lisa.barsotti@LIGO.ORG - posted 13:49, Wednesday 05 February 2014 - last comment - 00:44, Thursday 06 February 2014(9847)
Mirrors move less, X arm stably locked on green
Everyone - ITMX motion has been largely reduced by the seismic teem, now the motion at 0.5 Hz is around 0.03 urad, A LOT less than before; - The tuning of the ETMX is still in progress, but in the meantime Stefan implemented a 'dirty' optical lever feedback which reduced the ETMX PIT motion by about a factor of 5 at 0.5 Hz. With the OL feedback on, ETMX PIT @ 0.5 Hz is around 0.1 urad. There is some gain peaking around 1 Hz. - In this state, the one arm is stably locked on green with 32 uW (calibration to be confirmed) in transmission (~840 counts in ALS-C-TRX_A_LF_OUT) power fluctuations are small, around 5%. We are not seeing the 01 coming into resonance, so we can make a measurement of the frequency noise red/green. (P.S.: Sheila says that ~800 counts is a good number, corresponding to a good cavity alignment.)
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The OL design for ETMX PIT was based on Keita's vectfit of the ETMX L2 PIT to OL PIT plant:
sos(-0.000000198849, [ -0.99974066400116; 0.00000000000000; -1.00095625813547; 0.00000000000000;
-1.99993739410419; 0.99993764249344; -2.00093113886515; 1.00093232796495;
-1.99994835681455; 0.99994838427413; -1.99934725191269; 0.99934827919189;
-1.99996793385062; 0.99996797457313; -1.99994110527832; 0.99994113352954;
-1.99997421429503; 0.99997458606360; -1.99991282601661; 0.99991309284645;
-1.99998069701217; 0.99998073379973; -1.99995244319874; 0.99995248011907;
-1.99998283879917; 0.99998288208110; -1.99998212292679; 0.99998216522750;
-1.99999010413889; 0.99999013224953; -1.99999127808431; 0.99999130800992; ],"o")
or equivalently
zpk([-0.482248+i*2.71133;-0.482248-i*2.71133;-0.0712051+i*2.83338;-0.0712051-i*2.83338;
-0.389292+i*3.12401;-0.389292-i*3.12401;-0.146104+i*3.36657;-0.146104-i*3.36657;
-0.711974+i*8.43343;-0.711974-i*8.43343;-5.34064+i*15.7266;-5.34064-i*15.7266;7.63407+i*16.1483;
7.63407-i*16.1483;15.6598],[-0.422847+i*2.68189;-0.422847-i*2.68189;-0.080837+i*2.7458;
-0.080837-i*2.7458;-0.15783+i*3.13851;-0.15783-i*3.13851;-0.262356+i*3.29586;-0.262356-i*3.29586;
-0.140231+i*3.40571;-0.140231-i*3.40571;-0.510849+i*8.1497;-0.510849-i*8.1497;
-0.208194+i*9.98768;-0.208194-i*9.98768;-4.24951],-1.98998e-07)
This had three wrong half-plane zeros (and was therefore not invertable by switching poles and zeros) : 7.63407+i*16.1483; 7.63407-i*16.1483; 15.6598
To invert the plant, I moved the complex pole-pair to the left half-plane, and dropped the real pole completely.
On top of this inverse plant filter, I added zpk([0],[0.333333;0.333333],10,"n")*resgain(0.45,2,20) the shape the filter, and tuned it on.