peter.king@LIGO.ORG - posted 08:31, Thursday 21 February 2019 - last comment - 11:38, Thursday 21 February 2019(47049)
More FSS measurements
Following on from yesterday's measurements.
I checked the alignment on the RF photodiode (31 mV locked, 135-140 mV unlocked). Took a transfer
function measurement before and after adjusting the alignment (C28F15.tif, C28F15.txt for data). No
appreciable difference (32 mV locked, ~146 mV unlocked) in the transfer function.
For reference I took the same measurement with the common gain slider at 20 dB and the fast gain
slider at 9 dB, ie its old settings (see C20F9.tif, C20F9.txt for data) and sure enough the UGF dropped.
The mixer monitor (TP3) was plotted with the FSS locked and unlocked but with light incident on the
RF photodiode (ULOCKED.tif, ULOCKED.txt for data).
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Comments related to this report
Check the power (light) on the photodiode at the next opportunity.
The FSS RFPD DC readback is probably broken. The filter module implements a gain of -0.05, this isn't the conversion factor from counts to volts; it should be 3.05E-4 (as can be seen in FSS TPD DC). Furthermore, when the PSL was off, the readback value was 0.2; this only corresponds to -4 counts. When locked, the readback hovers around 0.15, i.e., -3 counts.
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