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Entry  Fri Oct 8 17:33:13 2021, Hang, Update, SUS, More PRM L2P measurements Screenshot_2021-10-08_17-30-52.png
    Reply  Mon Oct 11 11:13:04 2021, rana, Update, SUS, More PRM L2P measurements 
    Reply  Mon Oct 11 13:59:47 2021, Hang, Update, SUS, More PRM L2P measurements prm_l2p_tf_meas_white.pdfprm_l2p_tf_meas_opt.pdfprm_l2p_fisher_vs_data_white_vs_opt.pdfprm_l2p_Pxx_evol_v2.pdf
Message ID: 16388     Entry time: Fri Oct 8 17:33:13 2021     Reply to this: 16389   16390
Author: Hang 
Type: Update 
Category: SUS 
Subject: More PRM L2P measurements 

[Raj, Hang]

We did some more measurements on the PRM L2P TF. 

We tried to compare the parameter estimation uncertainties of white vs. optimal excitation. We drove C1:SUS-PRM_LSC_EXC with "Normal" excitation and digital gain of 700.

For the white noise exciation, we simply put a butter("LowPass",4,10) filter to select out the <10 Hz band.

For the optimal exciation, we use butter("BandPass",6,0.3,1.6) gain(3) notch(1,20,8) to approximate the spectral shape reported in elog:16384. We tried to use awg.ArbitraryLoop yet this function seems to have some bugs and didn't run correctly; an issue has been submitted to the gitlab repo with more details. We also noticed that in elog:16384, the pitch motion should be read out from C1:SUS-PRM_OL_PIT_IN1 instead of the OUT channel, as there are some extra filters between IN1 and OUT. Consequently, the exact optimal exciation should be revisited, yet we think the main result should not be altered significantly.

While a more detail analysis will be done later offline, we post in the attached plot a comparison between the white (blue) vs optimal (red) excitation. Note in this case, we kept the total force applied to the PRM the same (as the RMS level matches).

Under this simple case, the optimal excitation appears reasonable in two folds.

First, the optimization tries to concentrate the power around the resonance. We would naturally expect that near the resonance, we would get more Fisher information, as the phase changes the fastest there (i.e., large derivatives in the TF).

Second, while we move the power in the >2 Hz band to the 0.3-2 Hz band, from the coherence plot we see that we don't lose any information in the > 2 Hz region. Indeed, even with the original white excitation, the coherence is low and the > 2 Hz region would not be informative. Therefore, it seems reasonable to give up this band so that we can gain more information from locations where we have meaningful coherence.

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