How to make it work again?

Question

Hi;
I'm creating a heater system and i've used plant simulator.vi for the lag and dead time. However after inserting the plant simulator block into my VI, my PV no longer gets to my SP. But when i remove that block its seems fine again. Whats the problem?
The attached is the VI i've written
With Regards
Wormwood

Answer 1

Hi Wormwood,
1. The plant simulator is suppossed to mimic the system that needs to be controlled. So technically, you should be plotting the Manipulated Variable (output of the PID and input/control for the plant) versus the Process Variable. The manipulated variable tries to bring the Process Variable to the Set Point.
2. The PID needs to be able to output control action that is both positive and negative. So, the output range of the PID should be set to (-100, 100), for example. In your VI, it was set to (0, 100), which means that the PID could never output any negative control.
3. You are performing some numeric operations on your Process Variable in the lower part of the while loop. Although, these affect the PV, you donot need to plot them in the graph.
I made some changes in your VI, some calculation is gone but its useful to see how the Manipulated Variable can actually bring the Process Variable to the SetPoint.
-Jaidev
National Instruments
LabVIEW Embedded Product Support Engineer
Attachments:
Wormwood.vi ‏37 KB