2. Anemometer: Basics
A common weather
station instrument
The term is derived from the Greek
word anemos, meaning wind
Describe any air speed measurement
instrument used in
meteorology or aerodynamics
Invented in 1846 by
John Thomas Romney Robinson
Image: National Weather Service (NWS) Collection, Baltimore, Image
ID: wea00920
4. Anemometer: Types
Mechanical Type:
Cup Anemometer
Non-Mechanical Type:
Hot Wire Anemometers
Ultrasonic Anemometers
Laser/Doppler Anemometers
Pressure Anemometers
Plate Anemometers
Tube Anemometers
Propeller Type Anemometers
Image: Digital Anemometer, www.everflowscientific.com
5. Cup Anemometers
Most common wind speed measurement device
It consists of hemispherical cups, each mounted on one
end of horizontal arms
And the arms were mounted at equal angles to each other
on a vertical shaft
Image: www.directindustry.com
6. Cup Anemometers: Continued
The air flow past the cups in any
horizontal direction turned the
shaft in a manner that is
proportional to the wind speed
On counting the turns of the
shaft over a set time period
produced the average wind
speed for a wide range of
speeds
Animation: Anemometer 2 from Barani Design and Wind101.net
7. In a Nutshell: Cup Anemometers
Many cup anemometers have a vane attached to measure
wind direction
Advantages Disadvantages
Low Price
Flexible Design
Simple Installation
Most technicians
understand operating
principles and
necessary connections
Moving parts wear
out
Without provisions
for heating, they
don’t work well in
snow or freezing rain
They don’t work well
in rapidly fluctuating
winds
Image: http://www.photolib.noaa.gov/nssl/nssl0161.htm
8. Hot Wire Anemometers
Uses a very fine wire (on the order of several micro-
metres)
Electrically heated up to some temperature above the
ambient
Air flowing past the wire has a cooling effect on the wire
“The electrical resistance of most metals is dependent upon
the temperature of the metal”
Using above a relationship can be obtained between the
resistance of the wire and the flow speed
9. Probe Specifications
“Tungsten is a popular choice for hot-wires”
Tungsten or Platinum filament
~1 mm long
4-10 mm diameter
Benefits
Good spatial resolution
Flat frequency response
Limitations
Fragile
Requires clean flow
Cost (start at $300-400)
Image: www.tungstenringsco.com
10. Typical Specifications
Parameters Handheld/Economy Industrial Grade
Measurable velocities 0.2-20 m/s 0.2-90 m/s
Operating temp ranges 0-50 °C -40-200 °C
Velocity Accuracy ± 3% reading ± 1% reading
Time constant 200 ms 100 ms
Interfacing options Handheld reader,
RS232
RS232, RS485, voltage,
4-20 mA, Modbus,
Profibus, etc.
Source: http://www.extech.com/instruments/product.asp?catid=1&prodid=43
11. Ultrasonic Anemometers
First developed in the 1950s
Use of ultrasonic sound waves to
measure wind velocity
They measure wind speed based
on the time of flight of sonic
pulses between pairs
of transducers
Measurements from pairs of
transducers can be combined to
yield a measurement of velocity in
1-, 2-, or 3-dimensional flow
Figure: 2D ultrasonic
anemometer with 3 paths
Image: Anémomètre / girouette ultrasonique à trois chemins
12. Ultrasonic Anemometers
Advantage Disadvantage
The lack of moving parts
makes them appropriate for
long-term use in exposed
automated weather stations
and weather buoys where the
accuracy and reliability of
traditional cup-and-vane
anemometers is adversely
affected by salty air or large
amounts of dust
Main disadvantage is the
distortion of the flow itself by
the structure supporting the
transducers, which requires
a correction based upon
wind tunnel measurements
to minimize the effect
Figure: 3D ultrasonic anemometer
Image: Google
13. Laser/Doppler Anemometers
Laser/Doppler anemometers use a beam of light from
a laser that is divided into two beams, with one
propagated out of the anemometer
Particulates (or deliberately introduced seed material)
flowing along with air molecules near where the beam
exits reflect, or backscatter, the light back into a detector,
where it is measured relative to the original laser beam
When the particles are in great motion, they produce
a Doppler shift for measuring wind speed in the laser light,
which is used to calculate the speed of the particles, and
therefore the air around the anemometer
14. Plate Anemometers
Modern anemometers
Are simply a flat plate suspended from the top so that the
wind deflects the plate
The pressure of the wind on its face is balanced by a
spring
The compression of the spring determines the actual force
which the wind is exerting on the plate
This is either read off on a suitable gauge, or on a recorder
15. Plate Anemometers: Continued
Advantage Disadvantage
They are used on these high
places because they are in a
plate shape; has a good
measurement status on
higher altitudes
Instruments of this kind do
not respond to light winds, are
inaccurate for high wind
readings, and are slow at
responding to variable winds.
Image: www.stormdebris.net
16. Tube Anemometers
A tube anemometer uses
air pressure to determine
the wind pressure, or
speed
A tube anemometer
measures the air pressure
inside a glass tube that is
closed at one end
By comparing the air
pressure inside the tube to
the air pressure outside the
tube, wind speed can be
calculated
Figure: Invented by William Henry Dines in 1892,
The movable part (right) to be put on top of the
fixed part (left)
Image: Wikipedia
17. Propeller Type/Vane Anemometers
The axis on the vane anemometer is
parallel to the direction of the wind
and therefore horizontal
Since the wind varies in direction and
the axis has to follow its changes
Combines a propeller and a tail on the
same axis to obtain accurate and
precise wind speed and direction
measurements from the same
instrument
Image: nssl0161, National Severe Storms Laboratory (NSSL) Collection
18. Output from Anemometers
Signal conditioning is usually done within the instrument
The output can be an electrical signal to a data-logger or
readout device:
Pulse signal
Voltage signal
For example, 0-10 V corresponds to the velocity measurement range of
the instrument.
Current signal
Typically, 4-20 mA corresponding to the instrument range.
Eliminates voltage drop when the signal is transmitted over larger
distances.
19. Importance of Accurate Wind
Speed Measurements
The power obtained from the wind goes with the cube of
the wind speed
A small error in the measurement results in a much larger
error in the predicted wind power
For example, a 5% error at a wind speed of 10 meters/sec
leads to a 16% error in predicted wind power
10% anemometer error leads to 33% errors in power
prediction
This could be disastrous if one is monitoring a site for
feasibility of wind power development!
20. Thank You Very Much Indeed !!!
A Presentation by M. Tech Renewable
Energy Engineering
Debajyoti Bose: R120214007
Lt. Col. Ashis Khare: R120214006
Pravin Badarayani: R120214005
Department of Electrical Engineering