Jenne, Camilla
In 71559 Ryan C and Daniel found that there was a DHARD_Y Transient during DHARD_WFS state that was larger since June 29th, coinciding with the time the violins starting to ring up 71404.
Yesterday TJ and Oli increased the DHARD_P and _Y TRAMPs from 5s to 15s in this state 71672 and in the two relocks since then we've only had to stay in OMC_ WHITNIENTING damping violins <15 minutes 71676. The transient is much smaller after this TRAMP increase but still there and a factor 2 larger than pre-June 29th.
The step response of the only filter on at the time (FM6 "newcntrl") is very big when it's turned on, but over in 1sec, attached. Currently FM6 is turned on and then 1 second later the input and gain is turned on, plot attached. Jenne suggests as the step response starts when the input is turned on, we should turn the input on with FM6 and then after 1 second, ramp the gain up. I've added this to ISC_LOCK and loaded. Hope this will remove the transient and then we can reduce the tramp back to 5s.
Daniel pointed out that FM4,7,9 are turned off when FM6 is turned on. These filters all have 5 second ramp times so we are probably getting the transient from these filters being still ramping down as the gain is ramped up. I've accepted these as OFF in the safe.snap sdf see attached. So they should be reverted on sdf revert.
We saw a similar transient in DHARD_P but haven't looked at it yet so we should repeat this process with other filters.
Most of the individual filters in this module have a 2-5s ramp time. For whatever reason, FM4/5/7/9 are all on just before DHARY gets engaged, They then get turned off while FM6 is turned on, a short time before the input to the moduleis turned on. However, there is not enough time for these filters to ramp off, so they are still on during the inital gain ramping.
This transient is not visible in the optics anymore, see attached. I'll put the tramp back to 5s but ISC_LOCK will need to be reloaded when we are out of observe. Opened and closed FRS 28647.
Brina, Genevieve and Lance are going to look for transients from other filters and at other times, Elenna suggested checking DHARD_P.
