Artem, Sheila
We changed the bias on ETMX while adjusting the drivealign gain to compensate, similar to what was done in 73913. We might be seeing a small difference in the DARM spectrum between 30-40 Hz.
We scaled the drivealign gain with the bias, but also adjusted the gain at each step to keep the DARM OLG the same.
| voltage | references | quiet time start (UTC March 27th) | quite time end | DA gain | DA gain scaling (in addition to bias voltage scaling) | OLG change % |
| 140 | 0-6 | 184.65 | NA | NA | ||
| 190V | 8-13 | 15:41:40 | 15:58:51 | 126.895 | 0.93 | 0.5 |
| 240V | 14-20 | 16:02:54 | 16:19:05 | 96.167 | 0.89 | 1 |
| 289.6V | 21 -27 | 16:27 * | 16:43:30 | 77.22 | 0.865 | 1.2 |
| 415 | 28-34 | 16:49 | 16:59:30 | 51.628 | 0.829 | 1.8 |
People walking in LVEA and plugging in CM board seemed to cause some glitches. no evidence of people walking on seismometers from 16:37 on.
The first attachment shows the DARM OLG after gain adjustments. The second attachment shows long spectra at the various biases we checked. We also looked at coherence with the susrack magnetometer (Y) and ESD power monitor 18 V, and saw no coherences there.
The third attachment shows a comparison of the spectrum with 190V bias and 415V, making it easier to see that there might be a difference in noise. A next step would be to do some repeated steps between these bias settings to see if the difference is repeatable, and doing a broadband PCAL to DARM injection to check that the calibration is as consistent as we think it is between these settings.
Attached whitened DARM and my ESD noise model spectrograms for different bias levels. Not sure it shows something, in particular for 240V bias there were people walking so there are some glitches (I thought last 6 minutes were quiet - from seismic - but apparently they were not..). 415V bias spectrogram also has some glitches..
