jeffrey.kissel@LIGO.ORG - posted 15:02, Friday 02 March 2018 - last comment - 16:06, Tuesday 06 March 2018(40808)
ZM1 Infrastructure Filled In; First Driven TFs Show Rubbing or Electronics Issues
J. Kissel
I've filled in the infrastructure for ZM1, which was mostly copying over filters from ZM2, and filling in the standard OSEM2EUL and EUL2OSEM matrices for an HTTS. I found, however, that the damping loops don't work. So, I took some driven transfer functions and spectra to see if I could identify the problem. Sadly, the dynamics -- especially the common mode actuator longitudinal TF -- looks pretty dicey. See attached screen shots.
Data templates live here:
/ligo/svncommon/SusSVN/sus/trunk/HTTS/H1/ZM1/SAGM1/Data
2018-03-02_2225_H1SUSZM1_M1_WhiteNoise_L_0p01to50Hz.xml
2018-03-02_2225_H1SUSZM1_M1_WhiteNoise_P_0p01to50Hz.xml
2018-03-02_2225_H1SUSZM1_M1_WhiteNoise_Y_0p01to50Hz.xml
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Comments related to this report
Problem with ZM1 Identified / Diagnosed; Solution Proposed J. Kissel The above transfer functions -- especially the P to P and Y to Y transfer functions -- reminded me of what we typically see in the off-diagonal transfer functions (e.g. P to Y or Y to L). This lead me to suspect the basis transformation and/or the sign of actuation chain. I first confirmed that the OSEM2EUL or EUL2OSEM matrices were installed correctly, and they were (I just did it, so...). So, then I started applying offsets in the COILOUTF bank. Using the conventions defined in T1200015, I expect that a positive offset in the COILOUTF bank (if I've got the COILOUTF GAIN correct, and the magnets are arranged as in the HTTS controls design description, E1400316) would cause that corresponding OSEM sensor to go more positive. This worked for UL and LL, but I got a more negative response from UR and LR. I then flipped the COILOUTF GAIN sign on those two, and et voila! The transfer functions cleaned up nicely, and look exactly as expected (within the tolerance / varience of HTTS resonances that we've seen prior). I conclude that the UR and LR Flag/Magnets have N and S facing magnets, respectively (when looking at them from the back of the optic) when they hould have S and N, respectively. Nice -- "simple" solution! For now, I've left the non-conforming COILOUTF gains that make the SUS bhave as normal in place. I've spoken with TJ, and he'll (a) check the polarity of the flags to confirm, and (b) flip them, such that ZM1 conforms to E1400316 on Monday. If only the OPOS was this easy to diagnose... New data files live in /ligo/svncommon/SusSVN/sus/trunk/HTTS/H1/ZM1/SAGM1/Data/ 2018-03-02_2312_H1SUSZM1_M1_WhiteNoise_L_0p01to50Hz.xml 2018-03-02_2312_H1SUSZM1_M1_WhiteNoise_P_0p01to50Hz.xml 2018-03-02_2312_H1SUSZM1_M1_WhiteNoise_Y_0p01to50Hz.xml
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... But #RespectThePhase
J. Kissel
A keen observer will notice that although the labels in the legend say ZM1 for the reference, I copied over the template from
/ligo/svncommon/SusSVN/sus/trunk/HTTS/H1/ZM2/SAGM1/Data/
2018-01-24_1909_H1SUSZM2_M1_WhiteNoise_L_0p01to50Hz.xml
2018-01-24_1909_H1SUSZM2_M1_WhiteNoise_P_0p01to50Hz.xml
2018-01-24_1909_H1SUSZM2_M1_WhiteNoise_Y_0p01to50Hz.xml
then text search-and-replaced ZM1 with ZM2. Long-story-short: the reference trace is ZM2.
Now, respect the phase: see that ZM2's phase is 180 deg at DC, where ZM1's is 0 deg at DC for all DOFs? Grumble Grumble Grumble... That means where ZM2 requires a different damping loop sign than ZM1.
An inventory of our HTTS reveals that OM1, OM2, OM3, ZM2, and RM1 all require positive damping loop gains (all other digital signs being equal), and RM2 -- and now ZM1 -- requires negative.
Sadly -- this also means that ALL BUT RM2 and ZM1 ARE WRONG by an overall sign.
*now* I think that it's the *LEFT* sign of the magnets that are flipped the wrong way -- namely that UL and LL are S and N, respectively when they should be N and S, respectively.
But -- since we have access to ZM1 right now, and I'd rather we have to change one (two, if you count RM2) suspension than five.
So -- this is what I predict TJ will find (looking at the back / AR side of the optic):
UL UR
S S
N N
LL LR
and he should re-arrange the magnets to be
UL UR
S N
N S
LL LR
which is the exact opposite of what's shown in E1400316, so that we confirm to the apparent LHO convention.
THIS aLOG AND COMMENTS ARE FULL OF LIES: Go to LHO aLOG 40847 for final answer as to what was going wrong with the sign convention.