kiwamu.izumi@LIGO.ORG - posted 07:15, Friday 21 June 2013 - last comment - 10:57, Friday 21 June 2013(6835)
HIFO activity
[Alexa, Chris, Matt, Kiwamu]
Currently our focus is on two main tasks : refinement of Alexa's control model and the CARM control with the PFD (Phase Frequency Discriminator).
Yesterday we did the following items :
- Transfer function measurement at EY for the PLL and PDH loop
- Increased the input gain of the PDH common mode board by 4 dB to push the UGF higher. Now the UGF is -14 dB.
-
Measured the readout gain of the PFD at the floor.
- A coarse measurement gave ~ 40 deg / V. This sounds reasonable as the number written in the schematic 36 deg / V.
-
Unable to find the beatnote at the corner station
- This was probably due to the alignment of the arm cavity as we had touched them to quiet them for the transfer function measurement. TISCThis changed the alignment of the arm transmitted ligjt at the recombine BS at ISCT1.
- We decided to bring them back to the nominal alignment
-
Realigned ETMY and ITMY based on the oplev and L2 OSEMs respectively (as the ITMY oplev doesn't look trustable).
- We didn't get a chance to check if this alignment recovered the beatnote signal
As a result the UGF of the end PDH loop became 9.7 kHz with a phase margin of 50 deg. Probably we could go higher but we can't go higher than 17 kHz where the phase margin turns in zero.
[Kiwamu, Alexa, Matt]
Attached are the transfer functions Kiwamu refered to. The attachment are in the following order:
1) Current picture of the ALS model used for comparison of the transfer functions taken
2) Image of measure transfer function of End Y PLL Loop
3) Transfer function of End Y PLL Loop from ALS model
4) Image of measured transfer function of End Y PDH Loop
5) Transfer function of End Y PDH Loop from ALS model