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 40m Log Not logged in Message ID: 9149     Entry time: Fri Sep 20 22:49:10 2013     In reply to: 9136     Reply to this: 9158
 Author: Masayuki Type: Update Category: LSC Subject: LSC calibration screen

 Quote: I update the LSC calibration screen. This screen is for real time calibration of each DOF with using error signal and control signal. The formula of the calibration is x_dis = V_err/H + A V_fb ,where x_dis is the disturbance without surpression, V_err and V_fb are error signal and control signal, H is the transfer function from the displacement to output and A is the efficiency of the actuator. I will put the filter of 1/H into the CINV filter bank and actuator efficiency into the A filter bank.

I fixed the filter of the MICH real-time calibration. You can find C1CAL screen from the LSC menu 'calibration' of sitemap.

*Filter explanation

C1CAL_MICH_CINV : the servo to convert  the error signal to displacement.

Sen_MICH :

the inverse of the transfer function from the distance to the error signal, which has the unit of count/m. In the formula this filter is represented by 1/H.

I assume this H is independent of frequency and time, and I calculated by the amplitude of the fringe of error signal. But it may change every day by drift of laser intensity and so on.  So we should follow the actual H somehow.  The temporary value of H is 3.76*10^7 count/m .

C1CAL_MICH_A : the servo to convert the feedback signal to displacement. In formula This transfer function is represented by A

SUS_BS;

the transfer function of the suspension of the BS. This is modeled from the measurement in elog#9127. The resonant frequency is 1.029 Hz and Q is 12.25.

Res_A :

the response of the actuator on BS_SUS, which has the unit of m/count. The value is 1.99*10^-8 m/count. This value is measured in the measurement in elog#9121.

C1CAL_MICH_W : the servo to handle the calibrated signal.

m->um ;

the filter to convert the unit of signal from m to um. When this filter is on, the output is written in unit of um.

*Measurement

I measured the power spectrum of the calibrated free running noise. The measured port was C!CAL_MICH_W_OUT. The result is in attachment 1. Also in this figure there are the plots of the Verr/H and Vfb*A.

In low frequency region, where control loop suppresses the disturbance, you can see that the displacement is equal to the displacement of actuation (I'm not sure what happens at the point of 0.03Hz), and in high frequency region, where control loop doesn't work, the displacement is equal to the value of the Verr divided by MICH sensitivity. Also this result is similar to the my calibration result.elog#9131

 Attachment 1: plot.pdf  83 kB ELOG V3.1.3-