OTECH ENGINEERING, Inc. 630 Peña Drive, Suite 200 Davis, CA 95616-7726 Considerations in Anemometer Calibration Presented by: Presented by: John Obermeier, President John Obermeier, President Otech Engineering, Inc. Otech Engineering, Inc. In collaboration with: In collaboration with: Rachael Coquilla, Ph.D. candidate Rachael Coquilla, Ph.D. candidate Dept. Mechanical & Aeronautical Engineering Dept. Mechanical & Aeronautical Engineering University of California at Davis University of California at Davis
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OTECH ENGINEERING, Inc. 630 Peña Drive, Suite 200 Davis, CA 95616-7726 Considerations in Anemometer Calibration Presented by: John Obermeier, President.
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OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Considerations in Anemometer Calibration
Considerations in Anemometer Calibration
Presented by:Presented by:
John Obermeier, PresidentJohn Obermeier, PresidentOtech Engineering, Inc.Otech Engineering, Inc.
In collaboration with: In collaboration with: Rachael Coquilla, Ph.D. candidateRachael Coquilla, Ph.D. candidate
Dept. Mechanical & Aeronautical EngineeringDept. Mechanical & Aeronautical EngineeringUniversity of California at DavisUniversity of California at Davis
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Outline
Current Standards and Test Protocols
Anemometer Calibration
Quality Control
Calibration Comparisons
Calibration Standard Considerations
Summary
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Current Standards and Test Protocols
Current Test Standards for cup and propeller anemometers
ASTM D5096-02 ISO 17713
starting threshold
distance constant
transfer function **
off-axis response
Non-standard Protocols Measnet Otech Engineering, Inc.
…moving vehicle method…wind tunnel method
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Anemometer Calibration
BackgroundBackground
• 30 year history30 year history
• Most widely used instrument Most widely used instrument in wind industry (over in wind industry (over 150,000+ units installed)150,000+ units installed)
• Most tested anemometer in Most tested anemometer in the worldthe world
Performance characteristics
• Rugged and survives high wind environments
• Linear range matches wind turbine energy producing speed range
• Independent of temperature
• Maintains performance for extensive periods
NRG #40 Cup AnemometerNRG #40 Cup Anemometer
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Anemometer Calibration
Generation of an anemometer transfer function
Steady state wind speeds at set intervalsSteady state wind speeds at set intervals
Increasing and decreasing speedsIncreasing and decreasing speeds
Include specified speed rangeInclude specified speed range
Produce slope and offset from linear transfer functionProduce slope and offset from linear transfer function
Provide a measure of uncertaintyProvide a measure of uncertainty
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0 5 10 15 20 25 30
Reference Wind Speed, U (m/s)
Sp
eed
Res
idu
al, D U
(m
/s)
0
5
10
15
20
25
30
0 5 10 15 20 25 30 35 40
Anemometer Signal, f (Hz)
Ref
eren
ce W
ind
Sp
eed
, U
(m
/s)
Sample Transfer FunctionU = 0.7707 f + 0.318
R = 0.9999
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Anemometer Calibration
22VVV tSBU Uncertainty in
Velocity Measurement
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
3.5%
4.0%
2 4 6 8 10 12 14 16 18 20 22 24 26 28
Reference Wind Speed (m/s)
Rel
ativ
e U
nce
rtai
nty
in W
ind
Sp
eed
Mea
sure
men
t OEI Wind Tunnel
OEI Vehicle Test
NIST Wind Tunnel
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Quality Control
Recall sample transfer functionU = 0.7707 f + 0.318
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
0 10 20 30 40 50 60 70 80 90 100
time or unit count
% v
ari
ati
on
fro
m c
on
tro
lled
mea
n
UL
LL
Converted transfer functionConverted transfer functionusing using forced interceptforced intercept
U = 0.7693 U = 0.7693 ff + + 0.350.35
““slope+k” valueslope+k” value
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Quality ControlHistogram of Slope+K Values from OEI Vehicle Tests
Dec 2002 – Jul 2005 (11,834 new NRG #40 Cup Anemometers)Standard Deviation = 0.0031 m/s per Hz
95 % of the distribution are included within ± 0.8 % of the mean
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Calibration Comparisons
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.755 0.759 0.763 0.767 0.771 0.775
Slope (m/s per Hz)
Inte
rcep
t (m
/s)
OEI Vehicle CRES Wind Tunnel Consensus Value
Comparison of five NRG #40 anemometer calibrations (year 2002) between the OEI Vehicle and CRES Wind Tunnel test methods
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1 2 3 4 5
Reading Number%
dif
fere
nce
fro
m0.
765
m/s
per
Hz
OEI Vehicle CRES Wind Tunnel
Correlation Coefficient, R = 0.93
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Calibration Comparisons
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.755 0.759 0.763 0.767 0.771 0.775
Slope (m/s per Hz)
Inte
rcep
t (m
/s)
OEI Vehicle OEI Wind Tunnel Consensus Value
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
0 10 20 30 40 50 60 70 80 90 100
Reading Number%
dif
fere
nce
fro
m0.
765
m/s
per
Hz
OEI Vehicle OEI Wind Tunnel
Correlation Coefficient, R = 0.62
Comparison of 100 NRG #40 anemometer calibrations (year 2005) between the OEI Vehicle and OEI Wind Tunnel test methods
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Calibration Standard Considerations
Must agree upon a consensus standard anemometer Must agree upon a consensus standard anemometer calibration procedure and report process (i.e. Measnet).calibration procedure and report process (i.e. Measnet).
Consensus must remain an open process.Consensus must remain an open process.
Maintain a relation to a standard instrument via round Maintain a relation to a standard instrument via round robin comparisons (i.e. RR-3 experiment).robin comparisons (i.e. RR-3 experiment).
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Calibration Standard ConsiderationsPower, Speed Frequency, and Energy Distribution for a range of wind speeds (using GE 1.5 MW wind turbine power curve)
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
Wind Speed (m/s)
No
rmal
ized
% F
S
WT Power Speed Frequency ENERGY
OEI Test Range
Measnet Test Range
Mean = 7 m/s
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Calibration Standard Considerations
Considerations for advanced calibrations:Considerations for advanced calibrations:
Over-speedingOver-speedingDefinition: a cup anemometer’s over-estimation of Definition: a cup anemometer’s over-estimation of the mean wind due to its faster dynamic response the mean wind due to its faster dynamic response at the initial exposure to the wind than at the at the initial exposure to the wind than at the decrease of the same wind.decrease of the same wind.
Off-axisOff-axisASTM D5096-02 recommended testingASTM D5096-02 recommended testing test range test range ± 30° off-axis± 30° off-axis increments of 5° anglesincrements of 5° angles
Temperature dependenceTemperature dependence
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Summary
To add value in the manufacture of an anemometer, it is recommended to maintain quality control by using anemometer calibration and a statistical guideline (“Slope+K”). This assures buyers that the product clearly conforms to a defined performance criteria.
When a reliable calibration transfer function is available, it is recommended that users apply the tested transfer function rather than a generic transfer function.
Uncertainty in reference wind speeds for anemometer calibration are in the range of 2%. Uncertainty claims lower than NIST using LDA technology should be questioned.
An anemometer calibration standard needs to be defined.
OTECH ENGINEERING, Inc.630 Peña Drive, Suite 200Davis, CA 95616-7726
Related Measurement Standards and References
ASTM D5096-02 Standard Test Method for Determining the Performance of a Cup Anemometer and Propeller Anemometer
ASTM D4430-00e1 Standard Practice for Determining the Operational Comparability of Meteorological Measurements
ASTM D6011-96(2003) Standard Test Method for Determining the Performance of a Sonic Anemometer/Thermometer
ASTM D7145-05 Standard Guide for Measurement of Atmospheric Wind and Turbulence Profiles by Acoustic Means
ASTM D5741-96(2002)e1 Standard Practice for Characterizing Surface Wind Using a Wind Vane and Rotating Anemometer
ASTM D5527-00(2002)e1 Standard Practices for Measuring Surface Wind and Temperature by Acoustic Means
“The Maximum Type 40 Anemometer Calibration Project” Thomas J. Lockhart, CCM. Cnet, April 1998