I calibrated the AS error signal into the displacement of the YARM cavity in the same way as I did before (elog).

The open loop transfer function is:

The transfer function from ITMX excitation to AS error signal is:

Then I have got the calibration value : 5.08e+11 [counts/m]

The calibrated spectrum in unit of m/rtHz is

REF0: arm displacement
REF1: dark noise + demodulation circuit noise + WT filter noise + ADC noise (PSL shutter on)
REF2: demodulation circuit noise + WT filter noise + ADC noise (PD input of the circuit (at 1Y2) is connected to the 50 Ohm terminator)
(The circuit and WT filter seem to be connected at back side of the rack. Actually there is a connector labelled 'I MON' but it is not related to C1:LSC-ASS55_I_ERR)

Also we changed the AS gain so that ADC noise does not affect:

However, this did not make big change in sensitivity. I guess this means that circuit noise limits the sensitivity at higher frequencies than 400 Hz.
I tried to adjust the AS gain carefully but I could not do that because of the earthquake. Further investigation is needed.