Types and details on anemometers

1. Anemometers:
Measuring Wind Speed
Debajyoti Bose
Lt. Col. Ashis Khare
Pravin Badarayani

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

3. Anemometer: Reason For Use
 Two primary reasons to measure wind speed:
 To determine feasibility of wind power development at a site
 As part of a wind turbine control system
“Is it worthwhile to turn the turbine into the wind
and start it?”
Animation: How the air moves forming Winds, V. Ryan © 2005

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