Sheila, Thomas Vo, Hang Yu,
There was a magnitude 8 EQ off the coast of Mexico tonight. We went into LARGE_EQ_NOBRSXY on the seismic configuration node after the first waves hit, but all the ISIs tripped anyway. We were able to keep most of the quads damped most of the time, although ITMY was tripped for a little bit. LLO called and we set the WD thresholds up to allow us to bring the ISIs to damped after talking with them. This helped to stop the optics from swinging so much. A few minutes after we got everything damped, a few more ISIs tripped.
The attached screenshot shows a comparison of the ETMX STS during this EQ to the Montana one July 5th. The STS was saturated tonight.
We quickly checked that all four quads moved when we applied offsets to the top mass. Although ITMY only moved 2 urad for a 10 urad offset, I think this could be a calibration issue with the alignment slider. We left all ISIs‌ and suspensions damped for the night, with all HPIs isolated.
It probably would have been better to have switched the GS13s and T240s to low gain, rather than bypass the watchdogs (by setting the saturation threshold above the dac range). It seems like a particularly bad idea to bypass the HEPI actuators. If the HEPI drive is saturating with sensor correction turned off (i.e. SEI CONF is in LARGE_EQ or SC_OFF), it seems like it would be best to just let HEPI trip and try to get the ISI's damped with the sensors in low gain. Remember the senors can be switched from the Commands link on the ISI overview. The switch should be done with the ISI damped or off, switching to low gain while isolated will probably trip the ISI.