[Nagano, Iida]

We installed power supply (18 V) monitor in IY0 rack.
To measure it in digital system, the voltage is reduced by 0.27 with registers (for detail please see this document.)
In addition, we use whitening filter reported in here.
Because of the input impedance of the whitening filter, 4.7 kOhm, the voltage was reduced by 0.10 in total.

We are monitoring positive voltage (+18 V - GND) and negative voltage (-18 V - GND) of the power supply pins (Dsub 3pin).
The positive and negative voltages were monitered in K1:PEM-IY0_SENSOR1_OUT_DQ and K1:PEM-IY0_SENSOR2_OUT_DQ, respectively, which are calibrated to voltage (V).
(Sorry for their general names.)

The power spectrum and coherence are shown in the following figure.

As you can see in the spectrum plot, there are some structures around 120 Hz and harmonics of 21 and 23 Hz.
In the coherence, coherence between positive and negative voltages drop higher than 120 Hz structure.

We checked some sensor channels whose power is supplied by IY0 rack if they have coherence with the power supply fluctuation.
We found WAB oplevs (e.g. K1:AOS-WAB_OL_PIT_OUT_DQ) have coherence as shown in the following figure.
However, the seismometer whose power is not supplied by IY0 rack and channels whose power is not supplied by IY0 rack have no coherence with power fluctuation of IY0 rack.