• I tuned the ETMX TM actuator balances.
• Final values of TM_COILOUTF_Hx_GAIN (see also the attached medm display)
  • H1: -0.4195
  • H2: -0.5
  • H3: +0.5
  • H4: -0.372

Result of the balance performance

• TM L-excitation of 60,000 cnts (~30,000 cnts at each DAC output) at 5 Hz produces coupled peaks in the (P, Y) oplev spectra whose amplitudes are comparably small to the noise floor (see the attached spectra).

Rough description of the balancing procedure

1. Inject monochromatic excitation signals to each actuator
   • I chose 5 Hz in this adjustment work where the mechanical frequency responses are smooth enough (meaning no peaks nor notches)
2. Measure the peak height in the oplev spectra
   • Here only the peak in the diagonal DoF is monitored (e.g. H1 -> pitch, H3 -> yaw, in the case of Type-A payload)
3. Adjust the COILOUTF GAIN values so that the peak heights excited by the paired actuators become the same.
   • In this step, the first two (or three) significant digits of the peak height could be equalized read by the "cursor" in diaggui.
4. To confirm the balancing performance, inject the excitation in L DoF.
   • If a coupled peak doesn't appear in the spectra of angular DoFs, it could be OK.
   • If not, do a further adjustment with measuring the coupled peak heights and tweaking the GAIN value at the same time.
   • Note that I confirmed the L actuation was not affected through DRIVEALIGN nor COILMAT.