Sheila, Rahul

We have been trying to investigate how/why Guardian turns ON/OFF the damping settings for violin modes after lock acquisition. To understand this, first of all we looked at the guardian state (H1:GRD_VIOLIN_DAMPING_STATE_N) on ndscope - right at the beginning of the IFO lock (see figure attached - GRD_Damping.png). During lock loss guardian turns off damping and then moves to IDLE state (during lock). After damping settings state, it clears off the monitor level (to erase the history) and then moves to engage damping (on RF and so an...). Finally it reaches the state called as Damping_on_DC and remains here during the entire stretch of IFO lock.

Next we picked up two modes (ETMX mode 9 and mode 7) as a case study. Usually guardian turns ON the damping for mode 7 and keeps it OFF for mode 9, and we want to know that on what basis guardian makes this decision. In the ndscope we plotted the GAIN and monitor level (rms of excitation) and the guardian state, at the beginning of the lock - see figure attached (ndscope_mode9_mode7.png). In this plot, one can see the time stamp where the guardian clears the monitor level (first vertical broken line) and the point where it turns ON the damping (for mode 7 and keeps it OFF for mode 9 - second vertical broken line). On comparing the monitor levels at this time point (before damping is ON), we can see that mode 9 was at level 2.0  and mode 7 above 3.  Also, the monitor levels for both these modes were either stable or decreasing (and certainly not rising). One can also see that guardian waits for around 700 secs between clear monitor and engage damping. This should give the monitor level enough time to settle down (which is usually excited during lock loss and after).

Next we looked at the python code for violin mode damping and made a few changes. First of all we decreased the DC_noise_floor level to 1.0 (from 3.0) in lscparam file. This should tell the guarding to turn ON the damping during ENGAGE_DAMPING if the the monitor value is greater than 1. Secondly, we made some changes in VIOLIN_DAMPING.py, asking the guardian to look at the absolute value of the GAIN (calc_gain and max_gain) during Damping_on_DC. We also erased the condition (else if) to make the GAIN zero (unless the monitor level is growing) for Damping_on_DC.

The changes made in the python has not been loaded yet as this could lead to losing the ongoing observing mode, which we don't want to. We will wait for an appropriate time during the day to initiate these changes into guardian.