[Hirose, Yamamoto, Ushiba]

Abstract:

We found the ETMY dewhitening filters are mismatched between DGS filter banks and analog coil driver.
We swapped the DGS filters at TM_COILOUTF, so the filter mismatches are solved now.

Detail:

Hirose-san found that ETMY OpLev signals are about 10 times larger than the other Type-A suspensions when exciting from CHARD_P_SM_EXC at 13.125 Hz (fig1).
After several investigation, we found that ETMY TM high power coil driver was modified one and dewhitening filter frewuencies are different in each stage (JGW-S1707384).

Since we modified the real-time model to compensate 3rd analog filter with FM1 of COILOUTF filter bank (klog31874), filter shape mismatch happened.
So, we swapped the FM1 and FM3, and FM6 nd FM8 to adjust the filter shape on DGS to the analog filter.
Figure 2 shows the same measurement after changing the filters, which seems fine.

Also, we realized that current DAC noise when engaging one dewhitening filters are 1/10 not above 10Hz but above 100Hz because 3rd stage of dewhitening filter in ETMY HPCD is p10, z100.
So, to reduce the DAC noise, it is necessary to swap the ETMY TM HPCD to nominal one.