Where can i find the blocks of feedforward system?

[craigc]

Hi Wormwood,

Try looking under the following pallette, Addons -> Control - >Advanced -> Non-linear, for backlash vi and some more specific control vi's etc.  For some reason the advanced control vi's dont show up under my "Control" shortcut menu either tab either.

Craig

[McCarty]

Hello Wormwood,

In the Simulation - Cascade and Feedforward Surge Tank Level.vi example (Help>>Find Examples>>Browse according to Directory Structure>>control>>pid>>prctrlex.llb), the deadtime is accounted for in the Simulation Loop inside the Plant Simulator.vi.  You can double-click on this VI to see that the deadtime is specifically handled through a VI called Shift Register Delay.vi.  You could copy this VI and use it in your application.

There is no VI that just handles a first-order lag.  The  PID Lead-Lag.vi is your best bet, as demonstrated in the Simulation - Cascade and Feedforward Surge Tank Level.vi example.  For more information on PID control in LabVIEW, you may want to look at the following resources:

LabVIEW PID Control Toolkit User Manual

PID Theory Explained

PID Control

Best Regards,
T. McCarty
Applications Engineering 

[Barp]

Wormwood,

The Advanced Control VIs (vi.lib>>Addons>>Control>>Advanced), although are available with the PID Control Toolkit, are deprecated VIs that are shipping with this toolkit to allow back compatibility with previous code. You should use the Control Design and Simulation (CD&SIM) Module 8.5 (Or the Simulation Module 8.2, if you do not have the latest version) to have this capability. You can use those functions for now, but it is not guarantee that they will be support in future versions.

To implement first order transfer function with delay, you can easily implement that with CD&SIM, using the Time Delay in series with a transfer function with first order. That would be the recommended way to implement those functions. Again, notice that the Advanced Control VIs have Transfer Function and Time Delay that you could use, if you can't purchase the CD&SIM module, but they are much difficult to use (you need to wire "initialization" and "dT" signals everywhere in the VI).

Please let me know if you have more questions. I hope this helps!

[Wormwood]

Thanks, i'll go try and get back to you all if i still have any problem

With Regards

Wormwood

[Wormwood]

Hi all;

I'm now using the plant simulator.vi for the process deadtime and lag, however, when i was trying them out, i cant seem to get them to work. What i did was to put all other values in the plantsimulator.vi to 0 and leave my deadtime at a value of 2, when i start to run my VI i dont see the deadtime of 2sec on my graph.

Another question is --- is process gain on the plant simulator.vi same as steady-state gain,Kp, which appears on normal PID.vi

With Regards

Wormwood

[Wormwood]

Hi all;

I'm now using the plant simulator.vi for the process deadtime and lag, however, when i was trying them out, i cant seem to get them to work. What i did was to put all other values in the plantsimulator.vi to 0 and leave my deadtime at a value of 2, when i start to run my VI i dont see the deadtime of 2sec on my graph. What do i have to do to allow the deadtime to work?

Another question is --- is process gain on the plant simulator.vi same as steady-state gain,Kp, which appears on normal PID.vi

With Regards

Wormwood

[McCarty]

Hello Wormwood,

Can you clarify the difficulty you are having?  Remember that you can use Highlight Execution, Single Stepping, and the Probe tool to evaluate what is happening within your code.  As I mentioned earlier, the Shift Register Delay.vi is the specific VI that handles the deadtime.

The process gain is not the same as the proportional gain.  The process gain adjusts the static (DC) gain of the process.  The proportional gain determines the ratio of the output response to the error signal.

Best Regards,
T. McCarty
Applications Engineering