BRUEL & KJAER 2032 Instruction Manual page 166

Pzab(n) can be displayed in terms of:
Real part
Imaginary part
Magnitude
Phase
Nyquist plot
Nichols plot
In Spectrum Averaging Zero Pad and Signal Enhancement modes, the original Time
Records a(n), a(n), b(n) and 6(n) are extended by an additional record with a(n)
=
0,
a(n)
=
0, b(n)
=
0, or b(n)
=
0 giving biased estimate
P~ab(n).
To remove the error
caused by zero padding, a "bow-tie" correction can be applied:
N
Pzab
=
-N-- P;ab( n)
-In I
13.2.17. Impulse Response
156
In Spectrum Averaging mode:
0
~
n
~
N-1 , 0
~
k
~
N-1 , N
=
2048
W(k) is the weighting function applied to the Frequency Response.
The Analytical Impulse Response is defined as:
,.-.......)
hz(n)
=
h(n)
+
j h(n)
where
h(;;' )
=
Jr[
h(n)]
hz(n) is displayed for -1024 ~ n ~ 1023.
In Signal Enhancement mode:
hz(n)
=
y--1 [
W(k) . Ge (k)]
Ga (k)
0
~
n
~
N-1, N
=
4096, a(n) and 6(n)
=
0 for N/2
~
n
~N-1
where GA(k) and Ge(k) are the 1-sided spectra of the Enhanced Time Functions a(n)
and b(n) extended with zero padding. hz(n) is displayed for -2048
~
n
~
2047.
hz(n) can be displayed in terms of:
Real part
Imaginary part
Magnitude
Phase
Nyquist plot
Nichols plot