1 / 25

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.

finian
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related