Tomorrow during maintenance I plan to epoxy 2 L4Cs under HAM1 to try use for feedforward, with the hope I can get some improvement to the ~10hz motion of the HAM1 table. Each of the 4 pier modules on each HEPI has 1 extra L4C input called "witness", with the appriate pre-amp and wiring to send signal to the AA chassis and into the front end. Additionally, all of the HEPI models already have filter models, sensing matrices and INF filter banks that were intended for a 3d L4C array, but we never ended up installing the sensors. So, in order to attach the spare L4Cs I already have in hand, all I have to do is connect the right ADC channels in the model to the inputs to the vestigial 3d L4C path, and plug a couple of L4Cs into the pier modules. After that I will just need a couple of short measurements to design a feedforward filter.

The only hiccup to this is that the adc channels I need in the model are currently attached to a path called "WITNESS" in the model. But the adc channels go into the master part, go into this block called "WITNESS" with 4 filter banks, then go out of the master part and get terminated. GNDN. I can't even find a link to the witness path on the HEPI overview, but all of the 3d l4c stuff is there. I plan to just clip the adc wires going in to witness and reattach them to the 3dl4c path. First 3 attached screen shots show where the adc channels go in the master part on the witness ports, then come out to get terminated, the witness block and hidden filter modules, and the already existing 3d l4c inputs. Last image shows the medm representation of the 3d l4c path on the HAM1 HEPI overview, circled in red crayon, which follows the model infrastructure exactly.

The 4 adc channels currently attached to the witness path are 2, 7, 12 and 17. I think 2 is on the +x/+y pier (call it pier 1) , 7 is on -x/+y (pier 2) , 12 is -x/-y (pier 3) and 17 +x/-y (pier 4). I plan to put the L4Cs near pier 2 and pier 4, so channels 7 and 17, which I will connect to the 3DL4CA_Z and 3DL4CB_Z paths in the model. I still need to probe out the adc connections, before making the model changes.

ECR for this is https://dcc.ligo.org/LIGO-E2300202. No new channels, no daq restart needed.