An impulse is infinite at t ¼ 0 and zero elsewhere. The area under the unit impulse
is 1. An approximation of this type of waveform is used to place initial energy into a
system so that the response due to that initial energy is only the transient response of a
system. From this response the designer can derive a mathematical model of the system.
A step input represents a constant command, such as position, velocity, or
acceleration. Typically, the step input command is of the same form as the output. For
example, if the system’s output is position, as it is for the antenna azimuth position
control system, the step input represents a desired position, and the output represents
the actual position. If the system’s output is velocity, as is the spindle speed for a video
disc player, the step input represents a constant desired speed, and the output
represents the actual speed. The designer uses step inputs because both the transient
response and the steady-state response are clearly visible and can be evaluated.
Mathematical
description
Angular
output
Angular
input
FIGURE 1.12 Equivalent block
diagram for the antenna azimuth
position control system
18 Chapter 1 Introduction
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