topic Re: Cascading TF ?? in LabVIEW

Cascading TF ??

JohnnyKayak — Sun, 12 Sep 2010 23:37:42 GMT

Hello,

I used to work with Matlab and I'm in the process of evaluating Labview (specially the Process Control Suite).

This question might appears obvious for some of you since I consider myself as a beginner with Labview.

As a test, with the Toolbox CD&S, I've setup a simple control loop (inspired by some examples available in the distribution) for a 1st order process (Gp = 1/(s+1)) implementing the same simple PI controller different ways just to see if things work the same way as in Matlab.

I already figured that when I'm using PID object from PID toolbox (graph 1), I have to specify dt = step size. However, I don't understand why Graph4 example where I cascade Gc & Gp, I obtain a flat (=0) response ???

I'm using Labview 2010 (evaluation version from NI.com website) and the following toolkits: 2010CDSIM, LV2010SYSIDTK, 2010SIT, 2010PIDFuzzy, 2010MSRT-Win

Anyway to cascade TF as in graph4 example ?

Re: Cascading TF ??

Lucither — Mon, 13 Sep 2010 02:45:28 GMT

Would be a good idea to re-save and post your vi in an earlier version, possibly version 8. Not everyone has the latest version, including myself, so cannot open what you have done,

Regards,

Lucither

Re: Cascading TF ??

JohnnyKayak — Mon, 13 Sep 2010 20:00:28 GMT

As suggested, I just tried to save to LV v8.5. However, when I tried to load the VI (v8.5), the graph4 example works just fine.

So it seems it's related to the fact I'm using version 2010...

I'm surprised since linking TF in serial for a SISO system should be simple.

Anybody from NI can explain why I have this issue with version 2010 ?

Re: Cascading TF ??

Barp — Mon, 13 Sep 2010 22:04:05 GMT

Hello,

Unfortunately you are runnning into a known issue with the LabVIEW Control Design and Simulation Module in the 2010 version. Please install the patch:

http://digital.ni.com/public.nsf/allkb/F1435BA36246B84186257773007DD70F

and you should be able to see something different than a "flat zero".

Let me know if that helps!

Re: Cascading TF ??

JohnnyKayak — Mon, 13 Sep 2010 22:21:30 GMT

Yes, everything seem OK now ! The patch you recommend solve this issue.

Thanks a lot for your help !

Jean