J. Kissel, K. Izumi

After using the (new) in-vac ISS QPD on the "second-loop" ISS array a bit this past week, we've made two changes to the H1:PSL-ISS_SECONDLOOP_QPD_SUM filter bank, which comes with the generic CDS Simulink library part
/opt/rtcds/userapps/release/isc/common/models/QPD.mdl 
used in the h1psliss front-end model to represent it:
(1) Installed a low-pass filter ( zpk([],[0.01;0.1],1,"n") )
(2) Changed the gain to -1, to invert the SUM which comes in negative.
(1) makes determining whether the beam is on the QPD much easier in low-to-no light scenarios, and (2) is removing the analog inversion that seems common to aLIGO QPDs. A negative sum is less than the lower limit (1e-6) of the saturation block that's a part of the normalization scheme -- which means the PIT and YAW signals were always getting divided by 1e-6 creating ridiculously large numbers cut-off by the MEDM display.  

I've modified and committed the 
/opt/rtcds/userapps/release/psl/h1/burtfiles/iss/safe.snap
such that these settings stick after a reboot.

Things that still need to be fixed:
The link to the FULL version of the SUM filter is broken. I think it's related to the generic macro variables passed down from screen to screen, but as far as I can tell the screen it's calling exists...