= Geophones calibration=

Assuming that the IP LVDT driving and sensing calibration is correct I used it to intercalibrate the IP geophones.

We follow the same procedure used for the accelerometers on ETMX IP ( see entry 7341 ).

I injected noise in Yaw and measured the ratio between LVDT yaw and each geophone response (converted in diplacement):  (Yaw_LVDT*r)/(GEO)/(w)

Such function (shown on pic1 and pic2) should be flat in the region from 200 mHz to ~2 Hz (where the coherence is 1).

The extrapolated calibration factors are:

As expected, after implementing the calibration the fuction is one in the flat region (pic 3).

=Geophones sensing matrix=

Then I have computed the diagoanlized sensing matrix  by injecting a line at 2 Hz for each d.o.f and measuring the amplitude and phase of the TF between each GEO (converted in displacement) and the diagonalized LVDT sensor.

TF_ji = (GEO_j/(2pi*f0))/LVDT_i        j = 1, 2, 3    i = L, T, Y        f0 = 2 Hz.

This values are reported in a matrix where the columns correspond to  L, T and Y and the lines to the three geophones.

The sensing matrix, is computed as the inverse of such matrix, and it is reported below:

Now the calibration factors and Geo sensing matrix are implemented in the MEDM screen.

As a final check I have to measure the TF injeecting noise from the diagonalized virtual acutators and looking at the diagonalized LVDT and geophones and verify that: TF_LVDT = TF_GEO/w.