VIS (IX)

takafumi.ushiba - 18:47 Monday 13 May 2024 (29475)

ITMX trip due to the glitch on MN V1 photosensor

ITMX went to PAY_TRIPPED state around 11:42 today due to glitches on ITMX.
To investigate the glitch source, I kept ITMX in PAY_FLOAT state but it was again tripped around 11:55 today.
The trigger of the trip is large glitch on MN V1 photosensor (fig1).
Since there was almost no effect on the other sensors, it is very likely that the sensor trouble.

Figure 2 shows the MN V1 photosensor signal from about one month ago.
T cursor shows the time when vacuum pumping was started according to klog29307.

The timing when signals went zero is DGS maintainance, so the first glitch seemed to be occured on May 2nd and somehow the glitch rate was drasticaly increased in this morning.
I also checked the signals on IOP model and confirmed the signal shape in payload model and IOP model is almost same (fig3).
So, it is probably the hardware trouble of ITMX but I haven't confirmed yet if the source is inside the vacuum chamber or not.

Considerable solusions:

I haven't confirmed the trouble happens inside the chamber or outside but I listed up the considerable solusions here in case it is inside the vacuum.
1. Open vacuum chamber and repair.
2. Change sensing matrix not to use MN V1 photosensor for pitch damping control (we could not decouple pitch and vertical but not so probematic because MNV is very stiff and dominant signal should be pitch motion).
3. Use MN OpLev for pitch control not to use MN V1 photosensor for damping controls (This situation is same as ETMY just before the earthquake, so it should work).

Images attached to this report

29475_1715569598_Screenshot from 2024-05-13 11-57-02.png

29475_1715570621_Screenshot from 2024-05-13 12-10-09.png

29475_1715570661_Screenshot from 2024-05-13 12-24-14.png

Comments to this report:

takafumi.ushiba - 8:40 Tuesday 14 May 2024 (29491)

Figure 1 shows the one-day trend of ITMX MN V1 photosensor
glitch rate and amplitude become small now, somhow.
Also, DC value is changed about 15 hours ago but I have no idea why.

Images attached to this comment

29491_1715643463_Screenshot from 2024-05-14 08-36-12.png

takafumi.ushiba - 8:41 Wednesday 15 May 2024 (29509)

I modified the sensing matrix (fig1) not to use MN V1 photosnsor to avoid kickng the suspension during the alignment work.
No oscillation canbe observed at this moment.

Images attached to this comment

29509_1715730098_Screenshot from 2024-05-15 08-41-34.png

takafumi.ushiba - 16:23 Thursday 30 May 2024 (29697)

I performed swapping test of MN V1 photosensors on ITMX.
I swapped MN V1 and V2 cables at feedthrough at IXV.
Then, glitch channel was swapped to MN V2 (fig1), which represents that glitch source is inside the vacuum chamber.

Since IXC is already evacuated, it is difficult to fix the problem without opening the chamber.
However, I think it is not necessary to fix immediately because we can keep ALIGNED state with photosensor damping loop, thanks to the matrix modification reported in klog29509.

Images attached to this comment