Hey Miyamoto-kun,

Thanks for reporting this. I want to make sure a couple of poitns:

• What do you exactly mean by "unstable"? Are you referring to the period in which the pitch motion was large?
• Do you have any idea what frequency components dominated the pitch motion during the unstable period?

Thank you for your comment.

First :

Yes. Unstable mean is mainly from large pit motion period.

However I think this unstable was occurred from first pit jump ( around 2018-07-01 06:00:00).

Second :

This is first pitch mode.

I upload the transfer function from TM pit to TM pit.

This frequency is ~0.78Hz.

And we can see this frequency harmonic.

Hey Miyamoto-kun,

Thank you for clarifying the points that I raised. Though I am still wondering why you thought some part of the suspension is touching other mechanical structures.

Here is what it seems to me. According to the spectrum for pitch which showed the higher harmonics due to the optical lever nonlinearity, it seemingly indicates a high Q oscillation, meaning that the payload itself may be fine and free from undesired mechanical contacts with some other structures around. After all, I am guessing that the period with the large pitch motion was triggered by a large kick from something, and the damped oscillation lasted for hours. Or, do you think that the kick happened not only once but also multiple times during the period, leading to psuedo-continuous excitation of the pitch mode?

I’m sorry I didn’t make it clear enough.

• When I slapped the large flange of cryostat, the pitch and yaw signal of TM-oplev was excited.
• When I used the picomotore due to adjustment of yaw angle of test mass, H1, H2 and H3 of BF-LVDT DC signal was changed by picomotore. Usually, BF-LVDT position doesn’t change.

For those reasons, I thought that the suspension is touching.