Yutaro, Kiwamu,
We updated the noise budget code (4834) to include the optical lever sensing noises for the PR2 and BS. See the attached for the latest plots.
Associated measurements:
The coupling coefficients were measured by injecting a line at 18.375 Hz for each of (BS|PR2)_TM_DAMP_(P|Y)_EXC at a time and we took the magnitude value of the transfer coefficient at the frequency. Here is a summary of the measurement.
| coupling coefficient (transfer coefficient) @18 Hz | coupling coeff. translated to 1 Hz (assuming 1/f2) | excitation amp. | |
| BS pitch | 1.1e-17 strain/cnts | 1.1e-11 m/cnts | 1000 cnts |
| BS yaw | 9.2e-17 strain/cnts | 9.3e-11 m/cnts | 100 cnts |
| PR2 pitch | 3.6e-17 strain/cnts | 3.6e-11 m/cnts | 1000 cnts |
| PR2 yaw | 5e-18 strain/cnts (coherence was as low as 0.5) | 5e-12 m/cnts | 1000 cnts |
In order to implement the measured values, we translated them to the coefficients at 1 Hz for the 1/f2 coupling model. All the digital counts listed above are referred to those measured at (BS|PR2)_TM_DAMP_(P|Y)_OUT. The biggest contribution comes from the one from the BS yaw loop as seen in the second attachment. Assuming some kind of bilinear coupling, we believe that the increased RMS in the PR2 angular motion (4905) made the BS coupling worse. Also, the angular noise contribution in the noise budget plot is somewhat lower to explain the current noise, but this may be explained by the bilinear coupling mechanism. Perhaps.
