The PRX length has been measured as about 68 m. I did not estimate the error of this measurement, but this result would be consistent with the designed value 68.25 m.
Measurement Principle:
- Lock PRX with frequency (MCL) actuation. (PRX-MCL loop)
- Calibrate the PRX-MCL loop optical gain, and use CARM reconstraction channel as frequency reconstructed channel.
- Excite ITMX with Vexc, and measure df/dL = (A_MCL*V_MCL) / (A_ITMX*V_ITMX), where A and V are the actuator efficiency and control signal, resepctively.
- With exation in klog14565, find L_PRX
Measurement
- Lock PRX-MCL with VERTEX guardian.
- Measure the TF from MCL control signal (K1:LSC-MCL_OUT) to MCL error signal (K1:LSC-CARM_SERVO_MIXER_DAQ_OUT). Calibrate PRX optical gain by deviding by A_MCL. (Actually, we can directry obtain this TF by measuring K1:LSC-MCL_OUT to K1:CAL-CS_PROC_CARM_FILT_TM_OUT). This is shown in first attached figure. Shown data in the left top is the inverse of optical gain 1/H_PRX = 11000 Hz/cnts.
- Put above reuslt in the reconstruction channel (K1:CAL-CS_PROC_CARM_FILT_INVC). Now K1:CAL-CS_PROC_CARM_FREQUENCY is calibrated.
- Measure (A_MCL*V_MCL) / (A_ITMX*V_ITMX) * f_laser, specificully inverse of calibrated TF from K1:VIS-ITMX_TM_SUMOUT_L_OUT to K1:CAL-CS_PROC_CARM_FREQUENCY, and K1:CAL-CS_PROC_CARM_FREQUENCY was devided by f_laser. We obtain the PRX length as about 68 m as shown in the attached figure.
Here, I wanted to measure the PRY length, but the earthquake occured, and I postpone the measurement tomorrow.
