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fabian.arellano - 10:56 Tuesday 29 September 2020 (15122) Print this report
Asssessment of BF position with FR in midrange and control off.

In the context of remedying work towards O4 I wanted to know the postion of the BF keystone with the fishing rod (FR) in midrange and the control off.

Current status:

  • Temperature: 23.2 degrees Celsius.
  • The BF fishing rod is at its upper limit with the keystone at -123 µm.
  • Position of FR in units of steps of displacement: 3,000 steps.


  • According to JGW-E2011534, moving the FR stepper motor by 575,000 steps down would put the FR carriage in midrange.
  • I confirmed that when (displacement in steps > 0) keystone moves down.

I proceeded to move the motor to position 583,000 steps (= 575,000 + 3,000), however, at 405,000 steps the IM or BF keystone touches something. The LVDT signal shows no free oscillations at -1,470 µm as shown in the picture.

I moved back the FR to its upper limit as it was before. It went as high as -19,745 steps with the LVDT at -153 µm. The suspension went smoothly into ALIGNED state.

Images attached to this report
Comments to this report:
fabian.arellano - 16:13 Tuesday 20 October 2020 (15282) Print this report

Today I checked the results were reproducible.

  • BF keystone stops at -1,465 um, which is very close to the previously measured value.
  • Aditionally, I lifted F0 by approximately 170 um and the BF keystone did not come free. This means the IM might be touching the IRM.

When we take SR3 out of the chamber we must check whether any OSEM body touches a flag at BF LVDT = -1,470 um.

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