peter.king@LIGO.ORG - posted 14:30, Friday 22 April 2016 - last comment - 18:07, Friday 22 April 2016(26735)
Power stabilisation work
This morning I measured the AOM drive voltage as a function of "offset slider %", and also the amount
of diffracted light both with and without the digital support loop. All measurements were taken with
the HEPA fans running.
With no diffracted light, the maximum output voltage on PDA was (-9.6,-9.3) V and on PDB was
(-9.65,-9.4) V. No saturations were observed with the incident power at this level.
Attached are the spectra and transfer function measured. The relative power noise is about a
factor of 10 higher than it should be. In the spectrum is a peak at ~1 kHz, the source of which
is unknown, but is probably related to the problems mentioned by Keita. Pushing the gain higher
seems to increase the noise beyond 10 kHz. The noise at frequencies below 100 Hz is significantly
higher than with the low power mode.
At low frequencies the transfer function is not as clean as the measured result in the low power
mode. I am not sure but this might be related to the linearisation of the AOM drive.
Images attached to this report
Comments related to this report
Attached are the plots for the AOM drive voltage and diffracted power as a function of
the offset slider.
With the current settings with the offset slider at 6%, we are diffracting ~4.5 W.
The plotted and reported diffraction percentage on the MEDM screen needs to be recalibrated.
Images attached to this comment
The attached trend shows that while Peter was working this morning, analog PD outputs that are used for ISS (i.e. "filt" outputs that are monitored by PSL-ISS_PDA_OUT and PDB) were railing all the time.
Analog "DC" outputs might have been OK but they're not used for ISS.
There was about 3 minutes window where the PDs are less severely railing. Almost (but not quite) in the same window, NPRO noise eater monitor was smaller than usual. But during O1 NEMON was always about 28. I don't know what this means.
Images attached to this comment
