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Prepared by: Michael Wood Dept. of Electrical and Computer Engineering Utah State University PowerPoint PPT Presentation


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ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Hot Wire Anemometer. Prepared by: Michael Wood Dept. of Electrical and Computer Engineering Utah State University E:[email protected] ; T: ( 435)755-7682; F: (435)797-3054 (ECE Dept.). 2/02/09.

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Prepared by: Michael Wood Dept. of Electrical and Computer Engineering Utah State University

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Prepared by michael wood dept of electrical and computer engineering utah state university

ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Hot Wire Anemometer

Prepared by:

Michael Wood

Dept. of Electrical and Computer Engineering

Utah State University

E:[email protected] ; T: (435)755-7682;

F: (435)797-3054 (ECE Dept.)

2/02/09


Outline

Outline

  • Reference list

  • To explore further

  • Major applications

  • Limitations

  • Illustration of Hot Wire Probe

  • Pros and Cons

  • Constant Temperature Hot Wire Anemometer

  • Wheatstone Bridge Configuration

  • Using current to find flow rate

  • Calibration

  • Good to Know

  • Probe Cost Examples

  • Major Specifications

  • Where to buy

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Reference list

Reference list

  • http://www.qats.com/qpedia/Dec_Qpedia_ThermalAnalysis_122007.pdf

  • http://www.efunda.com/designstandards/sensors/hot_wires/hot_wires_intro.cfm

  • http://www.efunda.com/designstandards/sensors/hot_wires/hot_wires_theory.cfm

  • http://wb.olin.edu/ies/2006/lectures/Lecture_hotwire.ppt

  • http://www-g.eng.cam.ac.uk/whittle/current-research/hph/hot-wire/hot-wire.html

  • http://www.iaa.ncku.edu.tw/~jjmiau/exp/download/ch3_%20960129.pdf

  • http://www.dantecdynamics.com/

  • http://www.tsi.com/uploadedFiles/Product_Information/Literature/Technical_Notes/Hotwire_Calibration_in_ThermalPro-Tutorial.pdf

  • http://www.iop.org/EJ/article/0957-0233/9/9/020/e80919.pdf?request-id=d25c7ee3-d24b-4e19-8c03-a0b235617a58 Zou Yue

  • http://www.springerlink.com/content/g2x75j7l35763236/fulltext.pdf

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


To explore further survival pointers of web references etc

To explore further (survival pointers of web references etc)

  • Virginia Tech Department of Aerospace and Ocean Engineering, Aerospace Engineering Lab Notes: Hot Wire and Hot Film Anemometry, http://www.aoe.vt.edu/~simpson/aoe4154/hotwirelab.pdf.

  • Perry, A., Hot Wire Anemometry, Clarendon Press, Oxford, 1982.

  • Payne, S., Unsteady Loss in a High Pressure Turbine Stage, Chapter 4: Hot Wire Anemometry, DPhil thesis, University of Oxford, 2001. http://www.robots.ox.ac.uk/~sjp/publns/sjp_thesis_c4_chapter4.pdf

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Major applications

Major applications

  • Measuring velocity of fluids

  • Aerodynamics – lift, drag

  • Combustion – IC, gas turbine engines

  • Meteorology

  • Fires and fire safety

  • Ocean currents

  • Turbulence

  • Ordinary measurement tools, i.e. HVAC probes

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Limitations

Limitations

  • Very low speed (air flow speed lower than 1 m/s)

  • Highly turbulent and possibly reversed flow

  • Non-isothermal flows

  • Multi-phase flows

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Illustration of hot wire probe

Illustration of Hot Wire Probe

Picture from http://www.qats.com/qpedia/Dec_Qpedia_ThermalAnalysis_122007.pdf

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Pros and cons

Pros and Cons

 • Pros:  

- Excellent spatial resolution.  

  • High frequency response, > 10 kHz (up to 400 kHz).   

    • Cons:  

  • Fragile, can be used only in clean gas flows.  

  • Needs to be recalibrated frequently due to dust accumulation (unless the flow is very clean).  

  • High cost.

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Constant temperature hot wire anemometer

Constant Temperature Hot Wire Anemometer

  • Most Common type of Hot Wire Anemometer

  • Accurate over a large range of fluid velocities (very slow to very fast fluid speeds)

  • Placed in a Wheatstone bridge configuration to assure accurate data

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Wheatstone bridge configuration

Wheatstone bridge configuration

  • R1 & R2 are known

  • R3 is variable

  • Probe represented by Rw

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


How wheatstone bridge works

How Wheatstone bridge Works

  • The equation

    balances wheatstone circuit

    Making error voltage=0

  • Rw is a function of temperature

  • As the air speed around the probe changes Rw changes

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


How wheatstone bridge works1

How Wheatstone bridge Works

  • The Wheatstone bridge must

    be calibrated

  • R3 is adjusted until the bridge

    is in equilibrium

  • After calibration a change in

    Velocity changes Rw and creates an error voltage

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Using current to find flow rate

Using current to find flow rate

  • The error voltage inputted into the op-amp causes the op-amp to produce a feedback

  • The feedback current balances the Wheatstone bridge

  • This feedback current is measured

    and used to calculate fluid flow

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Using current to find flow rate1

Using current to find flow rate

Constants used in the derivation

I = current through the hotwire

Rw = resistance of the hot wire

Rg = resistance of the wire at gas temperature

E2 =square of the output of the hot wire anemometer bridge

U = calibration velocity

N = exponent (usually close to 0.5)

As = surface area of exposed wire

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Using current to find flow rate2

Using current to find flow rate

  • HG - heat generated

  • HT - heat transfer

  • HA - heat absorbed (assumed to = zero)

    HG = HT = (I is measured)

    Rw is the resistance at temperature qw and is found with the equation

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Using current to find flow rate3

Using current to find flow rate

C = temperature coefficient of resistivity

Qo = initial wire temperature

Ro = resistance at qo

disregard high order and using boundary conditions Ro = Rg and qo = qg yields

Dq = (Rw-Rg)/RoC

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Using current to find flow rate4

Using current to find flow rate

Dq = (Rw-Rg)/RoC

Rg = wire resistance when wire temp = fluid temp

Dq = difference between wire temp and fluid temp

  • Now we use the emperical heat transfer equation

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Using current to find flow rate5

Using current to find flow rate

More necessary constants

  • h = convective heat transfer coefficient

  • d = characteristic length (wire diameter)

  • k = fluid thermal conductivity

  • m = dynamic viscosity of the gas

  • r = gas density

  • cp = specific heat of gas at a constant temp

  • U = velocity of the flow

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Using current to find flow rate6

Using current to find flow rate

Assuming convection only

HT=hAsDq =

Where X and Y come from

R = Rw/Rg

(Kings Law)

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Sensor calibration

Sensor Calibration

  • To calibrate the sensor I2 is plotted vs

  • A best fit algorithm is used to find A and B of the equation

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Measurement errors to be accounted for during system calibration

Measurement Errors to be accounted for during system calibration

  • 1. Calibration measurement errors: Errors in measuring the calibration flow parameters and hot wire voltages.

  • 2. Calibration equation errors: Errors due to the fitting of a calibration equation, as well as the solution of the calibration equation and lookup table.

  • 3. Calibration drift errors: Errors caused by variations in calibration over time and due to switching the feedback circuitry on and off, as well as by probe contamination.

  • 4. Approximation errors: Errors caused by assumptions about the flow field that are used to solve the calibration equations.

  • 5. High frequency errors: Errors caused by the change in hot wire behavior at high frequency.

  • 6. Spatial resolution errors: Errors caused by spatial averaging of the flow field.

  • 7. Disturbance errors: Errors caused by the probe interfering with the flow field.

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Good to know

Good to Know

  • Anemometer wires are usually made of platinum or tungsten and is 4 ~ 10 µm in diameter and 1 mm in length.

  • Typical commercially available hot-wire anemometers have a flat frequency response (< 3 dB) up to 17 kHz at the average velocity of 9.1 m/s , 30 kHz at 30.5 m/s , or 50 kHz at 91 m/s .

  • The small fragile wire is suitable only for clean gas flow.

  • In liquid flow or rugged gas flow,

    a platinum hot-film coated on a

    25 ~ 150 mm diameter quartz fiber

    or hollow glass tube can be used instead.

    quartz fiber or glass tube

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Probe cost examples

Probe Cost Examples

Single Sensor ProbesDouble Sensor Probes

Triple Sensor Probe

Note:

Eur = 1.29 US Dollars

(according to Google Currency Conversion)

examples from http://shop.dantecdynamics.com

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Major specifications

Major Specifications

Technical data for miniature wire sensors

Medium Air

Sensor material Platinum-plated tungsten

Sensor dimensions 5 µm dia, 1.25 mm long

Sensor resistance R20 (approx) 3.5 W

Temperature coefficient of resistance

(TCR) a 20 (approx.) 0.36%/°C

Max. sensor temperature 300°C

Max. ambient temperature 150°C

Max. ambient pressure Depends on the type of mounting

Min. velocity 0.05 m/s *

Max. velocity 500 m/s

Frequency limit fcpo (CCA mode, 0 m/s) 90 Hz

Frequency limit fmax (CTA mode) 400 kHz

This example of Specification is for a miniature wire sensor from http://www.dantecdynamics.com/Default.aspx?ID=754

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Where to buy

Where to buy

  • www.dantecdynamics.com

  • www.extech.com

  • http://www.twenga.com

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


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