J. Kissel

I've taken weekly charge measurements. The results continue to show the expected trends -- ETMX has about +15 [V] accumulated effective bias voltage (which is low enough to be inconsequential), and ETMY has accumulated over -35 [V] of effective bias voltage, so we'd like to mitigate it.

As I have for the past two weeks, I recommend
Just before we vent on May 8th, during last minute preparations as we bring the IFO down, let's 
    - Turn OFF the ETMX ESD bias completely, and leave it OFF for the duration of vent and post-vent pump-down
      Enter the following in the command line:
        ]$ caput H1:SUS-ETMX_L3_LOCK_INBIAS 0                # Set Requested Bias to 0
        ]$ cdsutils switch H1:SUS-ETMX_L3_BIAS_OUTPUT OFF    # Make sure the output of the Bias Bank is OFF
        ]$ caput H1:SUS-ETMX_L3_ESDOUTF_LIN_BYPASS_SW 1      # Turn off any linearization, which turns off any requested bias on the Control Electrodes
        ]$ caput H1:SUS-ETMX_BIO_L3_RESET 1                  # Turn off the HIGH VOLTAGE driver entirely
                
    - Leave the ETMY bias ON at +9.5 [V] at the DAC (or +380 [V] at the ESD electrode), with the opposite sign as in observation for the duration of the vent and post-vent pump-down
      Enter the following the command line:
        ]$ caput H1:SUS-ETMY_L3_LOCK_INBIAS +9.5                    # Set Requested Bias to +9.5
        ]$ cdsutils switch H1:SUS-ETMY_L3_ESDOUTF_UL OFFSET OFF     # Turn off all request bias on the Control Electrodes
        ]$ cdsutils switch H1:SUS-ETMY_L3_ESDOUTF_LL OFFSET OFF     #   |
        ]$ cdsutils switch H1:SUS-ETMY_L3_ESDOUTF_UR OFFSET OFF     #   |
        ]$ cdsutils switch H1:SUS-ETMY_L3_ESDOUTF_LR OFFSET OFF     #   V

As last week's full actuator transfer functions confirm (see LHO aLOG 35867), the actuation strength as measured by calibration lines is dead-on. Thus the relative actuation strength from when we last updated the calibration model is measured to be 4% stronger. That's starting to push our comfort zone (even though we correct for it) so hopefully we can accumulate even charge of the opposite sign on ETMY during this vent that we can reset the actuation strength reference when at 0 [V] effective bias voltage.