Specifications

Table Of Contents

Time Delays

2-51

You can specify this model either as the first-order transfer function

with a delay of two sampling periods on the input

Ts = 1; % sampling period

H1 = tf(1,[1 –1],Ts,'inputdelay',2)

or directly as a third-order transfer function:

H2 = tf(1,[1 –1 0 0],Ts) % 1/(z^3–z^2)

While these two models are mathematically equivalent, H1 is a more efficient

representation both in terms of storage and subsequent computations.

When necessary, you can map all discrete-time delays to poles at the origin

using the command

delay2z. For example,

H2 = delay2z(H1)

absorbstheinputdelayinH1 intothetransferfunction denominatortoproduce

the third-order transfer function

Transfer function:

---------

z^3 – z^2

Sampling time: 1

Note that

H2.inputdelay

now returns 0 (zero).

Retrieving Information About Delays

There are several ways to retrieve time delay information from a given LTI

model

sys:

•Use property display commands to inspect the values of the ioDelay,

InputDelay,andOutputDelay properties. For example,

()

2–

z 1–

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

1 z 1–

()⁄