Patrick Godwin, Sheila Dwyer

We looked into why the POP45 whitening gain had to be reduced compared to O2 (44420) ; we are now engaging MICH filters which give us less gain at low frequencies compared to O2, and our resulting residual RMS is 4 times higher than it was.   We saw that REFL45 also is saturating it's ADC using the lockloss code addition that Patrick recently wrote to check for ADC saturations. 

Patrick found times in the past to compare the MICH error signal (see first attachment).  During O2 the noise below 3 Hz is much lower, the higher noise now is present in several states, including locked on 3F and before the ASC is engaged.  

The next two attachments show open loop measurements taken during O2 (see the blue trace) and recently.  The UGF used to be a little higher, 9 Hz, and we used to have less phase. 

Patrick and I found that the MICH filter states are different: MICH1 we are no longer using the boost in MICH2 FM3, there is a cut off filter engaged in FM2 that was not used in O2 which eats some phase.  In addition there was a boost in MICH1 FM1 which was engaged in O2 but is not engaged now.  The last screenshot shows a comparison.  We haven't gone back in the filter archive to check that the filters aren't changed since O2.  

We should try to restore this MICH configuration soon (before we try any more FF tuning).  We can't try it now because of seismic computer problems.