Conor, Jeff K Summary: - Conversion of ISI Suspoint motion into the DoF basis works for the arms, with limited fidelity. - Corner station DoFs seem not to work, possibly some problem with inclusion of the Beamsplitter. - IPC communication between ISI and SUS at ETMY is spoilt somehow. The GS-13s on stage 2 are used as witnesses for residual motion. Their outputs are calibrated to nm, and converted to suspension point motion using Euler matrices (Cart2Eul). The output is in the local suspension coordinates. For example, the channel 'H1:ISI-ITMX_SUSPOINT_ITMX_EUL_L_DQ' is the longitudinal motion of ITMX, which is along the normal vector pointing outward from the HR surface, in the global +X direction. These suspension point motions are IPC'd to the OAF model, and in the case of the ETMs this involves some multiplexing/AI-filtering for communication down the arm. In OAF they are combined into the IFO degrees of freedom based on T1500610 . As a sanity check, I fetched the ISI-model Suspoint channels and matrix'd them into the IFO DoFs in Matlab, for comparison with the OAF DoF channels. For the arms (XARM, YARM, CARM, DARM), things seem to be somewhat okay. I confirmed this by eye, and then took the spectrum of the subtraction (attachment 1, CARM_Spectrum). The residual is consistent with the dynamic range of single-precision floats (about 10^9), at least at high frequencies. A quick software-only transfer function using four poles at 0.1Hz and white-noise injection in a spare filter bank shows a similar total dynamic range (attachment 2, DTT_dynamic_range). The anti-imaging filters, for transmission of the ETM signals along the arm, should allow a considerably smaller residual than we see at low frequencies, and I don't really know what else might cause this. The corner station DoFs are substantially wrong, visible directly in the time series' (eg attachment 3, MICH_time_series). Since MICH only uses the ITMs (confirmed to be 'okay') and the Beamsplitter, presumably the difference arises there. PRCL and SRCL are similarly incorrect. Document T1500610 has some minor errors in the Suspoint->IFO-basis definitions, but the current matrix has correct values as far as I could see. It also points to the Suspension model versions of the Suspoint motion, eg 'H1:SUS-ITMX_M0_ISIWIT_L_DQ', but the model uses the ISI versions. Initial testing revealed discrepancies between: 'H1:ISI-ETMY_SUSPOINT_ETMY_EUL_L_DQ' 'H1:SUS-ETMY_M0_ISIWIT_L_DQ' visible in attachment 4 (ETMY_IPC_issue). The other 3 test masses didn't show this gross level of disparity.
The problem with the corner station calculations are a model mapping error. I pointed this out to Jeff but he must have thought I fixed it or he just spaced it out given his usual very full to-do list. I've never edited the OAF model and did not feel comfortable doing so. Attached is the errant part of the model. The BS PRM PR2 and PR3 are all mis-mapped in this section.
Dave, Conor, Jenne, Hugh
Jenne is fixing the mapping mis-wire for the corner station calculations.
Dave checked the data path and found the SUS and ISI versions of the CART2EUL matrix for the ETMY were not the same. This looks likely to be the issue rather than an IPC problem.
I checked the values against the data file I used to populate the matrices for all the suspensions and it still agrees. I suspect the values in the SUS ETMY matrix are out of date.
See alog 11036 for more details: Data file is
/opt/rtcds/userapps/release/isc/common/projections/ISI2SUS_projection_file.mat
Here is some detail on the GS13 signal paths. The six GS13 signals coming out of the ISI model are split, with one set going via Dolphin IPC to the SUS system, and the other set going through the ETMn_CAL into the ETMx_SUSPOINT part, in which is passes through a CART2EUL matrix. The SUS model receives the six dolphin channels, passes these through the ISIINF part, then through its CART2EUL matrix into the ISIWIT. It is these two CART2EUL matrices which have identical settings at ETMX and are slightly different at ETMY.
J. Kissel I've compiled, installed, and restarted the OAF model with the SUSPOINT to IFO basis transformation bug fix, and committed the top level model, /opt/rtcds/userapps/trunk/isc/h1/models/h1oaf.mdl Attached is a screen shot showing the current and correct channel ordering.
J. Kissel I've also updated the SUS version of the ETMY CART2EUL matrix (i.e. H1:SUS-ETMY_M0_CART2EUL channels) with the values found in /opt/rtcds/userapps/release/isc/common/projections/ISI2SUS_projection_file.mat that was apparently discrepant in only *some* of the rotational terms, and only by ~10%. I can't explain why these were off, and I'd trended the values for the past 850 days (with the stop time of June 2015, so I covered the time install time mentioned in LHO aLOG 11036) and they've not been changed. One of life's mysteries, I suppose. Fixed now! For the record, the new values are | L | | 0 -1.0000 0.2000 0 -0.2823 0 | | X | | T | | 1.0000 0 0.4294 0 0 -0.2823 | | Y | | V | = | 0 0 0 1.0000 -0.4294 0.2000 | | RZ | | R | = | 0 0 0 0 0 -1.0000 | | Z | | P | | 0 0 0 0 1.0000 0 | | RX | | Y | | 0 0 1.0000 0 0 0 | | RY |
Also, I posted some analysis of the relative motion between HAM2 and HAM3 in the DCC https://dcc.ligo.org/G1601390 differential Z is really small. differential X kind of sucks at the microseism. Not sure how much it matters for the IMC, but it is worth thinking about. I think there is some fruitful work to be done here - if it would be useful to reduce the relative motion of the ISI tables in the corner at the microseism.