Keita Kawabe, Sheila Dwyer

We investigated the lockloss that Ed and Camilla just had at LOWNOISE_ASC (1257191567), and we believe that the ISS second loop attempted to close while the PSL rotation stage was still moving. We have made some changes to prevent this, although we can't say with certainty that this was the cause of the lockloss, because this seems to have stopped about 4 seconds before the lockloss. The attached screenshot shows that the power input to the IMC was having large gltiches a few seconds before the lockloss, which show up in downstream powers and CARM channels.  

One of the recent changes to the guardian was moving the ISS second loop engagement from happening after DRMI locks to happening at the end of the power increase.  The other guardian change that might be a cause is that TJ recently changed the LASER POWER guardian to fine adjust the input power to get it closer to the requested power, so our input power will be more consistent from lock to lock.  The ISC_LOCK gaurdian was not checking that the LASER_POWER guardian was arrived and done before moving on to the next guardian state.  You can see in the attached screenshot that ISC_LOCK moves from 507 (Maximum power) to 508 (low noise ASC) while the laser power guardian was still changing the power.  

We have made two changes, moving the ISS engagement back to DRMI, and adding a check that the LASER POWER guardian has arrived before we return true from MAXIMUM power.  We still are not sure that we understand the behavoir of the rotation stage.