Wind Instrument Testing Apparatus Project

1
WITAP
Wind Instrument Testing Apparatus Project
Team Rob Koch Andy Lawrence
2

• Background
• An anemometer is a device used to measure wind
  speed.
• Commonly it is mounted on towers or inaccessible
  places.
• The data generated from these devices is used to
  assess the feasibility of wind power generation
  at that site.

3

• Problem Statement
• Vermont Technical College has an Anemometer Loan
  Program using NRG anemometers.
• The anemometers need to be checked periodically
  for function and calibration.

4
Type of Anemometer to be Tested

• Cup Anemometer
• Simplest type of anemometer
• Air flow past the cups turns the spindle
  outputting a varying frequency
  
  signal proportional to the wind speed
• Standard models use a sensitive 4-pole magnet
• Type to be calibrated in the device

5
Solution Statement

• Our proposed solution is to build an airflow
  chamber that can put out a steady and consistent
  air velocity to an open air anemometer and save
  cost.
• A workshop device needs to be developed with an
  effective range of air flow control and data
  acquisition capability to assess anemometer
  operation and accuracy.

6
System Requirements

• Non-Turbulent Air Flow Output
• Wind Velocity Controlled to 0.2 m/s
• Air Flow Capable of 1 to 20 m/s (45mph)
• Accuracy and Consensus of Measured Data
• Repeatability of Results

7
Work so Far

• Design and Build Chamber
• Test General Wind Flow Capability of System
• Test Specific Airflow Characteristics of Chamber
• Design and Build Mechanical Features
• Design and Build Electronic Control System
• Test, Test, Test,

8
Solution

• A wind tunnel with reduced outlet for higher
  velocity
• Powered by constant-speed 120VAC fan
• Wind speed can be varied with shutters at inlet
  to fan
• Wind speed is measured with a pitot tube
  connected to a pressure sensor that outputs 0 to
  4V DC
• Wind speed is controlled by using the 0 to 4 V
  signal and controlling the shutters accordingly
• Shutter control system consists of a Motorola
  HC08 microcontroller, a Reversible DC motor
  controller, and a DC motor connected to the
  shutters.

9
Test Sequence PC
Converted Setpoint Value
HC08
Pressure Sensor
0 to4v Signal
Compare Data
Time Delay
Adjust Damper
New Setpoint
Setpoint Velocity
Acquire Data From Anemometer and Sensor
No
Yes
10
H Bridge Motor Controller
HC08
RS232
PWM Signal
PC
A/D
-
. .
Differential Pressure Sensor
5V GND 0.25-4V
Setpoint Entry
Air hoses to sensor
Pitot Tube
Wind Outlet
Fan Dampers
Dampers
11
Measuring Air Velocity using Velocity Pressure
Velocity Pressure uses the differential pressure
in the output to determine velocity
Pt tap Ps tap
Manometer
Air Flow
Pt Ps
Pitot-Static Tube
Outlet
Simulated Wind
? v2g(Pt-Ps)/? General Equation g
acceleration of gravity, ? specific weight of
air ? vPv(1.289)2 Pv (Pa), ? (m/s) ?
vPv(4005)2 Pv (inH2O), ? (ft/min) Pt Total
Pressure Ps Static Pressure Pv Velocity
Pressure (Pt-Ps) ? velocity
12
Pitot Tube Function ? When a moving fluid is
caused to stop because it encounters a stationary
object, a pressure is created at that point that
is greater than the pressure in the fluid stream.
? The magnitude of this increased pressure is
related to the velocity of the moving fluid. ?
The pitot tube measures the stagnation pressure
due to the deceleration of the flowing fluid.
Stagnation pressure
13
Costs
14
Time breakdown
15
Questions?
16
System Requirements

• Air Flow Capable of Up to 20 m/s (45mph)
• Non-Turbulent Air Flow Output
• Constant Air Pressure at Setpoints
• Non-Intrusive Sensor
• Accuracy and Consensus of Measured Data
• Repeatability of Results

17
System Diagram
damper motor
controlled vent
Chamber
motor controller HC08
Fan
output opening
airflow
hot wire sensor
magnahelic
gauge reader
manometer
18

• System Modeling Considerations
• Whether flow is adiabatic
• Effective pressure difference needed
• Whether present model is relevant
• Type of flow, need for baffles
• Sensitivity requirements of control/monitoring
  instruments
• For adiabatic flow of a compressible fluid (air)
  from inside a chamber through an opening the
  velocity is given by
• ?2 (2gp1/?1)(k/k-1)1-(p2/p1)(k-1)/k1/2
• k adiabatic exponent 1.40 for air
• ? specific weight 11.81N/m3
• p1 pressure in chamber (Pascals), p2
  atmospheric (Pascals)

19
Model for System Analysis Using the Formula
Pressurized Chamber
P1 ?1 ?10
Control variable
Atmospheric
flow
P2 ?2 ?2
Ideally adiabatic (?1 ?2)
Formula for system analysis using differential
pressure between chamber and atmosphere ?2
(2gp1/?1)(k/k-1)1-(p2/p1)(k-1)/k1/2
20
(No Transcript)
21
Electrical Systems Diagram
damper motor
controlled vent
PC
Chamber
motor controller HC08
Fan
airflow
hot wire sensor
output opening
22
Measurement Devices Used

• Manometer and Magnehelic - measure differential
  pressure in inches water column

23
Measurement Devices Used
Extech and Dwyer Wind Measurement Device- measure
air flow directly in units of m/s
24
Possible Measurement Device to be Used

• Hot Wire Anemometer
• Use a very fine wire heated to a temperature
  above ambient
• Air flow past the wire has a cooling effect on
  the wire
• The electrical resistance of the wire is
  dependent on the temperature
• A relationship can be obtained between the
  resistance of the wire and the velocity
  of the air flow.
• High frequency response used to study turbulent
  flow and rapid velocity fluctuations.
• Can give an analog voltage output

25
Hot Wire Anemometer Schematics
Hot Wire Anemometer- this sensor measures volume
of air flow electronically through the use of a
thermistor, resistive heat element with positive
temperature coefficient, and bridge circuit
26
Chain of Events

• Design and Build Chamber
• Test General Wind Flow Capability of System
• Test Specific Airflow Characteristics of Chamber
• Design and Build Mechanical Features
• Design and Build Electronic Control System
• Test, Test, Test,

27
Costs
28
Time breakdown
29
Fan Dayton Duct Fan 4C661 18.5 inch effective
opening 21 inch base Max rpm_at_ 1HP 1988 Single
phase Dayton motor 6K760A 1HP, Capacitor start,
1725 rpm,
30
What types of methods are used for calibrating
wind speed sensors The cup anemometer is the
type to be calibrated by this apparatus Wind
tunnels Problems with wind tunnels?