National Instruments 370753C-01 Manual De Usuario

The response of a system to a unit step input is one of the most commonly 
used measures of how well a given control system’s output tracks the 
system input. A unit step is a time signal which is zero up until the 
beginning of the time period of interest, and one thereafter. This indicator 
is popular because it is easy to compute and interpret. It also is 
mathematically possible to calculate the response to any input if the 
response to a unit step is known. The performance measures associated 
with the step response are as follows:

•

Delay time (t

)—The time required for the response to reach half its 

final value.

•

Rise time (t

)—The time required for the response to rise from 10% 

of its final value to 90% of its final value.

•

Peak time (t

)—The time required for the response to reach the peak 

value of its first overshoot.

•

Maximum overshoot (M

)—The response value which most exceeds 

unity, expressed as a percent.

•

Settling time (t

)—The time required for the response to reach 5% of 

its final value.

These performance measures are obtained easily with a few lines of 
MathScript, as demonstrated in Example 4-9. For a plot of these 
performance measures, refer to Figure 4-6.

Y = step(Sys,T)

The 

step( )

 function computes the unit step response of a dynamic 

system over a time period which can be specified with the optional time 
vector 

T

. If 

T

 is not specified, 

step( )

 computes a default time vector 

using 

deftimerange( )

. 

The output, 

Y

, is a PDM where domain is the time vector and dependent 

matrices have row size equal to the number of inputs and column size equal 
to the number of outputs. 

Y = step(Sys, 0:.1:15);

plot (Y,{x_lab = "Time (sec)", 

ylab = "Amplitude", xinc=1, yinc=.1})