J. Kissel

More details to come later, but in order to continue the investigation of a potential ~1% level systematic error between H1 PCALX and H1 PCALY (see IIET Ticket 13577), I spent today's commissioning time parasitically tuning the amplitude and phase of a "cancelling" line, in which the same amplitude of PCALX and PCALY line is injected at slightly different phase, so as to leak a little bit of DARM motion into DELTAL_EXTERNAL at exactly 1153.1 Hz.

As a result of the tuning choices, the residual amount of DARM at that frequency I've left in DELTAL External is a factor of 4 above the noise floor in an ASD with frequency resolution of 0.02 Hz. This yields residual coherence between each PCAL and DELTAL EXTERNAL of 0.9, which should be plenty enough SNR to track ~1% or better level changes and discrepancies between these two PCALs.
Note, also, that these extra lines do not stress the limits of actuation range for either PCAL -- I was running these lines while all normal calibration lines and CW injections were running, including the PCALX high frequency roaming line, which happens to currently be at its highest frequency and loudest requested drive in the long duration sweep.

The first observation segment with this line installed is Sep 11 2019 23:51:24 UTC, and the intent is to leave it in indefinitely or at least for the foreseeable future.

The settings corresponding to this additional line have been accepted in to the SDF system.

The lines have been installed in the 9th oscillator, H1:CAL-PCAL[X,Y]_PCALOSC9_OSC, with individual amplitudes installed in such a way that the excitation results in equal *displacement* (to within 0.1%) as reported by the calibrated receiver photodiode signals, aka the RX PDs. The excitations requested of the DAC are not calibrated, and thus the funny differing amplitudes *requested* of 5000 ct on PCALX and 3619 ct on PCALY. The -15 deg phase installed on PCALY was the result of the above mentioned tuning.