&EPA
United States
Environmental Protection
Agency
Environmental Monitoring and Support cPA-600/4-80-028
Laboratory June 1980
Research Triangle Park NC 27711
Research and Development
An Evaluation of the
ASTM Standard
Method for
Determining the
Performance of a
Wind Vane
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2 Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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AN EVALUATION OF THE ASTM STANDARD METHOD FOR
DETERMINING THE PERFORMANCE OF A WIND VANE
Peter L. Finkelstein
Data Management and Analysis Division
Environmental Monitoring Systems Laboratory
Environmental Protection Agency
Research Triangle Park, North Carolina 27711
February 1980
ENVIRONMENTAL MONITORING SYSTEMS LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring Systems
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
Peter L. Finkelstein is a physical scientist in the Environmental Moni
toring Systems Laboratory. He is on assignment from the National Oceanic
and Atmospheric Administration, U.S. Department of Commerce.
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FOREWORD
Measurement and monitoring research efforts are designed to anticipate
potential environmental problems, to support regulatory actions by developing
an in-depth understanding of the nature and processes that impact health and
the ecology, to provide innovative means of monitoring compliance with regu-
lations and to evaluate the effectiveness of health and environmental pro-
tection efforts through the monitoring of long-term trends. The Environmental
Monitoring Systems Laboratory, Research Triangle Park, North Carolina, has the
responsibility for: assessment of environmental monitoring technology and
systems; implementation of agency-wide quality assurance programs for air
pollution measurement systems; and supplying technical support to other groups
in the Agency including the Office of Air, Noise and Radiation, the Office of
Toxic Substances and the Office of Enforcement.
This study was conducted in cooperation with the American Society for
Testing of Materials (ASTM). It was done to evaluate a proposed standard
method for determining the performance of a wind vane. This and other stand-
ard methods for testing meteorological monitoring equipment will be needed in
the development of a comprehensive quality control program for meteorological
measurements. A quality control and assurance program is needed for these
measurements in order to support pollutant dispersion studies, model valida-
tion studies, and mandated monitoring activities. A program to develop a
quality assurance plan for meteorological measurements is now under way at
EMSL/RTP.
Thomas R. Mauser
Director
Environmental Monitoring
Systems Laboratory
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ABSTRACT
The American Society for Testing and Materials (ASTM) has proposed a
standard method for testing the performance characteristics of a wind vane.
This report presents the procedures used to test and evaluate the ASTM
method, and the results of that evaluation. Twelve wind vanes were borrowed
from their manufacturers and tested using the ASTM procedures. The theory
of wind vane dynamics is briefly reviewed, and equipment and procedures are
described. The starting threshold, starting accuracy, delay distance, over-
shoot ratio, and damped wavelength were measured. Damping ratio and natural
wavelength were computed from the measurements. Based on the results of
these tests, it is concluded that the ASTM method provides a reasonable and
reliable technique for determining performance characteristics for many types
of wind vanes.
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CONTENTS
Foreward jii
Abstract iv
List of Symbols vi
Acknowledgment vii
1. Introduction 1
2. Theory 4
3. Apparatus 9
4. Procedure 16
5. Results 25
6. Conclusions and Recommendations 40
Bibliography 43
Appendices
A. The ASTM "Standard Method for Determining the
Performance of a Wind Vane" 44
B. A Letter Sent to Many Manufacturers of Wind Vanes 55
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LIST OF SYMBOLS
d Aerodynamic damping
d Critical damping
D Delay distance
F* Force of wind on vane
J Moment of inertia of vane
"N Torque per unit angle of wind on vane
r Distance between pivot and center of mass of vane
t Time
t, Damped period of time
t Natural period of vane
t. Delay time
u Wind velocity
u1 Turbulent fluctuation of wind speed
6 Angle between vane and wind
3Q Initial offset angle
BV Effective angle of attack
6 de/dt
B de/dt
AP Axial pressure differential in wind tunnel
n Damping ratio
A , Damped wavelength
A Natural wavelength
o Standard deviation
fi Overshoot ratio
VI
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ACKNOWLEDGMENTS
This work was able to be done only because of the cooperation of many
people and organizations. We are most grateful to the companies that loaned
us the wind vanes that were used in these tests; Bendix Co., Environmental
Science Division; Climet Instruments Company; Electric Speed Indicator Co.;
Meteorology Research Inc.; R.M. Young Company; Teledyne Geotech; Texas Elec-
tronics Inc., and WeatherMeasure Corporation. Clearly the support of EPA's
Fluid Modeling Facility was essential, and I wish to thank its director,
Dr. William H. Snyder, for his support and many helpful discussions of flow
vector orientation and members of the very capable staff, Milton Fabert,
Robert E. Lawson, Myron Manning, Michael Shipman, and Roger S. Thompson, fur
their generous help and many kindnesses. Finally and most especially I'd
like to thank Ms. Kathy Brehme (now Lieutenant, USAF) for her many hours of
excellent assistance collecting and reducing the data for this project.
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SECTION 1
INTRODUCTION
The U.S. Environmental Protection Agency (EPA) has a continuing need
for high quality meteorological data. There are, obviously, no legal stand-
ards based upon meteorological data, but air quality models used in multi-
million dollar decision-making are verified, validated, calibrated, modified
and used in rule-making that requires very accurate and representative data.
The Environmental Monitoring Systems Laboratory at Research Triangle Park
(EMSL/RTP) has recognized this need and, in response, has begun work to de-
velop a quality assurance program for meteorological data.
One part of any quality assurance program must be the determination cf
whether or not new and used instruments meet manufacturers and/or users
performance specifications. For meteorological instrumentation this area has
always been difficult, in part because there are no widely agreed upon test-
ing procedures for determining these performance characteristics. Thus,
while manufacturers may state in their literature certain properties of
their instruments, or state that they will meet users specifications, there
is usually no information available on how the manufacturer determined the
specifications of these instruments, and no uniform way the users can check
to see if instruments they purchase or are using will meet their requirements,
The American Society for Testing and Materials (ASTM) has started to
address this problem. They have published a standard for measuring pressure
1
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and are developing standards for measuring humidity and wind velocity. ASTM
is also developing a standard method to test the dynamic performance of a
wind vane, and it is that method that is the subject of this report.
Since EPA has published standards for the performance of wind vanes
(OAQPS, 1978) and is involved in the development and validation of air
quality models, it is apparent that a uniform method for evaluating wind
vanes would be of benefit to the agency. For this reason, EMSL/RTP decided
to undertake a program to test and evaluate the proposed standard method.
The purposes of these tests were to determine if (1) the procedures could be
carried out by personnel with a reasonable level of experience, (2) the pro-
cedures led to precise results, (3) the results were reproducible, and (4)
the method met the overall needs of EPA and ASTM.
The proposed ASTM standard method involves a specific detailed procedure
for determining the "starting threshold," "delay distance," "overshoot" and
accuracy of a vane in a wind tunnel. These values were determined by re-
cording the response of a vane after release from an initial displacement
and analyzing the response curves. Basically, this required holding the vane
ten degrees off the wind tunnel centerline axis, releasing .it without impart-
ing any torque, recording its response on a strip chart recorder, and analyz-
ing the results. (A copy of the proposed methodology is given in Appendix A.)
For the purpose of this evaluation, the method was applied to a number
of different new wind vanes which were loaned to EPA by their manufacturers
for these tests. (A list of vanes tested is given in Section 3.)
It must also be pointed out here that because, with one exception, only
one vane of each type was tested in this program, we know nothing about the
reproducibility of these tests vis-a-vis the particular model instrument.
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Therefore we do not advise anyone to use these results in evaluating whether
or not the vanes tested are or are not suitable for a specific function, or
meet any particular set of criteria.
This report presents a short review of the theory of wind vane behavior,
a description of the test method and procedures, and a presentation and eval-
uation of the results.
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SECTION 2
THEORY
Following the development of Wirenga (1967), the torque per unit angle
on a wind vane which is at some angle 3 to the wind (Figure 2.1) may be
expressed:
H= rF/B (2.1)
where N is the torque per unit angle and r is the distance from the pivot
point of the vane to the center of effort of the force (F) of the wind acting
on the vane.
Figure 2.1 The force on a wind vane.
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As the vane moves in response to a change in wind direction, the center
of force has a velocity rg. Air resistance to the motion of the vane pro-
duces a force on the vane and causes the effective wind angle to change to
ev- It has been shown (Barthelt and Ruppersberg (1957)) that:
- B + (rg/u) (2.3)
For a vane with moment of inertia J, the equation of motion may be written:
-j" = NB + (Nr/u)B (2.4)
Let:
d E Nr/u (2.5)
where (d) may be considered a damping force acting on the vane.
If "N" is a constant, equation (2.4) has two well known solutions; or,2
represents an overdamped or aperiodic return of the vane to equilibrium, and
the other represents a damped harmonic oscillation of the vane as it returns
to equilibrium. Since most wind vanes are not overdamped, we write the solu-
tion to (2.4) as:
(2.6)
where e is some initial position, and
t_, is the oscillation, or in this case, damped oscillation period of the vane
d
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The undamped, or natural period of the vane (t ), is given when d=0:
(2.8)
For critical damping the damping coefficient d=dQ and
N/J = (do/2J)2 (2.9)
The damping ratio (n) is defined as the ratio of actual to critical
damping coefficients.
n = d/do (2.10)
Substituting from (2.8), (2.9) and (2.5) into (2.10):
n = ur/uto (2.11)
but ut is the natural, or undamped wavelength of the vane (A ), so that
n = Trr/AQ (2.12)
Rearranging (2.7):
2 ~| -h
]
and, substituting from (2.8), (2.9) and (2.10):
td = to/x/T7 (2.14)
The damped, or actual wave length of the vane (A,) may now be defined
as:
? -^
Ad = utd - A0(l-n ) (2.15)
Figure 2.2 shows a typical response of a vane released from a position
BQ away from the wind direction and allowed to return to its equilibrium
position (6=0).
At a maximum, or minimum point on the curve (t=0, t=t,/2, t=t,, etc.),
the oscilatory term is ;+! , so that:
3 - SQexp(-dt/2J) (2.16)
-------
LLJ
_1
CJ
ti t1
TIME
Figure 2.2 Typical response of wind vane showing
displacement and overshoot.
7
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The overshoot ratio (n) is defined as the ratio of the amplitudes of two
successive peaks.
n = e-j/B-j.! = exp{-(d/2J)(td/2)} (2.17)
Substituting from equation (2.14), and then equations (2.8), (2.9), and
(2.10), we find:
n = exp(-WVl-Ti ) (2.18)
With some systems which are well damped (n>0.5), it may be difficult to
measure the damped period for a full wavelength. Some authors (Wolkovitch,
et. al , 1962; MacCready and Jex, 1964) have suggested measurement of the
delay distance, D, to solve this problem. The delay time (t-|) is defined as
the time required for the vane to move from its offset position (3 ) to 50
percent of its final equilibrium value. (See Figure 2.2). The delay dis-
tance, like the damped wavelength, should be invariant with wind speed
(Moses, 1968), and it is simply the delay time multiplied by the wind speed.
MacCready and Jex (op cit) have suggested the following empirical relation-
ship (Jex, 1979):
_ D(60 - 2.4n) /
How well this approach fits the data will be examined in Section 5. Acheson
(1970) has also suggested some alternative methods for measuring the response
characteristics of vanes which have large damping ratios (n>0.7). Since the
vanes we tested (and normally use) have damping ratios much less than that,
the method was not evaluated.
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SECTION 3
APPARATUS
The procedures used to evaluate the starting speed, delay distance, and
over-shoot of the wind vanes were done in a wind tunnel. The vane was held
in a fixed off-axis position, calibrated, and released. The position of the
vane was recorded as a function of time. The following equipment was used
for this program.
WIND TUNNEL
These tests were performed in a Kenney model 1391 wind tunnel located
in the Fluid Modeling Facility, Division of Meteorology, Environmental Sci-
ences Research Laboratory, EPA. The tunnel has a cross section of approxi-
mately 1 meter square, with a test length of 3 m. The tunnel has an air
speed range which is continuously adjustable between zero and 15 m/s. The
levels of turbulence in the tunnel are low, with the turbulence intensity
/~=F
(v u' /u) of approximately 1 percent at wind speeds greater than one meter
per second.
DATA COLLECTION
All but two of the wind vanes tested used a rotary potentiometer in
conjunction with a power supply to sense the position of the vane. In nor-
mal use the vane is connected to a regulated, fixed d.c. power supply, which
is usually part of the equipment supplied by the manufacturer of the vane.
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The output signal is usually conditioned in some way (frequently time
averaged) and passed on to a recording device.
Since one goal of this study was to measure the performance of the vanes
themselves, and not their accompanying electronics, and since it was desir-
able to have the small angular displacements used in the study amplified as
large as possible on the recording devices, it was deemed necessary to
supply a controllable voltage from an external source and record the output
from the vane directly, rather than use the manufacturers power supplies,
signal conditioning, and recording devices.
A fast response strip chart recorder or computer was set up between the
vane and a ten-thousand ohm adjustable biasing potentiometer (trim pot) as
shown in Figure 3.1. The power supply was a Dynoscan Precision Regulated
Power Supply, model 1601. For the lower wind speeds, an Esterline Angus
Speed Servo II recorder was used, while for higher speeds, the signal was
sent to an analog-to-digital converter, and thence to a PDP 11/40 computer,
which recorded the output on magnetic tape and then plotted the data in
graphic form.
10
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[VARIABLE
1 POWER
[SUPPLY
'/i r
WINDVANE
^ | RECORDER OR COMPUTER
[TRIM POT]
1 1 I
-r I
j
L
1 1
* '
f '
• 1 1
©
1 1
1 ^
i 1
Figure 3.1 Data collection arrangement.
VANE CALIBRATION AND RELEASE
The directional output of wind vanes was calibrated by holding the vanes
in an aluminum jig which was mounted on a theodolite head (Figures 3.2 and
3.3). A large mounting hole was made in the jig, and individual adaptors
machined for each vane to correspond to its individual geometry and mounting
requirements. Using this device the position of a vane could be determined
within an accuracy of +0.1 .
A 115 V a.c. solenoid with a throw of approximately 2.5 cm was used to
hold the vane tail off-axis in the wind tunnel. Attached to the throw arm
11
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Figure 3.2 Test apparatus with vanes in place.
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'*£• \.
Figure 3.3 Vane holder and theodolite head,
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of the solenoid was an aluminum rod approximately 5 cm long and 0.5 cm in
diameter. One centimeter of the tip of the rod was covered with a teflon
tube. This device was mounted on a laboratory ring stand, which held it in
place (see Figure 3.2), and the vane tail rested against the teflon tip.
When the solenoid was activated, the tip of the rod was pulled back parallel
to the axis of the vane, so that no lateral or turning force (except possibly
for a very small moment due to the friction between the vane and the teflon
tip) was applied to the vane. This was tested by resting the vane tail
against the solenoid arm and activating the solenoid when the tunnel was
off. No motion of the vane was observed.
WIND VANES
A letter (Appendix B) was sent to many major U.S. manufacturers of wind
vanes describing the purposes of this test and requesting the loan of one or
two models of the wind vanes they manufacture. A number of these companies
indicated that they were interested in participating in the EPA/ASTM program,
and subsequently sent vanes to EPA for testing. A list of the vanes which
were tested under this program is given in Table 3.1. As the letter pointed
out, the purpose of this program was to evaluate the ASTM draft method, not
the wind vanes themselves. The program had neither involvement with deter-
mining if any equipment was suitable for any specific function or compliance
with any regulation, nor was it evaluating equipment prior to purchase by the
government.
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TABLE 3.1 LIST OF WIND VANES TESTED
Name
Model
Bendix
Bendix
Climet
Meteorology Research Inc.
R.M. Young
R.M. Young
Weather Measure
Weather Measure
Weather Measure
Teledyne Geotech
Texas Electronics
Texas Electronics
Aerovane
Wind Vane
12-15
1022
Microvane
Wind Vane
102
200
204
53.2
2010(A)
2010(B)*
*Two similar vanes were sent and tested.
15
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SECTION 4
PROCEDURE
ASTM METHOD
As stated in the introduction, the purpose of this study was to evaluate
the "Standard Method for Determining the Dynamic Performance of a Wind Vane"
prepared by Sub-committee D22.ll of the American Society for Testing and Mate-
rials (ASTM). In this section we will review the requirements of the ASTM
method (reproduced in Appendix A), and the details of the procedures used to
meet these requirements.
The ASTM standard method gives a procedure whereby several dynamic
parameters of wind vane performance may be measured in a wind tunnel. These
parameters are starting threshold, delay distance, overshoot, and dynamic
vane bias.
Definitions
Starting threshold—the lowest wind speed at which a vane will turn to
within 5 degrees of the tunnel center! ine from an initial displacement of
10 degrees.
Delay distance (D)--the distance the air flows past a wind vane during
the time it takes the vane to return to 50 percent of the initial displace-
ment.
Overshoot ratio (fl)--the ratio of the amplitudes of two successive de-
flections of a wind vane as it oscillates about the equilibrium position
16
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after release from an offset position, as expressed by the equation:
(4.1)
n
where 6n and 3n+1 are the amplitudes of the n and n+1 deflections, respec-
tively. Because all deflections after the first to the side opposite the
release point are small, the initial release point (i.e., the n=zero deflec-
tion) and the first deflection after release (n=l) are commonly used in de-
termining overshoot.
Dynamic vane bias—the maximum displacement of the vane from the un-
disturbed flow direction at the center of the wind tunnel (typically the
wind tunnel centerline) caused by the free response of the vane to the tunnel
flow.
Derived Parameters
The ASTM method lists two calculated values as follows:
Damping ratio (n)--the ratio of the actual damping coefficient to the
critical damping coefficient. The damping ratio is calculated using the
overshoot ratio (o.) by:
n =
/2 1
V / + (In i)
(4.2)
Damped natural wavelength (xd)--at sea level in the U.S. Standard
Atmosphere, damped natural wavelength is related to delay distance (D) and
damping ratio (n) by the approximate expression (MacCready, 1964):
17
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. D (6.0 - 2.4.J (4>3)
d
These terms were discussed in more detail in Section 2.
Synopsis of Method
The standard method requires that wind vanes be tested in a previously
calibrated tunnel, with recording equipment which has a resolution of at
least 0.5° and will not distort the output signal.
Starting speed is measured by releasing the vanes from a 10° offset
from the tunnel centerline with the speed of the tunnel set quite low. In
this condition if the torque caused by the air is large enough, the vane
will move toward the centerline of the tunnel. It will continue to move
until the torque is no longer strong enough to overcome the dynamic friction.
At this point the vane slowly stops. The starting threshold is that speed at
which the vane will move from the 10° offset to within 5 of the tunnel
centerline. This requirement must be met on 10 consecutive releases; five
on each side of the centerline. The accuracy at starting speed is the mean
of the absolute value of the angular position at which the vane comes to
rest at that starting speed.*
*It was noted in this study that the mean of the at-rest positions when the
vane was released from one side were frequently quite different from that
when the vane was released from the other. Because the mean of these two
values may be misleading to the user of wind vanes, the method has been
changed to report the greater of the two average at-rest positions.
18
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Delay distance and overshoot are measured at 2, 5, and 10 m/s unless
the starting speed of the vane is 1.75 m/s or greater, in which case only 5
and 10 m/s speeds are used. For these tests the vane is released from a 10
offset, and as with starting speed, the response is recorded. At each speed
10 tests are done; five on each side, and the results from each test averaged.
Delay distance is measured by measuring the time required for the vane to go
from its offset position to a point halfway between the offset position and
the point at which it initially crosses the final equilibrium position (tunnel
center! ine). The time, multiplied by the air speed in the tunnel, gives the
delay distance.
Overshoot is measured on the same record used to compute a delay time.
It is simply the ratio of the first peak displacement to the initial displace-
ment. All ratios are averaged to arrive at the final overshoot ratio. This
value may then be used to calculate the damping ratio by equation (4.2).
TUNNEL CALIBRATION
Air speed in the EPA instrument wind tunnel is monitored with a tachom-
eter on the fan. This requires calibration before it can be used as a reli-
able monitor. Two methods of calibration were used. For speeds greater than
1 m/s a pi tot tube was used. For speeds less than 1 m/s, smoke puffs were
timed with a stop watch. The two methods gave comparable results near 1 m/s.
Pi tot Tube
A NPL standard pitot tube was placed in the mid-point of the tunnel.
Pressure differences were measured with a Baration pressure sensor. Veloc-
ity was calculated using the formula:
V(m/s) = 14.82 AP(mm Hg) at 20° C (4.4)
19
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Repeated calibration tests were made, and the standard deviation at several
speeds were calculated. The mean percent deviation (xlOO) was deter-
mined to be 2.5 percent.
Low Speed Calibration
For speeds between 0.3 and 1.0 m/s the wind tunnel was calibrated by
timing puffs of titanium tetrachloride smoke with a stop watch over a path
length of 2 m. Multiple runs at each speed were made. It was found that at
lower speeds (0.3 to 0.5 m/s) heat from photo flood lights placed in the
tunnel to more clearly observe the smoke caused convection currents which
upset the flow in the tunnel. Slight air flow caused by other wind tunnels
in the Fluid Modeling Facility also had a disruptive effect. After correct-
ing these problems, overall accuracy of speed determinations at this range
was estimated to be +_ 0.1 m/s. Below 0.3 m/s the flow in the tunnel was
judged to be too erratic to be used with confidence.
A device with photosensitive transistors was developed to time the smoke
puffs, but because of the ambiguity in the shape of the output, and resolu-
tion of the oscilliscope used to monitor the signal, the accuracy was not as
good as a hand-held stop watch. Development of this approach was not pursued
further.
VANE SIZE DETERMINATION
The ASTM method suggests that the cross sectional area of the wind vanes
perpendicular to the flow be no larger than 10 percent of the cross section-
al area of the tunnel. To avoid lengthy trigonometric calculations, a photo-
graph was taken of the vane set at the proper angle. Included in the photo-
graph was a square of known size (see Figure 4.1). A measurement of the
20
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Figure 4.1 Example of vane cross section determination.
21
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cross sectional area could then be made directly using a planimeter. A tele-
photo lens (300 mm) was used to minimize parallax error, which was estimated
to be approximately 5 percent.
The area at a 10° offset angle of the largest vane tested in this pro-
gram was 4 percent of the cross sectional area of the tunnel.
WIND VANE CALIBRATION
Once the tunnel was calibrated the individual vanes could be tested for
delay distance, overshoot, and starting threshold. The initial step in this
procedure was to calibrate the measurement system so that the strip chart
recorder pen would be centered on the paper when the vane was aligned with
the air flow in the tunnel, and on the outer edge of the paper when the vane
was displaced a known number of degrees (usually 20°) from the centerline.
As a first step the vane was mounted in the theodolite head vane holder
(individual adaptors were machined for each vane) which was placed in the
center of the test section of the tunnel.
The fan was then turned on to obtain a speed between 5 and 10 m/s, and
the vane allowed to freely line-up with the air flow. The d.c. voltage out-
put and trim pot were adjusted so that the chart recorder indicated a voltage
somewhere near mid-scale. The tunnel fan was stopped, and referring to the
chart output, the vane tail was clamped at the centerline position using a
ring stand and three-finger pipette clamp. The theodolite head and wind
vane base were rotated to the desired full scale deflection on the side which
caused the voltage to go toward zero. The chart recorder was then set to
zero using the trim pot. The wind vane base was next rotated to the same
number of degrees on the other side of f.hp renteHi^e, ?md & ^nii crpia
reading was obtained by adjusting the voltage control. Two or three iterations
22
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were usually sufficient to complete and stabilize this zeroing procedure.
The resolution and linearity of the vane were checked by stepping the
vane base through 0.1 increments and noting the output on the chart recorder.
TEST PROCEDURE
Starting Threshold
After calibration, the tail clamp was removed and replaced by the re-
lease mechanism. The vane was offset 10°, with the tail resting against the
teflon tip of the release rod. The air flow was set at some low speed, and
after waiting a few minutes for the flow to stabilize, the vane was released.
If the vane failed to move 5 or more degrees, the speed was increased
(usually in 0.1 m/s increments) and the test repeated. If the vane did move
the required 5 degrees, the position at which it came to rest was noted, and
the test repeated nine more times, five of which were done with the vane
displaced to the opposite side of the centerline. If the vane failed to move
the required 5 degrees during any of the 10 tests, the data were discarded;
the air flow was increased, and the tests were repeated. The starting speed
was, therefore, that speed at which the vane first succeeded in all ten trials.
Displacement Distance and Overshoot
Tests to determine displacement distance, overshoot, and damped wave
length were conducted in the same manner as starting speed, except that the
speeds were set at 2, 5, and 10 m/s. (The 2 m/s speed was not used on those
few vanes whose starting speed was close to, or greater than 1.75 m/s.) For
the 10 m/s, and some of the 5 m/s tests, the signals were analyzed by an
analog-to-digital converter and computer rather than the chart recorder be-
cause of the slow response time of the recorder. The resulting output data
23
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were analyzed manually, regardless of the method of collection.
As illustrated previously, Figure 2.2 shows a typical displacement dis-
tance and overshoot test. The displacement distance (D) is the length of the
column of air that passes the vane from the time it is released until it has
reached 50 percent of the initial displacement.
D = u(trt.) (4.5)
The overshoot ratio (ft) is the ratio of successive maxima. Usually it
was determined using the initial displacement and the first overshoot peak.
ft = B-|/30 (4.6)
For a perfect, damped system, this would equal the ratio of the second over-
shoot peak to the first, and so on,
ft = B2/6-, (4.7)
but it rarely is.
The damped wave length (\d) can also be found if the second peak is
clearly defined.
xd = "(VV (4'8)
Each of the thirty tests, plus starting speed tests were analyzed in
this way for each vane tested. The results are given in the following
section.
24
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SECTION 5
RESULTS
VANE TESTS
While the ultimate goal of this study was to evaluate the ASTM method-
ology, this was difficult to do without collecting some data on individual
vanes. Because this information may be of interest, it is presented in the
following tables. Certain caveats should be kept in mind, however, while
examining these results, or comparing them with manufacturers specifications
or other published results. These caveats are (1) for all but one case only
one vane of each model was tested. While care was taken to eliminate faulty
vanes, some of the ones tested may not have been representative of its species,
and (2) the ASTM method differs significantly from some other vane testing
techniques, and the results should not be expected to be comparable.
Table 5.1 gives the manufacturers' names and model numbers of the vanes
tested, the starting thresholds and accuracies, the delay distances, measured
damped wave lengths (where available), and overshoot and damping ratios. The
precision figures given are for one standard deviation. The various vanes
are given in alphabetical order by manufacturer. The starting threshold was
measured in 0.1 m/s increments between 0 and 1.0 m/s, and 0.25 m/s increments
above 1.0 m/s.
25
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TABLE 5.1 TABULATION OF WIND VANE TEST RESULTS
ro
Company
Bendix
Bendix
Climet
Meteorology
Research Inc.
R.M. Young
R.M. Young
WeatherMeasure
WeatherMeasure
WeatherMeasure
Starting
Threshold
Model (m/s)
Aerovane*
Windvane
12-15
1022
Microvane
Windvane/6301
102*
200*
204
1.5
0.9
0.7
0.4
0.5
0.6**
2.5
2.25
0.8
Starting
Accuracy
(deg.)
3.3+0.19
4.0+0.34
2.0+0.58
2.2+0.21
2.9+0.27
2.8+0.22
1.8+0.4
2.7+0.4
3.7+0.45
Delay
Distance
(m)
2.0 +0.20
1.0 +0.08
0.65+0.07
0.6 +0.08
0.8 +0.11
1.2 +0.10
2.2 +0.14
1.0 +0.07
1.1 +0.11
Damped
Wavelength
On)
11.5+0.40
5.5+0.22
3.3+0.21
3.4+0.14
4.8+0.24
7.2+0.26
10.6+0.40
4.6+0.06
5.8+0.11
Overshoot
Ratio
0.49+0.05
0.33+0.01
0.28+0.01
0.23+0.02
0.14+0.03
0.27+0.05
0.50+0.06
0.47+0.02
0.48+0.07
Damping
Ratio
0.22
0.33
0.38
0.43
0.53
0.39
0.21
0.23
0.23
(continued)
-------
TABLE 5.1 (Continued)
IX)
Company
Teledyne Geotech
Texas Electronics
Texas Electronics
Model
53.2
2010(a)
2010(B)
Starting
Threshold
(m/s)
0.3***
1.25
1.0
Starting
Accuracy
(cleg.)
1.7+0.26
2.9+0.5
4.3+_0.28
Delay
Distance
(m)
0.65+0.08
1.2 +0.10
1.1 +0.08
Damped
Wavelength
(m)
2.6+_0.18
6.0+0.20
Missing
Overshoot
Ratio
0.30+0.04
0.29+0.01
0.32+0.02
Damping
Ratio
0.36
0.37
0.35
*For vanes with starting threshold 1.75 m/s or greater, tests of delay distance and overshoot
at tunnel speeds of 2 m/s were not done. Results for these vanes is based on tests at 5 and
10 m/s only.
**A second test of the starting threshold of this vane done on a subsequent day showed a lower
starting speed. The reason for this is not known. The first result is given in conformity
with test procedures.
***The starting threshold of this vane is probably less than 0.3 m/s, but the wind tunnel was
not reliably calibrated below that speed, so no measurements could be made.
-------
UNSUCCESSFUL TESTS
A number of vanes were received for this program from various manufac-
turers which were not tested for one reason or another. In some cases the
vanes were slightly damaged. For example it was noted that small dents in
the tail of one vane caused it to continuously oscillate at wind speeds
above a few meters per second. Other vanes could not be properly balanced,
even though the balance weight was adjusted throughout its designed limit of
travel.
An Electric Speed Indicator Co. model F420C-2 Wind Direction Transmitter
was received from the National Weather Service. This vane was tested using
the standard procedure. The vane is designed to drive a pointer on a dial
to indicate wind direction, rather than give a linear electronic output.
Due to this factor, the resolution we were able to observe and record was
greater than 5 degrees. The instrument probably has a better resolution than
that when used in its normal configuration, and if rewired it could be set-up
to give a better resolution, but for purposes of this evaluation modification
of the vanes was not possible. It was estimated that the starting speed of
the vane was between 1.5 and 2 m/s. Estimates of the other variables, how-
ever, were impossible with any precision. Therefore we must conclude that
the test method as presently formulated is not applicable to this design of
wind vane. Substituting a standard potentiometer for the present electronics
in the vane could have been done, but this was deemed unwarranted because if
the friction or moment of inertia of the new parts were not substantially
similar to the originals the results would be misleading.
28
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STARTING THRESHOLD
Starting threshold and its corresponding accuracy are somewhat inde-
terminate numbers. They will depend on the size of the finite steps that
are taken in doing the tests as well as the desired accuracy range. In per-
forming these tests, the wind speed was increased in 0.1 m/s increments from
0.3 to 1.0 m/s and in 0.25 m/s increments above 1.0 m/s. The lowest speed
at which the first five tests on each side had a deflection of more than 5°
was recorded as the starting threshold. It was not unusual to have several
successful individual trials be followed by one with a deflection of less
than the required 5 degrees. Under the procedure one would then proceed to
the next higher speed and try again. Since the final rest positions were
somewhat random, however, it is not at all unlikely that five consecutive
successful tests which were all successful could be done at the lower speed.
On the other hand, if one wished to report a higher accuracy and was willing
to sacrifice a lower starting threshold, the test could be commenced at a
higher tunnel air speed. With this in mind, and considering that the accuracy
with which the air speed in the tunnel is known at the lower range is on the
order of 0.1 m/s, it is estimated that the accuracy of the threshold speed
determination is within +0.2 m/s.
Associated with each starting accuracy given in Table 5.1 is a one
standard deviation precision value. The coefficient of variation for this
measurement (o/S^) is approximately 13 percent.
Averaging Starting Accuracy
Early drafts of the ASTM method specified that the absolute value of
the accuracies from displacements to the left of the centerline and the right
29
-------
of the center!ine were to be averaged, with this value representing the
starting accuracy. Upon examining some preliminary results of this study,
the ASTM committee noted that there was a distinct bi-modal distribution, or
that the displacement on one side had a much lower degree of accuracy than
did the other. An average of the two sides then would give a misleadingly
optimistic picture of the accuracy of the vane. The committee changed the
method to require that the higher of the two average displacements (less
accurate) be reported as the starting accuracy. Figure 5.1 is a scatter plot
of the new, or one sided accuracy figures versus the old, or two sided fig-
ures. As can be seen, for most vanes the change was not substantial, but
for a few it was close to the maximum possible factor of two difference.
OVERSHOOT AND DAMPING RATIOS
Overshoot ratios ranged from 0.14 to 0.49, with a mean of 0.34. The
average standard deviation of the overshoot measurement for each instrument
had a wider range, from 0.008 to 0.07, with a mean value of 0.032 for all
instruments. The coefficient of variation for this measurement is 9.9 per-
cent. Thus 10 percent would be a good estimate of the precision of the over-
shoot measurements. Since the damping ratio (n) is roughly inversely propor-
tional to overshoot ratio, 10 percent is also a reasonable estimate for its
precision.
DELAY DISTANCE
Delay distances measured in this study ranged from 0.61 m to 2.2 m,
with a mean of 1.12 m. The standard deviation of the delay distance measure-
ment for each instrument ranged from 0.07 m to 0.2 m, with a mean value of
0.1 m for all instruments. The coefficient of variation was 9.6 percent,
30
-------
_ 4
CO
01
UJ
cc
u
LU
O
O
<
CC
D
O
u
<
O
UJ
o
CO
01
TWO SIDED ACCURACY (DEGREES)
Figure 5.1 Comparison of one sided and two sided
starting accuracy.
31
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thus implying that 10 percent is also a reasonable expectation for the
precision of this measurement.
In general, vanes with higher starting thresholds had longer delay dis-
tances. This can be seen in the scatter plot shown in Figure 5.2. Its
usefulness may be limited, but in principal one could design a vane with a
long delay distance and a low starting threshold.
DAMPED WAVELENGTH
The damped wavelength (A.) measured in this study ranged from 2.6 to
11.5 meters, with a mean of 5.94 meters. The average of the standard devia-
tions for all instruments was 0.22 meters, with a coefficient of variation of
3.9 percent. One could thus reasonably expect a precision of approximately
5 percent for this measurement.
Comparing this with 10 percent precision for the delay distance measure-
ment, it would seem that the damped wavelength would be the better of the two
measurements to take. However it should be realized that for vanes with
large damping ratios (0.5 or greater), the second peak may be very difficult
to define, and for these vanes, delay distance measurements may be much more
precise. In actual practice, either may be easily measured, and as shown
below, the relationships between the two is quite reliable.
Comparison of Delay Distance and Damped Wavelength
As is noted in Section 2, Jex (op cit) has suggested the relationship
between delay distance, damping ratio, and damped wavelength given in equa-
tion (2.19) and reproduced here.
o +%
X = D(6 - 2.4n)/(l-n ) . (2.19)
32
-------
1.5
LU
o
1.0
UJ
D
.5
STARTING THRESHOLD (m/s)
Figure 5.2 Comparison of starting threshold vs.
delay distance.
33
-------
A comparison of calculated xd> using the measured delay distance and
damping ratio, and measured \d is shown in Figure 5.3. As can be seen the
agreement is quite good. The line of best fit has a slope of 1.015 and an
intercept of 0.21. The standard error of estimate is 0.71 and the correlation
coefficient is 0.97 (using calculated xd as the dependent variable).
Equation (2.19) can be rewritten as:
\j = kD (5.1)
where
7 ^
k = (6-2.4n)/(l-n )
for n between 0.2 and 0.5 (the range of all vanes tested), k varies between
5.5 and 5.6.
The relationship between delay distance and measured AD is shown in
Figure 5.4. As can be seen, the assumption of a straight line fit is reason-
able. The linear regression best fit for the line is:
Ad = 5.27D + 0.06
with S = 0.64 and the correlation coefficient equal to 0.97.
J
There would seem to be little justification in the data for preferring
one form of the relationship over the other (equation (2.19) vs. linear) so
the choice is left up to the user.
DUPLICATE VANES
The Texas Electronics Co. sent two model 2010 vanes for the tests. The
results of these tests are summarized in Table 5.2.
34
-------
12
11
10
1 9
I
I-
o
Z o
Ijj «
HI
>
Q
HI
o.
D 5
in ^
U
O
V
i i
8
10
11
MEASURED DAMPED WAVELENGTH (Xd) (m)
Figure 5.3 Calculated vs. measured damped wavelength.
35
-------
12
Xd = 5.27D + .06
1.5
DELAY DISTANCE (m)
Figure 5.4 Measured damped wavelength vs. delay distance.
36
-------
TABLE 5.2 COMPARISON OF TWO TEXAS ELECTRONIC
MODEL 2010 VANES
Vane A Vane B
Starting Threshold 1.25 m/s 1.0 m/s
Accuracy 2.9° +_ 0.5° 4.3° +_ 0.3°
Delay Distance 1.2m +_ 0.10m 1.1m +_ 0.08m
Overshoot 0.29^0.01 0.32^0.02
Damping Ratio 0.37 0.35
This comparison indicates that the method gives reproducible results on
two similar vanes within the precision bounds given above, at least for these
two vanes. It is interesting to note that while vane "A" had a higher start-
ing threshold than did "B", its accuracy at that speed was better than "B's"
at its starting threshold. This is consistent with the discussion of start-
ing threshold and accuracy as given above. The differences in the other
parameters are statistically insignificant.
OFFSET ANGLE
The ASTM method requires an offset angle or displacement of 10 from
the tunnel center!ine. In the past other angles have been used by various
manufacturers and others studying vane response. We were able to do a very
limited comparison of the effects of various offset angles on the response
of one vane, the Texas Electronics 2010(A). The results of the tests are
given in Table 5.3. Slight differences can be seen in the 10° test between
Tables 5.2 and 5.3. The tests at 15° and 20° were run without the 10 m/s
37
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wind speed so the 10 m/s results from the 10° test were not used in order to
make the comparison more meaningful.
TABLE 5.3 COMPARISON OF VANE PARAMETERS FOR OFFSETS OF 10°, 15°
AND 20° MEASURED ON THE TEXAS ELECTRONICS 2010 VANE A
(Parameters for this test were not measured at 10 m/s)
10° 15° 20°
Starting Threshold 1.25 m/s 1 m/s 1 m/s
Accuracy 2.9° + 0.5° 2.1° + 0.8° 1.6° ±0.7°
Delay Distance l.ZmjHO.lm 1.3m+_0.1m 1.5m +• O.lm
Overshoot 0.26+_0.02 0.28 + 0.01 0.27 +_ 0.02
Damping Ratio 0.39 0.37 0.38
The results do confirm that the test results are dependent on offset
angle. All the vane parameters showed significant differences. Not sur-
prisingly, the starting threshold decreased (or the accuracy increased) with
increasing offset angle.
The delay distance also increased with increased offset angle. Since
the delay distance is in a sense the length of an air column needed to move
the vane from one position halfway to a new one, and since that distance is
increasing with increasing offset angle, the increase in delay distance may
also be an understandable event. One should note, however, that theoreti-
cally the natural and damped wavelengths are not functions of offset angle.
This implies a number of possibilities: (1) delay distance is a function of
offset angle and equation (2.19) needs to be modified; (2) natural and damped
wavelengths are a function of offset angle. A more complete study of the
38
-------
subject is suggested to investigate these effects.
Overshoot also changed with offset angle, although not in any obviously
systematic way. While the difference between the offset at 10° and 15 is
significant, the results may still be an artifact of the small sample size
or experimental error. This too could be resolved with a more thorough study
39
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SECTION 6
CONCLUSIONS AND RECOMMENDATIONS
CONCLUSIONS
The basic conclusion of this study is that the ASTM draft Standard
Method for Determining the Dynamic Performance of a Hind Vane does provide a
reasonable and reliable technique for determining standard performance charac-
teristics for many commercially available wind vanes. The method also pro-
vides good standard definitions for many terms which have a history of im-
precise use.
Using reasonable care, most laboratories with proper facilities should
be able to measure performance characteristics of many of the wind vanes on
the market today. For those vanes for which we were not able to perform
these tests, modifications which do not affect dynamic performance may be
possible so that organizations with interest in them will be able to evaluate
these vanes.
Because of the facilities required, it is not reasonable to expect that
many of the users of wind vanes will be able to test their own equipment. If
the manufacturers and various independent testing laboratories adopt the ASTM
method, vanes could then be certified by the manufacturer to meet specified
performance criteria and could be returned to the manufacturer or other lab-
oratory for recertification should it become necessary. A reliable program
of this type should take much of the guess work that is now necessary out of
the evaluation of meteorological data.
40
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RECOMMENDATIONS FOR FURTHER RESEARCH
One precept associated with any scientific research program is that it
should raise new questions as it answers old ones. This study has met that
requirement.
The general area of delay distance and its relationship to damped wave-
length, damping ratio, and offset angle has not been adequately resolved.
Theoretical relationships to replace the present empirical ones, plus a more
thorough experimental program would be needed to attack this problem.
The variability of results is a major area of uncertainty. This includes
variability between similar models, variability with age, and variability of
results measured at different laboratories. Variability between similar
models would be an easy question for the manufacturer of wind vanes to address
It should be addressed in order to determine whether all vanes performance
specifications need to be measured, or whether representative sampling of
vanes of the same design will be adequate.
Variability between laboratories would be easily addressed by an inter-
laboratory comparison test. Such a test is being planned by members of the
ASTM Meteorological Measurements subcommittee and should answer this question.
The question of variability with age could also be addressed in a
straight-forward test. It would be interesting to see if changes in the
various parameters could be related directly to bearing wear, so that simple
measurements of torque could be substituted for the wind tunnel tests on
older vanes as a method of field calibration.
A final area of concern is the bimodal nature of the vanes during start-
ing threshold and accuracy measurements. A preferred direction of motion is
obviously not a desirable characteristic for wind vanes. It is hoped that
41
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meteorological instrument manufacturers will look into this problem and cor-
rect or at least improve upon their wind vane performance.
42
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BIBLIOGRAPHY
Acheson, Donald T. 1970. "Response of Cup and Propeller Ratios and Wind
Direction Vanes to Turbulent Wind Fields." Meteorological Monographs, Vol.
11, No. 33, pages 252-261.
Barthelt, H.P. and G.H. Ruppersberg. 1957. "Die Mechanesche Wind fahne,
eine Theoretiscke und experimientelle Untersuchung." I. Beitr. Phys. Atmos.,
Vol. 29, pages 154-185.
Camp, Dennis W. and Robert E. Turner. 1970. "Response Tests of Cup, Vane,
and Propeller Wind Sensors." J. of Geophysical Res., Vol. 75, No. 27, pages
5265-5270.
Environmental Protection Agency. 1978. Ambient Monitoring Guidelines for
Prevention of Significant Deterioration. EPA-450/2-78-019, OAQPS, RTP, N.C.,
86 pages.
Jex, H.R. 1979. Personal communication.
MacCready, P.B. and H.R. Jex. 1964. "Response Characteristics and Meteoro-
logical Utilization of Propeller and Vane Wind Sensors." J. Appl. Meteor.,
No. 3, pages 182-193.
Moses, H. 1968. Meteorology and Atomic Energy. A.E.G., pages 257-308.
Wieringa, J. 1967. "Evaluation and Design of Wind Vanes." J. Appl. Meteor.,
Vol. 6, No. 6, pages 1114-1122.
Wolkovitch, J.R., et al. 1962. Performance Criteria for Linear Constant
Coefficient Systems with Deterministic Inputs. USAF, ASD-TR-61-501.
43
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APPENDIX A
The following is a copy of the ASTM "Standard Method for Determining the
Dynamic Performance of a Wind Vane."
44
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Draft No. 4
3/11/80
1.
STANDARD METHOD FOR DETERMINING
THE DYNAMIC PERFORMANCE OF A WIND VANE
1. 1 This method covers the determination of the
Starting Threshold
Delay Distance
Overshoot
Dynamic Vane Bias
of a wind vane from direct measurement in a wind tunnel for
•wind vanes having measurable overshoot.
1. 2 This method provides for determination of the performance
of the wind vane and its transducer in wind tunnel flow.
Transference of values determined by these methods
to atmospheric flow must be done with an understanding
that there is a difference between the two flow systems.
2. Applicable Documents
D 1356 Definitions of Terms Relating to Atmospheric
Sampling Analysis
E 380 Metric Practive Guide
3. Summary of Method
3. 1 This method requires a wind tunnel described in Section 6,
Apparatus.
3.2 Wind Direction (6 degrees) is measured as the angular
position of the vane with respect to some index (real or
45
-------
imaginary) position on the sensor assembly. Displace-
ments of 10 degrees must be within ± 1 degree.
3.3 Starting Threshold (S0, m/s) is determined by measuring
the lowest speed at which a vane released from a position
10 degrees off the wind tunnel centerline moves to within
five degrees of the centerline. Tests must include initial
displacements to each side of the centerline.
3.4 Delay Distance (D, m) may be measured at a number of
wind speeds but must include 5 m/s, and 10 m/s.
A measurement is made of the time required for the vane
to reach 50 percent of the initial displacement from 10
degrees off wind tunnel centerline release. This time in
seconds (s) is converted to the Delay Distance by multi-
plying by the tunnel wind speed in meters per second.
Tests must include displacements to each side of the
cente rline.
3.5 Overshoot (^ ) may be measured at the same time as the
Delay Distance. The maximum angular excursion on the
opposite side of the at-rest position from the initial 10
degrees off wind tunnel centerline displacement is
measured. This value is divided by the initial displace-
ment to obtain the ratio ft.
3.6 Dynamic Vane Bias (6 B) is the maximum displacement
of the vane from the undisturbed flow direction at the
center of the wind tunnel (typically the wind tunnel center-
line) caused by the free response of the vane to the tunnel
46
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flow at all speeds above three times the vane Starting
Threshold. This measurement will identify wind vanes
with unbalanced aerodynamic response because of
damage (bent tail) or design. 6B must be * I 1°| .
4. Significance and Use
This method will provide a standard for comparison of wind
vanes of different types. Specifications by regulatory
agencies (1-4) and industrial societies have specified per-
formance values. This standard provides an unambiguous
method for measuring Starting Threshold, Delay Distance,
Overshoot and Dynamic Vane Bias.
5. Terminology
5. 1 Definitions
delay distance (D)-- the distance the air flows past
a wind vane during the time it takes the vane to
return to 50 percent of the initial displacement
overshoot (^)--the ratio of the amplitudes of two
successive deflections of a wind vane as it
oscillates about the equilibrium position
after release from an offset position, as
expressed by the equation
e
n _
(" +
e
n
where 6 and 6 are the amplitudes of
n (n -I- 1)
the n and n + 1 deflections, respectively.
Because all deflections after the first to the
side opposite the release point are small, the
47
-------
initial release point (i.e., the n = zero
deflection) and the first deflection after
release (n = 1) are used in practice in
determining overshoot.
starting threshold- -the lowest wind speed at which a
vane will turn to within five degrees of 6S from
an initial displacement of 10 degrees.
5. 2 Calculated or Estimated Values
damping ratio (T7)--the damping ratio is calculated from
the overshoot ratio ( ty (5).
in
n
damping coefficient- -define
critical damping coefficient --de fine
damped natural wavelength (X )--at sea level in the U.S.
Standard Atmosphere, damped natural wavelength
is related to delay distance (D) and damping ratio
(H ) by the approximate expression (5)
._ D (6.0 - 2.4
"
1 -T?
6. Apparatus
6.1 Wind Tunnel
6. 1. 1 Size. The wind tunnel must be large enough so
that the projection of the sensor and vane in its
displaced position is less than 10 percent of the
tunnel cross sectional area.
48
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6. 1.2 Calibration. The mean flow rate must be verified
at the mandatory speeds by use of transfer standards
which have been calibrated at the National Bureau
of Standards or by a fundamental physical method.
Speeds below 2 m/s for threshold determination
must be verified by some other technique, such as
smoke puffs or heat puffs.
6.2 Measuring System
6.2. 1 Direction. The resolution of the wind vane trans-
ducer limits the measurement. The resolution of
the measuring or recording system must represent
the 10 degree displacement on each side of the wind
tunnel centerline with a resolution of 0.2 degree.
The accuracy of the position (resistance for ex-
ample) to output conversion must be within ± 0. 1
degree.
6.2.2 Time. The resolution of time must be consistent
with the distance accuracy required. For this
reason, the time resolution may be changed as
the wind tunnel speed is changed. If one wants
a distance constant measurement to 0. 1 meter
resolution one must have a time resolution of
0.05 seconds at 2 m/s and 0.01 seconds at
10 m/s. If time accuracy is based on 60 Hz
power frequency it will be at least an order of
magnitude better than the resolution suggested
t
above.
6.3 Techniques. One simple technique is to use a fast-
response recorder (flat to 40-60 Hz or better) with
49
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enough gain so that a vane can be oriented in the wind
tunnel with the tunnel centerline direction represented
at mid scale on the recorder and ± 10 degrees of
vane displacement providing zero and full scale on the
recorder. If the recorder has a fast chart speed of
10 to 50 mm/sec or more, one can record the vane
performance and extract the data properly. Care
must be taken to avoid electronic circuits with time
constants which limit the apparent vane performance.
Digital recording systems and appropriate reduction
programs will also be satisfactory if the sampling rate
is at least 100 per second.
An FM tape recorder may be used for the signal. When
played back at lower speed a slow analog strip chart
recorder is acceptable. Oscilloscopes •with memory and
hard copy capability may also be used.
7. Sampling
7. 1 Starting Threshold. Ten consecutive tests at the same
speed meeting the method requirement, five in each
direction off the wind tunnel centerline, are required
for a valid starting threshold measurement.
7.2 Delay Distance and Overshoot. The arithmetic mean of
ten tests, five in each direction off the wind tunnel center.
line, is required for a valid measurement at each speed.
The results of the measurements at two or more speeds
should be averaged to a single value for delay distance
and a single ratio for overshoot.
50
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8. Procedure
8. 1 Starting Threshold
8. 1. 1 Provide a mechanical method for holding and
releasing the vane at 10 degrees from SB.
Test the release mechanism with the wind
tunnel off to verify that the release method
moves the vane by less than 0.5 degrees when
activated. The release device must not move in
the direction the vane will move when released.
8. 1. 2 Set the wind tunnel to a speed which you expect
will be lower than the starting threshold. Dis-
place the vane 10 degrees and release by the
procedure described in 8. 1. 1. Observe where
the vane stops. Adjust the speed until the vane
consistently stops within five degrees of ^g.
8. 1.3 Using this speed record five consecutive samples
to one side of the centerline followed by five
samples to the other side.
8. 1.4 If all ten samples resulted in the vane coming to
rest within five degrees of SB, the wind speed
may be used as the starting threshold in accord-
ance witn tms metnoa. me average ol the absolute
angular displacement, 6B, on each side should be
calculated. The higher of the two is the accuracy
at the threshold speed. For example, if the aver-
age displacement is two degrees from 6» the
accuracy of the wind vane at threshold is specified
as two degrees* To match the accuracy at starting
51
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threshold to the accuracy of the vane measurement
at higher speeds, find the starting speed where the
accuracy at starting threshold equals the wind vane
measurement accuracy.
8.2 Delay Distance
8.2. 1 Set the wind tunnel speed to 2 m/s. Displace the
vane 10 degrees and release by method in 8. 1. 1.
Take four more samples in the same direction and
five samples in the opposite direction.
8.2.2 Repeat procedure of 8.2. 1 using 5 and 10 m/s.
8.2.3 Measure the time from release to crossing five
degrees (or 50 percent of the actual release dis-
placement at a nominal 10 degrees) for each of the
samples (10 at each speed). Convert each of these
times to a distance by multiplying by the tunnel speed.
Average the distances to arrive at the delay distance.
8. 3 Overshoot
8.3. 1 Read the maximum overshoot from the data re-
corded for 8.2 above. Convert each of the
samples to a ratio by dividing the overshoot by
the difference between initial displacement and
the equilibrium direction. Average the ratios
to arrive at the overshoot.
9. Precision and Accuracy
9. 1 Precision. Using this equipment and procedure, .an
estimate of the precision of the method follows.
52
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9. 1. 1 Starting Threshold. The precision of the speed
reported as the threshold relates to the wind
tunnel used for this method. A precision of the
average of the angular displacement from 68
is the same as the precision for measuring the
position of the direction vane. The apparatus
prescribed will provide a precision of 0.2
degree. A precision of one degree is required.
9. 1. 2 Delay Distance
The precision by this method is 0. 1 metre.
9. 1. 3 Overshoot
The precision by this method is 0. 02.
9.2 Accuracy
9.2. 1 Starting Threshold. The accuracy of the wind
tunnel is the accuracy of this method. An
accuracy of 0. 1 , IB is required. This must be
documented at the wind tunnel facility and be re-
lated to measurements at National Bureau of
Standards by National Bureau of Standards report
on the transfer standard which will carry the
same accuracy limit. Documentation of other
methods is required. The accuracy of the angle
measurement will be 0.5 degrees for this method.
9.2.2 Delay Distance
The accuracy of this method is 0. 1 metre. •
9.2.3 Overshoot
The accuracy of this method is 0. 05.
53
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References
1. American Nuclear Society-Guideline for Obtaining Meteorological
Information at Nuclear Power Sites (ANS-2.5, draft).
2. International Atomic Energy Agency-Safety Guide on Meteorology-
Climatology, Diffusion and Transport in Nuclear Power Plant
Siting.
3. U.S. Environmental Protection Agency-Ambient Monitoring Guide-
lines for Prevention of Significant Deterioration (PSD)
(OAQPS No. 1.2-096).
4. U.S. Nuclear Regulatory Commission-Safety Guide 1.23
5. MacCready, Jr., P. B. and H. R. Jex, 1964: Response character
istics and meteorological utilization of propeller and vane wind
sensors. J. Appl. Meteor., Vol. _3, No. 2, pp 185.
54
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APPENDIX B
On the following page is a copy of the letter sent to many manufacturers
of wind vanes, requesting their participation in this project;
55
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UNITED STATES ENVI RONMENTAL PROTECTION AGENCY
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
RESEARCH TRIANGLE PARK
NORTH CAROLINA 2771 '
May 23, 1979
Dear Sirs:
The ASTM sub-committee D22.ll (chaired by Tom Lockhart of MRI) has de-
veloped a draft "Standard Method for Determining the Performance of a Wind
Vane." This standard method specifies with needed clarity a way of deter-
mining starting threshold, delay distance, overshoot, and dynamic vane bias.
We and other laboratories are cooperating with the ASTM by testing the
proposed method. We hope to be able to determine the procedure's accuracy,
precision, ease of application, and general suitability. In order to do this
we would like to test a variety of different vanes, of different types, and
from various manufacturers. Since our budget for this project is very
limited, we will not be able to purchase the vanes for this test, but hope
that you will want to participate with us by loaning us one or two of the wind
vanes you manufacture. The equipment would be returned to you as soon as the
tests are complete. All of our tests will be conducted in our wind tunnel,
with none of the equipment being used out of doors.
1 must point out that we are not testing or evaluating the vanes them-
selves for suitability for any function, or compliance with any regulation,
nor are we evaluating the vanes prior to purchase.
Should you choose to join with us, the results of the tests will be made
available for your review prior to publication. Reports on the project will,
I anticipate, identify the various vanes used with the usual EPA disclaimer to
the effect that mentioning a product does not imply endorsement. I am en-
closing a copy of the EPA Property Loan Agreement form for your information.
I have been told by our purchasing office that this is the only paper work
required on this end.
I hope this project will be of interest to you and look forward to
hearing from you.
Peter L. Finkelstein, Ph.D.
Meteorologist
Statistical and Technical
Analysis Branch (MD-75)
(919/541-2347)
Attachment
56
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Draft No. 4
3/11/80
1.
STANDARD METHOD FOR DETERMINING
THE DYNAMIC PERFORMANCE OF A WIND VANE
1. 1 This method covers the determination of the
Starting Threshold
Delay Distance
Overshoot
Dynamic Vane Bias
of a wind vane from direct measurement in a wind tunnel for
wind vanes having measurable overshoot.
1.2 This method provides for determination of the performance
of the wind vane and its transducer in wind tunnel flow.
Transference of values determined by these methods
to atmospheric flow must be done with an understanding
that there is a difference between the two flow systems.
2. Applicable Documents
D 1356 Definitions of Terms Relating to Atmospheric
Sampling Analysis
E 380 Metric Practive Guide
3. Summary of Method
3. 1 This method requires a wind tunnel described in Section 6,
Apparatus.
3.2 Wind Direction ( 9, degrees) is measured as the angular
position of the vane with respect to some index (real or
57
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imaginary) position on the sensor assembly. Displace-
ments of 10 degrees must be within ± 1 degree.
3.3 Starting Threshold (S0 , m/s ) is determined by measuring
the lowest speed at which a vane released from a position
10 degrees off the wind tunnel centerline moves to within
o
five degrees of the centerline. Tests must include initial
o
displacements to each side of the centerline.
3.4 Delay Distance (D, m) may be measured at a number of
wind speeds but must include 5 m/s, and 10 m/s.
A measurement is made of the time required for the vane
to reach 50 percent of the initial displacement from 10
degrees off wind tunnel centerline release. This time in
seconds (s) is converted to the Delay Distance by multi-
plying by the tunnel wind speed in meters per second.
Tests must include displacements to each side of the
cente rline.
3.5 Overshoot (^) may be measured at the same time as the
Delay Distance. The maximum angular excursion on the
opposite side of the at-rest position from the initial 10
degrees off wind tunnel centerline displacement is
measured. This value is divided by the initial displace-
ment to obtain the ratio &.
3.6 Dynamic Vane Bias (ee) is the maximum displacement
of the vane from the undisturbed flow direction at the
center of the wind tunnel (typically the wind tunnel center-
line) caused by the free response of the vane to the tunnel
58
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flow at all speeds above three times the vane Starting
Threshold. This measurement will identify wind vanes
with unbalanced aerodynamic response because of
damage (bent tail) or de sign. 9B must be s |l°| .
4. Significance and Use
This method will provide a standard for comparison of wind
vanes of different types. Specifications by regulatory
agencies (1-4) and industrial societie s have specified per-
formance values. This standard provide s an unambiguous
method for measuring Starting Threshold, Delay Distance,
Overshoot and Dynamic Vane Bias.
5. Terminology
5. 1 Definitions
delay distance (D)-- the distance the air flows past
a wind vane during the time it takes the vane to
return to 50 percent of the initial displacement
overshoot (^)--the ratio of the amplitudes of two
successive deflections of a wind vane as it
oscillates about the equilibrium position
after release from an offset position, as
expressed by the equation
e
n _
e
n
where e and e, , ,. are the amplitudes of
n (n + 1)
the n and n + 1 deflections, respectively.
Because all deflections after the first to the
side opposite the release point are small, the
-------
initial release point (i.e., the n = zero
deflection) and the first deflection after
release (n = 1) are used in practice in
determining overshoot.
starting threshold--the lowest wind speed at which a
vane will turn to within five degrees of 6 s from
an initial displacement of 10 degrees.
5.2 Calculated or Estimated Values
damping ratio (*?)--the damping ratio is calculated from
the overshoot ratio ( ^) (5).
In 4
n • "
V '
damping coefficient--define
critical damping coefficient--define
damped natural wavelength (X )--at sea level in the U.S.
Standard Atmosphere, damped natural wavelength
is related to delay distance (D) and damping ratio
(7? ) by the approximate expression (5)
. . D (6.0 - 2.4 ?7)
V i - ^
6. Apparatus
6. 1 Wind Tunnel
6. 1. 1 Size. The wind tunnel must be large enough so
that the projection of the sensor and vane in its
displaced position is less than 10 percent of the
tunnel cross sectional area.
60
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6. 1.2 Calibration. The mean flow rate must be verified
at the mandatory speeds by use of transfer standards
which have been calibrated at the National Bureau
of Standards or by a fundamental physical method.
Speeds below 2 m/s for threshold determination
must be verified by some other technique, such as
smoke puffs or heat puffs.
6.2 Measuring System
6.2. 1 Direction. The resolution of the wind vane trans-
ducer limits the measurement. The resolution of
the measuring or recording system must represent
the 10 degree displacement on each side of the wind
tunnel centerline with a resolution of 0.2 degree.
The accuracy of the position (resistance for ex-
ample) to output conversion must be within ±0.1
degree.
6.2.2 Time. The resolution of time must be consistent
with the distance accuracy required. For this
reason, the time resolution may be changed as
the wind tunnel speed is changed. If one wants
a distance constant measurement to 0. 1 meter
resolution one must have a time resolution of
0. 05 seconds at 2 m/s and 0. 01 seconds at
10 m/s. If time accuracy is based on 60 Hz
power frequency it will be at least an order of
magnitude better than the resolution suggested
above.
6.3 Techniques. One simple technique is to use a fast-
response recorder (flat to 40-60 Hz or better) with
61
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enough gain so that a vane can be oriented in the wind
tunnel with the tunnel centerline direction represented
at mid scale on the recorder and ± 10 degrees of
vane displacement providing zero and full scale on the
recorder. If the recorder has a fast chart speed of
10 to 50 mm/sec or more, one can record the vane
performance and extract the data properly. Care
must be taken to avoid electronic circuits with time
constants which limit the apparent vane performance.
Digital recording systems and appropriate reduction
programs will also be satisfactory if the sampling rate
is at least 100 per second.
An FM tape recorder may be used for the signal. When
played back at lower speed a slow analog strip chart
recorder is acceptable. Oscilloscopes with memory and
hard copy capability may also be used.
7. Sampling
7. 1 Starting Threshold. Ten consecutive tests at the same
speed meeting the method requirement, five in each
direction off the wind tunnel centerline, are required
for a valid starting threshold measurement.
7.2 Delay Distance and Overshoot. The arithmetic mean of
ten tests, five in each direction off the wind tunnel center-
line, is required for a valid measurement at each speed.
The results of the measurements at two or more speeds
should be averaged to a single value for delay distance
and a single ratio for overshoot.
62
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8. Procedure
8. 1 Starting Threshold
8. 1. 1 Provide a mechanical method for holding and
releasing the vane at 10 degrees from 6B.
Test the release mechanism with the -wind
tunnel off to verify that the release method
moves the vane by less than 0.5 degrees when
activated. The release device must not move in
the direction the vane will move when released.
8.1.2 Set the wind tunnel to a speed which you expect
will be lower than the starting thre shold. Dis-
place the vane 10 degrees and release by the
procedure described in 8. 1. 1. Observe where
the vane stops. Adjust the speed until the vane
consistently stops •within five degrees of ®e.
8. 1.3 Using this speed record five consecutive samples
to one side of the centerline followed by five
samples to the other side.
8. 1.4 If all ten samples resulted in the vane coming to
rest within five degrees of 9B> the wind speed
may be used as the starting threshold in accord-
ance witn trns metnoa. me average ol the absolute
angular displacement, 9B, on each side should be
calculated. The higher of the two is the accuracy
at the threshold speed. For example, if the aver-
age displacement is two degrees from 9B the
accuracy of the wind vane at threshold is specified
as two degrees. To match the accuracy at starting
63
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threshold to the accuracy of the vane measurement
at higher speeds, find the starting speed where the
accuracy at starting threshold equals the wind vane
measurement accuracy.
8. 2 Delay Distance
8. 2. 1 Set the wind tunnel speed to 2 m/s. Displace the
vane 10 degrees and release by method in 8. 1. 1.
Take four more samples in the same direction and
five samples in the opposite direction.
8.2.2 Repeat procedure of 8.2.1 using 5 and 10 m/s.
8.2.3 Measure the time from release to crossing five
degrees (or 50 percent of the actual release dis-
placement at a nominal 10 degrees) for each of the
samples (10 at each speed). Convert each of these
times to a distance by multiplying by the tunnel speed.
Average the distances to arrive at the delay distance.
8. 3 Overshoot
8. 3. 1 Read the maximum overshoot from the data re-
corded for 8.2 above. Convert each of the
samples to a ratio by dividing the overshoot by
the difference between initial displacement and
the equilibrium direction. Average the ratios
to arrive at the overshoot.
9. Precision and Accuracy
9. 1 Precision. Using this equipment and procedure, an
estimate of the precision of the method follows.
64
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9. 1. 1 Starting Threshold. The precision of the speed
reported as the threshold relates to the wind
tunnel used for this method. A precision of the
average of the angular displacement from 6B
is the same as the precision for measuring the
position of the direction vane. The apparatus
prescribed will provide a precision of 0.2
degree. A precision of one degree is required.
9. 1.2 Delay Distance
The precision by this method is 0. 1 metre.
9. 1. 3 Overshoot
The precision by this method is 0. 02.
9. 2 Accuracy
9.2. 1 Starting Threshold. The accuracy of the wind
tunnel is the accuracy of this method. An
accuracy of 0. 1 , /s is required. This must be
documented at the wind tunnel facility and be re-
lated to measurements at National Bureau of
Standards by National Bureau of Standards report
on the transfer standard which will carry the
same accuracy limit. Documentation of other
methods is required. The accuracy of the angle
measurement will be 0.5 degrees for this method.
9.2.2 Delay Distance
The accuracy of this method is 0. 1 metre.
9. 2. 3 Overshoot
The accuracy of this method is 0. 05.
65
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References
1. American Nuclear Society-Guideline for Obtaining Meteorological
Information at Nuclear Power Sites (ANS-2.5, draft).
2. International Atomic Energy Agency-Safety Guide on Meteorology-
Climatology, Diffusion and Transport in Nuclear Power Plant
Siting.
3. U.S. Environmental Protection Agency-Ambient Monitoring Guide-
lines for Prevention of Significant Deterioration (PSD)
(OAQPS No. 1.2-096).
4. U.S. Nuclear Regulatory Commission-Safety Guide 1.23
5. MacCready, Jr. , P. B. and H. R. Jex, 1964: Response character
istics and meteorological utilization of propeller and vane wind
sensors. J. Appl. Meteor., Vol. 3_t No. 2, pp 185.
66
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TECHNICAL F K^ORT DATA
'lt-asc read liianictwns <>', I .. mm.- bc[nn ci>in/>lciun'
REPORT N
600/08-028
3. RECIPIENT'S ACCLSblOf* NO.
. TITLE AND SUBTITLE
AN EVALUATION OF THE AS.TM STANDARD METHOD FOR
DETERMINING THE PERFORMANCE OF A WIND VANE
6. PERFORMING ORGANIZATION CCOE
. AUTHORIS)
Peter L. Finkelstein
8. PERFORMING ORGANIZATION REPORT NO.
.PERFORMING ORGANIZATION NAME AND ADDRESS
Data Management and Analysis Division
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
. REPORT DATE
June 1980
10. PROGRAM ELEMENT NO.
A08A1D
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Data Management and Analysis Division
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA 600/08
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The American Society for Testing and Materials (ASTM) has proposed a standard method
for testing the 'performance characteristics of a wind vane. This report presents the
procedures used to test and evaluate the ASTM method, and the results of that evalua-
tion. Twelve wind vanes were borrowed from their manufacturers and tested using the
ASTM procedures. The theory of wind vane dynamics is briefly reviewed. Description
of the equipment and procedures used is given. Measurements of starting threshold,
starting accuracy, delay distance, overshoot ratio, and damped wavelength were made.
Damping ratio and natural wavelength were computed from the measurements. Based on the
results of this test, it is concluded that the ASTM method provides a reasonable and
reliable technique for determining performance characteristics for many wind vanes.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Wind Direction Measurement
Wind Vanes
Meteorological Measurements
Meteorological Quality Assurance
13. DISTRIBUTION STATE MEN!
Release to Public
b.lDENTIFIERS/OPEN ENDED Tt RMS
Meteorological
Instrument Evaluation
43F
68A
19, SfcCUniT Y CLASS (1/in Rr/mrti |21 NO OFPAuti:
Unclassified j 57
20. SECURITY CLASS ( / /i/.t~7>j\ ,'•/
Unclassified
EPA For"' 2220-1 (9-73)
------- |