Just so we have some numbers, I did a by-hand analysis of the PRMI sensing matrix numbers I posted here in the elog the other day. This analysis is ignoring the error bar data.
For each sensor (PD_I or PD_Q), I do loop compensation, since these measurements were taken fairly close to the UGFs of the loops, and notches were not in use at the drive frequency. To do the loop compensation, I multiply the complex value (lockin_I + i*lockin_Q) by (1-G), where G is the (complex) open loop gain of the degree of freedom I'm shaking.
When I'm shaking a single degree of freedom (ex. shaking the PRM to get PRCL information), for each PD_I or PD_Q, we get 2 numbers, the lockin_I and lockin_Q values. I check the phase between the lockin_I and lockin_Q values, since that phase (after loop compensation) should be either 0 or 180, and if it is not, something is wrong.
Of the 16 sensors I measure (where PD_I and PD_Q count as 2 sensors), 11 sensors had phases more than 20 degrees away from either 0 or 180. This is not good, and indicates that something is wrong with my measurement. I suspect that I may not be driving hard enough - I was using an amplitude 4x smaller than the previous value. Next time the PRMI is locked, I will turn on the drive oscillation, and ensure that I can see the line in all of the PD signals.
The results of my quickie analysis script:
Bad REFL11_I_MICH phase! Phase is -82.0185 degrees!
Bad REFL11_Q_MICH phase! Phase is -35.9697 degrees!
Bad REFL33_I_MICH phase! Phase is -134.952 degrees!
Bad REFL55_I_MICH phase! Phase is -79.7997 degrees!
Bad AS55_I_PRCL phase! Phase is -142.6016 degrees!
Bad AS55_Q_PRCL phase! Phase is 90.6194 degrees!
Bad REFL11_I_PRCL phase! Phase is 52.471 degrees!
Bad REFL11_Q_PRCL phase! Phase is 52.2324 degrees!
Bad REFL33_I_PRCL phase! Phase is 52.909 degrees!
Bad REFL33_Q_PRCL phase! Phase is 25.14 degrees!
Bad REFL55_I_PRCL phase! Phase is 52.8113 degrees!
Sensing Matrix, calculated even though most of the measurement data isn't any good:
AS55: MICH = 0.13502, -1.6122deg. PRCL = 0.14993, -2.245deg
REFL11: MICH = 29.6373, -2.6365deg. PRCL = 7376.3206, -2.9098deg
REFL33: MICH = 0.35649, -2.9633deg. PRCL = 69.5133, -3.1302deg
REFL55: MICH = 0.62084, -2.0261deg. PRCL = 75.0214, 3.1176deg |