jeffrey.kissel@LIGO.ORG - posted 13:18, Tuesday 04 March 2014 - last comment - 13:18, Tuesday 04 March 2014(10493)
H1 SUS ETMX PUM/L2 Coils Balanced
J. Kissel, A. Pele Following the same procedure outlined in LHO aLOGs 9453 and 9079, Arnaud and I balanced the coils on the PUM stage of H1 SUS ETMX. The final balanced gains in the L2_COILOUTF bank are H1 SUS ETMX Channel Balanced COILOUTF Gain L2 UL +1.034 L2 LL -1.014 L2 UR -0.986 L2 LR +0.966 The precision to which we could balance the coils was limited by the day-time ground motion (we saw an almost instantaneous loss in SNR once the day-time 1-10 [Hz] noise increased around 8:30a PT), but we believe the obtained values are good to within +/- 0.5%. This balancing has reduced the L3 P and Y caused by a L2 pringle excitation at 4 [Hz] by DOF Reduction Factor @ 4.0 [Hz] P > 6.0 (peak below the noise, and totally incoherent) Y > 7.3 (peak below the noise, and only ~60% coherent) The first attachment shows the result from which these values were obtained, comparing the optical lever ASD at 4 [Hz] driven from L2 at the same amplitude for both balanced and unbalanced configurations.
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Measurement Details ------------------- Coil Driver Configuration: State = -2, with all COILOUTF compensation filters turned off This is the configuration which gets the most drive to the coils, given that the analog driver in this "acquire" configuration has [z:p] = [1.35:80.5], see LLO aLOG 4495). Demodulator filters used: SIG band pass: BP4.0Hz = butter("BandPass",2,3.5,4.0) DEMOD I & Q low-pass: CLP50mHz = cheby1("LowPass",2,3,0.05) Demodulator Drive Parameters Freq [Hz] Amp [ct] Sin [ct] Cos [ct] 4.0 125000 10000 10000 4.0 125000 10000 10000 Note -- we started off at 6 [Hz], but was not able to get enough SNR with a half-hour's worth of effort, so we moved down to 4 [Hz]. Again, we want to stay away from any suspension resonances that might complicate the signal, but get the frequency high-enough that we get lots of cycles inside the 50 [mHz] band pass. SEI Configuration: HPI: Level 1 Isolation, "Pos" position sensor only blend filters ST1: Level 3 Isolation, "TCrappy" blend filters (in all DOFs) ST2: Level 3 Isolation, "TStart" blend filters (in all DOFs) Note -- we had started around 7:30a PT this morning, but the day-time ~1-10 [Hz] noise quickly started to create a lot of excess noise at our drive frequency. We played around with the ST2 blend configuration until we found something we'd liked. I'm not sure that it makes sense -- the TCrappy filters have a factor of 2e-4 displacement sensor isolation at 1 [Hz], where the TStart only has a factor of 0.3 -- but the SNR was clearly better with TStart on ST2. (see LHO aLOG 10408 for blend filter details). Resulting Demod Phases: Measured using a 300 second average of the demodulated signals, i.e. tdsavg 300 H1:SUS-ETMX_LKIN_P_DEMOD_I_OUT H1:SUS-ETMX_LKIN_P_DEMOD_Q_OUT H1:SUS-ETMX_LKIN_Y_DEMOD_I_OUT H1:SUS-ETMX_LKIN_Y_DEMOD_Q_OUT H1 ETMX L2 Demod Phase [deg] Unbalanced Value [ct] Balanced Value [ct] P 145 I +1.385 pm ~0.5 -0.12 pm ~0.75 Q -0.064 pm ~0.5 -0.08 pm ~0.75 Y 153 I +1.027 pm ~0.2 -0.09 pm ~0.25 Q 0.054 pm ~0.2 0.08 pm ~0.25 To perturb the PIT or YAW balancing by 1%: /ligo/svncommon/SusSVN/sus/trunk/Common/PythonTools/perturbcoilbalance_fourosem.py H1 ETMX L2 [PIT/YAW] 0.01 Exact balanced values: Measured using a simple command line caget, i.e. caget H1:SUS-ETMX_L2_COILOUTF_UL_GAIN H1:SUS-ETMX_L2_COILOUTF_LL_GAIN H1:SUS-ETMX_L2_COILOUTF_UR_GAIN H1:SUS-ETMX_L2_COILOUTF_LR_GAIN H1 ETMX L2 Coil COILOUTF Gain UL 1.03422 LL -1.01374 UR -0.98575 LR 0.96623 Of course, these values are set at arbitrary precession, they're rounded to the above quoted precession (a) because the measurement uncertainty is no better than 0.5%, and (b) the MEDM screen does not display out to higher precession, so further precision would not be visible.