There are several things that the CALCS calibration doesn't correctly calibrate, which are corrected later in the GDS calibration. As Jeff and Lili wrote in a dcc document yesterday, T1900169, if the real sensing function C = dC*C' where C' is the sensing function implemented in CALCS, and A=dA*A', then the correction that needs to be applied to the front end calibration R/R' = 1/delC*(1+CAD)/(1+CAD/(delA delC)) What is currently implemented (for example in the calibration of dtt templates) is just 1/delC, which is fairly different from the R/R' correction. The first attached pdf shows the difference between 1/delC and the full response function correction for the pyDARM model from April 2nd.
On March 31st, 48102 CAL CS filters based on the sensing and actuation measurements were installed, and checked with a boardband pcal to DeltaL measurement. (green squares in this plot). We are now very unsure about the calibration applied in this DTT template, but last week it was used to adjust the calibration, all the acutator gains were scaled by 0.95 to make the result from this template seem closer to 1 (red dots in the plot).
Today we took the data from the time of the broad band injection with the correctly fit CALCS filters installed, exported it with no calibration applied by dtt, and removed the whitening and 2 1Hz poles for the pcal response in meters, which results in the orage dots in the second pdf (delta L/pcal meters without correcting R). This reproduces the result from the dtt template fairly well, with an apparent 4% systematic error from 20-30 Hz, where the dtt template shows 5%. Applying the R/R' correction to this measurement, the apparent systematic error is reduced.
The script used to produce this plot is in the CALSVN /O3/H1/Scripts/CALCS_FE/process_broadband_pcal_20190331.py I have used the outputs of pyDARM for the corrections to the sensing function and the actuation function, but the calibration group has been checking these functions throughly, and Jeff is writing an alog right now about what they have found. Once we are confident about the corrections produced by pyDARM we can rerun this script.
For now it seems like we can take the 0.95 scale factor out of CALCS.
I've added an updated plot including the results of correcting 1/deltaC only.
There are two minor updates, which do not impact the overall results:
1) R/R' should be 1/delC * (1 + CAD delA delC) / (1+CAD) rather than 1/delC*(1+CAD)/(1+CAD/(delA delC)) [see T1900169]
2) Using the 20190328springfix model, the one installed in CAL-CS when taking the green BB measurements.
The actuation correction only curve explains why the green squares became blue triangles in this BB plot when tuning the actuation amplitudes. But the phase still does not match what we see in this BB plot.
Clarification: the last comment "R/R' should be 1/delC * (1 + CAD delA delC) / (1+CAD) rather than 1/delC*(1+CAD)/(1+CAD/(delA delC))" was wrong. I misunderstood the original parameters. Sheila's equation was the correct one. But the results are still the same.