KAGRA Logbook

VIS (PR3)

yutaro.enomoto - 21:14 Friday 20 April 2018 (4768)

Oplev sensor glitch

[Izumi, Yamamoto, Nakano, Enomoto]

Oplev outputs of PR3 are glitching.

= What we did =
We compared the power of the reflection with and without oplev control of PR3, to see if glitches seen in oplev signals correspond to real mirror motion or not.
The first picture shows the power at REFL without oplev control, and the second with oplev control.
In the second picture, you will find sudden degrades of the power coincident to the glitches. In contrast, in the first picture, there is no such degrades even though there were glitches in oplev signals.
This means that the glitches DO NOT correspond to real motion of PR3; if the oplev control was on, PR3 mirror angle was disturbed by the control loop.

= NOTE =
-- We left the oplev control of PR3 disabled.
-- We are not sure but this might be due to some strange behavior of the light source. It would be better if we swap the light source.

Images attached to this report

Comments to this report:

yutaro.enomoto - 13:57 Monday 23 April 2018 (4787)

Akutsu-san suggested that we look into OPLEV_LEN signals as well, to see if the glitch is related to the light source.
The attached figure shows OPLEV_{LEN|TILT}_{PIT|YAW|SUM} singals when the glitch happened this morning.
All 6 signals showed glitches at the same time, which indicates the light source would be suspicious.

Images attached to this comment

yutaro.enomoto - 14:17 Tuesday 24 April 2018 (4808)

[Iida, Michimura, Nagano, Enomoto]

We have conducted two tests:
1. Dark noise behavior of the oplev
We shut the light source and observed the oplev signals in time series.
--> No glitches found
2. Coincidence test with microphone
Michimura-san and Nagano-kun set a microphone to monitor the sound caused by a compressor nearby PR3
--> No coincidence found
3. Wind shield test
We put wind shield for the light source side and the reciever side (see the pictures).
--> behavior of the oplev output in time series did not change with and without the shields.
Note that Akutsu-san said that even mm-scale aperture would degrade effectiveness of wind shields.

Next step might be a swap of the light source.

Images attached to this comment

yutaro.enomoto - 8:56 Wednesday 25 April 2018 (4829)

For a temporary circumvention of the glitch, I implemented slow oplev controls for PIT/YAW, which should less sensitive to the glitch.

Images attached to this comment