Summary:

Last night's 8.2 in Fiji (at 0:49:00 UTC on August 19th 2018) is one of the larger EQ's we've had since the Montana EQ on July 6th 2017 6:35 UTC, on first glance it seems that the changes we made to protect our suspensions better after the Montana EQ were successful in reducing the amount of swinging that our quads did during this EQ. We will also want to make some charge measurements to make sure we didn't have any jumps in charge from hitting stops. 

Details:

Here is a comparison of ground velocity BLRMs: 

After the Montana EQ we saw that our suspensions didn't return to the same positions for the same applied torque, and we had problems with charge on the optics. During the Montana EQ all of our ISI WD's tripped so that ISIs weren't damped, and all 4 quad suspensions also had their damping turned off by watchdogs.  Since that time we have made several changes to the watchdogs to better protect our suspensions:

• The suspension guardians will continue to use top mass damping if lower stages trip now, but didn't during the Montana EQ (399392).
• Before the Montana EQ the suspension WD trip levels were set inconsistently, from 13000-80000.  Now they are all set to 80000.
• Increased damping time for ISI watchdogs as described in T1700481

In last night's EQ none of the quad suspensions tripped, while all the suspensions tripped and turned off top mass damping last July.   Looking at top mass pitch osem trends from last night, the peak to peak excursions were about a factor of 10 smaller than last July (300-600urad pp compared to 10mrad pp last July).  See the first attachment.  

For all the quad chambers, the ST1 trip was on the actuators and the stage 2 the first trip was on the CPSs.  Looking in more detail at ETMX (which seems similar to the others) The both ST1+ST2 watchdogs tripped within a second and did stay in state 2 (damping on, not checking for saturations) for 60 seconds before proceeded to state 3 as expected and described in T1700481.  The 60 second hold time was based on the Montana EQ (38919), and in this case it seems like 60 seconds was an adequate amount of time for the largest of the disturbances from the EQ to pass by.   Once both ST1+ ST2 watchdogs enter state3 where they begin to check for saturations again, the GS13s were still saturating and caused ST2 to go to state 4, full shutdown after about 7 seconds.  The shutdown of ST2 caused a kick to ST1, which saturated the L4Cs, and this caused the ST1 watchdogs to go to full shut down 2 seconds after ST2.  

We should also note that Stefan and T Vo pushed the VERY LARGE EQ button.  This button has been giving error messages lately, I don't know if it is really working. 

PS, I think I noticed a typo on the WD screen while looking at this, for ST1 where I think the monitor should be looking at  H1:ISI-ETMX_ST1_WD_L4C_SAT_COUNT it is looking at H1:ISI-ETMX_ST1_WD_MON_FIRSTTRIG