National Instruments 370753C-01 Manual De Usuario

© National Instruments Corporation

check(sys, {stable})

ans (a scalar) = 0

check(sys, {discrete, ss})

ans (a scalar) = 1

[, tfsys] = check(sys, {tf, convert})

tfsys (a transfer function) =

(z + 0.26)

---------------------

(z + 0.26)(z - 1.875)

initial delay outputs

0

0

System is discrete, sampling at 0.001 seconds.

Many systems where behavior derives from physical equations of motion 
can be modeled most naturally as continuous processes, using differential 
equations. Therefore, you often choose to discretize these models for use 
with a digital controller. A number of mathematical methods have been 
developed to approximate the behavior of a continuous system in a 
discrete-time representation with an appropriately fast sampling rate. 
Xmath provides two functions, 

discretize( )

 and 

makecontinuous( )

, which encompass a range of these techniques. 

discretize( )

 converts a system from its representation as a continuous 

function in the s-domain to a discrete-time z-domain function. 

makecontinuous( )

 does the reverse, transforming a discrete system to 

its continuous form. 

SysD = discretize(Sys,{dt,exponential,forward,backward,

tustins,ztransform,polezero,firstorder})

The 

discretize( )

 function has a number of keywords that correspond 

to the different methods of continuous-to-discrete conversion that are 
implemented within Xmath. The sampling interval (in seconds) for the 
discrete system should be set equal to the keyword 

dt

. If no value for 

dt

 

is specified, a default of 0.5 seconds is used. The default discretization 
method used is the exponential (step-invariant) transform. The different