Reports 1-1 of 1 Clear search Modify search
VIS (PRM)
fabian.arellano - 20:10 Sunday 09 May 2021 (16677) Print this report
Setting the mirror to nominal height.

This entry reports the work done on Saturday 8th of May 2021.

With Hirata-san.

See pictures at the album PRM Remedying work after O3.

We successfully set the mirrror to the appropriate height; additionally, we have around 2.05 mm of fishing rod range to cope with the buoyancy correction. Transfer fiunction measurements of the SF show it is in a healthy state.

  • The temperature was 24.0 °C when we began working. The O3GK temperature is 23.5 °C.
  • We set the BF keystone to the setpoint using the fishing rod.
  • We locked the SF keystone at the nominal height per the 3D-CAD: 65.5 mm from the base plate (see pictures) or 11.5 mm from the upper safety ring.
  • Using the laser level and the height markings we determined the mirror was 1.8 mm below the nominal position.
  • The mirror has some roll. See details in this page of the notebook.
  • Keeping the BF at the setpoint we moved the SF keystone up by 1.8 mm (9.7 mm from upper safety ring), measured with a vernier calliper, and locked it there.
  • We measured the mirror height again: approximately 0.05 mm above nominal height. (Very good given the uncertainties in the measurement.)
  • The readout of the GAS filters LVDTs at this suitable configuration were:
    • BF: 1242 µm, which is very close to the setpoint.
    • SF: 10,467 µm.
    • The LVDTs may not be properly calibrated due to a replacement of the LVDT cards.
  • In the SF fishing rod we moved the stop nuts all the way up to have more moving range, then we used the FR to moved the keystone to its upper limit:
    • Stepper motor: -920,000 steps. We set this as the limit in software.
    • SF LVDT: 15,682 µm.
    • Distance from upper safety ring: 7.65 mm.
  • The position of keystone means we have 2.05 mm to cope with the buoyancy effect. It's very good.
  • We moved the SF keystone to its lower limit:
    • Stepper motor: 1,160,000 steps. We set this limit in software.
    • SF LVDT: -870 µm (depends on temperature).
    • Distance from the upper safety ring: 11.98 mm
  • The total keystone moving range of the fishing rod is 4.33 mm.
  • We kept the BF at the setpoint and moved SF to a position such that the mirror was at the appropriate height, and then we measured transfer functions:
    • The BF transfer function looks exactly the same as the reference.
    • The SF transfer function has a slightly larger amplitude than the reference.
    • The SF looks healthy.
Images attached to this report
Comments to this report:
fabian.arellano - 17:23 Thursday 13 May 2021 (16741) Print this report

With Hirata-san.

See pictures at the album PRM Remedying work after O3.

Today we reviewed the height of the mirror in the context of measuring its pitch with thelaser level. When the BF was at the setpoint and the mirror was at the correct height, the LVDT readout was 7440 counts not 10467 counts as reported before (see notebook). We need to double check. It's important to point out that the SF LVDT is not calibrated and the LVDT readout is always in number of counts, not um as I had written in previous reports.

fabian.arellano - 10:31 Friday 21 May 2021 (16805) Print this report

This entry corresponds to the work carried out yesterday 20th of May 2021.

With Hirata-san.

See pictures at the album PRM Remedying work after O3.

We revisited the SF keystone suitable height measurement. In this context, "suitable" means that the mirror would be at the appropriate height when the BF is at the setpoint.

Including a measurement from yesterday, we had three different values for such a suitable height taken at different dates: 10,467 cnt, 7440 cnt and 6320 cnt. The LVDT is not calibrated so it's impossible to know how far these positions are from each other in physical units. What we did then was to lock the keystone at each of those positions and measure their relative distances with a caliper:

Name LVDT output at suitable height (cnt) Height (mm) LVDT output with keystone locked (cnt)
1 10,467 23.04 10,412
2 7440 22.50 7422
3 6320 22.33 6276
  •   The last column shows the values where the keystone was locked when measuring the height with the caliper. They are suficiently close to their corresponding values of the suitable height.
  • The difference between items 1 and 3 is 0.71 mm. Considering that the laser level line thickness is about 2 mm, having the measurements within  0.71 mm is acceptable due to uncertainties.
  • The reference point for measuring is the 2nd one in this diagram.

As the new setpoint we can take the average of the three measurements: 8076 counts.

fabian.arellano - 17:43 Monday 31 May 2021 (16891) Print this report

I input into the medm screen the information about the suitable position of the SF in order to have the mirror at the appropriate height.

  • I changed the offset in the LVDTINF filters such that the readout after the filter is zero when the SF is at the suitable height; I also turned on the offset switch:
    • K1:VIS-PRM_SF_LVDTINF_GAS_OFFSET: 0 → -8076 counts.
    • K1:VIS-PRM_SF_LVDTINF_GAS: IN, OT, DC → IN, OF, OT, DC.
  • I changed the setpoint to zero:
    • K1:VIS-PRM_SF_SET_GAS_OFFSET: 4350 cnt → 0.
  • I updated the SDF.
Images attached to this comment
Search Help
×

Warning

×