J. Kissel, R. Abbott, P. Fritschel

Koji’s system level block diagram is very useful. https://dcc.ligo.org/LIGO-D1300502
(I’m not sure what there are two “OMC_wiring .pdfs in v4)
(It’s also a bit out of date, the serial numbers aren’t right, the high-frequency PI path isn’t included, and the serial number of the chassis is now S1101627 as of ECR E1600252 and its installation in June 2018
LHO:42361)
(C’est le vie, I cc Koji if he has time to update it. )

(1) For independent, analog measurement of the OMC DCPD whitening chassis,
- The original, very long saga (many comments, which you must read to the end) about Kimamu fighting the details of his measurement:
	LHO aLOG 21101
- A quick aLOG documenting that he remeasured an refit after the PI path was first installed, ECR:E1600192
	LHO aLOG 28087

One must get the whitening chassis in analog, independently, so you can pull it out of your understanding when fitting the full-chain measurement.

We’re looking to quantify the response of the chain out to f = 1e5 Hz, since there are poles that impact the detector response (namely the phase) in the 10-100 kHz region. The O2 model had the following poles included:
        uncompOMCpoles_transAm = [13.7e3, 17.8e3]
        uncompOMCpoles_whitening = [(14.34e3 + 14.60e3)/2, (18.68e3 + 18.57e3)/2, (98.94e3 + 100.45e3)/2];
(taken out of the data stream with the GDS pipeline, of course, since one cannot compensate for such things in real time with a 16kHz system.)

As indicated in Kiwamu’s aLOG 21101, probably best to gather the data down to 0.5 Hz, in order to give whatever fitting program we use enough meat to create a good result on the expected ~1 Hz pole.

You’ll be measuring serial number S1101627 which is a split varient of the standard ISC whitening chassis,
	ISC_Split_Whitening_Module_assembly_v1.pdf

I’ve cartooned up a new diagram of the measurement for you (Peter and Rich have reviewed it for sanity), which lives under D1900027, specifically:
	OMCDCPDWhiteningChassisSetup.pdf
(we can discuss whether to simplify it or not...)
This diagram is attached for convenience (and historical reference, if it changes).

(2) For complete measure of OMC electronics using a single-bounce IFO configuration, injecting at the ISS inner loop, and measuring at several points along the way, check out LHO aLOG 20851.

I’ve confirmed with Koji that the transimpedance amplifiers have not changed since O2, so we don’t expect a change.
These were originally characterized in LHO aLOG 17647
which suggests there are zeros:poles at 
        DCPDA =  (7.094, 7.094):(73.131,83.167), 
        DCPDB = (7.689, 7.689):(78.912, 90.642)
for which we compensate digitally, and there are uncompensated poles at
        uncompOMCpoles_transAm = [13.7e3, 17.8e3]

Again — we can’t measure this separately, nor can we measure as high using the digital system, but we should be able to model the “whole chain” measurement using our new measurement of the whitening chassis. 

(The AA chassis also hasn’t changed since O2.)

(3) Metric for success in balancing once compensation is complete (including a template that we could possibly use?) LHO aLOG 27148