ME 322: Instrumentation Lecture 35 April 15, 2016 Professor Miles Greiner On/off feedback control, Lab 12 setup, Analog Output, Strobe light vi, On/off water temperature control vi

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Announcements/Reminders HW 11 is due now (will accept on Monday) Joseph will give tutorial Sunday at 4 pm in SEM 321 HW 12 due next Friday Next week: Lab 11 Unsteady Karmon Vortex Speed Sign up for 45 minute periods with your partner You cannot perform the experiment until you attend lab demonstration Please be on time and come prepared! Lab Practicum Final Guidelines, http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Tests/Index.htm Will publish schedule soon If you want to change your time, please trade with someone else, both send emails to Marissa and me, and get confirmation. Lab Practice Period Saturday and Sunday, April 30, May 1, 2016

Fry Pan Controller Increase TSP Decrease 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

On/Off Control The sensor and heater are not at the same location TSP T T Heater off Error e=T-TSP Heater on 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 to it. Eventually the sensor temperature decreases, and goes below TSP and the controller turns on the heater There is a delay before the sensor receives heat and detects a temperature rise Even though the sensor is very accurate and turns the heat on/off at TSP the delayed response of sensor to the 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.

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) Note: The controller regulates the sensor temperature, which is not necessarily the temperature of object being controlled

Controller Examples Thermostat Hot-film anemometer 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 the variable to be controlled, compare to desired value, and take corrective action

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 In Labs 7 and 9: the heater was on 100% of the time so the water boiled Lab 12: 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 = TEnvironment is there a need for control? What if TSP is > 100°C?

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 38) 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

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

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

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

Strobe Light VI Stacked sequence loop Milliseconds to Wait Vary cycle time and FTO

End 2016 Could do full on/off control, but would not have time to see it operate. May be better to keep it in next lecture and due strobe VI this lecture

Full on/off Control LabVIEW VI “logic” Starting point VI 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

Full On/Off Temperature Control

Front Panel

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