PID

[Drew15]

Hi People

I have put together a simple PID loop  and a transfer function which has a delay, but when I add or remove the delay I do not see any change in the response which i should. Could somene look at it and see what maybe wrong if anything ?

Thanks in Advance

[Barp]

The Transfer Function used by the Control and Simulation Loop ignores the 'delay' information that you provided in the Control Design transfer function.

To 'simulate' the delay inside the Control and Simulation Loop, use the Delay function.

For more information, please verify the following shipping example:

C:\Program Files (x86)\National Instruments\LabVIEW 2015\examples\Control and Simulation\Case Studies\Process Control\Smith Predictor\Smith Predictor.vi

Hope this helps.

[Drew15]

Hi Barp

thanks for the reply. i can not get it to work with my values it just does not work at all. I have made two loops now, one a pid and one a predictor but it does not seem to function however I managed to get the delay working.

[Barp]

Drew15

Please note that it makes harder for us to help you if you don't provide more details of what is 'not working'.

I look over your original code and I noticed that delay is NaN. Did you change the value to some other better than NaN. This would make the Control and Simulation Loop to freeze.

Also, the Root Locus and the Pole-Zero function will ignore the delay in the graphs, so not changes would happen if you try to just change the delay. To really try to study delay, you need to 

In attachment is the change to take into account the delay, modified in LV 2014:

a) I added the Pade Approximation to make the pole-zero map and the Root Locus to show the effect of the delay

b) Added the delay function in the simulation with delay to make the simulation more realistic

c) Used the ZPK format to your equation to show the location of the 3 poles.

d) Modified a bit the configuration of the Root Locus to properly show all traces without the need to feed all gains

e) Modified a bit the configuration of simulation to allow the simulation to run faster and more accurate.

When you run this example, change the Pade Approximation Polynomial Order and the delay to see how this would affect your Root Locus graph and simulation.