In 85846 on Friday 18th, Elenna notes a lockloss after YAW ASC excursion, we have been having very short locks and I see evidence of two more of these yaw excursion in the last 24 hours:
- 07/23 00:27UTC: Differnt type of LL, caused by small EQ plus some wind?
- 07/23 03:50UTC: YAW ASC excursion, Plot of L2 Quads, Plot of ASC signals
- 07/23 06:25UTC: Different type ofg LL, unsure why.
- 07/23 10:49UTC: YAW ASC excursion, Plot of L2 Quads, Plot of ASC signals
Seen in CSOFT, SRC1, PRC2 and mainly on the L2 stage of quads. In the last 1-2 seconds before LL.
The lockloss that Ryan S. reports as being from a sitewide power glitch in this alog had a similar behavior in the suspension channels and yaw loops. Apparently the power glitch that caused the lockloss also tripped the HEPI pumps, but I'm not sure how that relates to the control loop behavior. I'm not sure if this is useful to link with these other locklosses or not.
Generally, every yaw ASC loops sees this behavior, but it's hard to tell what is moving first, or the most, since the channels are not calibrated into useful units. As a note, the soft loops are not DC coupled, so I imagine they are just following the other loops. Our lockloss scopes plot the very slow ASC channels, so here is a faster plot of some of the ASC channels before one of these locklosses. The centering loop signals are moving away from zero, but not large enough that the beam is at the edge of the WFS.
I broke out my old TMS servo scope to see if we are being pulled off the TMS QPDs. Clearly the X TR B yaw signal is increasing, but it may be because it's trying to follow a large movement in the hard loops. TMS X yaw moves about 1 urad before the lockloss as well.
In the first yaw excursion lockloss Camilla notes above, the ETMX HEPI RZ appears to oscillate in the two seconds before lockloss. I don't see that in the other yaw excursion lockloss though.
Both of these YAW ASC locklosses saw TMSX_Y start oscillating a few seconds before the lockloss.
- 07/23 03:50UTC: YAW ASC excursion
- 07/23 10:49UTC: YAW ASC excursion
Follow up to add that although the lockloss that Ryan S noted on 7/13 had an ASC excursion, the TMSX yaw suspension did not have the similar strange behavior that these other few locklosses have (ndscope). It's possible that this TMSX yaw behavior is linked to the sat amp change on 7/15, 85770.
