ME 322: InstrumentationLecture 41

May 1, 2015Professor Miles Greiner

Review Labs 11 and 12

Announcements/Reminders• Cancel HW 14• Supervised Open-Lab Periods

• Saturday, Sunday 1-6 PM

• Drop Extra-Credit Lab 12.1 and LabVIEW Workshop• Add 6 points to everyone’s Midterm II scores

• Lab Practicum Finals • Starting Monday, schedule on WebCampus• Guidelines• http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Tests/Index.htm

• Monday• Answer questions• Reviewing course objectives and asking for feedback • Allow time to complete course evaluation at www.unr.edu/evaluate

Possible Elective Course• MSE 467: Radiation  Detection and Measurement

– Professor N. Tsoulfanidis nucpower@sbcglobal.net • TuTh 5:30-6:45 PM, LME 316 • Pre/Co-requisites:

– Interest in Nuclear Energy; – MATH 181

• Textbook: – Measurement & Detection of Radiation, N. Tsoulfanidis

and S. Landsberger, 3rd Ed, CRC Press (2010); ISBN-10: 1420091859

Other Opportunities• Summer position at the Nevada National Security

Site (NNSS) – http://www2.nstec.com– http://www2.nstec.com/job%20opportunities/110042.pdf– I’ll try to have more information Monday

• Please let me know if you’re interested in being an ME 322 Lab assistant next year

Lab 11 Unsteady Speed in a Karman

Vortex Street

• Nomenclature– U = air speed, VCTA = Constant temperature anemometer voltage

• Two steps– Statically-calibrate hot film CTA using a Pitot probe – Find frequency, fP with largest URMS downstream from a cylinder of diameter D

for a range of air speeds U• Compare to expectations (StD = DfP /U = 0.2-0.21)

Setup

• Measure PATM, TATM, and cylinder D • Find air m from text

– A.J. Wheeler and A. R. Ganji, Introduction to Engineering Experimentation, 2nd Edition, Pearson Prentice Hall, 2004, p. 430

• Tunnel Air Density

DTube

PP

Static

Total+ -

IP

Variable SpeedBlower Plexiglas

Tube

Pitot-Static Probe

3 in WC

BarometerPATM TATM

CTA

myDAQ

Cylinder

VCTAHot Film Probe

Hints

• When calibrating read IP visually while clicking Run on VI to get simultaneous measurement of VCTA

• Use 1/8 inch cylinder (closer to hot film)• Don’t use auto-scale for URMS.

– The 60 Hz signal is so large is swamps the Karman Vortex oscillatory amplitude

– Use ~0.1 full scale

Calibration Calculations• Based on analysis we expect

– Need to adjust transmitter current to be 4 mA when blower is off, or use actual current with no wind (don’t adjust span)• For: , find:

– a and b

IP

[mA]VCTA

[V]U

[m/s]U1/2

[m1/2/s1/2]VCTA

2

[V2]4.00 2.140 0.0 0.00 4.585.70 3.670 12.4 3.52 13.477.40 3.930 17.5 4.18 15.449.40 4.070 22.0 4.70 16.56

11.60 4.130 26.2 5.11 17.0616.80 4.460 33.9 5.83 19.8914.40 4.340 30.6 5.53 18.8413.30 4.290 28.9 5.38 18.4011.00 4.160 25.1 5.01 17.318.50 4.000 20.1 4.49 16.006.30 3.820 14.4 3.79 14.594.00 2.140 0.0 0.00 4.58

𝑆𝑉𝐶𝑇𝐴2 , √𝑈

𝑆√𝑈 ,𝑉 𝐶𝑇𝐴2

Hot Film System Calibration

• The fit equation appears to be appropriate for these data.

How to Construct VI (Block Diagram)

Spectral Measurements Selected Measurements: Magnitude (RMS) View Phase: Wrapped and in Radians Windowing: Hanning Averaging: None

Formula Formula: ((v**2-b)/a)**2

• Use for both static-calibration and unsteady measurements• Don’t need to store speed vs time

May not be thathelpful in this lab.

Use “eyeball” technique

Front Panel

May not be thathelpful in this lab.Use “eyeball” technique

Unsteady Speed Downstream of a Cylinder

• When the cylinder is removed the speed is relatively constant• When the cylinder is installed, downstream of it

– The average speed is lower compared to no cylinder– There are oscillations with a broadband of frequencies– You don’t need to plot this in the report

0

0.1

0.2

0.3

0.4

0 500 1000 1500 2000 2500 3000

f [Hz]

S rm

s [m

/s]

Fig. 4 Spectral Content in Wake for Highest and Lowest Wind Speed

(a) Lowest Speed

0

0.1

0.2

0.3

0.4

0.5

0 500 1000 1500 2000 2500 3000f [Hz]

S rm

s [m

/s] (b) Highest Speed

fp = 2600 Hz

fp = 751 HzURMS [m/s]

URMS [m/s]

• Hint: Don’t use auto-scale for URMS • The sampling frequency and period are fS = 48,000 Hz and TT = 1 sec.• The minimum and maximum detectable finite frequencies are 1 and 24,000 Hz (don’t show

the highest frequencies).• It is not “straightforward” to distinguish fP from this data. Its uncertainty is wfp ~ 50 Hz.

Dimensionless Frequency and Uncertainty

• UA from LabVIEW VI

• fP from LabVIEW VI plot– ½(1/tT) or eyeball uncertainty

• Re = UADr/m (power product)

• StD = DfP/UA (power product)

UA [m/s] WUa [m/s] fP [Hz] wfp [Hz] Re WRe St WSt

37.8 1.3 2600 50 7084 236 0.218 0.00834.1 1.2 2427 50 6385 224 0.226 0.00927.3 1.1 1892 50 5121 201 0.220 0.01023.0 1.0 1596 50 4312 184 0.220 0.01216.5 0.8 1218 50 3081 156 0.235 0.01511.8 0.7 751 50 2214 132 0.202 0.018

Fig. 5 Strouhal versus Reynolds

• The reference value is from A.J. Wheeler and A.R. Ganji, Introduction to Engineering Experimentation, 2nd Edition, Pearson Prentice Hall, 2004, p. 337.

• Four of the six Strouhal numbers are within the expected range.

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0 1000 2000 3000 4000 5000 6000 7000 8000Re

St

Expected St Range

Process Sample Data

• http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2011%20Karmon%20Vortex/Lab%20Index.htm

Lab 12 Setup

• Measure beaker water temperature using a thermocouple/conditioner/myDAQ/VI

• Use myDAQ analog output (AO) connected to a digital relay to turn heater on/off, and control the water temperature– Use Fraction-of-Time-On (FTO) to control heater power

VI Block Diagram

Write To Measurement File File Format: Microsoft Excel (.xlsx) File Path:C:\Users\Miles Greiner\Documents\LabVIEW Data\test.xlsx Mode: Save to one file Ask user to choose file: False If a file already exists: Use next available filename X value(time) columns: One column only Description:

• Modify proportional VI– http://

wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2012%20Thermal%20Control/Lab%20Index.htm

Hint

• Use Control-U to make wiring easier

Figure 1 VI Front Panel

• Plots help the user monitor the measure and set-point temperatures T and TSP, temperature error T–TSP, and control parameters

VI Components• Input tCycle, fSampling, TSP, DT, and DTi • Measure and display temperature T

– Plot T, T-TSP (error), TSP, TSP-DT, and log(DTi) • Increase chart history length, auto-scale-x-axis• Write to Excel file (next available file name, one time column, no headers)

• Calculate – and – (shift register), – Limit FTO = FTOp + FTOi to >0 and <1

• Display using slide indicators• Write data to analog output within a stacked-sequence loop

(millisecond wait)

Figure 3 Measured, Set-Point, Lower-Control Temperatures and DTi versus Time

• Data was acquired for 40 minutes with a set-point temperature of 85°C.• The time-dependent thermocouple temperature is shown with different

values of the control parameters DT and DTi. • Proportional control is off when DT = 0 • Integral control is effectively off when DTi = 107 [10log(DTI) = 70]

Figure 4 Temperature Error, DT and DTi versus Time

• The temperature oscillates for DT = 0, 5, and 15°C, but was nearly steady for DT = 20°C.

• DTi was set to 100 from roughly t = 25 to 30 minutes, but the system was overly responsive, so it was increased to 1000.

• The controlled-system behavior depends on the relative locations of the heater, thermocouple, and side of the beaker, and the amount of water in the beaker. These parameters were not controlled during the experiment.

Table 1 Controller Performance Parameters

• This table summarize the time periods when the system exhibits steady state behaviors for each DT and DTi.

• During each steady state period– TA is the average temperature– TA – TSP is an indication of the average controller error. – The Root-Mean-Squared temperature TRMS is an indication of controller

unsteadiness

DT [°C] Dti

Time Range [min] TA [°C]

TRMS

[°C]TA-TSP

[°C]0 1.E+07 4.43 to 7.50 88.22 3.42 3.22

5 1.E+07 9.45 to 14.48 85.85 2.79 0.85

15 1.E+07 17.62 to 22.34 83.01 0.62 -1.99

20 1.E+07 23.61 to 25.41 82.48 0.10 -2.52

20 1000 35.51 to 39.44 85.06 0.23 0.06

Figure 5 Controller Unsteadiness versus Proportionality Increment and Set-Point Temperature

• TRMS is and indication of thermocouple temperature unsteadiness

• Unsteadiness decreases as DT increases, and is not strongly affected by DTi.

Figure 6 Average Temperature Error versus Set-Point Temperature and Proportionality Increment

• The average temperature error– Is positive for DT = 0, but decreases and becomes

negative as DT increases. – Is significantly improved by Integral control.

Process Sample Data• http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/L

ab%2012%20Thermal%20Control/Lab%20Index.htm

• Add time scale in minutes– Calculate difference, general format, times 24*60

• Figure 3– Plot T, TSP, DT and 10log(DTi) versus time

• Figure 4– Plot T-TSP, -DT, 10log(DTi) and 0 versus time

• Table 1– Determine time periods when behavior reaches “steady state,” and

find and during those times• Figure 5

– Plot versus DT and DTi• Figure 6

– Plot versus DT and DTi