lisa.barsotti@LIGO.ORG - posted 18:52, Thursday 17 January 2013 - last comment - 16:49, Friday 18 January 2013(5145)
IMC working, left locked for the night
Giacomo, Paul, Keita, Hugo, Matt, Lisa The IMC is locked and happy. The stability problems were due to the ISI, Hugo put it in a configuration which allowed us to recover a stable lock. We measured the open loop TF of the whole system, it was stable up to 30 kHz UGF. We also measured the cross-over VCO/MC2_M3: it is about 15 Hz (it can be stable as high as 100 Hz). The MC2_M3/M2 cross over is well below 1 Hz. A detailed entry with the measured transfer functions and gain settings will follow. We also centered the WFSs on IOT2 and found that a 90/10 beam splitter was used instead of a 50/50 in front of WFS_A, explaining the factor 10 power difference between the two WFSs. We leave the IMC locked for the night, and we should be able to start checking the WFSs signal path tomorrow.
Paul has implemented a notch filter to push the UGF further up. He has measured the OLTF again and will post the new data in another entry.
The fast/slow path crossover frequency was measured by injecting an excitation signal before the MC2_M3 lock filters (H1:SUS-MC2_M3_LOCK_L_EXCMON) and taking the ratio of the signals immediatly before and after the injection point. With the settings of the relevant parameters specified below, the crossover is between 10 and 20 Hz (15 Hz? the shape of the TF is a bit funny there...). See attached plot.
Fast path gain (H1:IMC-REFL_SERVO_FASTGAIN): -2 dB
MC3 lock filters gain (H1:SUS-MC2_M3_LOCK_L_GAIN): -1000
MC3 lock filters enabled: FM5 (150:4) and FM8 (CLP100)
We used a similar setup to measure the MC3/MC2 crossover frequency, injecting an excitation signal before the MC2_M2 lock filters (H1:SUS-MC2_M2_LOCK_L_EXCMON). With the settings fo the relevant parameters specified below, the TF is well below unity at 1 Hz. See attached plot.
MC2 lock filters gain (H1:SUS-MC2_M2_LOCK_L_GAIN): 0.005
MC2 lock filters enabled: FM3 (0.1:1), FM4 (100:1) FM5 (0.01:0.1) and FM8 (ELP70)