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Message ID: 5468     Entry time: Mon Sep 19 20:56:36 2011
Author: Paul 
Type: Summary 
Category: SUS 
Subject: Remaining SRM and ITMY OSEMs calibrations 


I've now taken data for the pitch and yaw calibrations for the OSEMs of SRM and ITMY. Until such time as I know what the calibrated oplev noise spectra are like, I'm leaving the servo gains at zero.

I estimate the length of the lever arm from SRM to measurement position to be 3.06m, and the length of the lever arm from the ITMY to the measurement position to be 3.13m.

From the fits shown on the attached plots, this gives the following calibration factors for the SRM and ITMY OSEMs pitch and yaw counts (i.e. counts from channels such as SUS-ITMY_ULSEN_SW2 multiplied by a matrix of 1s and -1s) to pitch and yaw angle:


SRM PITCH: 1 OSEMs pitch count = 11.74 microradians

SRM YAW: 1 OSEMs yaw count = 12.73 microradians


ITMY PITCH: 1 OSEMs pitch count = 13.18 microradians

ITMY YAW: 1 OSEMs yaw count = 13.52 microradians


Next step is to do some DC offsets with the oplev paths back in place to get the final calibration between OSEMs counts and oplev counts, thus finally getting a conversion factor from oplev counts to radians.

I noticed while taking these measurements that the DC offsets I put on ITMY caused around 5 times larger change in angle than those on the SRM. The different path length is not enough to account for this, so I propose that the actuation is working differently for the two. I guess this should be taken into account when designing the output matrices (unless the control is passed through a different output matrix than the DC offsets?). I'll quantify the difference shortly, and write a conversion factor between output alignment count (e.g. SUS-ITMY_PIT_COMM) and angle.



Attachment 1: SRM_PITCH_calib_curve.png  8 kB  | Hide | Hide all
Attachment 2: SRM_YAW_calib_curve.png  7 kB  | Hide | Hide all
Attachment 3: ITMY_PITCH_calib_curve.png  7 kB  | Hide | Hide all
Attachment 4: ITMY_YAW_calib_curve.png  7 kB  | Hide | Hide all
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