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

2. 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!

3. 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 s to Marissa and me, and get confirmation.
Repeat one of the last three labs (10, 11 or 12)
Guidelines,
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

4. Install LabVIEW and DAQmx
DAQmx
This takes time and may be frustrating…

5. 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

6. 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

7. Full On/Off Temperature Control

8. Front Panel

9. 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?

10. 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?

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

12. 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?

13. 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

14. Proportional Control

15. End 2016

16. 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

17. 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.

18. 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?

19. 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