss in the presence of liquid water or ice water,
the invention uses these response characteristics to discriminate
between the presence of the different water phases as described
below.
[0115] If either the medium sensor 112 or thin sensor 114 show LWC
due to moisture AND the TWC from the scoop sensor 116 is greater
than the larger of the LWC from the medium sensor 112 OR thin
sensor 114 then the larger of the LWC calculations from the medium
or thin sensor gives a measure of the LWC and the TWC contains both
liquid water and ice water, i.e. the cloud is of mixed phase.
Subtraction of LWC from TWC gives a measure of the IWC.
[0116] If the TWC given by the scoop sensor 116 is substantially
equal to the larger of the value from the medium or thin sensor,
then the cloud water is substantially all water, the TWC is
substantially equal to the LWC.
[0117] Moreover, if the scoop indicates heat loss but neither the
medium or thin sensor indicates meaningful heat loss due to
moisture, then the water in the cloud is substantially all ice
water.
[0118] An alternate embodiment of the invention provides corrected
measurement and detection accuracy of LWC and IWC as follows. The
invention sense head 10 is placed in a wind tunnel or other
calibrated environment. A LWC ratio is formed by measurement of LWC
as measured by thin sensor 114, to a LWC measurement as measured by
a wind tunnel reference device and the ratio is recorded as a
function of MVD as given by an MVD reference device. In a preferred
embodiment, a best fit curve in the form of an exponential is
formed using the ratio and MVD values within a spread sheet
program. Data representing the best fit curve is preferable stored
in the form of a lookup table in the EPROM 424 of control unit 30
or 30a. Test data and a best fit curve in the form of an
exponential for thin sensor 114 are provided in FIG. 9.
[0119] This same process is repeated for medium sensor 112 and
scoop sensor 116.
[0120] In a flight environment, the invention calculates initial
LWC values from medium sensor 112 and thin sensor 114 based on wet
power measurements as previously described, and then selects the
higher of the two values storing both the higher value and an
indicator of which of the sensors experienced the higher value.
[0121] As an example, for a case where thin sensor 114 gives a
higher value of LWC, the invention uses a substantially
simultaneously determined value of MVD (by the ratio of wet powers
of medium sensor 112 to the wet power of thin sensor 114 as a
function of MVD curve) to enter a look up table based on FIG. 9 to
yield an LWC correction factor. The inverse of this factor is then
multiplied by the higher LWC to yield a corrected LWC.
[0122] Moreover subtraction of a corrected LWC from TWC gives an
improved value of IWC.
Power Fluctuations due to Approaching Cloud Water or Ice
[0123] An alternate embodiment of the invention combines
measurement of LWC and IWC using the wet power measurements with
information gained from fluctuations of total power for each sensor
that are experienced before significant measurements of wet power
as described below.
[0124] It was observed during testing in both wind tunnels and
on-board aircraft that, as the amount of cloud water begins to
rise, but prior to there being a significant level of average wet
power delivered to either of the medium 112, thin 114 or scoop 116
sensors to establish that the sensor head 10 is actually in a
cloud, fluctuations in total power (wet plus dry) to either or all
of the medium 112, thin 114 and scoop 116 sensors can increase
noticeably.
[0125] The rapid response of the sensors 112, 114 and 116 in
cooperation with the temperature control systems represented by
temperature control system 208 gives changing sensor power values
(wet plus dry) in response to random fluctuations in the amount of
water intercepted by the sensor. This response, which is estimated
to be less 0.01 seconds, is useful even though the cloud is, in
general, quite uniform (over a large distance) while having little
appreciable water. Said another way, while the average amount of
water over a large volume of the cloud may be small, the sensors
none the less respond to small pockets of water in the cloud.
[0126] Furthermore as the amount of cloud water increases, the
power fluctuations diminish and the calculated LWC and IWC
measurement indicate the presence of water in either liquid or ice
form.
Calculation of Power Fluctuations
[0127] In operation, a temperature controller 208, in order to
maintain a sensor at a preferred temperature of 140 degrees C.,
adjusts the power level to the sensor multiple times per second,
the preferred rate being twenty to forty times per second.
[0128] The presence of pockets of liquid water or ice water is
determined (for each sensor) as follows: [0129] 1. All the power
level samples for a given period of time, typically one second, are
averaged together giving an average power level for the particular
time period. [0130] 2. The average value calculated in Step 1 is
subtracted from each individual power sample taken in the time
period, giving the departure from average for each power sample.
[0131] 3. The absolute value of each sample's departure is then
calculated. The result is the magnitude of each samples fluctuation
around the average [0132] 4. An average of all the individual,
absolute values is then computed. [0133] 5. If the magnitude of
this averaged value exceeds the specified threshold value
associated with each sensor given below, then the associated sensor
is exposed to liquid water and or ice water as indicated.
[0134] The steps 1 through 5 are performed for the power values for
each of sensors 112, 114 and 116 and the resulting values are used
in the display logic given in a paragraph below. It is noted that
the magnitude of the power fluctuations developed above are termed:
"medium sensor power fluctuations", "thin sensor power
fluctuations" and "scoop sensor power fluctuations".
[0135] In an alternate embodiment, a Fourier analysis is done on
the stream of power level samples to provide an RMS value of the
resulting spectrum (with dc term removed) and therefore an
indication of the level of power fluctuations.
[0136] These calculations of sensor power fluctuations are
performed in control units 30 or 30A.
Data Reduction and Display
[0137] Data reduction processes and display functions are
preferably performed in processor 418 of Control Unit 30 as shown
in FIG. 10 and based on power calculations performed in a
temperature controller for each sensor representatively displayed
by temperature controller 208 shown in FIG. 4. Processor 418 in
control unit 30 receives multiplex serial power data 456 from each
temperature controller via UART 414 in control unit 30 as well as
ambient data 454 from a host aircraft (or wind tunnel facility if
appropriate) via an ARINC 429 link. Common data stream 456 also
includes power supplied to deice heaters 262, 264 and 266 via UART
414 of FIG. 5. Common stream 456 is formed in a multiplexer (not
shown) that combines the outputs of all UARTS represented by UART
244 and UART 344 of FIG. 5.
[0138] Processor 418 accesses RAM 420, EPROM 424, which stores
calibration data, and ROM 422 having program data stored therein.
Processor 418 also provides a signal to cockpit warning indicator
light 426 when an unsafe or potentially unsafe condition occurs in
flight.
[0139] Threshold driven indicators present in control unit 30 and
control unit 30a are controlled as follows. Note that like
reference numbers refer to similar items and functionality for both
control units 30 and 30A.
IWC Indicator 402 illuminates if the result of performing the
following logic yields a logical "TRUE" signal:
[0140] IF ((Calculated IWC exceeds a specified threshold #1) OR
((Scoop sensor power fluctuations exceed a specified threshold #2)
AND (medium sensor power fluctuations do not exceed a specified
threshold #3) AND (thin sensor power fluctuations do not exceed
specified threshold #4)))
SLD (Super-cooled Large Droplets) Indicator 404 illuminates if the
result of performing the following logic yields a logical "TRUE"
signal:
[0141] IF ((Calculated MVD exceeds a specified threshold #5) AND
((Calculated LWC from the medium sensor exceeds specified threshold
#6) OR (Calculated LWC from the thin sensor exceeds a specified
threshold #7)) AND (Air temperature is below specified threshold
#8))
LWC Indicator 406 illuminates if the result of performing the
following logic yields a logical "TRUE" signal:
[0142] IF ((Calculated LWC from the medium sensor exceeds specified
threshold #9) OR (Calculated LWC from thin sensor exceeds specified
threshold #10))
IN Cloud indicator 408 illuminates if the result of performing the
following logic yields a logical "TRUE" signal:
[0143] IF ((Measured LWC from the thin sensor exceeds specified
threshold #11) OR (Measured LWC from the medium sensor exceeds
specified threshold #12) OR (Measured TWC from the scoop sensor
exceeds specified threshold #13) OR (Thin sensor power fluctuations
exceeds specified threshold #14) OR (Medium sensor power
fluctuations exceeds specified threshold #15) OR (Scoop sensor
power fluctuations exceeds specified threshold #16))
Potential Icing Indicator 410 illuminates if the result of
performing the following logic yields a logical "TRUE" signal:
[0144] IF ((In Cloud indicator 408 is illuminated) AND (Air
temperature is below specified threshold #17))
[0145] Where sensor power fluctuations are fluctuations of total
power to a sensor, that is, wet power plus dry power and: [0146]
threshold #1 is preferably 0.020 gm/m3; threshold #2 is preferably
0.080 watts; threshold #3 is preferably 0.040 watts; threshold #4
is preferably 0.010 watts; threshold #5 is preferably 50.0 um;
threshold #6 is preferably 0.020 gm/m3; threshold #7 is preferably
0.020 gm/m3; threshold #8 is preferably +2.0 deg Centigrade;
threshold #9 is preferably 0.020 gm/m3; threshold #10 is preferably
0.020 gm/m3; threshold #11 is preferably 0.020 gm/m3; threshold #12
is preferably 0.020 gm/m3; threshold #13 is preferably 0.020 gm/m3;
threshold #14 (same as threshold #4) is preferably 0.010 watts;
threshold #15 (same as threshold #3) is preferably 0.040 watts;
threshold #16 (same as threshold #2) is preferably 0.080 watts; and
threshold #17 is preferably +2.0 deg Centigrade.
[0147] As one skilled in the art would appreciate, alternate
embodiments or modifications to the invention as well as desired
false alarm rates could affect a choice of thresholds.
[0148] Control Unit 30 includes an LCD display 444 which, in
addition to displaying the indicators described above, also provide
measurement data in analog form as described as follows. Bar graph
428 indicates MVD over the preferred range of 0-100 microns or
alternately in excess of 250 microns. Bar graphs 430, 432, 434 and
436 indicates IWC, TWC (from Scoop sensor 116) LWC from medium
sensor 112 and thin sensor 114 over a preferred range of about 0 to
about 3 g/m.sup.3 and alternative over the range of about 0 to
about 5 g/m.sup.3. Control unit 30 also includes time history 442
to shown present and past values of TWC, IWC and the larger of LWC
measured by the medium sensor or thin sensors.
[0149] Control Unit 30 is preferably used in a research environment
such as a research aircraft or wind tunnel facility. In a commuter,
commercial, private or military aircraft an alternate embodiment as
shown in FIG. 11 at 30A is preferred. The primary difference
between the embodiments 30 and 30A is that in control unit 30 only
the threshold indicators 402, 404, 406, 408 and 410 are used. In
addition, processor 418 of control unit 30 and shown in FIG. 10
preferrably has increased processing power/speed when compared to
processor 416 of control unit 30A to accommodate calculations
needed to control the display of measured values.
[0150] It can thus be seen that the present invention provides an
improved system and method for the calculation of cloud parameters
previously only possible by using multiple instruments on research
aircraft. In particular, the present invention provides an improved
system and method for providing a statistical measure of the size
of liquid water droplets, for detection and/or measurement of the
presence of a cloud and/or LWC, IWC and SLD parameters; for
overcoming difficulties of duplicating cloud conditions, and MVD in
particular, in wind tunnel testing; as well as an improved system
that is lightweight and suitable for use on non-research
aircraft.
[0151] For example, it can thus be seen that in one preferred
embodiment, the present invention is directed to a system for
determining a measure of cloud water droplet size based on sensor
cooling by cloud water and stored sensor power ratio and droplet
size data, the system comprising a first and second temperature
controlled co-located self heated sensors, the cooling of the
sensors being substantially independent of ice water; a self heated
compensation sensor oriented to be substantially independent of
cloud water cooling; a variable power source coupled to each first
and second sensor for keeping each sensor at a temperature and each
having a measurable output power; a variable power source coupled
to the compensation sensor for keeping the sensor at a temperature
and having a measurable output power; and a control unit for
correcting the measured power to each of the first and second
sensors to reflect only heat loss due to cloud water by subtracting
from the measured power an adjusted compensation sensor measured
value; and forming a ratio of corrected power of each of the first
and second sensors to identify a liquid water droplet size based on
the stored power ratio and droplet size data.
[0152] In another embodiment, the present invention is directed to
a system for measuring water droplet size in a cloud, wherein the
system comprises a sensor head comprising a first heated sensor
having a resistance characteristic that is temperature dependent,
wherein power loss from the sensor is at least essentially not
affected by the presence of ice water in an airflow thereacross; a
second heated sensor having a second resistance characteristic that
is temperature dependent, wherein power loss from the second sensor
is at least essentially not affected by the presence of ice water
in the airflow thereacross; a heated compensation sensor being
positioned to be responsive to the airflow thereacross and having a
power loss at least essentially not affected by the presence of
liquid water or ice water in the airflow thereacross; a respective
temperature controller associated with each of the first sensor,
second sensor and compensation sensor, each of which for
maintaining the temperature of the respective sensors at respective
temperature values using its temperature dependent resistance
characteristic, wherein, for each of the first and second sensors,
the respective controller maintains the sensor at the temperature
value by adjusting a power level fed to the sensor; calculates the
total power required to maintain the sensor at the temperature
value when the sensor is exposed to an airflow comprising at least
one of liquid water and ice water; and a control unit for receiving
power levels from each of the first sensor and second sensor;
subtracting, from each total power calculation, a dry power
component determined from the power required to maintain the
compensation sensor at its temperature value in the presence of the
airflow comprising at least liquid water, thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first and second sensors at the
respective temperature values in the presence of at least liquid
water in the airflow; and for forming a ratio of the wet power
value of the first sensor to the wet power value of the second
sensor to obtain an estimated value of the measure of water droplet
size in the cloud from a predetermined calibrated relationship of
wet power ratio to water droplet sizes.
[0153] In yet another embodiment, the present invention is directed
to a system for determining liquid water content in a cloud,
wherein the system comprises a sensor head comprising a first
heated sensor having a first resistance characteristic that is
temperature dependent, wherein the first sensor is at least
essentially not affected by the presence of ice water in an airflow
thereacross; a second heated sensor having a second resistance
characteristic that is temperature dependent, wherein the second
sensor is at least essentially not affected by the presence of ice
water in the airflow thereacross; a heated compensation sensor
being positioned to be responsive to the airflow thereacross and at
least essentially not affected by the presence of liquid water or
ice water in the airflow thereacross; a respective temperature
controller associated with each of the first sensor, second sensor
and compensation sensor, each of which for maintaining the
temperature of the respective sensors at respective temperature
values using its temperature dependent resistance characteristic,
wherein, for each of the first and second sensors the respective
controller maintains the sensor at the temperature value by
adjusting a power level fed to the sensor; calculates the total
power required to maintain the sensor at the temperature value when
the sensor is exposed to an airflow comprising at least liquid
water; and a control unit for receiving power levels from each of
the first sensor and second sensor; subtracting, from each total
power calculation, a dry power component determined from the power
required to maintain the compensation sensor at its temperature
value in the presence of the airflow thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first and second sensors at the
respective temperature values in the presence of at least liquid
water in the airflow; and calculating a liquid water content for
the first sensor and sensor wet power values and selecting the
higher LWC as the desired liquid water content.
[0154] In still another embodiment of the present invention, a
system is provided for determining liquid water content in a cloud,
the liquid water having a determined droplet size, wherein the
system comprises a sensor head comprising a first heated sensor
having a first resistance characteristic that is temperature
dependent, wherein the first sensor is at least essentially not
affected by the presence of ice water in an airflow thereacross; a
second heated sensor having a second resistance characteristic that
is temperature dependent, wherein the second sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a heated compensation sensor being positioned
to be responsive to the airflow thereacross and at least
essentially not affected by the presence of liquid water or ice
water in the airflow thereacross; a respective temperature
controller associated with each of the first sensor, second sensor
and compensation sensors, each of which for maintaining the
temperature of the respective sensors at respective temperature
values using its temperature dependent resistance characteristic,
wherein, for each of the first and second sensors the respective
controller maintains the sensor at the temperature value by
adjusting a power level fed to the sensor; calculates the total
power required to maintain the sensor at the temperature value when
the sensor is exposed to an airflow comprising at least liquid
water; and a control unit for receiving power levels from each of
the first sensor and second sensor and having a stored droplet size
verses liquid water content correction curve for each first and
second sensor; subtracting, from each total power calculation, a
dry power component determined from the power required to maintain
the compensation sensor at its temperature value in the presence of
the airflow thereby arriving at a wet power value attributable to
the incremental power associated with maintaining the respective
first and second sensors at the respective temperature values in
the presence of liquid water in the airflow; and calculating a
liquid water content for the first sensor and second sensor wet
power values, selects the higher of the calculated liquid water
content values, and corrects the higher of the two values using a
droplet size verses liquid water content correction curve.
[0155] In yet another embodiment, a system is provided for
determining the presence of ice water in an airflow, wherein the
system comprises a sensor head comprising a first heated sensor
having a first resistance characteristic that is temperature
dependent, wherein heat the from first sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a second heated sensor having a second
resistance characteristic that is temperature dependent, wherein
heat from the second sensor is at least essentially not affected by
the presence of ice water in the airflow thereacross; a third
heated sensor having a third resistance characteristic that is
temperature dependent, wherein heat loss from the third sensor is
affected by a presence of ice water in the airflow thereacross; a
heated compensation sensor being positioned to be responsive to the
airflow thereacross and having a heat loss least essentially not
affected by the presence of liquid water or ice water in the
airflow thereacross; a respective temperature controller associated
with each of the first sensor, second sensor, third sensor and
compensation sensors, each of which for maintaining the temperature
of the respective sensors at respective temperature values using
its temperature dependent resistance characteristic, wherein, for
each of the first, second and third sensors, the respective
controller maintains the sensor at the temperature value by
adjusting a power level fed to the sensor; calculates the total
power required to maintain the sensor at the temperature value when
the sensor is exposed to an airflow comprising at least ice water;
and a control unit for receiving power levels from each of the
first sensor and second sensor; subtracting, from each total power
calculation, a dry power component determined from the power
required to maintain the compensation sensor at its temperature
value in the presence of the airflow comprising at least ice water,
thereby arriving at a wet power value attributable to the
incremental power associated with maintaining the respective first,
second and third sensors at the respective temperature values in
the presence of at least ice water in the airflow; and calculating
a water content measurement for the first sensor, second sensor and
third sensor wet power values, selecting a higher water content
value from the first and second sensor and subtracting the higher
value from the water content value of the third sensor to indicate
a presence of ice water.
[0156] In still another embodiment, a system is provided for
warning of cloud water, the system comprising a first temperature
controlled self heated sensor, a variable power source for the
first sensor having a measurable output power responsive to changes
in cloud water; a processor for averaging the measured output power
of the power source and subtracting a substantially instantaneous
measure of the output power of the power source to determine
fluctuations around the average; and comparing the fluctuations to
a threshold indicative of the presence of cloud water.
[0157] In still further embodiments, the aforementioned
constructions could be modified by those skilled in the art while
remaining within the scope of the present invention. Thus, the
invention generally covers means for carrying out the
aforementioned functionality. For example, a single controller or
control unit could carry out the aforementioned functionality if so
desired, and therefore, the invention is not limited by the
specific construction set forth above.
[0158] As should now be seen, the present invention is also
directed to a plurality of methodologies. For example, in
accordance with a first embodiment, a method for determining a
measure of cloud water droplet size based on sensor cooling by
cloud water and stored sensor power ratio and droplet size data,
utilizing a system comprising a first and second temperature
controlled co-located self heated sensors, the cooling of the
sensors being substantially independent of ice water, a self heated
compensation sensor oriented to be substantially independent of
cloud water cooling; a variable power source coupled to each first
and second sensor for keeping each sensor at a temperature and each
having a measurable output power; and a variable power source
coupled to the compensation sensor for keeping the sensor at a
temperature and having a measurable output power, wherein the
method comprises the steps of correcting the measured power to each
of the first and second sensors to reflect only heat loss due to
cloud water by subtracting from the measured power an adjusted
compensation sensor measured value; and forming a ratio of
corrected power of each of the first and second sensors to identify
a liquid water droplet size based on the stored power ratio and
droplet size data.
[0159] In yet another embodiment, the present invention is directed
to a method of measuring water droplet size in an airflow,
utilizing a system comprising a sensor head comprising a first
heated sensor having a resistance characteristic that is
temperature dependent, wherein power loss from the sensor is at
least essentially not affected by the presence of ice water in the
airflow thereacross; a second heated sensor having a second
resistance characteristic that is temperature dependent, wherein
power loss from the second sensor is at least essentially not
affected by the presence of ice water in the airflow thereacross; a
heated compensation sensor being positioned to be responsive to the
airflow thereacross and having a power loss at least essentially
not affected by the presence of liquid water or ice water in the
airflow thereacross, wherein the method comprises the steps of
maintaining the temperature of the respective sensors at respective
temperature values using its temperature dependent resistance
characteristic; and wherein, for each of the first and second
sensors, the method comprises the steps of maintaining the sensor
at the temperature value by adjusting a power level fed to the
sensor and calculating the total power required to maintain the
sensor at the temperature value when the sensor is exposed to an
airflow comprising at least one of liquid water and ice water;
wherein the method further comprises the steps of receiving power
levels from each of the first sensor and second sensor;
subtracting, from each total power calculation, a dry power
component determined from the power required to maintain the
compensation sensor at its temperature value in the presence of the
airflow comprising at least liquid water, thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first and second sensors at the
respective temperature values in the presence of at least liquid
water in the airflow; and forming a ratio of the wet power value of
the first sensor to the wet power value of the second sensor to
obtain an estimated value of the measure of water droplet size in
the cloud from a predetermined calibrated relationship of wet power
ratio to water droplet sizes.
[0160] In still yet another embodiment, a method is provided for
determining liquid water content in an airflow, utilizing a system
comprising a sensor head comprising a first heated sensor having a
first resistance characteristic that is temperature dependent,
wherein the first sensor is at least essentially not affected by
the presence of ice water in an airflow thereacross; a second
heated sensor having a second resistance characteristic that is
temperature dependent, wherein the second sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a heated compensation sensor being positioned
to be responsive to the airflow thereacross and at least
essentially not affected by the presence of liquid water or ice
water in the airflow thereacross; wherein the method comprises the
steps of maintaining the temperature of the respective sensors at
respective temperature values using its temperature dependent
resistance characteristic, maintaining the sensors at the
temperature value by adjusting a power level fed to the sensor;
calculating the total power required to maintain the sensor at the
temperature value when the sensor is exposed to an airflow
comprising at least liquid water; receiving power levels from each
of the first sensor and second sensor; subtracting, from each total
power calculation, a dry power component determined from the power
required to maintain the compensation sensor at its temperature
value in the presence of the airflow thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first and second sensors at the
respective temperature values in the presence of at least liquid
water in the airflow; and calculating a liquid water content for
the first sensor and sensor wet power values and selecting the
higher LWC as the desired liquid water content.
[0161] Still in another embodiment, a method is provided for
determining liquid water content in an airflow, the liquid water
having a determined droplet size, utilizing a system comprising a
sensor head comprising a first heated sensor having a first
resistance characteristic that is temperature dependent, wherein
the first sensor is at least essentially not affected by the
presence of ice water in an airflow thereacross; a second heated
sensor having a second resistance characteristic that is
temperature dependent, wherein the second sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a heated compensation sensor being positioned
to be responsive to the airflow thereacross and at least
essentially not affected by the presence of liquid water or ice
water in the airflow thereacross; wherein the method comprises the
steps of maintaining the temperature, of the respective sensors at
respective temperature values using its temperature dependent
resistance characteristic and, for each of the first and second
sensors, maintaining maintains the sensor at the temperature value
by adjusting a power level fed to the sensor and calculating the
total power required to maintain the sensor at the temperature
value when the sensor is exposed to an airflow comprising at least
liquid water; wherein the method further comprises the steps of
receiving power levels from each of the first sensor and second
sensor and having a stored droplet size verses liquid water content
correction curve for each first and second sensor; subtracting,
from each total power calculation, a dry power component determined
from the power required to maintain the compensation sensor at its
temperature value in the presence of the airflow thereby arriving
at a wet power value attributable to the incremental power
associated with maintaining the respective first and second sensors
at the respective temperature values in the presence of liquid
water in the airflow; and calculating a liquid water content for
the first sensor and second sensor wet power values, selects the
higher of the calculated liquid water content values, and corrects
the higher of the two values using a droplet size verses liquid
water content correction curve.
[0162] In yet another embodiment, a method is provided for
determining the presence of ice water in an airflow, utilizing a
system comprising a sensor head comprising a first heated sensor
having a first resistance characteristic that is temperature
dependent, wherein heat the from first sensor is at least
essentially not affected by the presence of ice water in the
airflow thereacross; a second heated sensor having a second
resistance characteristic that is temperature dependent, wherein
heat from the second sensor is at least essentially not affected by
the presence of ice water in the airflow thereacross; a third
heated sensor having a third resistance characteristic that is
temperature dependent, wherein heat loss from the third sensor is
affected by a presence of ice water in the airflow thereacross; a
heated compensation sensor being positioned to be responsive to the
airflow thereacross and having a heat loss least essentially not
affected by the presence of liquid water or ice water in the
airflow thereacross; wherein the method comprises the steps of
maintaining the temperature of the respective sensors at respective
temperature values using its temperature dependent resistance and
wherein, for each of the first, second and third sensors,
maintaining the sensor at the temperature value by adjusting a
power level fed to the sensor and calculating the total power
required to maintain the sensor at the temperature value when the
sensor is exposed to an airflow comprising at least ice water;
wherein the method further comprises the steps of receiving power
levels from each of the first sensor and second sensor;
subtracting, from each total power calculation, a dry power
component determined from the power required to maintain the
compensation sensor at its temperature value in the presence of the
airflow comprising at least ice water, thereby arriving at a wet
power value attributable to the incremental power associated with
maintaining the respective first, second and third sensors at the
respective temperature values in the presence of at least ice water
in the airflow; and calculating a water content measurement for the
first sensor, second sensor and third sensor wet power values,
selecting a higher water content value from the first and second
sensor and subtracting the higher value from the water content
value of the third sensor to indicate a presence of ice water.
[0163] In still another preferred embodiment of the present
invention, a method is provided for warning of cloud water using a
first temperature controlled self heated sensor and a variable
power source for the first sensor having a measurable output power
responsive to changes in cloud water, wherein the method comprises
the steps of averaging the measured output power of the power
source; subtracting a substantially instantaneous measure of the
output power of the power source to determine fluctuations around
the average; and comparing the fluctuations to a threshold
indicative of the presence of cloud water.
[0164] It will thus be seen that the objects set forth above, among
those made apparent from the preceding description, are efficiently
attained and, since certain changes may be made in the above
constructions without departing from the spirit and scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative and not in a limiting sense.
[0165] It should also be understood that the following claims are
intended to cover all of the generic and specific features of the
invention described herein and all statements of the scope of the
invention that as a matter of language might fall therebetween.
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