ASTM D5096-96
(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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Standards Content (Sample)
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Designation: D 5096 – 96
Standard Test Method for
Determining the Performance of a Cup Anemometer or
Propeller Anemometer
This standard is issued under the fixed designation D 5096; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope anemometers is with the axis of rotation aligned with the
direction of flow. Note that if the anemometer axis is not
1.1 This test method covers the determination of the Start-
aligned with the direction of flow, the calculated wind speed
ing Threshold, Distance Constant, Transfer Function, and
component parallel to the anemometer axis is used to deter-
Off-Axis Response of a cup anemometer or propeller anemom-
mine starting threshold.
eter from direct measurement in a wind tunnel.
3.2.2 distance constant (L, m)—the distance the air flows
1.2 This test method provides for a measurement of cup
past a rotating anemometer during the time it takes the cup
anemometer or propeller anemometer performance in the
wheel or propeller to reach (1 − 1/e) or 63 % of the equilibrium
environment of wind tunnel flow. Transference of values
speed after a step change in wind speed (1). The response of
determined by these methods to atmospheric flow must be done
a rotating anemometer to a step change in which wind speed
with an understanding that there is a difference between the
increases instantaneously from U =0 to U=U is (2):
two flow systems. f
~2t/ G!
1.3 This standard does not purport to address all of the
U 5 U @1 2 e # (1)
t f
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
where:
priate safety and health practices and determine the applica-
U = is the instantaneous indicated wind speed at time t in
t
bility of regulatory limitations prior to use.
m/s,
U = is the final indicated wind speed, or wind tunnel speed,
2. Referenced Documents
f
in m/s,
2.1 ASTM Standards:
t = is the elapsed time in seconds after the step change
D 1356 Terminology Relating to Sampling and Analysis of
occurs, and
Atmospheres
G = is the time constant of the instrument.
D 3631 Test Methods for Measuring Surface Atmospheric
Distance Constant is: L 5 U G (2)
f
Pressure
D 4430 Practice for Determining the Operational Compara-
3.2.3 transfer function (Û =a+bR, m/s)—the linear rela-
bility of Meteorological Instruments
f
tionship between wind speed and the rate of rotation of the
D 4480 Test Method for Measuring Surface Winds by
Means of Wind Vanes and Rotating Anemometers anemometer throughout the specified working range. U is
f|AX
the predicted wind speed in m/s, a is a constant, commonly
3. Terminology
called zero offset, in m/s, b is a constant representing the wind
3.1 For definitions of terms used in this standard, refer to passage in m/r for each revolution of the particular anemometer
Terminology D 1356. cup wheel or propeller, and R is the rate of rotation in r/s. It
3.2 Definitions of Terms Specific to This Standard: should be noted that zero offset is not the same as starting
3.2.1 starting threshold (U , m/s)—the lowest wind speed at threshold. In some very sensitive anemometers the constant a,
o
which a rotating anemometer starts and continues to turn and zero offset, may not be significantly greater than zero. The
produce a measurable signal when mounted in its normal constants a and b must be determined by wind tunnel measure-
position. The normal position for cup anemometers is with the ment for each type of anemometer (3).
axis of rotation vertical, and the normal position for propeller 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
indicated wind speed at zero angle of attack (U ) multiplied by
f
This test method is under the jurisdiction of ASTM Committee D-22 on
the cosine of the angle of attack. This ratio compares the actual
Sampling and Analysis of Atmospheres and is the direct responsibility of Subcom-
mittee D22.11 on Meteorology.
Current edition approved May 10, 1996. Published July 1996. Originally
published as D 5096 – 90. Last previous edition D 5096 – 90. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 11.03. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5096
off-axis response to a cosine response. of wind speeds throughout the specified working range. In the
3.3 Symbols: range of wind speeds where the anemometer response is
non-linear (near threshold) a minimum of five data points are
recorded. A minimum of five additional data points are
a (m/s) = zero offset constant
recorded within the working range of the anemometer and
b (m/r) = wind passage (apparent pitch) constant or
wind tunnel but above the non-linear threshold region (see Fig.
calibration constant
2). Measurements are recorded for each data point with the
L (m) = distance constant
wind tunnel speed ascending and descending. The values of a
r (none) = a shaft revolution
and b are determined by least-squares linear regression of the
R (r/s) = rate of rotation
individual data points.
G(s) = time constant
4.5 Off-Axis Response may be measured at a number of
t (s) = time
wind speeds but must include 5 m/s, and 10 m/s.
U (m/s) = starting threshold
o
4.5.1 Cup Anemometers—A measurement is made of the
U (m/s) = indicated wind speed (used in off-axis test)
output signal when the anemometer is inclined into the wind
U (m/s) = final indicated wind speed or wind tunnel
f
speed (representing a down-draft) and away from the wind (repre-
U (m/s) = anemometer application range senting an updraft), while the wind tunnel is running at a steady
max
U (m/s) = instantaneous indicated wind speed at time t
speed. The output signal is measured with the anemometer axis
t
Û (m/s) = predicted wind speed
at 5° intervals from vertical to plus and minus 30° from
f
u (deg) = off-axis angle of attack
vertical. The measured signal is then converted to a ratio for
each interval by dividing by the normal signal measured with
4. Summary of Test Method
the anemometer axis in the normal, or vertical, position.
4.1 This test method requires a wind tunnel described in
4.5.2 Vane Mounted Propeller Anemometers—A measure-
Section 6, Apparatus.
ment is made of the output signal when the anemometer’s axis
4.2 Starting Threshold (U , m/s) is determined by measur-
o
of rotation is inclined downward into the wind (representing a
ing the lowest speed at which a rotating anemometer starts and
down-draft) and inclined upward into the wind (representing an
continues to turn and produce a measurable signal when
updraft), while the wind tunnel is running at a steady speed.
mounted in its normal position.
The output signal is measured at 5° intervals from a horizontal
4.3 Distance Constant (L, m) may be determined at a
axis of rotation to 6 30° from the horizontal. The measured
number of wind speeds but must include 5 m/s, and 10 m/s. It
signal is then converted to a ratio for each interval by dividing
is computed from the time required for the anemometer rotor to
by the normal signal with the anemometer in the normal, or
accelerate (1 – 1/e) or 63 % of a step change in rotational speed
horizontal position. This test may be conducted either with the
after release from a restrained, non-rotating condition. The
vane in place or with the vane removed and the axis of rotation
final response, U , is the wind tunnel speed as indicated by the
f
fixed in the down-tunnel direction.
anemometer. In order to avoid the unrealistic effects of the
4.5.3 Fixed Axis Propeller Anemometer—A measurement is
restrained condition, as shown in Fig. 1, the time measurement
made of the output signal when the anemometer is rotated in
should be made from 0.30 of U to 0.74 of U . This interval in
f f
the air stream throughout the complete 360° angle of attack.
seconds is equal to one time constant (G) and is converted to
The signal is measured at a number of angles but must include
the Distance Constant by multiplying by the wind tunnel speed
10° intervals with additional measurements at 85, 95, 265, and
in meters per second (m/s).
275°. The measured signal for each angle of attack is then
4.4 Transfer Function (Û =a+bR, m/s) is determined by
f
converted to a ratio by dividing by the signal measured at 0°
measuring the rate of rotation of the anemometer at a number
angle of attack (axial flow). Additionally, the stall angle of the
propeller is measured by orienting the anemometer at 90° and
slowly rotating into and away from the air flow until the
FIG. 1 Typical Anemometer Response Curve FIG. 2 Typical Anemometer Calibration Curve
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5096
propeller starts rotating continuously. Stall angle is the total been calibrated at the National Institute of Standards and
contained angle within which the propeller does not continu- Technology or by a fundamental physical method. Speeds
ously rotate. The procedure is repeated at 270°. below 2 m/s for the threshold determination must be verified by
a sensitive anemometer or by some fundamental time and
5. Significance and Use
distance technique, such as measuring the transition time of
5.1 This test method will provide a standard for comparison 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
rpm or some other index relating method of control to flow rate
by regulatory agencies (4-7) and industrial societies have
should be established by this technique for speeds of 2 m/s and
specified performance values. This standard provides an un-
below.
ambiguous method for measuring 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). Differences of greater than 3 % 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-
tion of the anemometer shaft and the transducer output must be
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 shall be
recording system must represent the indicated wind speed with
reported for each independent measurement.
a resolution of 0.02 m/s.
6.1.2 Time—The resolution of time must be consistent with
7. Sampling
the distance accuracy required. For this reason the time
7.1 Starting Threshold—The arithmetic mean on ten con-
resolution may be changed as the wind tunnel speed is
secutive tests is required for a valid starting threshold mea-
changed. If one wants a distance constant measurement to 0.1
surement.
meter resolution one must have a time resolution of 0.05 s at 2
7.2 Distance Constant—The arithmetic mean of ten tests is
m/s and 0.01 s at 10 m/s. If timing accuracy is based on 50 Hz
required for a valid measurement at each speed. The results of
or 60 Hz power frequency it will be at least an order of
the measurements at two or more speeds are averaged to a
magnitude better than the resolution suggested above.
single value for distance constant.
6.1.3 Angle of Attack—The resolution of the angle of attack
7.3 Transfer Function—Two measurements of U and R are
f
(u) must be within 0.5°. An ordinary protractor of adequate size
recorded for each data point, one with the wind tunnel speed
with 0.5° markings will permit measurements with sufficient
ascending and one with the wind tunnel speed descending. The
resolution. A fixture should be constructed to permit alignment
values are then tabulated for each data point.
of the anemometer to the off-axis angles while the wind tunnel
7.4 Off-Axis Response—The results of the measurement at
is running at a steady speed.
two or more speeds are averaged to a single value for each
6.2 Recording Techniques:
angle of attack. The averaged values are tabulated for each
6.2.1 Digital recording systems and appropriate reduction
angle of attack.
programs will be satisfactory if the sampling rate is at least 100
samples/s. Exercise care to avoid electronic circuits with time
8. Procedure
constants which limit the proper recording of anemometer
8.1 Starting Threshold (U ):
o
performance. Oscilloscopes with memory and hard copy capa-
8.1.1 Provide a mechanical method for holding the an-
bility may also be used. Another simple technique is to use a
emometer in its normal position (see 3.1) and for releasing the
fast-response strip chart recorder (flat to 10 Hz or better) with
anemometer from a restrained, or non-rotating condition, while
enough gain so that the signal produced by the anemometer
the wind tunnel is running at the test speed. Test the release
when the wind tunnel is running at 2 m/s is sufficient to provide
mechanism with the wind tunnel off to verify that the release
full scale pen deflection on the recorder. The recorder chart
method does not move the anemometer rotor when activated.
drive must have a fast speed of 50 mm/s or more.
8.1.2 Set the wind tunnel to a speed that is lower than the
6.3 Wind Tunnel (8):
starting threshold. Slowly increase the wind tunnel speed until
6.3.1 Size—The wind tunnel must be large enough so that
the cup wheel or propeller continues to rotate and produce a
the projection of the cup wheel or propeller, sensor, and
measurable signal.
support apparatus, is less than 5 % of the cross sectional area
8.1.3 Repeat the procedure of 8.1.2 ten times and record the
of the tunnel test section.
results.
6.3.2 Speed Range—The wind tunnel must have a speed
control which will allow the flow rate to be varied from 0 to a
NOTE 1—Vibration caused by the wind tunnel or by o
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