KAGRA Logbook

VIS (BS)

fabian.arellano - 17:56 Thursday 06 October 2022 (22382)

IP geophone diagonalization.

With Lucia.

We realized the geophone degrees of freedom had large coupling with respect to each other (see Fig. 6). Therefore, we did diagonalization using the same method as for the LVDTs (see klog 22336).

First, we set the matrix ACC2EUL to the geometrical matrix (shown below and calculated with the script already linked from the medm screen).
Then, we calculated the diagonalization matrix and wrote it in ACCALIGN. The matrix is shown in a picture below.

ACC2EUL =
[[ 0.64395 , -0.4714045 , -0.172546 ],
[ 0.172546 , 0.47140452, -0.64395 ],
[ 0.563539 , 0.563539 , 0.563539 ]]

Comment on the results will follow.

Images attached to this report

22382_1665046534_BS_IP_geo_coupling_before_diagonalization.png

Comments to this report:

lucia.trozzo - 17:06 Friday 07 October 2022 (22404)

Today I investigate the geophone residual coupling between DOF and I estimated the inter-calibration factors between the geophones and LVDTs along L, T, and Y directions.
Pic.1 shows the broadband residual coupling, as a function of the frequency, before and after changing the geophone align matrix.
Looking at this plot, it is possible to note that the sensing couplings, especially the terms L2T, L2Y, T2L, and Y2T, are reduced.
The matrix seems to work fine.

Concerning the inter-calibration, a way to do that is to rescale the gain of the diagonalized geophone to match the amplitude of the TFs measured by the diagonalized LVDT_(L, T, Y). Keeping this idea in mind, I extrapolated the calibration factor of each geophone, at 0.2 Hz, calculating the ratio LVDT_(L, T, Y)/GEO_(L, T, Y).
Here are the values:

GEO_L= 1.0476
GEO_T= 1.1221
GEO_Y=1.2971

In pic. 2, Pic.3, and Pic.4, the comparison of the TFs before and after the calibration is shown. Looking at these plots, it is possible to see that the TFs between and GEOs are matching.

Note.
I haven't yet implemented these values in the MEDM, but I will as soon as the suspension is available.

Images attached to this comment

lucia.trozzo - 17:39 Tuesday 11 October 2022 (22441)

The calibration factors have been implemented in MEDM. Pic.1, Pic.2, and Pic.3 show the comparison of the TFs measured with LVDT and GEOs after the implementation of the calibration factors. We can see that now are matching.

Images attached to this comment