ME 322: Instrumentation Lecture 26 March 27, 2015 Professor Miles Greiner Radiation temperature errors, Lab 9.1 Sensors and instructions

Announcements/Reminders Next Week: Lab 9 Transient Temperature Response HW 9 is due Monday – Ch 6(86a), Ch 11(6, 10, 11, 14), Ch.9 (37), L9PP add Ch.9(43, 42 (but assume thermocouple conductivity is modeled as iron k = 68 W/mK) Midterm II, Wednesday, April 2, 2014 – Review Monday – Marissa Tsugawa review sessions: WebCampus? Two Extra-Credit Opportunities – Both 1%-of-grade extra-credit for active participation – Open ended Lab 9.1 (described in this lecture) – “Possible” LabVIEW Computer-Based Measurements On- line Seminar Time and Place TBA

Radiation Error: High Temperature (combustion) Gas Measurements Radiation heat transfer is important and can cause errors Convection heat transfer to the sensor equals radiation heat transfer from the sensor – Q = Ah(T gas – T S ) = A  (T S 4 -T W 4 )  = Stefan-Boltzmann constant = 5.67x10 -8 W/m 2 K 4  Sensor emissivity (surface property ≤ 1) T[K] = T[C] Measurement Error –  T Cond = T gas – T S = (  /h)(T S 4 -T W 4 ) Q Conv =Ah(T gas – T S ) TSTS Q Rad =A  (T S 4 -T W 4 ) T gas TWTW Sensor h, T S, A, 

Conduction through Support (Fin Configuration) T∞T∞ h x L A, P, k T0T0 TSTS

Example A 1-cm-long, 1-mm-diameter thermocouple (whose conductivity is k = 20 W/mK, stainless steel) is mounted inside a pipe whose temperature is 350 ° C. The heat transfer coefficient between gas in the pipe and the support is 100 W/m 2 K, and a sensor at the end of the support reads 500 ° C. What is the gas temperature? Assume  sensor = 0 Steady or unsteady Radiation or Conduction error

Solution

Extra Credit Lab 9.1 1% of grade, April 6-10, 2015 – 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 3, 2015 Some Possibilities – Get a sample from – Available in lab (See Lab 9.1 website) Photo Diode, Hall Effect (magnetic field) Chip, Accelerometer Chip, LM35 temperature sensor chip Lab%2009.1%20Extra%20Credit/Lab9.1%20Index.htm Lab%2009.1%20Extra%20Credit/Lab9.1%20Index.htm

+ 5 AI0 DAQ GND Needs 200Ω Resistor across output. Use referenced signal EWD (RSE) because V S & V out use the same ground. 200 Ω LM35 precision temperature chip

LM35 Data Sheet Calibrated directly in ˚ Celsius (Centigrade) Linear 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

-0.55V 1.5V -55 C 150 C

Possibilities Measure boiling water temperature using an 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 – Dominant car frequency on a bumpy road – Kitchen oven temperature stability using a thermocouple

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/m 2 -C. ID: Steady or Unsteady? What if there is uncertainty in emissivity?

Power 4 – 10 watts V S & GND Output Sensitivity LM 35

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