I measured the spectra of MN LEN OpLev for decoupling L2Y coupling of MN OpLevs and found that SEG1 has a strange behaviour.
Figure 1 shows the spectra of each segment and TF (ratio) of SEG1 and SEG2.
As you can see, SEG1 spectrum seems to have 1 Hz pole and 10 Hz zero.
So, we need to check the whitening filter setting of IY MN LEN OpLev for decoupling.
[kTanaka, Ushiba]
We checked the situation at IYV and found that the switch #5 of config board for SEG1 was turned off.
So, we engaged it.