daniel.sigg@LIGO.ORG - posted 09:36, Friday 09 November 2018 - last comment - 09:55, Monday 12 November 2018(45157)
Common mode board swapped
Fil Marc Daniel
We modified the spare CM board (s/n S1102622) according to E1800338 and swapped it with the existing one (s/n S1102621). This modification includes low pass filters for the DAQ readbacks, and a frequency change in the first two boost stages to 10Hz/500Hz.
Comments related to this report
daniel.sigg@LIGO.ORG - 11:57, Friday 09 November 2018 (45161)
Looking at one of the higher power runs with a REFL fast gain of +24dB, IMC IN2 gain of -24dB and a REFL IN1 gain of 9dB, we can see that both error and control signal readbacks show again excess noise. The fast/in2 gains may be too high and we should try 16dB instead. Not sure what's up with the error signal readback, maybe too much in-loop gain with the additional boost.
These modifications improve our readbacks. Previous data is in alog 45131.
Fig 1 shows the readbacks of the modified board.
Fig 2 shows the new 10/500Hz analog boost filter. The RMS of the error signal gets reduced by ~400.
Looking at one of the higher power runs with a REFL fast gain of +24dB, IMC IN2 gain of -24dB and a REFL IN1 gain of 9dB, we can see that both error and control signal readbacks show again excess noise. The fast/in2 gains may be too high and we should try 16dB instead. Not sure what's up with the error signal readback, maybe too much in-loop gain with the additional boost.