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daniel.sigg@LIGO.ORG - posted 16:03, Tuesday 24 February 2015 - last comment - 19:08, Wednesday 25 February 2015(16893)

OMC/LSC Model Split

(Kiwamu, Dave, Jim, Jeff, Daniel)

The LSC and OMC models have been re-partitioned, so that DARM and CARM (to the ifo) are processed in the OMC.

New input and output matrices have been added. We are upgrading the guardian to use Jamie's new matrices which uses channel names rather than numeric indices as rows and columns. This should make us more robust against changes in the future.
All DARM signals are now processed in the OMC model, ie., ALS_DIFF, ASAIR_A_RF45 and DCPDs. This should eliminate 62µs of delay in the DARM path.
A new MCL feedback path was added to the LSC to take over what has previously been done by the CARM module (feedback to MC2).
We fixed the long standing naming conflict in the IMC servo, the filter module is now called IMC-MCL.
All references to OAF have been replaced by CAL (mainly in names of IPC modules).
The IMC-F signal is additionally routed to the OMC model and out as the common tidal signal to the end stations. The tidal script is no longer required.
New medm screens are available.
And committed to svn.

The current processing times are:

	mean (µs)	max (µs)
lsc	30	37
omc	13	14
alsex	32	35
alsey	32	34
iscex	5	7
iscey	5	7
susetmx	48	50
susetmy	50	56

Only the OMC sends data to the ETMX/Y, and only ISCEX/Y send data back to the LSC. With no more than 13µs processing time one might expect that there is plenty of time to send the DARM signal to the ETMs without an IPC errors. But no! We still have one every couple of seconds. This is down from a ~10Hz error rate. Strangely, the ALS, which picks up the common tidal signal and is located after the SUS in the fiber loop, does not see any errors. We now suspect a problem at the receiving end. More investigations ongoing.

Comments related to this report

jeffrey.kissel@LIGO.ORG - 19:08, Wednesday 25 February 2015 (16926)CAL, DetChar, INJ

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A few comments on the DARM topology changes that were made as a result of this split:

* Now that the OMC's DCPD's are fed into the DARM filter bank and the output is sent directly to the suspensions, we have removed one, inter-process communication, 16 [kHz] cycle (61e-6 [s]), delay or the equivalent of 22 [deg] of phase loss at 1 [kHz] (among other benefits like decreasing the turn-around time on the LSC computer, removing a whole bunch of will-never-be-needed input and output matrix elements, and just general cleanliness).

* The location / topology of where MICH, and SRCL feed-forward corrections are made has changed. The infrastructure for PRCL feed-forward correction does not exist (why? Every interferometer I know has *some* that has been corrected for in the past...).
Now, the MICH, and SRCL control signals are picked off, feed through a "MICHFF" or "SRCLFF" bank, respectively, and the outputs are sent to the LSC model's LSC output matrix. The LSC output matrix still have outputs for the ETMs, but their outputs are now fed via shared memory to the OMC model, and added in independently and respectively directly after the OMC model's LSC output matrix.

* Similarly, any *other* corner station photo-diode signals (POP, REFLA, POPAIR, REFLAIRA, REFLAIRB, TRX, TRY and their various combinations, REFL9, The Digitized Additive Offset for CARM, etc.), which can be chosen in the LSC model's LSC input matrix are fed over IPC directly to the output of the OMC model's input matrix.

* That means the location of feed-forward, with respect to hardware injections has changed, but this does not affect their impact on the loop. It has *not* changed with respect to the calibration lines, i.e. the calibration lines are still added *before* DARM_CTRL is picked off.

I attach an updated diagram (the .pdf) of how the DARM path gets distributed about the interferometer. This updated diagram also lives here
/ligo/svncommon/CalSVN/aligocalibration/trunk/Common/Documents/T1300088

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calibrationlayout_frontendcode_v2.pdf