[Kamiizumi, Tomura, YamaT]
 

Abstract

This is series work of klog#24726 (IX), klog#24725 (IY) and klog#24916 (BS).
Some peaks can be seen on AI output as same situation as other suspensions.
If it's possible, one more de-whitening filter stage should be engaged for MNH to reduce DAC noise.

A coil driver chassis for TM is modified one (S1707384).
Because of this modification the 3rd stage doesn't contribute to reduce peaks in DAC noise so much.
If we will replace nominal one, we need to re-measure noise at the output port of the coil driver.
 

Details

The detail of the measurement setup is same as one in ITMY (See also klog#24725)

We can see the series of ~26-27Hz peaks on DAC noise ("AI out" in attachments) as same as other suspensions.
These peaks can be removed on the output of coil driver ("COIL out" in attachment) thanks to the de-whitening filters
on IMV (Fig.1-3), IMH (Fig.4-6), and MNV (Fig.7-9).
In OBSERVATION state, 3, 3, and 2 stages of de-whitening filters are engaged for IMH, IMV, and MNV, respectively.

On the other hand, these peaks remain at coil driver output of MNH (Fig.10-12).
Only one stage of de-whitening filter is now engaged for MNH.
So if DAC range is enough for outputs of the local control, ASC and/or something,
it's better to engage one more de-whitening filter for MNH in the OBSERVATION state.

For TM coils, we measured the coil out noise in all situations of de-whitening filters (see Fig.13-16).
Except H1 coil, two or three stages of de-whitening filters are enough for removing series of 26-27Hz peaks.
But these peaks slightly remain on H1 output even when three stages of de-whitening filters.

At this time, I noticed that coil driver chassis for TM was still used
as a special one that zero/pole frequency is modified for O3GK (S1707384).
The second and the third stages of zeros/poles were changed
from 1Hz/10Hz to 1.5Hz/30Hz and 10Hz/100Hz, respectively on this de-whitening filter board
(see also Shimode-san's report http://gwclio.icrr.u-tokyo.ac.jp/lcgtsubgroup/electronics/2020/03/high-power-coil-driver-board.html).

From the view point of the DAC noise suppression below 30Hz, effect of the 3rd stage of the de-whitening filter is small.
So 26-27Hz peaks may be able to be removed with three stages of de-whitening filters of a normal high power coil driver.
Though modified coil driver was used also for ETMX during O3GK, it was already replaced as a normal one in klog#22248.
If we will replace as a normal one also for ETMY, we will re-measure noise at the output port of the coil driver again.