I've remotely closed the H2 SUS ITMY M0 and R0 damping loops, and confirmed that they are now functional, as they were when confirmed by Jeff G ! Just to be sure we don't loose this information, I've burt captured two states

/opt/rtcds/lho/h2/userapps/release/sus/h2/burtfiles/itmy/
h2susitmy_damped.snap (Damping loops ON)
h2susitmy_safe.snap (Damping loops OFF)


One thing I'm confused about: the COILOUTF gains shown above are inconsistent with the polarity of the magnets (as per E1000617):

          COILOUTF Gain      Magnet Sign
M0 F1          +                 N
M0 F2          +                 S
M0 F3          -                 N
M0 LF          -                 S
M0 RT          +                 N
M0 SD          -                 S

R0 F1          +                 N
R0 F2          +                 N
R0 F3          -                 S
R0 LF          +                 N
R0 RT          -                 S
R0 SD          -                 S

From the chart above, it would be consistent (N == +, S == -), if the M0 F2 and M0 F3 magnet signs were flipped -- either in E1000617, or physically on the suspension. 

Now -- this raises a flag -- M0 F2 and M0 F3? We had some unresolved cross-coupling between Longitudinal and Yaw drive while the cartridge was still on the mechanical test stand, originally seen in LHO aLOG 1839 and further confirmed in LHO aLOG 1852. If the magnet sign was/is flipped on one of these two sensors and the COILOUTF gains did not properly compensate for them, we would expect to have excess cross-coupling between Yaw and Longitudinal.

For now, we have damping loops running, and we will leave the suspension as such, so that the seismic group can press forward. However, in the down-times between the seismic testing suite, and before we close up the chamber, we should (among other planned tests)
(1) Retake the low-frequency Y2Y and Y2L transfer functions, to confirm that the cross coupling is still present.
(2) If so, we should measure OSEM Basis transfer functions (F2toF2, and F3toF3, and maybe others) and compare. (This should really be a part of our standard testing suite.)
(3) If we're still confused, we'll need to take off the F2 anf F3 OSEM sensors and measure the magnet signs.

While discussing with Anamaria about what might be going ON, I drew up two tables to help me better elucidate the problem. I include them here, 'cause they might be useful for broader discussion.

If we take the magnet polarity from E1000617 as cannon, then I would expect the M0 face sensors to have the following signal-sign-flip chain (assuming a positive coil current repels a N, and attracts a S magnet)

Test OUT	E2O Gain	COILOUTF Gain	Current Out	Magnet Pol.	Resulting Force		Resulting Motion

         { F1	0		+1		0		N               none  }
+ Long---{ F2	+		-1		-		S               Push  }	-- 		+ Long
         { F3	+		+1		+		N               Push  }

         { F1	-		+1		-		N               Pull  }
+ Pitch--{ F2	+		-1		-		S		Push  } -- 		+ Pitch
         { F3	+		+1		+		N               Push  }

         { F3	0		+1		0		N              	none  }
+ Yaw----{ F2	+		-1		-		S              	Push  }	-- 		+ Yaw
         { F3	-		+1		-		N               Pull  }
This is how I had set up the COILOUTF gains before today (though I was off by an overall minus sign). 

However, since Jeff G.'s has re-installed COILOUTF gains as he has shown above, and the damping loops close and are stable, then that implies the following magnet polarity 

Test OUT	E2O Gain	COILOUTF Gain	Current Out	Magnet Pol.	Resulting Force		Resulting Motion

         { F1	0		+1		0		N               none  }
+ Long---{ F2	+		+1		+		N               Push  }	-- 		+ Long
         { F3	+		-1		-		S               Push  }

         { F1	-		+1		-		N               Pull  }
+ Pitch--{ F2	+		+1		+		N		Push  }-- 		+ Pitch
         { F3	+		-1		-		S               Push  }

         { F1	0		+1		0		N              	none  }
+ Yaw----{ F2	+		+1		+		N              	Push  }	-- 		+ Yaw
         { F3	-		-1		+		S               Pull  }

In other words, though the magnet polarities are properly compensated for, it doesn't match E1000617. That means if any other suspensions are assembled to the E1000169 specification, we can't necessarily use these COILOUTF gains.

Other thoughts:
- Because both of the above arrangements should result in the same motion, I'm lowering my EURIKA! flag a little on the guess that this is the source of the cross-coupling.
- It's strange that the cross coupling does not appear in both degrees of from, i.e. Yaw resonances don't show up in the L2L TF, but L resonances show up in Y2Y. I think I may have thought this before which let me down the "it's air currents!" path.

Anyways, my path forward outlined above still holds... we need a few more measurements before we start changing hardware -- or close the chamber and "aLIGO accept" the suspension.