ME 322: Instrumentation Lecture 36 April 18, 2016 Professor Miles Greiner On/Off control Program, Proportional Control concept

Announcements/Reminders HW 11 due now HW 12 due Friday This 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 3-hour Lab Practicum Final Schedul Doodle Poll to schedule Will publish schedule soon If you want to change your time, please trade with someone else Both parties must send emails to Marissa and me, and get confirmation. Repeat one of the last three labs (10, 11 or 12) Guidelines, http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Tests/Index.htm Solo, start to finish Generate LabVIEW, Excel and PowerPoint during final Only given instructions, book, and 1 page of notes No sample lab, partner, or connection to internet Make sure to prepare yourself during the labs The lectures are very important Lab Practice Periods Saturday and Sunday, April 30, May 1, 2016 Lab-in-a Box (has anyone used them yet?) All equipment for Labs 10 and 12 in basement of DeLaMare Library Troubleshoot labs and practice for Final

Install LabVIEW and DAQmx https://lumen.ni.com/nicif/US/GB_ACADEVALSOFTWARE/content.xhtml DAQmx https://www.ni.com/dataacquisition/nidaqmx.htm This takes time and may be frustrating…

Lab 12 Setup Measure beaker water temperature using a thermocouple/conditioner/myDAQ/VI Use myDAQ analog output (AO) to operate a digital relay that turns heater on/off to control the water temperature

Full on/off Control LabVIEW VI “logic” Starting point VI Measure thermocouple temperature for 1 sec Continuous Samples, 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

On/Off Control Temperature Response Full On/Off control Reaches TSP after ~3 minutes Gives oscillatory response Average temperature TAvg > TSP Maximum error is roughly 2.5°C Want heater power to be high to reach TSP quickly Would oscillations decrease if power decreased near T ~ TSP?

How to reduce heater power using a relay? FTO = 0.1 FTO = 0.5 FTO = 0.9 Reduce the Fraction of Time the heater is On (FTO) Maximum heater power QMax = V2/R Reduce FTO to decrease heater power Heater Q = (FTO)(QMax) How to implement this in LabVIEW?

Remember Strobe Light VI Stacked sequence loop Milliseconds to Wait How to find and calculate FTO?

Proportional Control Reduce heater power (FTO) when T is within a small increment DT of TSP Define 𝑓 𝑇 = 𝑇 𝑆𝑃 −𝑇 𝐷𝑇 (=1 𝑎𝑡 𝑇= 𝑇 𝑆𝑃 −𝐷𝑇; =0 𝑎𝑡 𝑇= 𝑇 𝑆𝑃 ) Three temperature zones: For T< 𝑇 𝑆𝑃 −𝐷𝑇 , f > 1 FTO = 1 For 𝑇 𝑆𝑃 −𝐷𝑇 <𝑇< 𝑇 𝑆𝑃 , 1 > f >0 𝐹𝑇𝑂=𝑓 For 𝑇> 𝑇 𝑆𝑃 , f < 0 FTO = 0 For DT = 0, Proportional is same as full power On/Off What is Q when T= 𝑇 𝑆𝑃 ? Why isn’t that good?

How to construct a Proportional-Control VI Current Temperature Calculate FTO Indicate FTP using a bar, dial and/or numeric indicator Use stacked sequence loop to turn heater on and off Write to a Measurement File VI Segment Headings (No Headers) X value (time) Column (one column only) Starting Point

Proportional Control

End 2016

Proportional-Control Temp versus Time On/Off Proportional Proportional TSP = 65°C and TSP = 85°C As DT is increases (control becomes more proportional) Oscillatory amplitude decreases Temperature eventually becomes steady The “steady-state” average temperature 𝑇 𝐴𝑉𝐺 decreases Error magnitude 𝑒 = 𝑇 𝐴𝑉𝐺 − 𝑇 𝑆𝑃 increases with DT and 𝑇 𝑆𝑃

Average Temperature Error and Unsteadiness versus DT and TSP The average temperature error 𝑒= 𝑇 𝐴𝑉𝐺 − 𝑇 𝑆𝑃 Is positive for DT = 0, but decreases and becomes negative as DT increases. Decreases as TSP increases TRMS (same as standard deviation) is and indication of thermocouple temperature unsteadiness Unsteadiness decreases as DT increases, and as TSP decreases.

Proportional-Control Questions Why is the steady temperature below the set-point (desired) value? Why do temperature oscillations disappear as DT gets larger? Is there another control technique that eliminates the steady state error?

Steady State Temperature Error 𝑄−𝑊= 𝑄 𝐼𝑛 − 𝑄 𝑂𝑢𝑡 = 𝑑𝑈 𝑑𝑡 =𝜌𝑐𝑉 𝑑𝑇 𝑑𝑡 𝑄 𝑀𝑎𝑥 𝑇 𝑆𝑃 −𝑇 𝐷𝑇 −ℎ𝐴 𝑇− 𝑇 𝐸𝑛𝑣 =𝜌𝑐𝑉 𝑑𝑇 𝑑𝑡 Let 𝑇 𝑆𝑆 be the temperature under steady state conditions 𝑑 𝑇 𝑆𝑆 𝑑𝑡 =0 𝑄 𝑀𝑎𝑥 𝑇 𝑆𝑃 − 𝑇 𝑆𝑆 𝐷𝑇 =ℎ𝐴 𝑇 𝑆𝑆 − 𝑇 𝐸𝑛𝑣 𝑄 𝑀𝑎𝑥 𝑇 𝑆𝑃 − 𝑇 𝑆𝑆 =ℎ𝐴 𝐷𝑇 𝑇 𝑆𝑆 − 𝑇 𝐸𝑛𝑣 𝑄 𝑀𝑎𝑥 𝑇 𝑆𝑃 +ℎ𝐴 𝐷𝑇 𝑇 𝐸𝑛𝑣 = 𝑇 𝑆𝑆 ℎ𝐴 𝐷𝑇 + 𝑄 𝑀𝑎𝑥 𝑇 𝑆𝑆 = 𝑄 𝑀𝑎𝑥 𝐷𝑇 𝑇 𝑆𝑃 +ℎ𝐴 𝑇 𝐸𝑁𝑉 𝑄 𝑀𝑎𝑥 𝐷𝑇 +ℎ𝐴 𝑒 𝑆𝑆 = 𝑇 𝑆𝑆 − 𝑇 𝑆𝑃 =− 𝑇 𝑆𝑃 − 𝑇 𝐸𝑁𝑉 1+ 𝑄 𝑀𝑎𝑥 ℎ𝐴 𝐷𝑇 Magnitude increases with 𝑇 𝑆𝑃 − 𝑇 𝐸𝑁𝑉 and ℎ𝐴 𝐷𝑇 𝑄 𝑀𝑎𝑥