Discrete Transfer Function Control Design

[Argon]

I am working with a PI Temperature Control. I was given a Heating, Ventilation, and Air Conditioning Trainer (HVACT) with a VI that turns on and off a halogen bulb whenever it reaches certain temperature. Everything works perfect the way it is right now. What I want to do is to change a "filter" [50/(s + 50)] in the block diagram from CONTINUOUS (s domain) to DISCRETE (z domain) form. Can I just convert the given transfer function from Laplace to Z domain and use the Discrete Transfer Function.VI to represent the new transfer function in terms of z? Do I need to add an A/D and a D/A before and after the Discrete Transfer Function.VI?

[Barp]

Argon

If you have Control Design Toolkit, you can you the "CD Convert Continuous to Discrete.vi" and generate the Discrete Equivalent of the Continuous Transfer Function and use the "Discrete Transfer Function.vi" to implement the Transfer Function.

Notice that you have to choose the correct sampling time and correct discretization method to avoid creating an incorrect filter. You don't need to have the a/d or d/a in place since the DAQ board is actually doing this for you.

Alex Barp - Control Design and Simulation Group - National Instruments