Jim, Sebastien

We did a high resolution measurement on HAM3-ISI (bandwidth of 1mHz), with and without the sensor correction. At this point, we can say that:

- the feautre appears only when the sensor correction is ON

- it appears on all DOFs except RZ

- it's a very high Q 0.66Hz feature. This last point convinces us that it must be an electronic issue somehow.

I attached the plots and committed the DTT sessions of those measurements in the svn:

/ligo/svncommon/SeiSVN/seismic/HAM-ISI/H1/HAM3/Misc/HAM3_debug

/ligo/svncommon/SeiSVN/seismic/HAM-ISI/H1/HAM3/Misc/HAM3_debug-with_SC

We also checked that this feature was not due to a beating between the HEPI IPSs. We turned the position loops of HEPI HAM3 off. We even powered off the pier electronic boxes we no change: the peak is still here when the sensor correction is ON.

The investigation continues...