sebastien.biscans@LIGO.ORG - posted 09:54, Wednesday 30 April 2014 - last comment - 11:09, Thursday 08 May 2014(11643)
HEPI ETMY issue fixed
Jim reported some issues on ETMY HEPI yesterday https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=11618
Turns out that the position loops used were adding extra amplification at 10Hz (a 10Hz already amplified by the pier on this chamber). This was causing the HEPI to go unstable, dragging the ISI with it.
I switched to the controllers installed in FM2&FM3 (Cont_2), which are more generic, less aggressive loops. It works just fine.
ETMY chamber is used by the commissioners right now, but as soon as I have a chance I'll modified the design of the Cont_1 loops.
More info about this HEPI instability:
- This instability shows up mostly in Y (see ETMY_Sensors.png)
- This unstability is seen by the postion sensors and the actuators on HEPI (see ETMY_drive.png). The thing is that the HEPI-L4Cs, then the ISI-GS13s saturate (and make the platform trips) way before the IPS and ACT do.
- Find attached a screenshot of the actual filter installed. Removing the "bumps" at 10Hz and 45Hz fixed the problem.