How To Set the double demod phases for the Short DOFs.
THIS PAGE IS DEPRECATED Instead, you should follow the directions in How_To/Diagonalize_the_DRMI_Length_Control
Ensure that the IFO alignment is optimal, and that any electronic offsets are cancelled.
Lock the DRM using the single demod signals. Do this a couple of times so you don't get confused by gravity offsets. Make sure the low-frequency gain is high enough that the error signals do not have large DC offsets (you can turn on the integrators).
Adjust the demod phase of the signal you're considering using for control until the offset in that signal is zero.
Measure the relative gains of your initial and final signals, and put the appropriate value in the input matrix.
Do (2) and (3) for all the signals you're planning to use (REFL133&199, PO133&199, AS133&199).
Now unlock and re-lock the DRM, and check that the offsets are still good. If not, do it again.
Example: SRC handoff tuning
Read the DD_handoff script. It shows that PD11_I is the error signal used in the single demod path and PD7_I, PD8_I are the new error signals used by the SRC double demod path.
The open loop transfer functions of these paths (C1:LSC-PD7_I/C1:LSC-SRC_IN2 and analogously for PD8) look like the single path's (C1:LSC-PD2_I/C1:LSC-SRC_IN2) except for an offset. This offset has first to be measured and then reduced by changing accordingly the coefficients of PD7_I and PD8_Iin the LSC matrix.