Reports until 19:55, Monday 23 July 2012
H2 AOS
thomas.vo@LIGO.ORG - posted 19:55, Monday 23 July 2012 - last comment - 17:17, Tuesday 24 July 2012(3551)
H2 ETMY/ITMY Optical Lever Quad Mappings via SUS Offsets 
Jeff K, Jeff G, Thomas V


We thought it might be necessary to map out the quadrants of the ETMY and ITMY optical levers via offsets induced onto the suspension stages, namely M0.

After centering the beam on the optical lever QPD on ETMY, we offset the pitch on the M0 stage by a positive amount and expected the two lower quadrants of the QPD to have a spike in intensity (as deduced by the coordinate system set by SUS to determine which direction is positive and negative pitch and yaw).  Then offset yaw in a positive amount, which we expect to see the the two left quadrants to have a spike in intensity.  This was different than was what showing as pitch and yaw in the SUS medm and also is different than what I had used in my earlier calibration parameters.  This being said, the outcome of the mapping is as follows as viewed facing the QPD for ETMY:
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42 

Repeating the test with the same process on ITMY OptLev, we found that the mapping didn't correspond once again to what was previously recognized as the mapping and is as follows:
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13

The plot thickens:
As you can see, the two QPD's are not the same rotated about the center axis, which begs a confusing question of what might be going wrong. The most obvious answer is that the pitch signs are flipped, but where might this come from?  It could be a wiring issue in the hardware connecting the QPD to the ADC, a problem with a few negative signs somewhere in the readouts, or a difference in polarity of the output coil drivers F2 and F3 on the M0 stage of the ITMY.  The last option was found when we were trouble shooting and found that aLOG 2109 written by Jeff K. had addressed this issue but we couldn't find a log that resolved it.  It might be a combination of these things, still a work in progress.  It might be worth it to put in the glass viewport protectors and remove the enclosures to do a laser pointer test again on these QPDs.  Either way, the discrepancy between the two scenarios via the same process is perplexing.
Comments related to this report
thomas.vo@LIGO.ORG - 17:17, Tuesday 24 July 2012 (3573)
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Opening up the Optical Levers on both ETMY and ITMY and used a laser pointer , I mapped out definitively the quadrants for both optical levers. This is as facing the front of the optical lever QPD and the channels correspond to the channels outputted by the SUS MEDM for ITMY and ETMY.

ETMY:
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42

ITMY:
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42

Now, the good news is that the OptLev electronics match between the ITM and ETM.  Also cross refrencing with LLO's HAM 3 optical lever QPD, it matches ours as well.  The interesting part is that when we give a positive pitch to the ITMY suspension, it shows exactly opposite of what we expect to see on the QPD.  A mystery still yet to be solved.  ETMY suspension and optical levers matched beautifully, a sign convention is the difference between them which come from a positive pitch misalignment on the suspension yields a higher intensity on the two lower quadrants of the optical lever QPD.  The same goes for positive yaw offsets on the suspension, both of these can be easily remedied.