TJ & Hugh--WP 5640

This is a copy of SEI log 893.

I installed the new Guardian code at LHO 24 Nov (LHO aLog 23695) and tested it on a few chambers.  Yesterday, we had a big EQ which tripped most ISI platforms (LHO alog 24007) and we saw that HAM2 & 3 had difficulty isolating--trouble with the GS13 switch.  I'll talk about that separately but that issue led us to investigate more closely this morning (this WP) about the GS13 switching.  We worked on HAM3 and LVEA activity tripped HAM4 ISI allowing us to confirm observations there too.

In SEI log 862 Hugo itemizes the modifications:

[1]The GS13 gains are switched at the following points of the guardian sequence:

   a) Switch GS13s to low gain at the end of the damping process

   b) Switch GS13s to high gain at the end of the isolating process

   c) Switch GS13s to low gain at the beginning of the de-isolating process

2) automate the feedforward path on/off switch:

   d) Turn ON the feedforward switches at the end of the isolation process

   e) Turn OFF the feedforward switches at the beginning of the de-isolating process

And this is just what is done.  However, the process of the way the guardian works or Hugo's particular implementation of this, and my acceptance of Hugo's verbiage above causes difficulties.

1c and 2e should be included immediately after watchdog trip, they do not switch:

If the ISI trips rather than being explicitly deisolated, the FF path is never turned OFF, and, the GS13s are not switched to low gain until after DAMPING step is complete.

1a should be done before doing anything, not at the end of damping.  I'm not sure where to do this but 1a should really only be processed when coming up from a FE restart especially if the above is satisfied but otherwise should be executed as soon as possible.  If things work right, the GS13s being in low gain will be the safe.snap state and will start low.

Problems--1) the FF path is basically never turned off.  It is not turned off in the up process (it should not need to be) and should be turned off as soon as the Watchdog Trips.

2) The GS13s need to move to low gain in the Watchdog trip process, otherwise, the watchdog is trying to be cleared while the GS13s are still in high and are tripping more.  We want to get the platform damping again as soon as possible and the watchdog will successfully untrip sooner with the GS13s in low gain.

My apologies to Hugo and all for not explicitly expressing the need to have the switching done during trip condition although I assumed de-isolation was a consequence of tripping.  It is not.  And also for seeing the  "Switch GS13s to low gain at the end of the damping process"  and not reading that close enough.