Dither loops
I have moved the dithers of the soft loops (PIT4, PIT5, YAW4, YAW5) to lower frequencies (6-10Hz), I've yet to move PIT3 and YAW3.
I have tested lock reacquisition with the PIT loops at their new dither frequencies, but not yet with the YAW. In addition I've moved Dan Brown's dither monitor lines. See first attached screenshot of DARM spectrum tonight, note the high frequency noise is bad as the ISS second loop is off currently. The current oscillator frequencies are summarised in an updated table below (amplitudes are for NLN, for acquisition in PREP_ASC, the amplitudes are all 1600).
| PIT3 | PIT4 | PIT5 | |
| f (Hz) | 19.7 | 9.12 | 6.9 |
| A (cnts) | 10 | 150 | 150 |
| LO actuator | IY | EX | EY |
| Demod actuator | PRM | IX/EX | IY/EY |
| YAW3 | YAW4 | YAW5 | YAW1 | YAW2 | YAW9 | YAW10 | |
| f (Hz) | 18.4 | 8.65 | 6.46 | 8.25 | 7.55 | 7.3 | 6.1 |
| A (cnts) | 15 | 100 | 100 | 25 | 25 | 25 | 25 |
| LO actuator | IY | EX | EY | PRM | PR2 | DSOFT | DHARD |
| Demod actuator | PRM | IX/EX | IY/EY | - | - | - | - |
Method
I switched the LOs of these loops one-by-one, at NLN. Allowing the original loops with ~20Hz dithers to converge before turning off the inputs and tuning the loops for a lower LO frequency. I tuned the clock gains so the lines are visible over the DARM noise, made bandpasses for the signal path (previous lines are all in FM6, new lines in FM4), lowered the gains (since the DARM noise is much higher at low frequency).
I tried re-phasing the loops by adjusting the A2L gain of the test mass the dither is applied to, and checking all the signal was in the I path, however the old phases seemed just fine.
I've left the change in frequency of YAW5 out of the guardian for now since it seems slower to converge than the old loop and I didn't want to cause problems for future commissioners, so on the next lock there'll still be a line at 21.9Hz from that one (as well as the PIT3 and YAW3 lines).
TCS y chiller flow
We got a verbal alarm that the TCS Y chiller flow was low. Seconds screen shot is of the flow rate channel around the time of the alarm. We didn't go check for leaks or anything.
A new ALS x-arm problem
We had some problems locking the x arm in green. When the ALS_XARM guardian said the arm was locked the transmitted power was extremely noisy and the transmission camera looked like it was possibly rapidly mode hopping. We struggled with this for a while, eventually with better arm alignment we managed to lock with no problem (coincidence?).
