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ME 322: Instrumentation Lecture 26

ME 322: Instrumentation Lecture 26. March 28, 2014 Professor Miles Greiner. Announcements/Reminders. Next Week: Lab 9 Transient Temperature Response HW 9 is due Monday Ch 6(86a ), Ch 11(6, 10, 11, 14), L9PP add Ch.9(37) Midterm II, Wednesday, April 2, 2014 Review Monday

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ME 322: Instrumentation Lecture 26

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  1. ME 322: InstrumentationLecture 26 March 28, 2014 Professor Miles Greiner

  2. Announcements/Reminders • Next Week: Lab 9 Transient Temperature Response • HW 9 is due Monday • Ch6(86a), Ch 11(6, 10, 11, 14), L9PPadd Ch.9(37) • Midterm II, Wednesday, April 2, 2014 • Review Monday • Josh McGuire review sessions: • Monday 5-6PM PE 215, Tuesday 7-8 PM, DMS? • He will e-mail specifics • Two Extra-Credit Opportunities • Both 1%-of-grade extra-credit for active participation • LabVIEWComputer-Based Measurements Hands-On Seminar • Friday, April 18, 2014, 2-4 PM, Place TBA • Signup on WebCampus “soon” (first 30 students) • Open ended Lab 9.1 (described in this lecture)

  3. High Temperature (combustion) Gas Measurements QConv=Ah(Tgas– TS) Sensor h, TS, A, e Tgas • Radiation heat transfer is important and can cause errors • Convection heat transfer to the sensor equals radiation heat transfer from the sensor • Q = Ah(Tgas – TS) = Ase(TS4-TW4) • s = Stefan-Boltzmann constant = 5.67x10-8W/m2K4 • e = Sensor emissivity (surface property ≤ 1) • T[K] = T[C] + 273.15 • Measurement Error = Tgas– TS= (se/h)(TS4-TW4) TS TW QRad=Ase(TS4 -TW4)

  4. Problem 9.39 (p. 335) • Calculate the actual temperature of exhaust gas from a diesel engine in a pipe, if the measuring thermocouple reads 500°C and the exhaust pipe is 350°C. The emissivity of the thermocouple is 0.7 and the convection heat-transfer coefficient of the flow over the thermocouple is 200W/m2-C. • ID: Steady or Unsteady? • What if there is uncertainty in emissivity?

  5. Conduction through Support (Fin Configuration) TS T∞ • Sensor temperature TS will be betweenthose of the fluid T∞and duct surface T0 • Support: cross sectional area A, parameter length P, conductivity k • Convection heat transfer coefficient between gas and support h • Fin Temperature Profile (from conduction heat transfer analysis): • (dimensionless length) • Dimensionless Tip Temperature Error from conduction • , (want this to be small) • Decreases as • L, h and P increase • k and A decrease h x L A, P, k T0

  6. Example • A 1-cm-long, 1-mm-diameter stainless steel support (k = 20 W/mK) is mounted inside a pipe whose temperature is 200°C. The heat transfer coefficient between gas in the pipe and the support is 100 W/m2K, and a sensor at the end of the support reads 350°C. What is the gas temperature? Assume esensor = 0 • Steady or unsteady • Radiation or Conduction errors

  7. Solution • Sensor temperature: • What is given and what must be found? • What if esensor = 0.2?

  8. Extra Credit Lab 9.1 • 1% of grade, April 10-12, 2014 • Not Required • Use a low-cost chip to make a measurement • Open Ended • Turn in a one paragraph proposal summarizing your test plan, and the supplies you need by Friday, April 4, 2014 • Some Possibilities • Get a sample from www.ti.com • Buy one from RadioShack • Available in lab (See Lab 9.1 website) • Photo Diode, Hall Effect (magnetic field) Chip, Accelerometer Chip, LM35 temperature sensor chip • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2009.1%20Extra%20Credit/Lab9.1%20Index.htm

  9. + 5 DAQ AI0 200 Ω GND Needs 200Ω Resistor across output. Use referenced signal EWD (RSE) because VS & Vout use the same ground.

  10. LM35 Data Sheet • Calibrated directly in ˚ Celsius (Centigrade) • Linear + 10.0 mV/˚C scale factor • 0.5˚C accuracy guaranteeable (at +25˚C) • Rated for full −55˚ to +150˚C range • Suitable for remote applications • Low cost due to wafer-level trimming • Operates from 4 to 30 volts • Less than 60 µA current drain • Low self-heating, 0.08˚C in still air • Nonlinearity only ±1⁄4˚C typical • Low impedance output, 0.1 Ω for 1 mA load

  11. Possibilities • Measure boiling water temperature or heat transfer coefficient using LM35 • Photo diode output voltage versus distance from a light source (florescent or incandescent) • Hall effect chip output voltage versus distance from a magnet • Vibration of a weighted, cantilevered steel or aluminum beam • There are three “Lab-in-a-Box” setups available for check out from the DeLaMare (Engineering) Library, which can be used at home if you like. • Measure outdoor light and temperature levels during a 24 hour period • Car acceleration on a bumpy road • Kitchen oven temperature stability

  12. LM 35 Power 4 – 10 watts VS & GND Output Sensitivity

  13. 1.5V -55 C 150 C -0.55V

  14. For RSE Absolute Voltage Accuracy: AVA = 14.7mV = 0.00147 V Absolute Tem Accuracy:

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