This alog gives a quick status of the seismic systems (HEPIs and ISIs) used for the single arm test (BSC6 and BSC8).
BSC-ISI:
ISI-BSC8 has been running with damping loops and Isolation loops since the end of May with decent isolation performance. https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=2976
ISI-BSC6 commissioning started more recently. An overall amplification of the motion was immediately noticed around 1Hz (QUAD mode). By the time, writing the commissioning scripts and controlling HEPI was the priority and the no time was spent on ISI-BSC6 to fix the “1Hz” issue.
This week, some modifications were made to the complementary filters that are used to build the blend filters. The initial filters were replaced by less aggressive ones (smaller bump around the blend frequency (750mHz, 250mHz) and less roll off on the low pass. I have attached a link to bode plots of the 4 complementary filters currently used.
LHO_ISI_BSC6_BSC8_OAT_Complementary_Filters_2012_07_20.fig
The blend and isolation filters currently implemented on the two ISIs are designed using the following parameters:
- Blend at 750mHz on all degrees of freedom except on stage 1 in the Y direction where a 250mHz Blend is used instead.
- UGF: 15Hz on all DOFs
- Phase margin > 45deg
- Gain margin>20dB
- Gain peaking <2
The isolation filters used on the two ISIs are pretty closed. Spectra were measured on the ISIs in the undamped and the isolated state. The performances are OK for now. Optimization will be done later.
Stage 2 GS13 spectra are presented below. The scrip that is used to measure the spectra in the different configuration is currently being reworked. The tails of the spectra in the two uncontrolled and the controlled configurations should match better.
BSC-ISI – ITMY (BSC8):
- LHO_ISI_BSC8_ASD_m_CART_ST2_GS13_Undamped_vs_Isolated_2012_07_18_162209.fig
BSC-ISI – ITMY (BSC6):
- LHO_ISI_BSC6_ASD_m_CART_ST2_GS13_Undamped_vs_Isolated_2012_07_19_151614.fig
The HEPI was commissioned fairly quickly to lock stage 0 of the ISI to the ground. Recently, the TMS-QUAD alignment offsets were offloaded on HEPI-BSC6 (250*10^-6 rad in the +RZ direction).
The HEPI are tuned using the following parameters:
- Blend at 800mHz
- UGF: 10Hz
- Phase margin > 45deg
- Gain margin>20dB
- Gain peaking <2
- Pringle modes are controlled (AC)
- No sensor corrections but the STS-2 are in place, connected, leveled and working.
I have attached spectra of the super sensor signals when the HEPI is uncontrolled and controlled.
HEPI – ITMY (BSC8):
- LHO_HPI_BSC8_ASD_m_Super_Sensors_H_Undamped_vs_Isolated_2012_06_20_170452.fig
- LHO_HPI_BSC8_ASD_m_Super_Sensors_V_Undamped_vs_Isolated_2012_06_20_170452.fig
HEPI – ETMY (BSC6):
- LHO_HPI_BSC6_ASD_m_Super_Sensors_H_Undamped_vs_Isolated_2012_07_02_155724.fig
- LHO_HPI_BSC6_ASD_m_Super_Sensors_V_Undamped_vs_Isolated_2012_07_02_155724.fig
Calibration check:
Some measurements were made to check the calibrationand the basis change matrices used on HEPIs and ISIs. Spectra All sensors when no damping on the ISI. Some glitches still need to be fixed (factor of two on HEPI). Couple of glitches still needs to be fixed.
- LHO_ISI_BSC8_ASD_HEPI_BSC_ISI_Undamped_2012_07_18_020214.fig
- LHO_ISI_BSC6_ASD_HEPI_BSC_ISI_Undamped_2012_07_18_020214.fig
During the “1Hz chase” on ISI-BSC6, the reconstruction scripts that are used to build the hundred of filters, required to control the ISI, from a unique set of measurements (ISI undamped) were fully verified for the first time. Excellent agreements between measurements and simulations were seen even on the cross couplings between stages. These scripts allow a huge gain of time during commissioning.
A nice step forward was done during the last few weeks.