National Instruments 370757C-01 用户手册

Figure 2-4.  Bound for Sensor Uncertainty

A value of l

 at one radian per second of –20 dB indicates that modeling 

uncertainties of up to 10% (–20 dB = 0.1) are allowed.

The actuator and sensor uncertainties 

δ

1

 and δ

2

 are bounded by –20 dB 

at all frequencies. You will use these values to interpolate to obtain l

3

. 

First, create the bound for 

δ

3

 in Hz.

L3 = pdm([-20,-20,10,10],[0.1,1,30,100]/2/pi);

3.

Now interpolate to obtain 30 points:

L3 = interpolate(L3,logspace(0.01,10,30),{xlog});

4.

Create L1 and L2 (bounds for 

 and  ):

L1=-20*ones(L3); L2 = L1;

delb = [L1,L2,L3];

5.

Calculate the stability margin:

marg=smargin(H,delb);

The output indicates that Perron-Frobenius scaling (the default) is 
used. Refer to the 

 section.

The stability margin plot is shown in Figure 2-5. The minimum margin 
is about 8 dB at about 1/2 Hz. This implies that all three l

1

 values 

(uncertainty bounds) could be increased (relaxed) simultaneously 
by 8 dB, and the system would still remain robustly stable. 

0.1

1

30

100

10

0

–20

Frequency, Radian/Second

dB

δ

1

δ

2