&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)

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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)

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                                               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.

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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

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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

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_    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

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     1.5
LU
o
     1.0
UJ
D
      .5
                         STARTING THRESHOLD (m/s)
           Figure 5.2  Comparison of starting threshold vs.
                       delay distance.
                                  33

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     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

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12
                                                    Xd = 5.27D + .06
                                              1.5
                          DELAY DISTANCE (m)
    Figure 5.4  Measured damped wavelength  vs.  delay  distance.
                                36

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                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

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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

-------
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

-------
                                                          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

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                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

-------
           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

-------
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

-------
           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

-------
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)

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