Stefan, Alexa, Sheila, Arnaud, Kiwamu

Since we have loaded the blend filters and plant inversion filters on ETMX QUAD, we tried the hierarchical control on ETMX in order to close the ALS diff loop with a high gain. We didn't really see a good sign of suppression yet.

What we did:

• Arnaud and Stefan loaded the inversion plant filters (alog 11676), which makes every stage look like a single pendulum with a resonance at 1 Hz and Q of 1.
• Arnaud set up the relative gains of the stages such that all the stages are identical to TST.
  • This was implemented in the filter bank.
• To confine the ALS diff beatnote within the VCO range, we used the local slow feedback onto ETMY. As we knew, this worked well.
  • Sheila changed the gain from -95 to -24 in order to reduce a kick on the suspension.
  • We also copied the M0 L2P filer of ETMX over to ETMY because the high frequency part had too much gain, which could saturate the DAC.
• We changed the calibration of the ALS diff signal.
  • Now this is calibrated into meters.
• We tried closing the loop.
  • We used TOP, UIM and TST on ETMX with Jeff's blend filters in.
  • We designed a simple servo filter, which gives us a wide 1/f range from DC to 40 Hz in the open loop transfer function for the initial trial.
  • The positive gain seemed right. The gain needed to be more than 1e9 because the signal is already tiny tiny by the new calibration.
  • As we increase the gain, something become unstable and eventually saturates the ETMY DAC (I forgot which stage saturated mostly).
  • Another thing is that, because the inversion plant on TST has a high Q in it, it takes 1 min or so to ring itself down. This easily saturated the DAC. Sad.

The commissioning of ALS diff continues. We will/should attack ALS diff more quantitatively.