The filter cavity IR detuning is monitored from 2021-07-08 11:40 to 2021-07-09 11:40. (The time used in DGS is JST minus 9 hours) The minute trend data is saved in standalone desktop/detuning/20210709.

The screenshot of this monitor is attached.

Although there are many peaks in the detuning data, only 4 of them come from the unlock of filter cavity. Others are due to the suspended mirror sudden position changes but pointing loop has limited bandwidth.

We see change of detuning even when fc length is controlled. 

The FC length control change may also come from the main laser frequency change, which is due to we use laser frequency as a reference at low frequency. Especially, we don't have a reference cavity as used in gravitational wave detectors, such as KAGRA.