Last time we noticed that the Transfer Function along T direction was a bit suspicius (IP mode 0.125 Hz and very low quality factor (see klog 8088)), today I did the following test.
To understand if the IP was rubbing or softly touching inside the chamber and, also, to verifie that the IP were free to move in different positions along L and T:
1) I moved it by using the stepping motor in different positions (see Pic1);
2) for each of these positions I measured the TFs along L,T and Y.
In Pic2,Pic3 and PIc4 the L,T and Y TFs measured when the IP was in these different configurations are shown.
We can see that when I moved the IP along L from -1650 micron to -900 micron and along T from -1354 micron to -850 micron the TFs along L and T are changed:
1) The IP resonance frequency in L is changed from 0.063 (red curve) Hz to 0.115 Hz ( blue curve)
2) The IP resonance frequency in T is changed from 0.125 (red curve) Hz to 0.078 Hz ( blue curve) and the quality factor is incresed;
3) The TF for Y does't changed.
Also in the other configurations, as shown in the Plots (green,pink, black curves etc..), the situation does't changed:
1) In these new position the IP is moving and looks free in all d.o.fs;
2) the IP resonace frequencies along L and are 0.115 Hz and 0.078 Hz respectively.
According with these measurements, it seems that in the old position (L=-1650, T=-1350) the IP (or some pendula mass) was rubbing and this explain the low quality factor.
Concerning the L TF the resonace at 0.115 Hz could be explain from an unbalanced distribution of ballast mass on the IP legs.
After that, to be shure that the IP was freely I centered it (L=0,T=0,Y=0) and for check I measured again the driving matrix (It was the similar to the old one).
Since the IP modes are changed I tuned the Damp filters for L and T and I turned on the loops.
Note*
When I moved the IP the BF yaw position is changed and I turned on the damping filter at these new position: 455 microrad (the old offset was 1255).
By the way, before to move IP in the OPLEV seg there was not ligth (not centered) and I think we have to center by using the BF yaw picomotors.
