It was pointed out to me by Terrence, that the quantity that I was using from the geophones was the velocity rather than the displacement. Therefore, I turned the integrator on and measured the transfer functions again.

The coincidence between the measurement made with the geophones and LVDTs is good, so I guess the inter calibration was done already. However, there are small bumps around 1 Hz, that may suggest that the calibration filters of the geophones are inaccurate.

I measured transfer functions from IP actuation in yaw to the individual geophone outputs.  Besides measuring the usual geophone output in units of displacement, I also measured  the raw output in number of  counts. The aim is to check each of the calibration filters and identify the reason of the yaw transfer function having a bump at 1 Hz (see Fig. 3).

The file is at /kagra/Dropbox/Subsystems/VIS/vis_commissioning/sr2/inter_calibration/

I calculated a new preliminary calibration filter for H1 geophone. It corrects a bump that appeared at 1 Hz in the transfer function when using the previous filter. This bump also appears in the TFs for H2 and H3, which also need correction. See screenshot.

A more detailed description will follow.

After calculating new calibration transfer functions for the geophones (klog yet to be written), I went back to checking the inter-calibration between the geophones and LVDTs. The plot shows the transfer function for IP-L, measured with the LVDTs and the geophones. The coincidence is already very good. Still, I'll take a quantitative look at the data.

After getting rid, to a good extent, of the bumps in measured IP transfer functions, I calculated inter-calibration factors between geophones and LVDTs in L, T and Y.

In klog entry 20778, the ratio ( IPL-lvdt / IPL-geo ) is shown in dB, which is not a suitable scale. For this analysis the appropriate scale is linear.  What I did is the following:

1. I measured the usual IP transfer function in L, T and Y, using the LVDTs and the geophones.
2. Using the cost function written in klog 20410 for SRM, I calculated the inter-calibration factor a, which should multiply the geophone transfer function. 

The results are the following and are also shown in the plots:

• Longitudinal: 1.02922
• Transverse: 1.03941
• Yaw: 0.97688

These values still have to be written in the filter banks.

I added the inter-calibration factors, reported in klog 20812, to filters banks SR2_IP_ACCBLEND_{ACCL,ACCT,ACCY}, under the names intercal_{LVDTL,LVDTT,LVDTY}. I turned them on and then I updated the SDF.