Reports until 13:34, Tuesday 04 August 2015
H1 PSL
jason.oberling@LIGO.ORG - posted 13:34, Tuesday 04 August 2015 - last comment - 05:27, Wednesday 05 August 2015(20204)
PMC/ISS TF Measurements

J. Oberling, P. King

Today we measured the OLTF of the ISS inner loop and the PMC.  This was done in response to LLO's recent measurement of the same documented here.  Peter has all the TF data and will post it as a comment to this report.  For the ISS inner loop, the gain was changed from 6dB to 16dB in the last couple of days, so we measured the TF at 6dB and at 16dB of gain to see how the increased gain changed things.  For the PMC we ended up increasing the gain to 22dB (up from 18dB).  This brought the UGF to ~7.5 kHz, closer to what we expect from E1200385.

I also had a chance to turn off the ISS without disturbing anything else and calibrate the 2 PDs discussed in alog 20043, and therefore complete the work in WP 5391.  The new gain values for the these PDs are as follows:

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peter.king@LIGO.ORG - 04:42, Wednesday 05 August 2015 (20244)
Link 

Attached is the measured pre-modecleaner OLTF.  Two values of gain slider were used.  The initial one, 18 dB was where it was set to when we started the measurements.  To increase the UGF we increased the gain to 22 dB.

With the gain slider at 18 dB, the UGF is ~3.56 kHz with a phase margin of 70 deg.  With the gain slider at 22 dB, the UGF is 7.7 kHz with a phase margin of 75 deg.

We could push the gain a bit higher but that comes at the cost of robustness.
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peter.king@LIGO.ORG - 05:27, Wednesday 05 August 2015 (20246)
Link 

Attached is the first loop OLTF.  It should be noted that this measurement was performed whilst Robert and Cheryl were working inside the PSL Enclosure and so the HEPA fans were on (ditto for the PMC measurement).  Plots are for the old value of gain slider and for the current value.  Currently the UGF is about ~65 kHz with a phase margin of ~25 deg.  The measurements are consistent with those taken around the time installation was completed and more recent measurements done by Kiwamu and Sudarshan.

We took a high frequency measurement but unfortunately the results don't seem right.
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