With Hirata-san.
I tried to measure a transfer function using the geophones (Fig. 1), but they don't seem to be working properly. The amplitudes of their outputs are too low (Fig. 2) compared, for example, with SRM ones (Fig. 3). Hirata-san checked that the cables were connected to the chamber.
Tomorrow we will replace the geophone distributor.
The spare geophone distributor is in the IYV room (2F).
With Takahashi-san and Hirata-san.
Summary: after investigation, we identified the problem was in geophone #2. Next week, need to check the in-vacuum connections first and, depending on the result, change the geophone preamplifier.
We began by changing the distributor, and then we changed the power cable and the socket it's connected to in the power strip. In these cases, the switch break-out at the back of the distributor would turn itself off. Finally, we disconnected the geophones cables one by one, and identified the problem was geophone #2.
Then we measured the resistance values between the pins powering the geophones, which are 4, 5 and 9 for VP, VN, PWR_P respectively (per JGW-D1503600-v16 page 8). For geophone #2, we found the resistance between pins 4 and 5 to be about 10 Ohm, whereas for the other two it was open circuit or of the order of many MOhms.
Next week we will investigate the in-vacuum cable first and then consider whether we need to change the preamplifier.
With Takahashi-san.
Summary: we changed the geophone together with the pod; the readout is as expected now.
We opened the vacuum chamber and checked the resistance between pins 4 and 5 at the cable directly connected to the geophone pod. The resistance was about 7.5 Ohm, indicating that the problem was not at the extension cable. Next we checked the resistance measuring directly at the electrical feedthrough at the pod. The resistance was low again, which implied that the problem was inside the pod.
Therefore, we changed the geophone together with the pod. The amplitude of the readout is now as expected.
The plot shows the calibration result for the new H2 geophone (#37) compared with the seismometer (X) on the ground. The value of the resonant frequency and Q came from the inspection data sheet. The efficiency was selected so as to be consistent with the seismometer.
I checked the broken geophone opening the pod. The cabling inside the pod has no problem. I found a short on the pre-amp board.
I investigated the broken pre-amplifier board for the geophone. The shorted part was a tantalum capacitor of 100uF (in the photo and circuit diagram) on the positive power line.
