Using simulations for online control?

Question

Hi
When using Labview 8.2.1 what is the best way of implementing model based control, can the simulation environment, which has some nice transferfunction features be synchronized in a timed loop, to do online control in a real time system. I couldn't find an input in the simulation loop triggering the simulation with the timed loop rate. An example would be nice. Also is it at all possible to change integration algorithms, or should I make the desired adjustments myself.
Best Regards
soeren  

Answer 1

Hi soeren
1) If you double click the simulation loop and choose the 'Timing Parameters' tab, you have to check the 'Synchronize loop to timing source' box.
Then if you expand the inputs on the left hand side loop you will see the 'Source Name' appearing. This is where you can wire in an external timing source.
2) Create a timing source and wire it to the inputs of the timed and the simulated loop that you want to sync. The timing source can be the 1KHz clock Windows use
or the 1MHz clock that can be found in the latest NI Real time controllers.
3) Determine the rate at which the loops will run. The simulation rate has to be expressed in seconds and the timed loop rate will be in ticks ( for a 1KHz source the tick will be 1 msec). The photos attached depict two loops that are synchronized to run every 10msec. Please note that you need to choose a Fixed step solver from the simulation loop configuration box.
With regard to the integration block, it's behavior will depend on the ODE ( Ordinary Differential Equation) solver you choose. Therefore, you can play around with the simulation loop parameters to find out which method gives you the most meaningful results.
I hope that helped,
Kostas
Attachments:
SimulationTiming.PNG ‏26 KB
Sync_Timed_Sim.PNG ‏20 KB