[Chiara, Jenne, Jim]
We did a first round of PRCL offloading to the ISI. Chiara will post plots later of our filter designs and stability, but just quickly here I post a plot showing the effect on the IFO.
Following Chiara's convention, Pink is with offloading on and Green is off. We offload some of the low frequency (but not the DC) of the PRCL control to the ISI rather than the M1 suspension stage. We see clear improvement in the motion of the PRM (as witnessed by the OSEMs), and no effect in the IMC (as witnessed by the MC2 OSEMs). Seeing no effect in the IMC is expected since we showed on Tuesday that when we push HAM2 and 3 together they really move together.
However, we see a pretty significant degredation of the DARM low frequency signal. We'll need to think more on this.
We had the offloading on during commissioning time, but we turned it off before going to Observe.
UPDATE: Second attachment has a few more plots with same pink/green on/off definitions. The left side plots are the same as the original first attachment. The left side plots are PRCL, SRCL, and MICH controls. It seems that turning on the PRCL offloading to the ISI impresses the 1.1 Hz line from PRCL onto SRCL and DARM, which is not so great. Perhaps this line could be fixed by (Jim's suggestion of) swapping our CPS offloading between HAM2 and HAM3. Right now, we're pushing on HAM3 to follow HAM2. But, since HAM3 has the big 1.1 Hz line, perhaps we should push on HAM2 to follow HAM3. This would make HAM2 move at 1.1 Hz, but would hopefully reduce the line's appearance in PRCL, and then offloading PRCL to the ISIs wouldn't put the line onto SRCL and DARM.
In both sets of traces, the CPS_DIFF was on. So, the only difference should have been the LSC PRCL offloading. We do not plot any angular signals since they were corrupted due to end station sensor correction being off for other parasitic commissioning.
Jim points out that in fact the ~1.1 Hz line is NOT at the same frequency in PRCL and SRCL (and DARM). The PRCL line, which comes from HAM3, is at 1.101Hz. The SRCL line at 1.012 Hz comes and goes, and has been doing so for some time now (since mid-Oct?). So, that line is probably not related to our PRCL offloading this morning, but rather is just happenstance that it shows up at the time of our 'on' measurement.
The broad low frequency injection in DARM is almost certainly related to the PRCL offloading, however.
Jim and Robert went out onto the LVEA floor (during a brief Corrective Maintenance interlude) to see if anything was touching the HAM5 HEPI, but they didn't see anything out of the ordinary.
