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

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:mikewood_55@hotmail.com ; 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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  1. 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:mikewood_55@hotmail.com ; T: (435)755-7682; F: (435)797-3054 (ECE Dept.) 2/02/09

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. Wheatstone bridge configuration • R1 & R2 are known • R3 is variable • Probe represented by Rw ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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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