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ME 322: Instrumentation Lecture 35

ME 322: Instrumentation Lecture 35. April 18, 2014 Professor Miles Greiner. Announcements/Reminders. HW 11 is due now, HW 12 Due Friday, 4/25/2014 Don’t start L12PP until next week (revising) Next week: Lab 11 Unsteady Karmon Vortex Speed 1.5-hour periods with your partner

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ME 322: Instrumentation Lecture 35

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  1. ME 322: InstrumentationLecture 35 April 18, 2014 Professor Miles Greiner

  2. Announcements/Reminders • HW 11 is due now, • HW 12 Due Friday, 4/25/2014 • Don’t start L12PP until next week (revising) • Next week: Lab 11 Unsteady Karmon Vortex Speed • 1.5-hour periods with your partner • Schedule (please be on time and come prepared) • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2011%20Karmon%20Vortex/Lab%20Index.htm • Extra-Credit LabVIEW Workshop • Today, 2-4 PM, Jot Travis Room 125D • Make sure you sign-in to get credit • Lab Practicum Final • Guidelines, Schedule • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Tests/Index.htm • Practice Periods • May 2-4, 2014

  3. Fry Pan Controller Increase TSP • Bi-metallic strip deforms as its temperature changes • Opens switch (turns heater off) when it gets to hot, and closes it (turn heater on) when too cool • Dial physically moves strip and sets desired or “set-point” temperature TSP (at which heater turns off) • Feedback Control • Measures temperature and adjusts corrective action • Full on/off control • “Bang/Bang” control • Would not work for a cruise control Decrease TSP

  4. On/Off Control TSP T T • The sensor and heater are not at the same location • By the time the sensor reaches the set-point temperature TSP and turns off the heater, the heater is above TSP • The sensor temperature continues to rise as energy from the heater diffuses it. • Eventually the sensor temperature decreases below TSP and the controller turns on the heater • There is a delay before the sensor detects a temperature rise • Even though the sensor is very accurate and turns the heat on/off at TSPthe delayed responseof sensor to heater causes on/off control to exhibit oscillations. • Oscillations might be smaller if we did not use full on/off control • We would like the error e = T-TSP to be zero. Heater off Error e=T-TSP Heater on

  5. Desired Characteristics • Reach desired temperature quickly • Minimize error e = T – TSP • Robust to changes in the environment • Such as wind and external temperature • Be able to follow time-dependent set point TSP(t)

  6. Controller Examples • Thermostat • Oven • Motor speed controller • Garage door opener, fan • Car cruise control (not full on/off) • Unmanned Autonomous Systems (UAS) • Direction, speed, altitude, level • Missile or rocket guidance • Correct for wind conditions • Self-driving cars • Sense distance between cars and maintain it • In each case, sense variable to be controled, compare to desired value, and take corrective action

  7. Lab 12 Temperature Feedback Control • Measure temperature in a beaker of water, T • Thermocouple, signal conditioner, myDAQ, VI • You’ve done this already • Is the water temperature uniform? What is T? • Control power to heater to bring water to TSP • Before: the heater was on 100% of the time so the water boiled • Now: Actively turn the heater on/off according to different control logic structures • i.e. On/Off, Proportional, Integral… • Use myDAQ analog output to control a digital relay that turns heater on/off • If TSP = TEnvironmentis there a need for control? • What if TSP is > 100°C?

  8. Lab 12 Setup • myDAQ has two analog output(AO) channels • V = ±2 and ±10 volt ranges, N = 16 (216 = 65,536), • Low current (2 mA, can’t power heater) • http://www.ni.com/pdf/manuals/373060e.pdf (page 36) • Solid State Relay = voltage-controlled switch • Switch is on (closes) when V > 3 volt; Off when V < 1 volt • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2012%20Thermal%20Control/Lab%20Index.htm

  9. Schematic Heater Solid State Relay Tyco SSRT-240-0-10 Power Switch TC TC Signal Conditioner myDAQ Analog Input ±10 and ±2 Volt,16 bit Analog Output ±10 and ±2 Volt,16 bit Input + Ground

  10. Turn light on/off • NI Measurement and Automation explorer • Analog Output • Update • LabVIEW VI • Create Channel (Digital Output) • Write Data • While Loop

  11. VI to turn light on/off • Block Diagram and Front panel

  12. Full on/off Control • LabVIEWVI “logic” • Measure thermocouple temperature for 1 sec • Average, T, display • Compare to TSP(compare and select icons) • Turn 200 W heater on/off if T is below/above TSP • Waveform Chart • T and TSP versus time • e = T-TSP versus time • Repeat • Starting Point VI • Temperature versus time from earlier labs • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2012%20Thermal%20Control/Lab%20Index.htm

  13. Full On/Off Temperature Control

  14. Front Panel

  15. Next time • Review program construction/logic • Consider proportional control • Heater Power is proportional to error e = T-TSP

  16. Fractional Time On (FTO) If DT = 0 then full on/off If DT > 0 then proportional 3 Temp Domains • 3) T < TSP – DT FTO = 1 • 2) (TSP – DT) < T < TSP T = TSP f = 0 T = TSP – DT f = 1 • 3) T > TSP FTO = 0

  17. Strobe Light VI

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