J. Kissel

I found the SPI L MEAS and REF IFO signals -- namely in its unwrapped phase signal form -- off in the weeds this morning at ~1700 [rad] and ~1000 [rad], indicating that the phase unwrapping algorithm needs to be reset.

I'm probably just gathering statistics here rather than identifying a cause, but since the system is still new, I figure calling out *when* and "what else was going on?" the SPI longitudinal (L) phase signal shows events in which the unwrapping algorithm glitches or drifts off into the weeds is worth it. There were two back-to-back phase excursions on Wednesday 2026-08-26 17:16 and 17:17 UTC (10:16a and 10:17a local PDT). 

Here're a few trends of *some* channels that I thought might be the obvious culprits -- 
    (1) Did the HAM2 or HAM3 (H23) ISIs trip? No.
    (2) Was there large excess motion or glitches in the H23 ISIs? No. (Only X is shown, but I checked Y, Z, RX, RY, and RZ and they also don't show anything)
    (3) Did the SPI's optical levers see anything? Yes, but not excellently correlated.
    (4) Was there main IFO laser light scattered from within the chamber into the SPI? Doubtful. While the IMC was struggling to lock, locking events (i.e. flashes on MC2 TRANS) are not obviously correlated.

I only show the MEAS_A raw phase signal (first row), but the trend of the unwrapped phase shows you that all PDs saw these glitches.

Zooming out, look at the second trends, the phase signal shows that it was "buzzing" at a max and min of -2*pi and +2*pi through out a time from 17:11:32 UTC to 17:17:44 UTC -- which looks very suspiciously like some excitation.
BUT -- the phase excursion doesn't happen until ~80% of the way through whatever excitation this is...

As of this morning -- There haven't been any unwrapped phase excursions since this one.

I've reset the phase unwrapping algorithm on 2026-08-31 16:43 UTC but hitting the H1:SPI-H23_IFO_PHASE_UNWRAP_RESET button, available to hit on each of the MEAS_IFO and REF_IFO CONDITIONING screens, linked from the SPI OVERVIEW.