With Hirata-san.
We measured transfer functions of the IP in L and T. The resonance frequencies were:
- IP-L: 70 mHz,
- IP-T: 70 mHz.
- Resolution: 10 mHz.
The frequiencies are low enough (below 80 mHz), but they are very close to each other.
Following the analysis done in SR3 of the asymmetric values of IP-L and IP-T resonance frequencies (klog 17281), I carried out the same analysis in SR2 in which there is no asymmetry or it's jut too hard to distingush.
I measured the transfer functions at the individual LVDT-actuator units H1, H2 and H3 separately. As can be seen in the plots attached, the lowest resonance frequencies in each case are:
- H1: between 66 and 70 mHz,
- H2: 66 mHz,
- H3: between 66 and 70 mHz.
- Frequency resolution: 5 mHz.
- Temperature: 23.6°C (O3GK T = 23.5 °C).
The resonance frequencies are either the same or very close together when measuring with the current frequency resolution.
There is an apparent discrepancy between the IP resonant frequency along L when measured with the force TF and the free-swing ASD. Namely, with the TF, it shows at 66 mHz, whereas in the ASD, it appears at 80 mHz.
I realized about this while testing the LVDT sensor correction (klog 22554). The figures show the TF and the ASD in the same plot, for L and T separately. The ASD was scaled to be able to show it along the TF.
In the Transverse direction, in the TF and the ASD the resonance appears consistently at 66 mHz.
The files I used to produced the plots are those used in klogs 22554 and 22451. The script is IP_resonance_comparison.ipynb at /kagra/Dropbox/Subsystems/VIS/vis_commissioning/sr2/inter_calibration/.
