Calibrated ETMY M0 OSEM drive, plus calibration of M0/L1/L2 OSEM sensing, by injecting 0.1Hz drive to M0 while the cavity is locked without low frequency offloading from VCO to ETMY. M0 damping was on but L1 damping was off.
| Length drive (e.g. output of TEST and DAMP filters) to displacement |
0.48 nm/cts |
| M0 DAMP_L_IN1 sensing | 31 nm/cts |
| L1 DAMP_L_IN1 sensing | 3.2 nm/cts |
| L2 DAMP_L_IN1 sensing | 37 nm/cts |
Length drive calibration for M0 stage is 0.48nm/cts, not 1nm/cts.
M0 and L2 OSEM sensing calibration is in a ballpark. According to Stuart JeffK, it should be 38 nm/cts.
L1 OSEM sensing calibration is off by a factor of 10. I checked digital gains but they look OK to me. JeffK called me to tell that Matt put a factor of 10 in SENSALIGN matrix for L which I forgot.
If SENSALIGN matrix element for L were 1, L1 DAMP_L_IN1 calibration would be 32 nm/cts.
And for the record, the ballpark BOSEM calibration (+/- 50% because of variations in OSEMs open light current) is [m / ct] = (avg sensitivity * Sat Amp. Transimpendance * ADC gain)^(-1) = (62.5 [uA/mm] * 240e3 [V/A] * 2^16 / 40 [ct / V])^(-1) = 4.0e-8 [m/ct] The ballpark AOSEM calibration is about the same, [m / ct] = (avg sensitivity * Sat Amp. Transimpendance * ADC gain)^(-1) = (80 [uA/mm] * 240e3 [V/A] * 2^16 / 40 [ct / V])^(-1) = 3.2e-8 [m/ct]What was done:
Disabled VCO to ETMY offloading servo.
Disabled L1 damping.
Injected 0.1Hz 30000 counts excitation into ETMY M0 L lock filter (though I should have done this to DAMP L filters in a retrospect to make it simpler).
Measured the transfer coefficient from the exc to Lock filter output and OSEM DAMP L input of M0, L1, L2, and H2:ISC-ALS_EY_ARM_IN1_DQ which is calibrated in nm for the entire frequency range.
H2:ISC-ALS_EY_ARM_IN1_DQ had a coherence of 0.995 for an average of 5, everything else had a coherence of practically 1.
Since M0 damping might have some effect on the measurement (and that's the reason why I should have injected into DAMP_L), I "reproduced" the overall length drive output by adding TEST filter output and DAMP_L filter output transfer coefficients. In the end that didn't matter (only made 1% change).
Drive calibration = [H2:ISC-ALS_EY_ARM_IN1_DQ]/[reconstructed length drive].
Sensing calibration = [H2:ISC-ALS_EY_ARM_IN1_DQ]/[DAMP_L_IN1_DQ].
Measuement files are here:
/ligo/home/controls/keita.kawabe/OAT_2012/EY_cal