So I can better help, can you clarify which software you are using? Do you have the LabVIEW PID toolkit, the Control Design Toolkit, the Simulation Module, or LabVIEW Real-Time? Once we have a little more information, we can provide some further help.
Have you tried looking for a solution in the examples that ship with LabVIEW? Go to Help->Find Examples to look for examples related to your application or products.
Regards,
Kristi H
National Instruments