J. Kissel, for K. Izumi, S. Ballmer, and S. Dwyer
One of the tricks to get ALS DIFF working without saturation was to tweak the distribution filter design. I attach a comparison between the filters installed on 2014-05-08 vs. those tweaked last night (2014-05-14). Only two small changes:
(1) To the UIM-TST LP, whose composition included
(a) two poles at 6 [Hz], three poles at 150 [Hz]
(b) elliptic filter of (freq,order,ripple,stopDB,zQ) = (9, 3, 1, 20, 1.4)
(c) elliptic filter of (freq,order,ripple,stopDB,zQ) = (19, 3, 1, 20, 1.4),
now has the second elliptic filter's corner frequency much lower, at 6 [Hz], i.e. a new (c) of
(c) elliptic filter of (freq,order,ripple,stopDB,zQ) = (6, 3, 1, 20, 1.4),
(2) To the TST-UIM HP, whose composition included
(a) (1 - UIM-TST LP)
(b) an elliptic high-pass of (freq,order,ripple,stopDB,zQ) = (.7, 2, 1, 10, 3)
now has an additional high-pass filter,
(c) two zeros at 0 [Hz], two poles at 0.2 [Hz], normalized to unity at high frequency, i.e. zpk([0;0],[0.2;0.2],1,"n")gain(25)
Note that this extra low-pass has been installed, ignoring its affect on the complementarity with the UIM-TST LP. This needs to be fixed if we desire complementarity.
These tweaks served to (1) to move the elliptic filter's gain peaking bump out of the way of the 10 [Hz] features in the input noise, and (2) roll off the low-frequency end of the test mass drive faster.
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Details
The New H1 SUS ETMX Filter Configuration:
H1:SUS-ETMX_M0_LOCK_L (same as before)
FM1 "invL2L1" (part one of plant inversion filter)
FM2 "invL2L2" (part two of plant inversion filter)
FM3 "top/tst" (gain only filter to compensate for the gain ratio)
FM5 "blendLP"
H1:SUS-ETMX_L1_LOCK_L
FM6 "invL2LNEW" (part one of plant inversion filter)
FM7 "patch" (part two of plant inversion filter)
FM8 "LISOfit" (part three of plant inversion filter)
FM9 "uim/tst" (gain only filter to compensate for the gain ratio)
FM3 "blendHP" (UIM-TOP HP complement)
FM4 "blendLP-2" (UIM-TST LP complement, with lower frequency elliptic filter)
H1:SUS-ETMX_L3_LOCK_L
FM6 "MatchedinvL2L" (part one of plant inversion filter)
FM7 "patch" (part two of plant inversion filter)
FM4 "blendHP-M0" (TST-TOP HP complement)
FM5 "blendHP-L1_2" (TST-UIM HP complement)
FM9 "hp.2" (extra high-pass for TST-UIM HP complement)
In order to create these modifications to the UIM-TST LP, Kiwamu grabbed my design script from
/ligo/svncommon/SusSVN/sus/trunk/QUAD/Common/FilterDesign/HierarchicalControl/DARMmodel_ALS_20140428.m
copied it to his home directory,
/ligo/home/kiwamu.izumi/
to play around,
/ligo/home/kiwamu.izumi/Desktop/farm/matlab/
modified the filters mentioned above, and then used a fancy new script,
/ligo/home/kiwamu.izumi/Desktop/farm/matlab/fofon.m
which takes in a continuous zpk filter, and produces a foton design string to be copied and pasted into Foton. If the filter is a high-pass, the only other step is to use the "Gain" field to set the gain to be unity at high-frequency.
The modification to the TST-UIM HP was done later in the evening after I'd left, but by the simplicity of its design, I think it was just added directly without testing any stability or complementarity in Matlab prior to install.
[[elliptic filters are generated using ${SeiSVN}/seismic/Common/MatlabTools/myellip_z2.m]]
[[hp elliptic filter is generated by ${SeiSVN}/seismic/Common/MatlabTools/myhpellip_z.m]]
