ASTM D6011-96

Standard Test Method for Determining the Performance of a Sonic Anemometer/Thermometer

SCOPE
1.1 This test method covers the determination of the dynamic performance of a sonic anemometer/thermometer which employs the inverse time measurement technique for velocity or speed of sound, or both. Performance criteria include (a) acceptance angle, (b) acoustic pathlength, (c) system delay, (d) system delay mismatch, (e) thermal stability range, (f) shadow correction, (g) velocity calibration range, and (h) velocity resolution.  
1.2 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.

General Information

• Status: Historical
• Publication Date: 09-Oct-1996
• Technical Committee: D22 - Air Quality
• Drafting Committee: D22.11 - Meteorology

Relations

• Replaced By: ASTM D6011-96(2003) - Standard Test Method for Determining the Performance of a Sonic Anemometer/Thermometer
• Effective Date: 10-Apr-2003

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 6011 – 96
Standard Test Method for
Determining the Performance of a Sonic
Anemometer/Thermometer
This standard is issued under the fixed designation D 6011; 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 at which an abrupt decrease in an object’s drag coefficient
occurs (2).
1.1 This test method covers the determination of the dy-
3.2.2.1 Discussion—The transducer shadow corrections are
namic performance of a sonic anemometer/thermometer which
no longer valid above the critical Reynolds number due to a
employs the inverse time measurement technique for velocity
discontinuity in the axial attenuation coefficient.
or speed of sound, or both. Performance criteria include: (a)
3.2.3 Reynolds number (R )—the ratio of inertial to viscous
e
acceptance angle, (b) acoustic pathlength, (c) system delay, (d)
forces on an object immersed in a flowing fluid based on the
system delay mismatch, (e) thermal stability range, (f) shadow
object’s characteristic dimension, the fluid velocity, and vis-
correction, (g) velocity calibration range, and (h) velocity
cosity.
resolution.
3.2.4 shadow correction (v /v )—the ratio of the true
dm d
1.2 This standard does not purport to address all of the
along-axis velocity v , as measured in a wind tunnel or by
dm
safety concerns, if any, associated with its use. It is the
another accepted method, to the instrument along-axis wind
responsibility of the user of this standard to establish appro-
measurement v .
d
priate safety and health practices and determine the applica-
3.2.4.1 Discussion—This correction compensates for flow
bility of regulatory limitations prior to use.
shadowing effects of transducers and their supporting struc-
2. Referenced Documents tures. The correction can take the form of an equation (3) or a
lookup table (4).
2.1 ASTM Standards:
3.2.5 speed of sound (c, (m/s))—the propagation rate of an
C 384 Test Method for Impedance and Absorption of
adiabatic compression wave
Acoustical Materials by the Impedance Tube Method
0.5
D 1356 Terminology Relating to Sampling and Analysis of
c 5 ~g]P/]r! (1)
s
Atmospheres
where:
D 5527 Practice for Measuring Surface Wind and Tempera-
r = density,
ture by Acoustic Means
g = specific heat ratio, and
E 380 Practice for Use of the International System of Units
4 s = isentropic (adiabatic) process (6).
(SI) (the Modernized Metric System)
3.2.5.1 Discussion—The velocity of the compression wave
3. Terminology
defined along each axis of a Cartesian coordinate system is the
3.1 Definitions—For definitions of terms related to this test
sum of propagation speed c plus the motion of the gas along
method, refer to Terminology D 1356.
that axis. In a perfect gas (5):
3.2 Definitions of Terms Specific to This Standard:
0.5
c 5 ~gR* T/M! (2)
3.2.1 axial attenuation coeffıcient—a ratio of the free stream
wind velocity (as defined in a wind tunnel) to velocity along an The approximation for propagation in air is:
acoustic propagation path (v /v ) (1). 0.5 0.5
t d
c 5 403 T 1 1 0.32 e/P 5 403 T (3)
@ ~ !# ~ !
air s
3.2.2 critical Reynolds number (R )—the Reynolds number
c
3.2.6 system clock—the clock used for timing acoustic
wavefront travel between a transducer pair.
3.2.7 system delay (dt, μs)—the time delay through the
This test method is under the jurisdiction of ASTM Committee D-22 on
Sampling and Analysis of Atmospheresand is the direct responsibility of Subcom-
transducer and electronic circuitry (7).
mittee D22.11on Meteorology.
3.2.7.1 Discussion—Each path through every sonic array
Current edition approved Oct. 10, 1996. Published December 1996.
axis can have unique delay characteristics. Delay (on the order
Annual Book of ASTM Standards, Vol 04.06.
Annual Book of ASTM Standards, Vol 11.03. of 10 to 20 μs) can vary as a function of temperature and
Annual Book of ASTM Standards, Vol 14.02.
direction of signal travel through the transducers and electronic
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.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 6011
circuitry. The average system delay for each axis in an acoustic range of velocity between creeping flow and the flow at which
array is the average of the delays measured in each direction a critical Reynolds number is reached.
along the axis 3.2.12.1 Discussion—The shadow correction is valid over a
range of velocities where no discontinuities are observed in the
dt 5 ~dt 1dt !/2 (4)
1 2
axial attenuation coefficient.
3.2.8 system delay mismatch (dt , μs)—the absolute differ-
t
3.2.13 velocity resolution (dv, (m/s))—the largest change in
ence in microseconds between total transit times t in each
t
an along-axis wind component that would cause no change in
direction (t , t ) through the system electronics and transduc-
t1 t2
the pulse arrival time count.
ers.
3.2.13.1 Discussion—Velocity resolution defines the small-
3.2.8.1 Discussion—Due principally to slight differences in
est resolvable wind velocity increment as determined from
transducer performance, the total transit time obtained with the
system clock rate. For some systems, dv defined as the standard
signal originating at one transducer can differ from the total
deviation of system dither can also be reported.
transit time obtained with the signal originating at its paired
3.3 Symbols:
transducer. The manufacturer should specify the system delay
mismatch tolerance.
c = speed of sound, m/s,
dt 5 ? t 2 t ? (5)
t t1 t2
C = specific heat at constant pressure, J/(kg·K),
p
3.2.9 thermal stability range (°C)—a range of temperatures
C = specific heat at constant volume, J/(kg·K),
v
over which the corrected velocity output in a zero wind
e = vapor pressure, Pa,
chamber remains at or below instrument resolution.
d = acoustic pathlength, m,
3.2.9.1 Discussion—Thermal stability range defines a range
f = compressibility factor, dimensionless,
of temperatures over which there is no step change in system
M = molecular weight of a gas, g/mol,
delay. P = pressure, Pa,
3.2.10 time resolution (Dt, μs)—resolution of the internal R* = universal gas constant, 8.31436 J/(mol·K),
RH = relative humidity, %,
clock used to measure time.
t = transit time, μs,
3.2.11 transit time (t, μs)—the time required for an acoustic
t = total transit time, μs,
t
wavefront to travel from the transducer of origin to the
T = absolute temperature, K,
receiving transducer.
T = sonic absolute temperature, K,
s
3.2.11.1 Discussion—Transit time (also known as time of
U = upper limit for creeping flow, m/s,
c
flight) is determined by acoustic pathlength d, the speed of
U = critical Reynolds number velocity, m/s,
s
sound c, the velocity component along the acoustic propaga-
v = velocity component along acoustic propagation
d
tion path v , and cross-path velocity components) v (8)
d n
path, m/s,
2 2 0.5 2 2 2
t 5 d c 2 v ! 6 V / c 2 v 1 v ! (6) v = tunnel velocity component parallel to the array axis
@~ # @ ~ #
n d d n dm
(v , cos u), m/s,
t
The transit time difference between acoustic wavefront propagation
v = velocity component normal to an acoustic propaga-
n
in one direction (t , computed for + v ) and the other (t , computed
1 d 2
tion path, m/s,
for − v ) for each transducer pair determines the magnitude of a
d
v = free stream wind velocity component (unaffected by
velocity component. The inverse transit time solution for the along-axis t
velocity is (9) the presence of an obstacle such as the acoustic
array), m/s,
d 1 1
v 5 2 (7)
F G dt = system delay, μs,
d
2 t t
1 2
dt = system delay mismatch, μs,
The total transit times t and t , include the sum of actual transit t
t1 t2
Dt = clock pulse resolution, s,
times plus system delay through the electronics and transducers in each
a = acceptance angle, degree,
direction along an acoustic path, d and d . System delay must be
t1 t2
removed to calculate v , that is, g = specific heat ratio (C /C ), dimensionless,
d p v
dv = velocity resolution, m/s,
t 5 t 2d (8)
1 t1 t1
u = array angle of attack, degree, and
r = gas density, kg/m .
t 5 t 2d (9)
2 t2 t2
3.4 Abbreviations:Units—Units of measurement are in ac-
3.2.11.2 Discussion—Procedures in this test method include
cordance with Practice E 380.
a test to determine whether separate determinations of d t and
4. Summary of Test Method
dt are needed, or whether an average dt can be used. The
relationship of transit time to speed of sound is
4.1 Acoustic pathlength, system delay, and system delay
2 mismatch are determined using the dual gas or zero wind
d 1 1
2 2
c 5 1 1 v (10)
F S DG
n
chamber method. The acoustic pathlength and system clock
2 t t
1 2
rate are used to calculate the velocity resolution. Thermal
and the inverse transit time solution for sonic temperature in air is as
sensitivity range is defined using a zero wind chamber. The
follows (6):
axial attenuation coefficient, velocity calibration range, and
2 2 2
d 1 1 v
n
transducer shadow effects are defined in a wind tunnel. Wind
T 5 1 1 (11)
S DF G
s
1612 t t 403
1 2
tunnel results are used to compute shadow corrections and to
3.2.12 velocity calibration range (U to U , (m/s))—the define acceptance angles.
c s
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 6011
5. Significance and Use 6.2 Pathlength Chamber—See Fig. 2.
6.2.1 Design the pathlength chamber to fit and seal an axis
5.1 This test method provides a standard method for evalu-
of the array for acoustic pathlength determination. Construct
ating the performance of sonic anemometer/thermometers that
the chamber components using non-expanding, non-outgassing
use inverse time solutions to measure wind velocity compo-
materials. Employ O-ring seals made of non-outgassing mate-
nents and the speed of sound. It provides an unambiguous
rials to prevent pressure loss and contamination. Design the
determination of instrument performance criteria. The test
chamber for quick and thorough purging. The basic pathlength
method is applicable to manufacturers for the purpose of
chamber components are illustrated in Fig. 2.
describing the performance of their products, to instrumenta-
6.2.2 Gas Source and Plumbing, to connect the pathlength
tion test facilities for the purpose of verifying instrument
chamber to one of two pressurized gas sources (nitrogen or
performance, and to users for specifying performance require-
argon). Employ a purge pump to draw off used gases. Required
ments. The acoustic pathlength procedure is also applicable for
purity of the gas is 99.999 %.
calibration purposes prior to data collection. Procedures for
6.3 Temperature Transducer (two required), with minimum
operating a sonic anemometer/thermometer are described in
temperature measurement precision and accuracy of 60.1°C
Practice D 5527.
and 60.2°C, respectively, and with recording readout. One is
5.2 The sonic anemometer/thermometer array is assumed to
required for the zero wind chamber and one for the pathlength
have a sufficiently high structural rigidity and a sufficiently low
chamber.
coefficient of thermal expansion to maintain an internal align-
6.4 Wind Tunnel:
ment to within the manufacturer’s specifications over its
6.4.1 Size, large enough to fit the entire instrument array
designed operating range. Consult with the manufacturer for an
within the test section at all required orientation angles. Design
internal alignment verification procedure and verify the align-
the tunnel so that the maximum projected area of the sonic
ment before proceeding with this test method.
array is less than 5 % of tunnel cross-sectional area.
5.3 This test method is designed to characterize the perfor-
6.4.2 Speed Control, to vary the flow rate over a range of at
mance of an array model or probe design. Transducer shadow
least 1.0 to 10 m/s within 60.1 m/s or better throughout the test
data obtained from a single array is applicable for all instru-
section.
ments having the same array model or probe design. Some
6.4.3 Calibration—Calibrate the mean flow rate using
non-orthogonal arrays may not require specification of trans-
transfer standards traceable to the National Institute of Stan-
ducer shadow corrections or the velocity calibration range.
dards and Technology (NIST), or by an equivalent fundamental
physical method.
6. Apparatus
6.4.4 Turbulence, with a uniform velocity profile with a
6.1 Zero Wind Chamber, sized to fit the array and accom-
minimum of swirl at all speeds, and known uniform turbulence
modate a temperature probe (Fig. 1) used to calibrate the sonic
scale and intensity throughout the test section.
anemometer/thermometer. Line the chamber with acoustic
6.4.5 Rotating Plate, to hold the sonic transducer array in
foam with a sound absorption coefficient of 0.8 or better (Test
varying orientations to achieve angular exposures up to 360°,
Method C 384) to minimize internal air motions caused by
as needed. The minimum plate rotation requirements are 660°
thermal gradients and to minimize acoustic reflections. Install
in the horizontal and 615° in the vertical, with an angular
a small fan within the chamber to establish thermal equilibrium
alignment resolution of 0.5°.
before a zero wind calibration is made.
NOTE 1—Design the plate to hold the array at chosen angles without
disturbing the test section wind velocity profile or changing its turbulence
level.
6.5 Measuring System:
FIG. 2 Pathlength Chamber for Acoustic Pathlength
FIG. 1 Sonic Anemometer Array in a Zero Wind Chamber Determination
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 6011
6.5.1 Counter, to log the anemometer velocity component apparatus permits. Reverse the process, going back through 0°
readings, with a count resolution equaling or exceeding the to − 60°, and return to 0°. Average the results to a single value
clock rate of the sonic anemometer/thermometer. for each angular position. Use a measurement period of 30 s at
6.5.2 Recorder, with at least a 10 Hz rate and a resolution each angle, and begin measure
...