On 19.01.11 16:00, Doug Stewart wrote:
On Wed, Jan 19, 2011 at 9:38 AM, Rudolf
Widmer-Schnidrig
<address@hidden>
wrote:
On 19.01.11 13:32, Doug Stewart wrote:
On Wed, Jan 19, 2011 at 3:19
AM, Rudolf Widmer-Schnidrig
<address@hidden>
wrote:
Dear List,
I have measured (in the time domain) input and
output of a mechanical system (a seismometer) and
would like to derive a filter model B(s)/A(S)
based on this data.
I see the path via the frequency domain:
[H, F] = pwelch(input,output,.....'trans')
[B, A] = invfreqs(H,F,nA,nB)
Question: is there a way to find A and B without
going first into the Fourier domain?
many cheers - Ruedi
--
+---------------------------------------------------------------+
Rudolf Widmer-Schnidrig
What Input did you use?
If it was an impulse then Yes
if it was a step then yes
and maybe more.
Doug
Dear Doug, I have used both a sweep and a random telegraph
signal. -Ruedi
OK
A sweep is inherently a frequency domain type of test so
maybe you can use Bode type analysis to find the corner freq.
and gain and type of role off etc.
Dear Doug,
Since my input sweep has constant amplitude the amplitude variation
with frequency of the output signal shows immediately how the gain
of the instrument varies with frequency. From a comparison of input
and output signals in the time domain one can - at least
qualitatively - also see the phase delay and how it varies with
frequency. What I am after is a precise estimation of the poles and
zeros to within hopefully 1% or better.
is the random telegraph signal a white noise type of
signal??
The random telegraph signal is band limited white noise.
My seismometer can be modeled as a band-pass filter. I also have a
good idea on the number of poles and zeros (nA and nB) needed for a
description in the s- or z-plane. So maybe I'll just have to do a
grid search and perturb the locations of the A and B values until
norm(output - H(z)*input)
is minimal. Fortunately in the case of the z-transform the serach
is limited to the real axis.
-Ruedi
--
+---------------------------------------------------------------+
Rudolf Widmer-Schnidrig