Biomedical Engineering Reference
In-Depth Information
CHAPTER
2
System Classification
As mentioned in Chapter 1, a system as defined in engineering terms is “a collection of
objects interacting with each other to accomplish some specific purpose.” Thus, engineers
tend to group or classify systems to achieve a better understanding of their excitation,
response, and interactions among other system components. It should first be noted that
the general conditions for any physical system can be reflected by the following general
model equation (2.1):
A
n
(
t
)
d
n
y
dt
n
A
n
−1
(
t
)
d
n
−1
y
dt
n
−1
A
1
(
t
)
dy
+
+···+
dt
+
A
o
(
t
)
y
B
m
(
t
)
d
m
x
dt
m
B
m
−1
(
t
)
d
m
−1
x
dt
m
−1
B
1
(
t
)
dx
=
+
+···+
dt
+
B
o
(
t
)
x
(2.1)
Thus, the necessary conditions for any physical system are (1) that for an excitation
(input) the function
x
(
t
)
=
f
(
φ
) exists for all
t
<
t
◦
and (2) that the corresponding
response (output) function
y
(
t
)
t
◦
. These conditions are
important because natural physical system cannot anticipate an excitation and responds
before the excitation is applied.
Classifying a signal typically involves answering several questions about the system,
as shown in Table 2.1.
Let us begin with definitions of terms used to characterize systems.
=
f
(
φ
) must also exist for all
t
<
2.1 ORDER
What is the order of a system? The order of a system is the highest order derivative.
Determining the order of a system is important because it also characterizes the response
Search WWH ::
Custom Search