The suspension seems healthy although more investigation is required on the conditions in which we can achieve a healthy IM-V and BF transfer functions. So far this has happened when movint the IM vertically by small amounts (e.g. 42µm peak to peak) during the measurement.
The files are in /kagra/Dropbox/Subsystems/VIS/TypeBData/SRM/TF/Measurements/20190415/
After pump down we recovered the alignment of the suspension and measured transfer functions. However, the F0, F1, BF and IM-V had one peak missing each. See the first three pictures.
After several measurements with the Top Filter at different heights (-1600 µm, -1300 µm and -1900 µm, where -1600 µm is nominal) I realized that reducing the amount of actuation when measuring the BF transfer function increases the coherence and yields an appropriate transfer function.
For instance, the fourth picture (file with the word "test" in the name) shows a healthy IM-V TF, with 10000 cnt actuation. The IM moves at the most vertically 42 µm peak to peak. The fith picture shows the BF TF with 10000 counts actuation, which moves the IM vertically 149 µm peak to peak (also with the word "test" in the name). The coherence is lower. These two measurements were taken when F0 was at -1300 µm.
After several measurements I moved all the GAS filters to nominal (F0 at -1600 µm, F1 at 0 and BF at 0) and measured the BF transfer function with only 1000 counts. See 6th picture (test 6 file). The coherence is good. The 7th picture is the IM-V TF (test2), which has a good coherence also.
The TFs of the IP and of the remaining IM degrees of freedom show what is expected with good coherence.
A new set of GAS filters and IM TFs should be measured with less actuation for the GAS filters.
