ASTM D5096-02(2007)
(Test Method)Standard Test Method for Determining the Performance of a Cup Anemometer or Propeller Anemometer
Standard Test Method for Determining the Performance of a Cup Anemometer or Propeller Anemometer
SCOPE
1.1 This test method covers the determination of the Starting Threshold, Distance Constant, Transfer Function, and Off-Axis Response of a cup anemometer or propeller anemometer from direct measurement in a wind tunnel.
1.2 This test method provides for a measurement of cup anemometer or propeller anemometer performance in the environment of 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.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D5096–02 (Reapproved 2007)
Standard Test Method for
Determining the Performance of a Cup Anemometer or
Propeller Anemometer
This standard is issued under the fixed designation D5096; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope direction of flow. Note that if the anemometer axis is not
aligned with the direction of flow, the calculated wind speed
1.1 This test method covers the determination of the Start-
component parallel to the anemometer axis is used to deter-
ing Threshold, Distance Constant, Transfer Function, and
mine starting threshold.
Off-Axis Response of a cup anemometer or propeller anemom-
3.2.2 distance constant (L, m)—the distance the air flows
eter from direct measurement in a wind tunnel.
past a rotating anemometer during the time it takes the cup
1.2 This test method provides for a measurement of cup
wheelorpropellertoreach(1−1/e)or63%oftheequilibrium
anemometer or propeller anemometer performance in the
speed after a step change in wind speed (1). The response of
environment of wind tunnel flow. Transference of values
a rotating anemometer to a step change in which wind speed
determinedbythesemethodstoatmosphericflowmustbedone
increases instantaneously from U =0toU=U is (2):
with an understanding that there is a difference between the f
~2t/ t!
two flow systems.
U 5 U ~1 2 e ! (1)
t f
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
where:
responsibility of the user of this standard to establish appro-
U = is the instantaneous indicated wind speed at time t in
t
priate safety and health practices and determine the applica-
m/s,
bility of regulatory limitations prior to use.
U = isthefinalindicatedwindspeed,orwindtunnelspeed,
f
in m/s,
2. Referenced Documents
t = is the elapsed time in seconds after the step change
2.1 ASTM Standards:
occurs, and
D1356 Terminology Relating to Sampling and Analysis of
t = is the time constant of the instrument.
Atmospheres
DistanceConstantis: L 5 U t (2)
D3631 Test Methods for Measuring Surface Atmospheric f
Pressure
3.2.3 transfer function (Û =a+bR, m/s)—the linear rela-
f
3. Terminology
tionship between wind speed and the rate of rotation of the
3.1 For definitions of terms used in this standard, refer to anemometer throughout the specified working range. Û is the
f
Terminology D1356. predicted wind speed in m/s, a is a constant, commonly called
3.2 Definitions of Terms Specific to This Standard: zero offset, in m/s, b is a constant representing the wind
3.2.1 starting threshold (U ,m/s)—thelowestwindspeedat passageinm/rforeachrevolutionoftheparticularanemometer
o
which a rotating anemometer starts and continues to turn and cup wheel or propeller, and R is the rate of rotation in r/s. It
produce a measurable signal when mounted in its normal should be noted that zero offset is not the same as starting
position. The normal position for cup anemometers is with the threshold. In some very sensitive anemometers the constant a,
axis of rotation vertical, and the normal position for propeller zero offset, may not be significantly greater than zero. The
anemometers is with the axis of rotation aligned with the constantsaandbmustbedeterminedbywindtunnelmeasure-
ment for each type of anemometer (3).
3.2.4 off-axis response (U/(U cos u))—the ratio of the
f
indicated wind speed (U) at various angles of attack (u)tothe
This test method is under the jurisdiction of ASTM Committee D22 on Air
Quality and is the direct responsibility of Subcommittee D22.11 on Meteorology.
indicated wind speed at zero angle of attack (U) multiplied by
f
Current edition approved Oct. 1, 2007. Published December 2007. Originally
thecosineoftheangleofattack.Thisratiocomparestheactual
approved in 1990. Last previous edition approved in 2002 as D5096-02. DOI:
off-axis response to a cosine response.
10.1520/D5096-02R07.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5096–02 (2007)
3.3 Symbols: of wind speeds throughout the specified working range. In the
range of wind speeds where the anemometer response is
non-linear (near threshold) a minimum of five data points are
a (m/s) = zero offset constant
recorded. A minimum of five additional data points are
b (m/r) = wind passage (apparent pitch) constant or
recorded within the working range of the anemometer and
calibration constant
windtunnelbutabovethenon-linearthresholdregion(seeFig.
L (m) = distance constant
2). Measurements are recorded for each data point with the
r (none) = a shaft revolution
wind tunnel speed ascending and descending. The values of a
R (r/s) = rate of rotation
and b are determined by least-squares linear regression of the
t(s) = time constant
individual data points.
t (s) = time
4.5 Off-Axis Response may be measured at a number of
U (m/s) = starting threshold
o
wind speeds but must include 5 m/s, and 10 m/s.
U (m/s) = indicated wind speed (used in off-axis test)
4.5.1 Cup Anemometers—A measurement is made of the
U(m/s) = final indicated wind speed or wind tunnel
f
speed output signal when the anemometer is inclined into the wind
U (m/s) = anemometer application range (representing a down-draft) and away from the wind (repre-
max
U(m/s) = instantaneous indicated wind speed at time t
sentinganupdraft),whilethewindtunnelisrunningatasteady
t
Û(m/s) = predicted wind speed
f speed.Theoutputsignalismeasuredwiththeanemometeraxis
u (deg) = off-axis angle of attack
at 5° intervals from vertical to plus and minus 30° from
vertical. The measured signal is then converted to a ratio for
4. Summary of Test Method
each interval by dividing by the normal signal measured with
4.1 This test method requires a wind tunnel described in
the anemometer axis in the normal, or vertical, position.
Section 6, Apparatus.
4.5.2 Vane Mounted Propeller Anemometers—A measure-
4.2 Starting Threshold (U , m/s) is determined by measur-
ment is made of the output signal when the anemometer’s axis
o
ingthelowestspeedatwhicharotatinganemometerstartsand
of rotation is inclined downward into the wind (representing a
continues to turn and produce a measurable signal when
down-draft)andinclinedupwardintothewind(representingan
mounted in its normal position.
updraft), while the wind tunnel is running at a steady speed.
4.3 Distance Constant (L, m) may be determined at a
The output signal is measured at 5° intervals from a horizontal
number of wind speeds but must include 5 m/s, and 10 m/s. It
axis of rotation to 630° from the horizontal. The measured
iscomputedfromthetimerequiredfortheanemometerrotorto
signal is then converted to a ratio for each interval by dividing
accelerate(1–1/e)or63%ofastepchangeinrotationalspeed
by the normal signal with the anemometer in the normal, or
after release from a restrained, non-rotating condition. The
horizontal position.This test may be conducted either with the
final response, U, is the wind tunnel speed as indicated by the
vaneinplaceorwiththevaneremovedandtheaxisofrotation
f
anemometer. In order to avoid the unrealistic effects of the
fixed in the down-tunnel direction.
restrainedcondition,asshowninFig.1,thetimemeasurement
4.5.3 Fixed Axis Propeller Anemometer—Ameasurementis
should be made from 0.30 of U to 0.74 of U. This interval in made of the output signal when the anemometer is rotated in
f f
secondsisequaltoonetimeconstant(t)andisconvertedtothe
the air stream throughout the complete 360° angle of attack.
Distance Constant by multiplying by the wind tunnel speed in The signal is measured at a number of angles but must include
meters per second (m/s).
10° intervals with additional measurements at 85, 95, 265, and
4.4 Transfer Function (Û =a+bR, m/s) is determined by 275°. The measured signal for each angle of attack is then
f
measuring the rate of rotation of the anemometer at a number
converted to a ratio by dividing by the signal measured at 0°
angle of attack (axial flow).Additionally, the stall angle of the
propeller is measured by orienting the anemometer at 90° and
FIG. 1 Typical Anemometer Response Curve FIG. 2 Typical Anemometer Calibration Curve
D5096–02 (2007)
slowly rotating into and away from the air flow until the 6.3.3 Calibration—The mean flow rate must be verified at
propeller starts rotating continuously. Stall angle is the total the mandatory speeds by use of transfer standards which have
contained angle within which the propeller does not continu- been calibrated at the National Institute of Standards and
ously rotate. The procedure is repeated at 270°. Technology or by a fundamental physical method. Speeds
below2m/sforthethresholddeterminationmustbeverifiedby
5. Significance and Use a sensitive anemometer or by some fundamental time and
distance technique, such as measuring the transition time of
5.1 Thistestmethodwillprovideastandardforcomparison
smoke puffs, soap bubbles, or heat puffs between two points
of rotating type anemometers, specifically cup anemometers
separated by known distance. A table of wind tunnel blower
and propeller anemometers, of different types. Specifications
rpmorsomeotherindexrelatingmethodofcontroltoflowrate
by regulatory agencies (4-7) and industrial societies have
shouldbeestablishedbythistechniqueforspeedsof2m/sand
specified performance values. This standard provides an un-
below.
ambiguousmethodformeasuring Starting Threshold, Distance
6.3.4 The wind tunnel must have a relatively constant
Constant, Transfer Function, and Off-Axis Response.
profile (known to within 1%) and a turbulence level of less
than 1% throughout the test section.
6. Apparatus
6.3.5 Environment(9-11).Differencesofgreaterthan3%in
6.1 Measuring System:
the density of the air within the test environment may result in
6.1.1 Rotation—The relationship between the rate of rota-
poor intercomparability of independent measurements of start-
tionoftheanemometershaftandthetransduceroutputmustbe
ing threshold (U ) and distance constant (L) since these values
o
determined. The resolution of the anemometer transducer
are density dependent. The temperature and pressure of the
limits the measurement. The resolution of the measuring or
environment within the wind tunnel test section, and the
recordingsystemmustrepresenttheindicatedwindspeedwith
ambient air pressure (Test Methods D3631) shall be reported
a resolution of 0.02 m/s.
for each independent measurement.
6.1.2 Time—The resolution of time must be consistent with
the distance accuracy required. For this reason the time 7. Sampling
resolution may be changed as the wind tunnel speed is
7.1 Starting Threshold—The arithmetic mean on ten con-
changed. If one wants a distance constant measurement to 0.1
secutive tests is required for a valid starting threshold mea-
meter resolution one must have a time resolution of 0.05 s at 2
surement.
m/s and 0.01 s at 10 m/s. If timing accuracy is based on 50 Hz
7.2 Distance Constant—The arithmetic mean of ten tests is
or 60 Hz power frequency it will be at least an order of
required for a valid measurement at each speed. The results of
magnitude better than the resolution suggested above.
the measurements at two or more speeds are averaged to a
6.1.3 Angle of Attack—The resolution of the angle of attack
single value for distance constant.
(u)mustbewithin0.5°.Anordinaryprotractorofadequatesize
7.3 Transfer Function—Two measurements of U and R are
f
with 0.5° markings will permit measurements with sufficient
recorded for each data point, one with the wind tunnel speed
resolution.Afixture should be constructed to permit alignment
ascendingandonewiththewindtunnelspeeddescending.The
of the anemometer to the off-axis angles while the wind tunnel
values are then tabulated for each data point.
is running at a steady speed.
7.4 Off-Axis Response—The results of the measurement at
6.2 Recording Techniques:
two or more speeds are averaged to a single value for each
6.2.1 Digital recording systems and appropriate reduction
angle of attack. The averaged values are tabulated for each
programswillbesatisfactoryifthesamplingrateisatleast100
angle of attack.
samples/s. Exercise care to avoid electronic circuits with time
8. Procedure
constants which limit the proper recording of anemometer
performance. Oscilloscopes with memory and hard copy capa- 8.1 Starting Threshold (U ):
o
bility may also be used. Another simple technique is to use a
8.1.1 Provide a mechanical method for holding the an-
fast-response strip chart recorder (flat to 10 Hz or better) with emometer in its normal position (see 3.1) and for releasing the
enough gain so that the signal produced by the anemometer
anemometerfromarestrained,ornon-rotatingcondition,while
whenthewindtunnelisrunningat2m/sissufficienttoprovide the wind tunnel is running at the test speed. Test the release
full scale pen deflection on the recorder. The recorder chart mechanism with the wind tunnel off to verify that the release
drive must have a fast speed of 50 mm/s or more.
method does not move the anemometer rotor when activated.
6.3 Wind Tunnel (8): 8.1.2 Set the wind tunnel to a speed that is lower than the
6.3.1 Size—The wind tunnel must be large enough so that starting threshold. Slowly increase the wind tunnel speed until
the projection of the cup wheel or propeller, sensor, and the cup wheel or propeller continues to rotate and produce a
support apparatus, is less than 5% of the cross sectional area measurable signal.
of the tunnel test section. 8.1.3 Repeattheprocedureof8.1.2tentimesandrecordthe
6.3.2 Speed Range—The wind tunnel must have a speed results.
control which will allow the flow rate to be varied from 0 to a
NOTE 1—Vibration caused by the wind tunnel or by other sources can
minimum of 50% of the application range of the anemometer
cause erroneous measurements of starting threshold. Care must be
under test. The speed control should maintain the flow rate
exercised to eliminate any vibration in the wind tunnel test section during
within 60.2 m/s. threshold measurements.
D5096–02 (2007)
8.2 Distance Constant (L): 8.4.2 Repeat the procedure of 8.4.1 at 10 m
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:D5096–96 Designation: D 5096 – 02 (Reapproved 2007)
Standard Test Method for
Determining the Performance of a Cup Anemometer or
Propeller Anemometer
This standard is issued under the fixed designation D5096; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the determination of the Starting Threshold, Distance Constant , Transfer Function, and Off-Axis
Response of a cup anemometer or propeller anemometer from direct measurement in a wind tunnel.
1.2 This test method provides for a measurement of cup anemometer or propeller anemometer performance in the environment
ofwindtunnelflow.Transferenceofvaluesdeterminedbythesemethodstoatmosphericflowmustbedonewithanunderstanding
that there is a difference between the two flow systems.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
D3631Test Methods for Measuring Surface Atmospheric Pressure
D4430Practice for Determining the Operational Comparability of Meteorological Instruments
D4480Test Method for Measuring Surface Winds by Means of Wind Vanes and Rotating Anemometers
D3631 Test Methods for Measuring Surface Atmospheric Pressure
3. Terminology
3.1 For definitions of terms used in this standard, refer to Terminology D1356.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 starting threshold ( U , m/s)— the lowest wind speed at which a rotating anemometer starts and continues to turn and
o
produce a measurable signal when mounted in its normal position. The normal position for cup anemometers is with the axis of
rotation vertical, and the normal position for propeller anemometers is with the axis of rotation aligned with the direction of flow.
Note that if the anemometer axis is not aligned with the direction of flow, the calculated wind speed component parallel to the
anemometer axis is used to determine starting threshold.
3.2.2 distance constant (L, m)—the distance the air flows past a rotating anemometer during the time it takes the cup wheel or
propeller to reach (1−1/e) or 63% of the equilibrium speed after a step change in wind speed (1). The response of a rotating
anemometer to a step change in which wind speed increases instantaneously from U =0toU=U is (2):
f
~2t/G!
U 5 U[12e # (1)
t f
f ~1 2e ~2t/ t!!
where:
U = is the instantaneous indicated wind speed at time t in m/s,
t
U = is the final indicated wind speed, or wind tunnel speed, in m/s,
f
t = is the elapsed time in seconds after the step change occurs, and
This test method is under the jurisdiction ofASTM Committee D-22 on Sampling andAnalysis ofAtmospheres and is the direct responsibility of Subcommittee D22.11
on Meteorology.
Current edition approved May 10, 1996. Published July 1996. Originally published as D5096–90. Last previous edition D5096–90.
This test method is under the jurisdiction of ASTM Committee D22 on Air Quality and is the direct responsibility of Subcommittee D22.11 on Meteorology.
Current edition approved Oct. 1, 2007. Published December 2007. Originally approved in 1990. Last previous edition approved in 2002 as D5096-02.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
, Vol 11.03.volume information, refer to the standard’s Document Summary page on the ASTM website.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5096 – 02 (2007)
Gt = is the time constant of the instrument.
DistanceConstantis: L 5 U G (2)
f
f t
3.2.3 transfer function (Û =a+bR, m/s)—the linear relationship between wind speed and the rate of rotation of the
f
anemometer throughout the specified working range. UÛ is the predicted wind speed in m/s, a is a constant, commonly called
f|AXf
zerooffset,inm/s,bisaconstantrepresentingthewindpassageinm/rforeachrevolutionoftheparticularanemometercupwheel
or propeller, and R is the rate of rotation in r/s. It should be noted that zero offset is not the same as starting threshold. In some
very sensitive anemometers the constant a, zero offset, may not be significantly greater than zero. The constants a and b must be
determined by wind tunnel measurement for each type of anemometer (3).
3.2.4 off-axis response (U/( U cos u))—the ratio of the indicated wind speed (U) at various angles of attack (u) to the indicated
f
wind speed at zero angle of attack (U) multiplied by the cosine of the angle of attack. This ratio compares the actual off-axis
f
response to a cosine response.
3.3 Symbols:
a (m/s) = zero offset constant
b (m/r) = wind passage (apparent pitch) constant or calibration constant
L (m) = distance constant
r (none) = a shaft revolution
R (r/s) = rate of rotation
Gt(s) = time constant
t (s) = time
U (m/s) = starting threshold
o
U (m/s) = indicated wind speed (used in off-axis test)
U(m/s) = final indicated wind speed or wind tunnel speed
f
U (m/s) = anemometer application range
max
U(m/s) = instantaneous indicated wind speed at time t
t
Û(m/s) = predicted wind speed
f
u (deg) = off-axis angle of attack
4. Summary of Test Method
4.1 This test method requires a wind tunnel described in Section 6, Apparatus.
4.2 Starting Threshold (U , m/s) is determined by measuring the lowest speed at which a rotating anemometer starts and
o
continues to turn and produce a measurable signal when mounted in its normal position.
4.3 DistanceConstant (L,m)maybedeterminedatanumberofwindspeedsbutmustinclude5m/s,and10m/s.Itiscomputed
from the time required for the anemometer rotor to accelerate (1 – 1/e) or 63% of a step change in rotational speed after release
fromarestrained,non-rotatingcondition.Thefinalresponse, U,isthewindtunnelspeedasindicatedbytheanemometer.Inorder
f
to avoid the unrealistic effects of the restrained condition, as shown in Fig. 1, the time measurement should be made from 0.30
of U to 0.74 of U. This interval in seconds is equal to one time constant (G)(t) and is converted to the Distance Constant by
f f
multiplying by the wind tunnel speed in meters per second (m/s).
4.4 Transfer Function (Û =a+bR, m/s) is determined by measuring the rate of rotation of the anemometer at a number of
f
wind speeds throughout the specified working range. In the range of wind speeds where the anemometer response is non-linear
FIG. 1 Typical Anemometer Response Curve
D 5096 – 02 (2007)
(near threshold) a minimum of five data points are recorded. A minimum of five additional data points are recorded within the
working range of the anemometer and wind tunnel but above the non-linear threshold region (see Fig. 2). Measurements are
recorded for each data point with the wind tunnel speed ascending and descending. The values of a and b are determined by
least-squares linear regression of the individual data points.
4.5 Off-Axis Response may be measured at a number of wind speeds but must include 5 m/s, and 10 m/s.
4.5.1 Cup Anemometers—A measurement is made of the output signal when the anemometer is inclined into the wind
(representing a down-draft) and away from the wind (representing an updraft), while the wind tunnel is running at a steady speed.
The output signal is measured with the anemometer axis at 5° intervals from vertical to plus and minus 30° from vertical. The
measuredsignalisthenconvertedtoaratioforeachintervalbydividingbythenormalsignalmeasuredwiththeanemometeraxis
in the normal, or vertical, position.
4.5.2 Vane Mounted Propeller Anemometers— A measurement is made of the output signal when the anemometer’s axis of
rotation is inclined downward into the wind (representing a down-draft) and inclined upward into the wind (representing an
updraft), while the wind tunnel is running at a steady speed. The output signal is measured at 5° intervals from a horizontal axis
ofrotationto 630°fromthehorizontal.Themeasuredsignalisthenconvertedtoaratioforeachintervalbydividingbythenormal
signal with the anemometer in the normal, or horizontal position.This test may be conducted either with the vane in place or with
the vane removed and the axis of rotation fixed in the down-tunnel direction.
4.5.3 Fixed Axis Propeller Anemometer—Ameasurement is made of the output signal when the anemometer is rotated in the
air stream throughout the complete 360° angle of attack. The signal is measured at a number of angles but must include 10°
intervals with additional measurements at 85, 95, 265, and 275°. The measured signal for each angle of attack is then converted
to a ratio by dividing by the signal measured at 0° angle of attack (axial flow). Additionally, the stall angle of the propeller is
measuredbyorientingtheanemometerat90°andslowlyrotatingintoandawayfromtheairflowuntilthepropellerstartsrotating
continuously. Stall angle is the total contained angle within which the propeller does not continuously rotate. The procedure is
repeated at 270°.
5. Significance and Use
5.1 This test method will provide a standard for comparison of rotating type anemometers, specifically cup anemometers and
propeller anemometers, of different types. Specifications by regulatory agencies (4-7) and industrial societies have specified
performance values. This standard provides an unambiguous method for measuring Starting Threshold, Distance Constant ,
Transfer Function, and Off-Axis Response.
6. Apparatus
6.1 Measuring System:
6.1.1 Rotation—The relationship between the rate of rotation of the anemometer shaft and the transducer output must be
determined. The resolution of the anemometer transducer limits the measurement. The resolution of the measuring or recording
system must represent the indicated wind speed with a resolution of 0.02 m/s.
6.1.2 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
musthaveatimeresolutionof0.05sat2m/sand0.01sat10m/s.Iftimingaccuracyisbasedon50Hzor60Hzpowerfrequency
it will be at least an order of magnitude better than the resolution suggested above.
6.1.3 Angle of Attack—The resolution of the angle of attack (u) must be within 0.5°. An ordinary protractor of adequate size
with0.5°markingswillpermitmeasurementswithsufficientresolution.Afixtureshouldbeconstructedtopermitalignmentofthe
anemometer to the off-axis angles while the wind tunnel is running at a steady speed.
FIG. 2 Typical Anemometer Calibration Curve
D 5096 – 02 (2007)
6.2 Recording Techniques:
6.2.1 Digital recording systems and appropriate reduction programs will be satisfactory if the sampling rate is at least 100
samples/s. Exercise care to avoid electronic circuits with time constants which limit the proper recording of anemometer
performance. Oscilloscopes with memory and hard copy capability may also be used. Another simple technique is to use a
fast-response strip chart recorder (flat to 10 Hz or better) with enough gain so that the signal produced by the anemometer when
the wind tunnel is running at 2 m/s is sufficient to provide full scale pen deflection on the recorder. The recorder chart drive must
have a fast speed of 50 mm/s or more.
6.3 Wind Tunnel (8):
6.3.1 Size—The wind tunnel must be large enough so that the projection of the cup wheel or propeller, sensor, and support
apparatus, is less than 5% of the cross sectional area of the tunnel test section.
6.3.2 SpeedRange—Thewindtunnelmusthaveaspeedcontrolwhichwillallowtheflowratetobevariedfrom0toaminimum
of 50% of the application range of the anemometer under test. The speed control should maintain the flow rate within 60.2 m/s.
6.3.3 Calibration—The mean flow rate must be verified at the mandatory speeds by use of transfer standards which have been
calibratedattheNationalInstituteofStandardsandTechnologyorbyafundamentalphysicalmethod.Speedsbelow2m/sforthe
threshold determination must be verified by a sensitive anemometer or by some fundamental time and distance technique, such as
measuringthetransitiontimeofsmokepuffs,soapbubbles,orheatpuffsbetweentwopointsseparatedbyknowndistance.Atable
of wind tunnel blower rpm or some other index relating method of control to flow rate should be established by this technique for
speeds of 2 m/s and below.
6.3.4 The wind tunnel must have a relatively constant profile (known to within 1%) and a turbulence level of less than 1%
throughout the test section.
6.3.5 Environment(9-11).Differencesofgreaterthan3%inthedensityoftheairwithinthetestenvironmentmayresultinpoor
intercomparabilityofindependentmeasurementsofstartingthreshold(U )anddistanceconstant(L)sincethesevaluesaredensity
o
dependent.Thetemperatureandpressureoftheenvironmentwithinthewindtunneltestsection,andtheambientairpressure(Test
Methods D3631) shall be reported for each independent measurement.
7. Sampling
7.1 Starting Threshold—The arithmetic mean on ten consecutive tests is required for a valid starting threshold measurement.
7.2 Distance Constant—The arithmetic mean of ten tests is required for a valid measurement at each speed. The results of the
measurements at two or more speeds are averaged to a single value for distance constant.
7.3 Transfer Function—Two measurements of U and R are recorded for each data point, one with the wind tunnel speed
f
ascending and one with the wind tunnel speed descending. The values are then tabulated for each data point.
7.4 Off-Axis Response—The results of the measurement at two or more speeds are averaged to a single value for each angle of
attack. The averaged values are tabulated for each angle of attack.
8. Procedure
8.1 Starting Threshold (U ):
o
8.1.1 Provide a mechanical method for holding the anemometer in its normal position (see 3.1) and for rele
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