[JeffK, Jenne]

Jeff pointed out that the PI damping gain (if no changes were made to guardian) would now be 4x higher than they were throughout O4, due to the work done today.  See alog 88285 for the actual work by Jeff and Oli.  To account for this, the SUS_PI guardian now has a 1/4 in the gain setting line.

Details for remembering later:

In June 2020, we upgraded from 18-bit to 20-bit DACs, and as Jeff notes in alog 88285, we didn't have a place to nicely account for the effective gain change digitally in the PI damping path.  Effectively, we should have put in a filter with gain of 4x to account for the number of bits changed.  Since we didn't, we have been actuating PIs (assuming same digital gains) 4x less during O4 than we had been in O3.  Not a huge deal, since we had PI dampers and PI damping settings that were effective. 

With today's work, Jeff and Oli have put in a digital place to correctly account for the gain change with the new 28-bit DACs.  To keep the 'accounting' neat and tidy, they've put in the whole correction gain from 18-bit to 28-bit (not just 20-bit to 28-bit).  This means that they've put in the forgotten-during-O4 gain of 4x, so if things were left alone in the SUS_PI guardian, we'd be sending 4x actuation strength to the ETMs.  In O4, the 4 PI modes we've been damping have only gone to the ETMs.  Since we don't have automatic gain adjustment in the PI damping guardian, I've divided the gain setting line by 4 in SUS_PI, so that we'll end up with the same actuation strength now as we did have in O4.