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fabian.arellano - 17:31 Wednesday 17 April 2019 (8672) Print this report
SRM recovery after pump down

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.

Images attached to this report
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fabian.arellano - 15:32 Wednesday 24 April 2019 (8733) Print this report

This is an assessment of the IM-V transfer function after the condition explained in entry 8672.

The previous assessment was done were with the BF GAS at 0 and IM-V at 178 µm. They should both be zero simultaneously and we should investigate how we ended up with such a discrepancy.

I wanted to measure transfer functions with the IM and IRM in a different relative position, therefore, I moved the IM down with the BF fishing rod.

  1. I noticed that when the BF was at approximatelly at -30 µm the IM and the BF did not seem to move freely vertically. See first picture. It is shown that when the BF is above -30 µm the BF and IM seem to oscillate freely and when the BF goes back down to -31 µm they don't oscillate as expected.
  2. In those conditions (BF at -30 µm) I took the following transfer functions: IM-L, IM-T, IM-P and IM-R. They all look healthy, including the ones measured with the IM vertical OSEMS. The files are in /kagra/Dropbox/Subsystems/VIS/TypeBData/SRM/TF/Measurements/20190424/
  3. The IM-V and BF GAS don't look alright. See second and third pictures.

Items 2 and 3 suggest the problem may be in the BF and not IM or IRM.

At the end of the exercise I moved the BF back to zero and measured the BF and IM-V TFs again (see test1 files in the same directory). They look healthy.

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fabian.arellano - 12:36 Thursday 22 October 2020 (15305) Print this report

Yesterday 21st of October 2020 I checked the BF condition again.

Some conditions and what I did:

  • Suspension in NEUTRAL mode.
  • Current keystone nominal position 100 um.
  • I moved the keystone down using coil-magnet actuation in the test channel.
  • I measured BF transfer functions in some positions.

What I found, see the picture:

  • When the keystone is at 50 um an oscillation at about 40 mHz appears with a small amplitude.
  • As the kestone keeps going down the oscillation increases.
  • I measured the BF transfer function three times, and the only healthy one is the one with the keystone above 100 um.

What this suggests:

  • The problem doesn't seem to be a hard physical stop. The keystone is always moving.
  • I tend to think a cable pulling is producing coupling with another body.
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