After looking at all the L4C plots, Krishna suggested we look at the IPS thinking that with the loops closed by the HEPI Platform servo which has lots of gain, it should suppress the IPS signal and the L4C coherence we are seeing was from something else...like the fluid moving the piping...  Seem reasonable although really?

However, see attached:  Same times as the L4C coherence I posted Tuesday.  I show HAM5 at the local position sensor (IPS.)   It is very clear the Horizontal IPS have great coherence from 0.5 down to .02 hz when the pressure sensor loop is closed.  The Vertical IPS coherence isn't nearly as strong but certainly present.  The output drive to the HAM5 Actuators is very small both horizontal and vertical.

I attach too the coherences from the End Stations.  The second attachment has ETMX in the left plots and the ETMY in the right plots.  Both pressure servo loops are closed but ETMX pressure signals do seem to be quieter (although not as quiet as I've seen the corner station's back before December) and the ETMX is servoing on the direct output pressure at the Pump Station.  Whereas, at the ETMY, we are servoing on the actual remote pressures at the BSC10 differenced in the epics database.  The signals at ETMY have always been very noisy and so when I switched ETMY to the differential mode, I added serious smoothing to the signals before differencing.

Looking at the the comparison of the ETMs there are distinctions but what causes what them is not clear.  The quieter EndX is evident in the amplitude and dispite the smoothing, the EndY has a much sharper and higher amplitude peak at 150mhz.  Don't ask me what's happening at 3.5hz...

The lower plots at interesting in that unlike at HAM5, there is no coherence with the vertical IPS on either platform but the horizontals are very coherent.  This coherence at ETMX is narrower in band though maybe somewhat more like the band at HAM5...related to the quieter pressure signal at ETMX or due the ETMY servoing on the difference rather than the direct supply pressure or the smoothing...?