ME 322: Instrumentation Lecture 37 April 22, 2015 Professor Miles Greiner Proportional control characteristics, Shift register and integral control program

Announcements/Reminders HW 12 Due Friday X2 (write a Proportional Control VI) HW 13 Due Monday L12PP (on/off, proportional and integral control) HW 14 Due Wednesday X3 Review for final (Next Wed. & Fri.) Open Lab Practice (Next Saturday and Sunday) Lab Practicum Finals (Schedule on WebCampus) – Guidelines This week: Lab 11 Unsteady Karmon Vortex Speed One-hour periods with your partner How is it going?

Lab 12 Setup Measure the beaker water temperature using a thermocouple/conditioner/myDAQ/VI Use myDAQ analog output (AO) to turn heater on/off to control the water temperature – Use Fraction of Time On (FTO) to control heater power

Proportional Control Current Temperature

Proportional Control VI construction (start at midpoint)midpoint

Set-Point, Lower-Control, and Measured Temperatures vs Time

Unsteadiness and Error versus DT Unsteadiness T RMS decreases as DT increases – And as T SP decreases – Want this to be zero The average steady-state error e = T SS -T SP – Is positive for DT = 0, but decreases as DT increases – Magnitude increases as DT increases – Want this to be zero

Proportional Control is Flawed Proportional control is able to eliminate unsteadiness. But, we found that if DT is large enough to make the temperature steady, then the steady-state temperature is below the desired set-point value What should Q (and FTO) be?

Energy Balance T Q IN = FTO(Q MAX ) Q OUT = hA(T-T ENV ) T ENV

Integrate Error If T-T SP > 0, then Decrease FTO If T-T SP < 0, then Increase FTO

How to implement this in LabVIEW

Figure 2 VI Block Diagram

Figure 1 VI Front Panel Plots help the user monitor the measure and set- point temperatures T and T SP, temperature error T– T SP, and control parameters

Figure 3 Measured, Set-Point, Lower-Control Temperatures and DTi versus Time Data was acquired for 40 minutes with a set-point temperature of 85°C. The time-dependent water temperature is shown with different values of the control parameters DT and DTi. Proportional control is off when DT = 0 Integral control is effectively off when DTi = 10 7 (10log(DTI) = 70)