[Nakano, Akutsu, Michimura]
We have calibrated PRM actuator using PRY cavity.
Measured actuation efficiency ratio between PRM and BS was PRM/BS = 16.8.
Using Ogaki-kun's cablibration of BS actuator (klog #11754), this suggests that PRM actuation efficiency is 1.0e-9/f^2 m/cnt in the free mass region.
Method:
1. Locked PRY (PRM-ITMY cavity) with a UGF of 60 Hz.
2. Measured the transfer function from K1:LSC-PRCL2_OUT to K1:LSC-PRCL1_IN1 when PRY is locked with BS or PRM (see attached).
3. Did the weighted fitting of the transfer functions with Act/freq^2. Act for BS was 3.1e-2 and that for PRM was 5.2e-1 (see attached).
4. According to Ogaki-kun's calibration in Nov 25, A_BS = 6.02e-11/f^2 m/cnt (I think this is with a high power coil driver and we are still using a high power coil driver for BS TM). Therefore,
A_PRM = 5.2e-1/3.1e-2 * 6.02e-11/f^2 m/cnt = 1.0e-9/f^2 m/cnt.
Discussion:
PRM TM also uses a high power coil driver. Theoretical actuation efficiencies for PRM and BS OSEM are 0.129 N/A and 0.0138 N/A, respectively, and the mirror masses of PRM and BS are 10.8 kg and 18.9 kg, respectively [1]. This suggests that actuation efficiency ratio will be
PRM/BS = (0.129 N/A / 10.8 kg) / (0.0138 N/A / 18.9 kg) = 16.4 .
So, the ratio is consistent with the measurement.
[1] https://iopscience.iop.org/article/10.1088/1361-6382/aa90e3
Next:
- Calibrate PRCL and check the displacement sensitivity and the residual RMS during locking
We have implemented this actuation efficiency to PRCL reconstruction filter K1:CAL-CS_PROC_PRCL_FILT_TM.
FM2 "gainFeb18" is now 1e-9 m/cnts
FM7 "modelFeb18" is now a zpk suspension model generated with VIS Plotter http://10.68.10.102:8000/ModelPlotter/plot_model/?opt=PRM&in_stage=TM&in_dof=L&out_stage=TM&out_dof=L , with gain calibrated to 1 at 1 Hz.
I forgot to consider the fact that BS longitudinal motion changes PRY length sqrt(2) more compared with PRM since the incident angle to BS is 45 degrees.
Ogaki-kun said that his calibration factor for BS 6.02e-11/f^2 m/cnt is in the unit of counts to meters in differential length between BS to ITMX and ITMY (not meters in BS longitudinal motion).
This is equal to the unit of counts to meters in PRY length from PRM to ITMY.
Therefore, my calculation for PRM acuation efficiency 1.0e-9/f^2 m/cnt should be correct.
However, the expected value for the ratio between PRM and BS will be
PRM/BS = (0.129 N/A / 10.8 kg) / (sqrt(2) * 0.0138 N/A / 18.9 kg) = 11.6 .
Discrepancy between the expected value and the measured value would be from measurement uncertainty or OSEM actuation efficiency variance.