1 / 17

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

bayard
Download Presentation

ME 322: Instrumentation Lecture 35

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related