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

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators 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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators 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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators 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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Limitations Very low speed (air flow speed lower than 1 m/s) Highly turbulent and possibly reversed flow Non-isothermal flows Multi-phase flows 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Illustration of Hot Wire Probe Picture from http://www.qats.com/qpedia/Dec_Qpedia_ThermalAnalysis_122007.pdf 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators 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. 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Wheatstone bridge configuration R1 & R2 are known R3 is variable Probe represented by Rw 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Using current to find flow rate Assuming convection only HT=hAsDq = Where X and Y come from R = Rw/Rg (Kings Law) 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Sensor Calibration To calibrate the sensor I2 is plotted vs A best fit algorithm is used to find A and B of the equation 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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. 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators 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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Probe Cost Examples Single Sensor Probes Double Sensor Probes Triple Sensor Probe Note: Eur = 1.29 US Dollars (according to Google Currency Conversion) examples from http://shop.dantecdynamics.com 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators 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 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Where to buy www.dantecdynamics.com www.extech.com http://www.twenga.com 4/17/2017 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators