Ed, Sheila

Today we are having useism above 1um/sec, almost 2um/sec in the z direction, and wind speeds mostly between 15-35 mph with a few gusts up to 40 mph.

This morning Ed collected many examples of ALS locklosses, and together we looked at several of them.  

We found at least 3 different mechanisms-

X arm VCO runs out of range ( H1:ALS-X_REFL_CTRL_OUT_DQ, which is calibrated in um, reaches around 6 um)  An example is shown in the first attached screenshot. We found 4 example of this 19:05:22 UTC, 19:07:25, 19:44:09 and 19:48:12) 

DIFF tried to lock when the PLL is moving through its linear range rather quickly, ETMX L3 saturates before the offloading to L1 can relieve it. (2nd screenshot, 19:01:12 and 20:30)  

Lockloss while CM board gain is ramping up during COMM locking, large glitches from CM board saturate MC2 M2.  Only one example, 19:45:22

We have done a few things to try to mitigate the situation.  The most important probably was increasing the X arm PDH offloading to the suspension,  H1:LSC-X_ARM_CTRL_UGF from 0.02 to 0.08.  This matches the ugf used for the Y arm, which has not been dropping lock as often as the X arm.  

I also reduced the wait time that the COMM guardian  uses to check if the PLL is locked from 5 seconds to 2, this means less waiting for it to lock. Lastly I changed the step in the ramp of the CM board gain durring the engaging of ALS COMM from 1dB steps to 3dB steps.     

I've reverted the gain stepping back to 1dB since it didn't seem like an improvement after several locking attempts.