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Reports until 21:00, Wednesday 12 September 2018
H1 ISC (ISC)
hang.yu@LIGO.ORG - posted 21:00, Wednesday 12 September 2018 - last comment - 08:39, Thursday 13 September 2018(43978)
MICH_DARK_ALIGN works again

We reduced the ASC loops gain by a factor of 4 in the MICH_DARK_ALIGN state in ALIGN_IFO guardian and now it seems to be working again. We should be able to use it for again for doing simple mich contrast defect measurements.

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gabriele.vajente@LIGO.ORG - 08:39, Thursday 13 September 2018 (43986)
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MICH_DARK_ALIGN was not working this morning.

The reason was that the PREP_MICH_DARK_ALIGN state will set the sensing matrix and engage the input of the ASC-MICH filter banks, with zero gain. But FM3 is almost an integrator, with a pole at 0.03 Hz. Therefore any input offset in the error signal was running into this low frequency pole, accumulating history.

I changed the way the ASC-MICH loops are engaged and now MICH_DARK_ALIGN works:

  1. PREP_MICH_DARK_ALIGN will set the sensing matrix, but keep the input switch off for ASC-MICH_*
  2. MICH_DARK_ALIGN will switch on the input and ramp in the gain
  3. Then MICH_DARK_ALIGN will switch on a real integrator and engage the BS M1 stage
Displaying report 1-1 of 1.