1. 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

2. Senior Exit Survey

3. 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,
Will publish schedule soon
If you want to change your time, please trade with someone else, both send s to Marissa and me, and get confirmation.
Lab Practice Period
Saturday and Sunday, April 30, May 1, 2016

4. 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

5. 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.

6. 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

7. 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

8. 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?

9. 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)
(page 38)
Solid State Relay = voltage-controlled switch
Switch is on (closes) when V > 3 volt; Off when V < 1 volt

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

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

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

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

14. 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

15. 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

16. Full On/Off Temperature Control

17. Front Panel

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